I have a 400 amp continuous duty solenoid to merge the house bank with the alternator. This is the second one I have installed. It seems to be failing as the first one did. The big ring that snaps to the two contacts in the solenoid gets dirty and of course begins to heat up and pits the ring causing more and more resistance. Eventually it won't carry any voltage through the switch at all. I can recycle the coil a few times with the dash switch and see the volt meter jump up when it makes a good contact. The coil switch is #12 wire through a 30 amp relay, so the coil should be getting ample power to engage the solenoid.
I talked to Dick Wright about this two years ago and he quit selling them because of the above described failure. He only recommends a battery isolator now. I know several of you guys have these solenoids and wonder about your success. On my last trip I couldn't get more than 12.7 volts on the Trace meter while the bus alternator was showing 14.2, and I wasn't running any appliances off the inverter. I have 0000 wire from the alternator to the Trace in the circuit. When it was new I was getting 13.9 volts at the Trace meter which is more than enough to run one rooftop air.
I do suspect that having the solenoid in the engine room subjects the coil to a lot of heat, maybe weakening the strength of the switch closure. I located it there out of convenience but it could be moved into the bay near the inverter. Where did you guys mount yours?
Any ideas as to what I'm doing wrong here? It's nice to tie those batteries together when you drive and don't need the genny to charge things up.
David
see--> http://www.hydrogenappliances.com/solenoidrelay.html
400 amps & silver alloy contacts
David,
I've had similar experience using 200 amp rated contactors, with silver alloy contacts, to connect my buss battery & alternator to the house bank and inverter. Mine look just like the ones Pete gave a link to that proport to be 400 amps, I noticed that they had a 200 amp fuse in their test circuit so I question the rating. Mine works fine for awhile then contact resistance seems to build up and eventually there is 1/2 volt drop (while under full inverter load) across the contactor. So I replace the contactor. But I take apart the bad one, I file the contacts, put it back together and, when I feel like it swap the repaired unit back. It seems like I get about a year of use before the problem resurfaces. I carry a near new one and the tools to make the swap. I think it's simply the nature of the beast. My contactor is mounted in the former HVAC bay so heating isn't the issue. I think it's simply airborne dirt eventually leads to burned contacts. The good news is after disassembly and filing them, it seems to last just as long as a new contactor.
Regards
Jerry 4107 1120
It sounds like you're using contactors rated for a continuous duty without due regard to the connect and disconnect surge and arc currents.
The fuses that are rated 200Amp for typical inverter applications are usually designed to blow after a high average current (the rating of the fuse), while sustaining brief surges (around 1000amps).
If the soleniod is connecting a high load (like a discharged battery bank to a charging supply) you can easily exceed the rating and pit the contacts with the arc. Diode battery isolators have no contacts to arc and ar always "on" whenever there is enough voltage to bias the diode, it will begin to conduct. This makes the flow of current/voltage more gradual and "less damaging". The drawback is that the diode requires that voltage rise to get across the diode gap - which in some diodes can be as high as 1.5volts. This voltage is lost as heat within the diode package. This also requires that the voltage regulator be turned up to overcome the loss from the diode (or the batteries won't see the correct charge voltage and will fail sooner than they should).
Diodes can fail if there is a short burst of high current too, so it's important to be careful when hooking up a jumper cable (go directly to the batteries the input to the isolator).
Cheers!
-Tim
P.S. if you want to tie the banks together for a prime-mover start in the cold, try an IGBT or MOSFET rated at a couple hundred volts and 1000Amps. Putting a resistor or halogen light bulb in parallel with the IGBT/MOSFET will reduce the surge a bit (if you wait until the light bulb is dimmed, it means the differential between the packs is almost less severe, and the IGBT/MOSFET can be turned on without "punch-throught"). -T
I used two 150 amp continuous duty solenoid relays that are in parallel with a heavy strap between them. I know it is capable of handling starting current since I've started the bus when my starting batteries were dead. I do not though run the current for the inverter through this solenoid-it is only for tying the starting batteries and deep cycles together. Good Luck, TomC
Jerry,
I missed the part where you described H O W you took that thing apart and i really want to know.
Thank you,
John
Johned,
My solenoid switches had a cap over the cylindrical section that was swagged over a slight flare on the cylindrical portion. I pried the swagged material outward, very small sections at a time and working around the circumference, with a pair of end cutting pliers. Once the cap is off the rest is obvious. When I reinstalled the cap I only swagged a few points, no sense making future disassembly more tedious.
Regards
Jerry 4107 1120
QuoteI think it's simply airborne dirt eventually leads to burned contacts.
Wrongo. It's a laws of physics thing.
You send electrons through a wire, it becomes an electromagnet. You move a magnetic field past a wire, it becomes a generator.
When you remove the current flow from a wire, the magnetic field around that wire collapses. This collapsing magnetic field is in motion; it's moving inwards. This collapsing magnetic field generates voltage. This voltage is the opposite polarity of the voltage which caused the magnetic field to expand. A big honking negative voltage spike. About 300 volts.
This spike creates arcs and sparks. These arcs and sparks burn and sandblast the contacts. This explains the fat blue spark when you unplug things.
There is a solution, for DC circuits. Commutating diodes. Commutating describes the job the diode is doing, not the diode itself. Don't ask the guy at Radio Shack for a commutating diode; you will just get a blanker blank stare than the usual blank stare.
http://www.allaboutcircuits.com/vol_3/chpt_3/9.html (http://www.allaboutcircuits.com/vol_3/chpt_3/9.html)
Bottom line: Big diode. Cathode ( the end that normally connects to the negative ) on the load side of a switch. Anode ( the side that normally connects to positive, has a band of paint on this end ) to ground. Shunts the spike to ground, not through the contacts.
