House Bank Solenoid Problem

[wagwar]

I finally got to road test my house bank to coach bank solenoid system yesterday. All was well and both rooftop A/C running cold! That lasted for a couple of hours and then - nothing. It all shut down. I was able to continue running one of my rooftop units from the inverter, but that was running off the house batteries with no engine assist. Once we got parked, I tested the solenoid and it was open. It had a good 24vdc signal, but no continuity. I have to assume it is blown.
So, its a 200Amp continuous duty unit. There is no reason I can think of that it should blow!  Did I just get a bad one OR is this likely to happen to the next one, and the next one? Is it heat? The solenoid is in the front bay, so it is not in a particularly hot spot. I spoke to another bus nut and they said they got tired of replacing their solenoids all the time and went with a manual switch. Is this what I need to do or is there a solenoid out there that can do the job. If I replace it with a switch, will a 200A unit be sufficient?

[Lin]

Just guessing here, but although 2 AC units could be running at less than 200 amps @ 24v, they could be drawing a good deal more at start up.  Over a period of time, it would certainly happen that both would be kicking in together.

[robertglines1]

volts x amps = watts   ac running  14 amps each @ 120 volts    start up  up to  19-20 amps @120 volts   Most inverters rated at 4000watts are only like 3000 and change continious.  for what it's worth.     if you are charging off stock bus alternator it puts out more than 200 amps @ 24 volts

[Lin]

But, since it is a 24v solenoid, the amperage is 5 times higher. So 2 units could be 200+ amps at startup depending on other charteristcs of the system.  My knowledge here is pretty basic though. I definitely could be missing something.

[robertglines1]

what I as trying to point out was at start up they could draw 100amps each at 24 volts each plus any battery depletion the alternator was trying to replace plus other bus loads. Sean will probably be able to explain better.  need really big selonoids.  

[David Anderson]

I second Bob's post.  Two AC's on one inverter and solenoid may be too much.  I went through dying solenoids with my SW2512 and one Coleman 13.5k btu.  I finally isolated it under a dust cover box and eliminated my failures.  I don't believe dust is your problem, however.  Sean will chime in and give you some ideas.  He's our inverter guru on the forum.

David

[tuccitown]

I spent a lot of time researching the solenoid house bank charging options. I decided that the best case would be if I were just charging my batteries a 200 AMP solenoid would work but if I also wanted to run an AC unit or two, I had better plan to keep an inventory of spare solenoids. I am not sure what your charging output is but mine is in the range of 300 AMPs. I went with a isolatetor method as I knew I would eventually forget to switch a disconnect switch.

Jack

[gus]

You can always run two solenoids in parallel so that each shares 1/2 the amp load.

[wagwar]

so two or how about one of these:

http://www.ebay.com/itm/GE-EV-100-300-AMP-24VDC-SPNO-IC4482CTTA300AH124XN-/120567578558?pt=LH_DefaultDomain_0&hash=item1c12633fbe

[gus]

Parallel 200 amp units will give you 400 amp capacity, 33% more than the one in the link.

[wagwar]

Thanks Gus,

Sorry, but I'm not sure how to wire that. By parallel, do you mean the coach bank connects to one side of one unit and a jumper to the same side? Both units would be activated from the same signal.

[gus]

Both units would have like terminals wired together, then the bus wires connected just like to one. This way both will be activated at the same time and split the amps.

Same idea as wiring two batteries in parallel.

This will only solve your problem if it is actually caused by the single solenoid being of too little capacity.

It could also be caused by the large contacts in the single solenoid being so burned they have too much resistance to carry the current.

However, since solenoids aren't terribly expensive, having two in parallel is not a bad plan because it gives you an automatic backup.

[Sean]

... both rooftop A/C running cold! That lasted for a couple of hours and then - nothing. It all shut down..
... Once we got parked, I tested the solenoid and it was open. It had a good 24vdc signal, but no continuity. I have to assume it is blown.
...

First off, let me start by saying that I run two air conditioners, plus the rest of the normal bus loads, all the time using my 270-amp alternator ans a single, 200-amp solenoid.  The solenoid has lasted eight years and 140,000 miles and is still going strong, so there is nothing conceptually wrong here.

You may just have a bad solenoid.  But let me put the load issue to rest:  There is no way the actual load passing through the load contacts can cause the coil to blow.  Usually overloading the contacts has the opposite effect: welding the contacts in the closed position.