No, I can't give you a part number and source. I would just go to my friendly neighborhood surplus store and get the biggest diode there.
kd5kfl hit the nail on the head. His explanation was great.
Anytime you break a DC circuit it produces a high induced current, which causes arcing/pitting of the contacts. This can be reduced by silver alloy plating but not completely eliminated.
Reducing the load before switching helps.
That is also why you should use only DC rated switches on DC circuits. AC only rated switches aren't plated to withstand the arcing.
Ed
Kd5kfl,
I mostly agree with your explanation, the disagreement is with '300 volts'. In fact there is no limit to the voltage, it increases very rapidly until something breaks down. In the case of these solenoids what breaks down is the air in the gap between the contacts, hence the arc, which may well exceed 300 volts. Diodes are a solution ONLY IF the direction of current flow prior to the contact's opening is known. In the case of a merge solenoid what's needed is something that can breakdown, nondestructively, before the airgap, regardless of the current direction. I will try a pair of 'back to back' Zener diodes. In fact I have a collection of devices made just for this purpose They are called, among other things, 'double anode transient suppression zener diodes'. I'm embarrassed to say I hadn't thought of what's really going on. Thank you for pointing it out.
Regards
Jerry 4107 1120
I'm curious as to what solenoids you guys are using that are failing. I've seen generic ones that look like a Ford starter solenoid called 'continuous duty', but I didn't think they looked up to the task. I used a White-Rodgers from www.grainger.com/Grainger/items/6C025 (http://www.grainger.com/Grainger/items/6C025). I'm wondering if this is any better (or worse) than some of the solenoids others have used.
David
Mine are the type that looks like the old Ford starter solenoid-the key is that it is rated at continuous duty. I've left them on for days at a time with no problem. Good Luck, TomC
We use the White-Rogers solenoids that David mentioned where I work in 36v mules (forward/reverse and interlock switching). They are incredibly robust and have an almost not existent failure rate in our application.
http://www.taylor-dunn.com/vehicle_details.aspx?mode=base&id=22
I'm kind of leaning to a manual switch and merge the banks only before I start the engine and disconnect them only after stopping to avoid the voltage differential problem. How would that idea work?
David
I am using this, for the past 7 years, no problems works great..... :) :)
Cole Hersee
Continuous Duty Solenoid
24V
Part Number: CH 24144
200 Amp SPST w/ Silver Contacts
Normally Open
I use it to connect my house 24V bank with my starting 24V bank. Charge with the bus alternator going down the road.
I have a switch on the drivers panel which I turn on to activate the solenoid and connect the batts systems together. The switch is connect to the start system, so if I turn the bus off, it also disconnects power from the solenoid and separates the batt systems when stopped.
No problems with arcing or anything else. I believe I also have a wiring diagram of how I installed it, including a diode to resist back flow/arcing. Just have to locate it. ??? Email me if interested and I'll try to find it and email it back to ya.
Has worked flawlessly for the past 7 years, in 2001 it cost me $33.34 for the unit at a truck supply store. I believe these can even now be ordered right off the Internet at CH's website. If you go into their website you can of course search for this solenoid, it will give you a picture, measurements, specs, etc., etc.
Chris
David,
I know your system is 12V and mine is 24V, another option check out:
http://www.wranglernw.com/pc-6420-1008-isolation-relay.aspx
Dave,
I know my system is 24V, and your's is 12V............so another option check out:
http://www.wranglernw.com/pc-6420-1008-isolation-relay.aspx
Kd5kfL,
I perused the link you sent and thanks. Excellent illustrations. I will bookmark that one. I think a diode would be very simple and work well as the link explained. Now, how are they sized? What do I ask for at the electronics store? Radio shack has them, and I can find them there without asking, but give me something to go on to look at. Are there AC and DC diodes or all the same? What would be the physical size of the diode? Excuse my ignorance, but this is new territory for me.
Also, just a comment about Jerry's post about current flow, the alternator will always be at higher voltage than the house bank, ie. 14.2 vs 13.5~. Therefore, I'm making an assumption the house bank will always be the "downstream" the current flow. The voltage on the house bank side of the solenoid will always be lower than the alternator side. Is that a valid assumption?
Thanks,
David
David,
Not if one charges the coach battery with the inverter/charger when plugged in. I keep my bus plugged in and have the solenoid wired to close if shore power is present or if no shore but the bus alternator is charging..
Regards
Jerry 4107 1120
David,
Current also flows the other direction if you find your start batteries low and use the solenoid to boost the start batteries with the house bank. Even if the start bank is charged and you start the engine with the solenoid engaged it with flow current to the starter because of the heavy draw. Bottom line is the solenoid will flow current both direction.
Good luck
Don 4107
Mr. Anderson,
If you think of tanks of water with a hose at the bottom between them - they will equalize at the rate allowed by the "flow" through the hose. If you correlate the battery banks to the water-tanks - and the tie-together-solenoid as the "hose", you can kind of see where I'm going with this.
If you tie together two banks - the bank with the lower charge will immediately take charge from the bank with the higher charge at the rate allowed by the tie-link (solenoid, fuses, wire) - even with the alternator not adding charge to the overall load.
The alternator's voltage regulator is designed to maintain a voltage. When the alternator is spinning, and the voltage regulator is "on", you will get a voltage at the set-point (assuming the alternator is spinning fast enough to support the current load of the charging bank{s}...).
The alternator is like a tap filling the tanks (if you want a water analogy for arcing - think of the water hammer effect in plumbing...).
What this means is there is a higher voltage source with the alternator running in conjunction with the battery bank(s). The surge when the solenoid is connected/disconnected with the alternator outputting power will be higher than if the solenoid was connected/disconnected with the alternator "off".
If anything - this only indicates a probable "best practice" (i.e. not connecting the tie together during high load/charge conditions in the battery bank{s}).
If you intend to tie together the banks for something like a "start assist", I recommend the same thing people recommend when jumping a car: tie together the banks and let the charges equalize a bit before trying to start the prime-mover again. Once you've started the prime-mover and the alternator is running, wait until the current through the tie-together link is down under the rating of the contactor before opening it (or just leave it hooked up until the charge current is at a "float" level).
Remember that if you remove the load from an alternator quickly, the alternator will try to continue outputting the same current as the voltage regulator is trying to sustain - but will come back down as the voltage regulator changes its contol of the field in the alternator (in the order of milliseconds). This short transient can end up being 5x the rated voltage of the charging system at the current that was being supplied by the alternator before the event (14.4 * 5 = 72 ... 72volts * 120Amps = 8,640watts even if this is a short transient, it can exceed the rating of the contactor quickly eroding the contact plating). The previous comment about the air (as a dielectric insulator) is spot on. Over about 50Volts DC, arcing becomes a problem (and as you can see from the above numbers, this gets exceeded during an alternator load dump event) the air will conduct enough current to jump the gap between the two contact points while the points are close enough to have a low resistance in the air.
If you want to pick a diode for the transient supression role in your charging system - take the 5x system voltage number and the full output current of the charging system and use that as your "rule of thumb". FYI - the diodes will get pretty big if the alternator puts out a lot of current at a high voltage.
The electric car contactor is a good place to start - but most electric vehicles have either a solid-state controller which does the final connection (so there is little arcing at the master contactor) or a resistive (old-school) pot-box which just limits the current/voltage to the motor (and wastes the rest as heat). The Tayor-Dunn or Cushman (or any other industrial cart variant) contactors are not really intended to continuously switch the full rated load of a motor drive system (rather as a low leakage cut-out for the electronics, or a failsafe system in the event of a semiconductor punch-through failure). I'd recommend looking at switches that are desiged for cutting a load to a large UPS battery bank at full rated load called "load break rated" (600VDC @ 800amps or more) if you are using it frequently. These will have better alloys for open arcs (withstanding high temperatures which would normally vaporize or pit other metals)- and will often have arc fingers that spread the wear out over a larger area (instead of localizing the arcs at the center of the contact points).
Like this one: http://www.boltswitch.com/125.pdf
Cheers!
-Tim
P.S. I wrote this out with a few tall glasses of wine in me - sorry if this is a little wandering ;D -Tim
I've spent two hours learning about diodes and it appears the best fit is a silicone transient suppression diode. However, I haven't been able to match the available numbers with the appropriate size.
Using the formula 14.2 x5 =71 My alternator is 350amp peak output 71 x350 =24850 watts. Based on the formula I need a diode of at least 71 volts and 350 amps. So far, all the searches haven't led me to the right one.
I'm not sure, but in my reading it seems I could use a small diode with a resistor to snub the voltage to a managable level. I feel like I've been in an online electrical engineering class for 2 hours. My head hurts from all the reading.
David
David,
Tim is far to conservative. All you need is a voltage rating slightly above normal system voltage and a peak current rating above what the alternator can ever deliver. This is because we are NOT EVER disconnecting the alternator from the start battery. A suitable device for 12 volt systems is the 'Littelfuse' 15KP17CA which is rated at 17 volts and has a peak current rating of 512 amps. The best answer for a 24 volt system is to use 2 of the above device in series. These are from the Digi-Key catalog.
Regards
Jerry 4107 1120
Thanks Jerry, and sorry about the drawn out explanation David.
Jerry, the part you listed also comes in a 75Volt rating at 15,000Watts (http://production.littelfuse.com/data/en/Data_Sheets/15kp_revised.pdf) - a few of these in parallel right next to the contactor would be a good start (say two or three) as they are only about $9 a piece. Make sure they are on the alternator-side of the contactor and ground as this is where the transient will be.
The "standard" which the automotive industry plans around for load dump scenarios for 12-Volt systems is about 40Volts (keep in mind this is with alternators that are usually design-limited to a 60-90Amp output).
While the 5x number may be a bit higher than one would think is necessary while the batteries are still connected to the alternator, it is prudent to consider a battery bank that may not be able to absorb that pulse quickly enough (and some of that spike will end up at all of the attached devices). Some devices like GPS systems, or household LCD TV's with the wall power supply removed (drawing 12-14 volts directly from the battery), are more sesitive to spikes than batteries ;). These parts are avilable, and aren't that expensive (granted they cost more than your average 1N4001), and this meathod produces a setup that is likely to not need service ever.
Cheers!
-Tim
Tim,
The objective is/was to protect the merge solenoid. This can be done with 1 for 12 volt systems or 2 in series for 24 wired across the merge solenoid's contacts. If one wanted to limit the system voltage during a load dump event, which,I think, you are suggesting, then connecting from the engine side of the contactor to ground would be appropriate. But why chose such a high limiting voltage? With this type of device parallel connections should be avoided as, due to tolerances, current will not divide evenly.
Regards
Jerry 4107 1120
How I do this:
These go on the load side of almost everything; headlights, heater fan, AC clutch. Not so much the horn, I have a finger that performs that function:
http://www.allelectronics.com/cgi-bin/item/D660/205/RECT_DIODE_6AMP_600PIV_.html
RatShack has something close to this, about the size of a pea.
This protects the switches for each individual item. I don't tear apart existing vehicles and install them, but if I'm working on a problem or starting from scratch, I use them.
Big coils and big loads; Starter solenoid, starter, battery banks:
http://www.allelectronics.com/cgi-bin/item/1N1190AR/205/40_AMP_600_VOLT_RECTIFIER_.html
Just get the biggest thing the surplus store has.
Where you need this is at any load which can be disconnected, as close to the switch as possible. If you have multiple battery banks, one for entertainment electronics and one for the coach and one for security electronics, you need one diode per battery bank. Assuming that each bank can be switched to the charging system. One load, one diode, connected to the load side of the switch..
Ok, it is getting clearer but not quite there yet.
Jerry says to connect the rectifier/diode to the engine side of the merge solenoid, and Tim says the alternator side, both I assume mean the same. Kd5kfl says to connect to the load side of the solenoid which would be the house bank lug. Which one????
The diode in the link: http://www.allelectronics.com/cgi-bin/item/1N1190AR/205/40_AMP_600_VOLT_RECTIFIER_.html shows the picture with the arrow pointing to the circle lug which I assume is the cathode. So, this is wired to the post of the solenoid load (house bank side) and the screw post is bonded to the bus frame. Am I describing this correctly?
Thanks,
David
Boy...............
I hope you are getting all this David! :-\ ;) I'm doing - I think - the same thing you are and I am wore out trying to decipher it all. (My brain hasn't been working up to 100% capacity lately anyway. ;D)
Hang in there buddy, I'll try and put this all together when YOU finally get it all figured out. I know we have some REALLY GOOD guys here who understand this sort of thing very well.........................................................And I'm THANKFUL!!!!!!!!!!!!!!!!!
Chaz
David
Some how you are missunderstanding what I'm advocating. The merge solenoid's contacts connect the bus system positive side to the house system's positive side. I'm advocating connecting a suitable device in parallel with the merge solenoid's contacts, it also will have one end on house positive and the other on bus positive. The device I'm advocating is a double anode zener transient suppression diode, rated with a voltage rating just above the peak system voltage and a peak current rating greater than the alternator's rated output.
Regards
Jerry 4107 1120
Wow - I think I may know where all of the confusion came from (i.e. ME). Some times it's a really bad idea to chime in to a topic when I'm not really reading the thread ::) - or even putting forth the effort to logically proof the concept I'm attempting to explain before hitting "post". Allow me to redeme myself while actually adding to the clarity of this topic (wouldn't that be nice...)
But first off, my most sincere appologies to the board... Jerry L here is correct and his instruction is going to saving you a bit of headache.
I realize I have above instructed you to connect the diode between the Alternator side of the contactor to the ground. This is correct for clamping the colapsing field of the contactor coil - almost... actually, not even really close :-X.
Below is a schematic diagram for the contactor an suggested (and correct this time - I promise) TVS diode installation.
Cheers!
-Tim
Quote from: Tim Strommen on November 07, 2007, 01:38:38 PM
below is a schematic diagram for the contactor an suggested (and correct this time - I promise) TVS diode installation.
Cheers!
-Tim
Tim I am having a problem understanding your diagram.
It appears that the TVS diode is just connected to itself (short circuit) via a set of normally open contacts. You really need to explain things good for us ole' WV hillbillies. You probably know we are "dumber than a sled track".
Richard
Richard,
Tim and I finally agree, the diagram is correct. The TVS diode is in parallel with the normally open contacts. What the TVS does is prevent arcing of the contacts WHEN they are OPENED. An arc is possible because there may have been considerable current flowing in the wires to and from the contacts and the magnetic field the current created around the wires contains considerable energy. The TVS allows the energy stored in the wires to be dissipated in a path around the contacts. Tim's diagram also shows an ordinary diode to protect the switch that controls the solenoid's coil.
Regards
Jerry 4107 1120
Quote from: Jerry Liebler on November 07, 2007, 03:13:19 PM
Richard,
Tim and I finally agree, the diagram is correct. The TVS diode is in parallel with the normally open contacts. What the TVS does is prevent arcing of the contacts WHEN they are OPENED. An arc is possible because there may have been considerable current flowing in the wires to and from the contacts and the magnetic field the current created around the wires contains considerable energy. The TVS allows the energy stored in the wires to be dissipated in a path around the contacts. Tim's diagram also shows an ordinary diode to protect the switch that controls the solenoid's coil.
Regards
Jerry 4107 1120
OK. if you guys say so.
I just thought it should be in series with a connection between the two battery banks. I only see one battery banks.
Quote from: DrivingMissLazy on November 07, 2007, 03:22:17 PM
Quote from: Jerry Liebler on November 07, 2007, 03:13:19 PM
Richard,
Tim and I finally agree, the diagram is correct. The TVS diode is in parallel with the normally open contacts. What the TVS does is prevent arcing of the contacts WHEN they are OPENED. An arc is possible because there may have been considerable current flowing in the wires to and from the contacts and the magnetic field the current created around the wires contains considerable energy. The TVS allows the energy stored in the wires to be dissipated in a path around the contacts. Tim's diagram also shows an ordinary diode to protect the switch that controls the solenoid's coil.
Regards
Jerry 4107 1120
OK. if you guys say so.
I just thought it should be in series with a connection between the two battery banks. I only see one battery bank.
I went back and blew the diagram up and it showed the other battery bank. When I just clicked on the diagram, the right bank was cut off. The drawing was so large I needed to scroll sideways to see it all.
Richard
Quote from: Tim Strommen on November 07, 2007, 01:38:38 PM
Wow - I think I may know where all of the confusion came from (i.e. ME). Some times it's a really bad idea to chime in to a topic when I'm not really reading the thread ::) - or even putting forth the effort to logically proof the concept I'm attampting to explain before hitting "post". Allow me to redeme myself while actually adding to the clarity of this topic (wouldn't that be nice...)
But first off, my most sincere appologies to the board... Jerry L here is correct and his instruction is going to saving you a bit of headache.
I realize I have above instructed you to connect the diode between the Alternator side of the contactor to the ground. This is correct for clamping the colapsing field of the contactor coil - almost... actually, not even really close :-X.
Below is a schematic diagram for the contactor an suggested (and correct this time - I promise) TVS diode installation.
Cheers!
-Tim
Ok, Tim, I mostly understand the diagram. So, you depict a diode on the solenoid coil, and you depict back to back diodes on the house bank side and alternator side. You said "TVS". Is that something we haven't discussed previously? I'm symbol challenged so the backwards S on the cathode side of the two back to back diodes means what? Are they hooked together cathode to cathode?
Also what is a TVS diode and where do I find it? The link Kd5fl gave didn't help in the search.
Thanks for your patience.
David
All,
Sorry I had a brain fart.
Regards
Jerry 4107 1120
David,
Tim's symbol is that of 2 zener diodes in series (back to back). This is the symbol for the device I led you to earlier, it conducts in either direction above the specified voltage but negligible current flows through it below that voltage. TVS is an acronym for Transient Voltage Suppression, which is the function of the diode.
Regards
Jerry 4107 1120
All-right, a little more clarity:
There are two types of TVS diodes made: "unidirectional" (DC), and "bidirectional" (AC). I think this should be fairly self-explanitory, but I do know that there are some non-electrically endowed people on the board.
Rectifier diodes (like the classic 1N4001) are designed to allow voltage/current to pass though in one direction after the Positive/Negative gap has been saturated, but block voltage/current in the opposite direction (also known as "reverse biased"). You have really high current rectifier diodes in your alternator which turns the AC signal into a DC output with ripple - and those of you who have battery isolator devices have two rectifier diodes (one to each battery bank) in one package. Even these come in two basic configurations: "general" and "Schottky". General is designed to block reverse bias throughput, but allow forward biasing with a moderate forward "saturation voltage" (this is the voltage diference that must exist at the anode/cathode for it to begin to condict, this is usually between 0.7-Volts to 2-Volts). Schottky is designed to do the same thing, but with a much lower saturation voltage (typically around 0.5-volts or less - they are also typically more expensive).
Zener diodes will do the same thing, but they are also designed to allow voltage to pass in the "wrong" direction (reverse bias) once the voltage reaches a certain level (but only for a limited current throughput) known as the "avalanche" or "breakdown" voltage. This function is very useful if you want to limit the voltage being applied to a voltage sensative device when the supply current is very low (like to a microprocessor drawing less than 10milli-Amps). The point at which the Zener begins to conduct in reverse bias is very programmable by the process at which the diode is built (you can get voltages at commonly used points, like 3.3-Volts, 5-Volts, 9-Volts, 12-volts, 15-Volts, etc.). With appropriate circuit design, this "regulation" of voltage can be done continuously, but this is usualy done by a linear voltage regulator or other type of task-specific power-supply (or DC-DC converter), as the regulation effect is through "dissapating" the excess energy as heat (this is why it's only every used for very low current applicatoins - as it would litterally burn up if the dissapated power at the silicon exceeded what the [typically] glass-package could transfer to the air).
Transient Supression Diodes are designed to do exactly what it sounds like they are designed to do - absorb a quick, high impulse power surge of energy. They are not designed to continuously absorb a steady voltage. The Uni-directional TVS diode (meaning one-way) is a variation to the Zener, in that it will conduct a forward voltage, but dissapate a reverse biased pulse over its avalanche voltage. Since it can't sustain the current of a forward biased rectifier role, designers will typically place a general or Schottky rectifier diode in series to prevent forward conduction through the TVS (to block any signal except a transient pulse). With an AC signal, this would mean doubling the devices (one set of TVS and rectifier for each direction of flow of the alternating direction of current). Silicon manufacturers logically placed two TVS diodes in series within one package but cathode to cathode in order to reduce the parts count for AC applications (by 3x). This is what we call a bidirectional TVS - it will only absorb a transient in any direction above the avalanche voltage for the part, while blocking voltage/current in any direction below the avalanche threshold.
Since you are using a pair of battery banks, where logically one would want to plan for each one potentially having a higher charge, (Jerry recommended and) I used a bidirectional TVS across the Contactor switched pins, to absorb any impulses above the expected system voltage regardless of which battery bank has the higher potential/charge (electrons don't care which way they go, so you don't want to have a TVS diode that does ;)).
Below are the two schematic symbols for the two TVS variants.
As an asside (somewhat related, and since we went into this we might as well go all the way) - companies like Tyco Electronics, and Siemens Electronic Controls, suggest that DC arcing can sometimes be encoraged (and damage done to the contacts) by having a reverse biased general rectifier diode across the coil. Their research appears to suggest that the diode may slow slightly the movement of the contact armature as the diode and reverse collapsing pulse may create a small eddy-current (the same effect that Temla electric retarders are based on), resisting the pull of the return spring until the coil dissapates the remaining field as heat - all the while and arc might be sustainable in the "slowly" opening gap. They recommend replacing the general rectifier diode, with a TVS diode and series general rectifier diode to clamp the immediate pulse (protecting the switch, electronics), but allow the mechanics of the relay to operate the contact opening as designed. This may be something to consider before you just put a general rectifier diode reverse biased across the contactor coil terminals. I've attached a Tyco App-note I had in my collection as refference.
Cheers!
-Tim
P.S. Since we're working with DC, a trick used in the industry to break high current arcs in battery disconnect switches is to place a permanent magnet near the arc area - as arcs are magnetically influencable. By pushing the arc with a strong permanent magnet, you can litterally "push" the arc until it is too long to sustain itself on the conductance of the air. For sealed contactors this is not controllable, but it's interesting and usefull to note if you upgrade to one of the larger non-sealed electric vehicle contactors, or knife switches (as you can place a magnet which will push an arc to parts of the contactor that are not used for the primary conduction while closed, or edges of the contact points which will encorage the arc to break sooner due to distance). -T
Tim,
Thank you for an outstanding tutorial on Zener TVS devices.
A very good point about the diode across the coil slowing the opening of the contactor, thus increasing arc issues on the contacts. I would suggest that it would be simpler and more reliable (because of fewer connections) to use a bidirectional TVS across the coil. The coil TVS shouldn't need to be very big, say a 1500W pulse rated device at twice the system voltage.
Regards
Jerry 4107 1120
Tim,
Thanks for the primer on diodes. I've learned more in the past two days about electomagnetic circuits than I've known in my lifetime. The sad thing is I'll probably forget most of it when I wake up tomorrow morning. :-\
It appears the 15KP17 CA bipolar diode from Little Fuse that Jerry referred to should do the trick. The VR is 17 volts, VBR 18.9 volts, and Ipp rating up to 512 amps. I should be able to print that reference page and go to some place in San Antonio TX and find the diode I need. Not sure where to look, but at least have a reference to ask someone.
Using your diagram I'll wire the diode from lug to lug on the contactor's switched loads (house bank & alternator)
Just for clarification, should I put a unidirectional diode on the coil terminals of the contactor? The 15KP17A Little Fuse diode should suffice in this position.
David
Well Dave - that's the great thing about this board - You can always come back to the thread ;D.
For the coil, it's probably easier from a parts locating point of view to just get another of the same bidirectional TVS diodes since you're probably running at the same system voltage for both the chassis/house batteries, as you are the contactor coil control voltage. When companies build electonic products (Jerry apparently can confirm this per the PM he sent me with some of his background), EEs will try to use the same part in many places to ease the purchasing and qualification process - and take advantage of the price-breaks due to the "economy of scale". It also makes locating and maintaining a "spares" inventory less complicated and more compact.
If you can't find a local shop, Digikey (http://www.digikey.com) will take your money without complaint ;). I buy from them, Mouser, Future Electronics, Avnet, etc. all the time for personal projects.
If none of them have it, you can always try to purchase sample quantities from the manufacturer directly (they'll usually support this, but some manufacturers can be pricks...)
For the contactor coil, simply replace the general rectifier diode in the schematic with the TVS diode part (if you get the bidirectional type like we recommend, it won't matter which way you hook it up across the coil). Just remember to keep the leads insulated to prevent shorts.
Cheers!
-Tim
Again - My appologies for my stupidity earlier in the thread :P -T
All,
For these little electronic parts it's real hard to beat Digi-Key. http://www.digikey.com/
They take small orders online with a credit card, have incredible stock, ship promptly and offer decent prices. The Littlefuse 15KP17CA is a very good choice to protect the merge solenoid's contacts but it's a $8.91 part ( use 2 in series for 24 volt systems). That's way more than we should spend for use across the coil. For all the coils I'd suggest a 1.5ke30ca. This is a 30 volt device, it will limit arcing on the switch without slowing the solenoid much and it's much more reasonably priced at $0.27.
Regards
Jerry 4107 1120
Thanks guys,
I won't have time to do this for a while. I'll post back when it's done. It may be a couple of weeks. This has been a great learning experience for me.
David
I think my golf cart has one of those TVS diodes across the contactor terminals. ( it keeps the contacts from arcing/welding ) when you press the pedal the solenoid clicks to apply power to the controller.
Sorry.. The thread just refreshed my memory about the diodes function.
Dave.....
Sorry about bringing this back to the top, but I finally ordered this from Digikey. They didn't stock the 15000 watt diode so I could only get the 5000 watt. 5Kp18CALFCT-ND. I ordered two. I hope this will work.
David
Now if we could get 'Diode' added to the title so I have a chance of finding it next year. ::)
Lee, what about Diode for Battery Bank Merge Solenoid?
Richard
That would be great. Much easier to spot a thread title in the search results for 'battery solenoid' or 'solenoid diode' or what ever I remember by then.
I'm going to jump in here and suggest that there may be a different reason for your failure, not at all something diodes of any kind will fix. Though I respect Tim and Jerry on all of this stuff, I'm sitting here wondering where they think there's enough inductance in the mains to generate the kind of inductive kick that will trash contactor contacts. Yes there's plenty of inductance in a contactor's *coil* to cause some havoc in other things (not the contacts though), but in a piece of 0000 cable there's not enough inductance even in a big long run to create the kind of failure you're seeing, especially considering the frequency of closures your solenoid is seeing... ie if it were being turned on and off 100 times an hour on a 24/7 basis, yes inductive spikes may eventually roast the contacts but once or twice a day and not many of those days in a year, I just can't see this being the cause.
My take is that there's too much current being carried by the contacts during closure or opening, probably due to the two battery banks being very different in charge from each other when the contacts are closed or opened, and that 0000 cable. That was suggested early in the thread before it went off to diode-land. A very easy way to fix this would be to replace the 0000 sized wire going to and from the solenoid with some wire of a much smaller gauge, sized to carry solely the current that the alternator can produce. I've been using #6 on my setup for 35,000 miles now and only a simple 100 amp solenoid with total success and zero failure. The theory is that the wire adds enough resistance in the circuit that the current thru the solenoid is somewhat limited to what the alternator can produce, and everything's happy. I have a 100 amp alternator and four T-125's and no matter how dead I make them I NEVER see more than 40 amps going thru that contactor. I have a feeling that the way your system is wired and with the 0000 wire, you may be seeing hundreds of amps going thru yours.
In your case you'd need to make sure that your Trace or some other device isn't trying to get it's major share of power thru the solenoid, etc. The solenoid's purpose should be solely to share the alternator with the two banks of batteries. So the best way to wire it would be take a dedicated piece of #6 wire from bank 1's positive directly to the solenoid, and then another dedicated piece of #6 from the other contact of the solenoid directly to bank 2's positive. This way, the batteries will balance but the resistance of the wire itself will become a current limiting factor that will keep things from going spark-spark inside your solenoid, and the size of the wire itself will preclude any massive load drawing devices from trying to nab power via the contactor....
Bottom line in my humble opinion, yes use diodes on the coils and your stereos will probably be much happier (I've had my coil's inductance take out my stereo prior to my putting diodes there!!) but for this problem diodes are far from the correct solution. An hour and a few pieces of #6 should cure you instantly.
Cheers
Gary
Gary,
The actual inductance, and energy stored therein may well surprise you. I have about 30 feet of 00 wire between my house battery and the coach battery. This calculates, using a calculator on the www, as 13.75micro henries which at 200 amps is storing over 1/4 of a joule, enough to do serious damage quite easily.
Regards
Jerry 4107 1120
Gary,
I'd like to voice a concern about the description of the system you have. You say:
Quote from: boogiethecat on November 28, 2007, 08:36:03 AM
...My take is that there's too much current being carried by the contacts during closure or opening...
...A very easy way to fix this would be to replace the 0000 sized wire going to and from the solenoid with some wire of a much smaller gauge, sized to carry solely the current that the alternator can produce...
...The theory is that the wire adds enough resistance in the circuit that the current thru the solenoid is somewhat limited to what the alternator can produce...
What it sounds like you are suggesting is diliberately using an undersized wire, to "current limit" the link between the two banks. What I don't see here is any mention of a fuse... This is the concern I have.
A wire, no matter how undersized, will attempt to transmit the full power demand of the circuit regardless of its size. If a wire is replicating a "current limiting" effect, this means that the resistance of the wire is preventing further increases in power transfer. How this happens is that at a specific point in the increasing slope of transfer, the wire becomes saturated and the electrons instead of flowing through the wire like a stream - are forced through like a 1500psi pressure-washer hose. This causes the conductor to become hot and its resistance to increase, which eventually (assuming that the load is not continuously too high) will balance and "limit" the ammount of current through the conductor.
Unfortunately this heating of the conductor can melt an insulating jacket well before the current and temerature reach equilibrium, or cause the conductor itself to open (think
electrical fire here please). This is the whole point of a fuse - it has a smaller gauge conductor which is designed to open when a sustained current transfer throught its package exceeds the rating of the part. By having a small device in a known location, one can control the failure of the long cable run (ensuring that the fuse opens before the cable gains heat which is too much to dissapate safely). Without a fuse, the heat will build up in a cable where the conductor cannot radiate the heat fast enough to keep the temperaure from compromising the integrety of the cable - and an open will result. The other risk, is that the insulating jacket is rated for a specific temperature - if this is exceeded internally, the jacket will melt losing the insulating characteristics (thinning, or dripping off of the cable) and the conductor can short against an exposed ground surface causing arcing, welding, or (if close enough to a wood structure) a major fire.
What you are hitting at Gary, but not recommending - is the use of a current limiting resistor - however, I would recommend that one design the bank-tie with a device like this doing the limiting - not the cable! Just like a fuse, this allows us to select a regulation point and locate that part in a known and suitable location.
The math is very simple for a current limiting resistor - one need to know the expected worst-case voltage and current to be limited to and do some simple math:
(Resistor Minimum Value in Ohms) = (Voltage) / (Current limit set-point in Amps)
(Resistor Minimum Power Rating in Watts) = (Voltage) x ("Current limit set point" x 1.25)
For example if you are expecting a differecne between a 12Volt Chassis Battery and a 12Volt House battery of 4Volts, and you want to limit your current to 40Amps the math would be:
4Volts/40Amps =
0.1Ohms (100 milliohms)
at
4Volts x 40Amps =
160WattsWhat you can see here is that value is in the order of milliohms - an undersized conductor can easily have several milliohms of resistance per foot, so the risk is real.
Now that's the subject of current limiting resistors - but just like with high power LEDs (current limiting resistors are fine for an LED with a drive current of 0-20mA), a current limiting resistor quickly errodes the efficiency of a system. As you can see in the above math, the resistor will actually convert 160Watts of your precious power into heat while it is protecting the wire! This is like running your headlights. To maximize the transfer of energy from one bank to the other - one must design the system to support the full surge load of the banks (this can easily mean a current number somewhere in the odds of >500Amps).
Back to the example of the LED, lets assume a 3.25Volt 15mA blue LED (because I think they're cool). If we want to run that LED from a 28.8Volt supply, we need a current limitting resistor which will consume the difference between the 28.8volt supply and the 3.25Volt rating of the LED.
28.8 - 3.25 = 25.55Volts
To pick the current limiting resistor, we do the same math as we did for the bank tie:
25.55Volts / 15Milliamps = about 1.7KOhms
With a power rating of at least:
25.55 x 15mA = 0.383Watts
With a resistor, you always pick the next part UP in size - so this would be a 1.7KOhm 1/2Watt resistor. Looking at the efficiency, we see that the LED consumes (3.25Volts x 15mA =) 0.049Watts and the resistor consumes 0.383Watts out of the total power consumed (0.383 + 0.049 = 0.432Watts) the LED only consumes 11.343% of the total power used for the circuit!! That's almost 10% efficiency and 90% waste as heat!
This same lesson can be applied to the battery bank tie circuit with a wire acting as a current limitting device - you'll probably lose more in the wire loss that you gain with the transfer itself, if you have an under-designed circuit. This has a significant impact for those who boondock or full-time. Careful selection of components and special attention to design have a vast impact in the power consumption of the final system.
And please everyone - Always place a fuse with a value picked to protect the wire it is attached to (and place the fuse within 8-inches of the circuits +supply). And place a fuse or fuse block any time you have a transition from one wire size to another - to protect the smaller of the two wires! Only you, can prevent electrical fires in your rig.
Cheers!
-Tim
Gary,
I certainly agree with Tim on the cautions about fuses and wire sizes. My alternator, like most bus alternators is able to produce about 300 amps. My intertie has a 200 amp circuit breaker and is a 00 wire. I want and need the full 200 amps to run my AC, while driving, from the inverter. As it is my wire size is smaller than I'd like. The burning of the contactors contacts is, no doubt due to the energy stored in the inductance of that 00 wire. Remember above I estimated the energy at 1/4 joule. A watt is a joule per second. If the arc lasts 10 microseconds, a very reasonable estimate, during that time the average power in the arc is 25,000 watts. That 'in a nutshell' is why the contacts burn.
Regards
Jerry 4107 1120
I've got a 100 amp fuse in the [solenoid] line and it's never blown.
So....
Hi Gary, I'm gald to hear that ;). A 100Amp fuse is about the limit for a #6 wire with a 12volt system - depending on the length and whether or not the ambient temps are high (like in an engine compartment). That shouldn't be an issue.
Assuming that you take very good care of your batteries and never let them get dicharged below 50-60%, there shouln't be to much load.
-Tim
Quote from: Tim Strommen on November 28, 2007, 04:40:32 PM
Hi Gary, I'm gald to hear that ;). A 100Amp fuse is about the limit for a #6 wire with a 12volt system - depending on the length and whether or not the ambient temps are high (like in an engine compartment). That shouldn't be an issue.
Assuming that you take very good care of your batteries and never let them get dicharged below 50-60%, there shouln't be to much load.
-Tim
That probably makes the difference right there. Gary knows, and will maintain his system well enough to not put those stresses on it.
Jay
87 SaftLiner
Thanks Jay, right on. My first set of batteries was four T-105's that I bought from a Burning Man nutcase for $5. He'd bought them new and abused them so badly in their first week that the posts were melted off!! I spin-welded plugs in the holes and repoured the posts, and the batteries performed flawlessly for 4 years! I finally changed over to a new set last season only because they leaked acid a little bit- you can only do so much to save melted batteries- and they were getting a bit out of hand on corrosion issues. I gave all 4 to a friend who is still using them in his RV today. The new T-125's are happy as can be.
Tim and all, YES I use the resistance of the wiring to the solenoid to soften any massive currents that the solenoid would see. The 100A fuse keeps things safe but since it's never blown it's obvious that the wire is doing it's job happily and currents are well within limits. I still maintain that current is the problem in this thread, not inductance spikes. For heavens' sake, how many systems do you think are out there that join battery banks with a solenoid and how many require diodes to keep in working condition? Likely the answers are, in order, many and zero.
There's something going on with David's system that is out of the ordinary, and I'm willing to bet that it has nothing to do with inductance spikes. It's just too difficult to kill this kind of solenoid especially with a system that is in extremely common usage that has, to my knowledge, NEVER needed spike suppression diodes in the contact side of the system... Solenoids of this type routinely operate starter motors, golf cart motors, which represent massive inductive loads, and they live on happily. On the flip side, running too much current or making/breaking contact into too much current through solenoids will kill these things in a jiffy and I've seen that MANY times. I really think that the diode discussion on this thread is informative, but has little to do with Dave's actual problems.
Cheers
Gary
Gary,
80-100Amps is the limit for conducting power to a load with only .5Volts drop. If you are never seeing more than 40Amps across the cable, the difference in battery charge is probably more in the area of a volt and less. This is great for your system (and speaks well of your battery state/maintenance), but it also means that current limiting is not being done by the cable (since you're nowhere near the capacity for that gauge wire).
Current golf-cart/forklift contactors rarely ever see a switching instance under load - the speed controllers have internal transistors/MOSFETs which do the load switching.
The surge-load topic I brought up way in the beginning of this thread is also something to return to. If the contactor is being opened or closed at the same time as the starter solenoid is being opened/closed - this will cause a HUGE kick (since the load increases dramatically when the starter is turning. If you tie the batteries together - it should be done before the starter is enabled, and should remain tied until after the starter is off for a bit.
Cheers!
-Tim
I installed the diode as below. I cleaned the solenoid and it had rust in it. Somehow moisture had penetrated the shell. The 0000 cable on the left is from the alternator. Cable on the right is from the house bank.
After cleaning I had no voltage drop to the house bank. I ran the rooftop AC with no trouble. Hopefully it will stay that way.
David
If anyone could post a current part number or link for the recommended diode to use on a 24v interconnect solenoid, I'd be grateful.
Those listed in this thread are 7 years old and not working, and having no experience with diodes, I don't trust myself not to screw it up.
Wow, you have been searching way down the board pages to find this and bring it back. I found it made no difference and removed the diode about 3 years ago. The solenoid has worked fine without it. I do have to pull it apart about every 2 years and clean the contacts, but overall, I'm pleased with it.
David
I ganged three ,300 Amp golf cart solenoids on a buss bar .Seems to be doing just fine however I'd need to run that set up for several years like some of you have to see if it will really lasts. If I had to do it over gain I'd get a "Smart Solenoid" (Google) that takes out all the guess work and the "oops I forgot the switch" out of the equation.
What's draining your batts that you need this so often? Should be looking at that problem first.