If you switch the solenoid on and off repeatedly under load, the arcing that inevitably results can pit the contacts and/or char them, leading to high resistance and which, left unchecked, can ultimately lead to an "open" reading.  For this reason I recommend that any high-current loads such as air conditioners be switched off while the engine is being started and the contactor closes, and likewise before stopping the engine when the contactor opens.  Note that I am too lazy to follow this recommendation myself.

But your description here suggests you have not had this system in place nearly long enough for carbon deposits to build up on the contacts.  Moreover, if this was the problem, you should still hear the plunger moving when operating voltage is applied.

I suspect instead that the operating coil is damaged.  This can come from improper voltage -- for example, using a 12-volt coil on 24-volts.  It can also come from high back-emf when the operating voltage is suddenly removed.

The first thing I would do here is to disconnect the operating coil and measure its resistance with a quality ohmeter.  The manufacturer of your solenoid should publish the specification for coil resistance.  If the coil reads either shorted or open, it's a problem.

If the operating coil reads OK, it might be possible to open the unit to look at the load contacts.  What make and model is your solenoid?  Also, see if you can find a part number on it -- it's possible they sent you a 12-v model in error.

You can always run two solenoids in parallel so that each shares 1/2 the amp load.

and

Parallel 200 amp units will give you 400 amp capacity, 33% more than the one in the link.

Actually, this is incorrect.  First of all, you can't simply double the rating when ganging relays in parallel.  That's because there is no way to guarantee that half of the current will go through each one, and, in practice, one always gets more than the other.  For double-pole relays, manufacturers usually publish the de-rating factor that needs to be applied when ganging poles together to increase capacity; when no specification is published, the accepted standard is 25%.  So a pair of 200-amp poles ganged together is good for no more than 300 amps -- not 400 amps as your post would suggest.

But when it comes to separate, power-to-hold, normally-open solenoids, there is an even bigger problem: a failure in one solenoid would shunt the full current onto the other solenoid.  For this reason, simple, single-contact solenoids are not permitted to be ganged together to increase capacity in this way.  Certain types of contactors can be ganged, but it requires them to have "auxiliary contacts."  The control power is wired through these contacts so that if any contactor drops (opens), then all contactors will open simultaneously.  Operating this type of ganged arrangement requires momentary, rather than continuous, control signals.

For applications in the under-1000-amp range, it's cheaper to just buy a contactor rated for what you need rather than buying multiple contactors with auxiliary contacts and ganging them together.

All of that said, 200 amps continuous-duty rating should be sufficient for this application.  Remember that the amount of current drawn by the air conditioners is not the controlling factor, but rather the amount of current that can be supplied by the alternator minus whatever is being used on the chassis side.  We have a shunt and a high-quality ammeter on our inter-tie, and while inrush current can spike to just above 200 amps when the house bank (920 ah) is depleted, I have never seen it remain above 200 for more than 2-3 seconds.  The alternator simply can not supply any more than that (the inrush spike is higher due to the chassis batteries).

-Sean
http://OurOdyssey.BlogSpot.com

[wagwar]

Thanks to all who have responded!

I leave the solenoid connected all the time we are driving, so it doesn't get cycled very often. This is really the first time I've been able to test it thoroughly - as it always worked just fine in the driveway. I am also careful to turn the a/c units off before starting and stopping the engine.

The solenoid is a White-Rodgers Type 586. Part No.:586-114111

I'm using a 24vdc relay to send the signal to the solenoid, tapped off the main master bus in the front junction block. I'm sure it is a 24vdc signal and solenoid.

Sean wrote: We have a shunt and a high-quality ammeter on our inter-tie, and while inrush current can spike to just above 200 amps when the house bank (920 ah) is depleted, I have never seen it remain above 200 for more than 2-3 seconds.

Sean, I wished that I could also monitor at least the voltage running through the solenoid, but amperage would be even better. Please explain how you are using a shunt and ammeter to monitor the solenoid? I assume that by 'inter-tie' you are referring to this.

Thank you, in advance.


 

[Sean]

The solenoid is a White-Rodgers Type 586. Part No.:586-114111

That model is perfectly adequate for this application, and, in fact, is usually the exact item I recommend.  It supports up to 600 amps of inrush current and is rated for 200 amps continuous  -- you'd be hard pressed to get more than 200 continuous amps to your house system from your alternator.

The coil resistance for this model is nominally 47 ohms.  Check the coil with a good ohmmeter and tell me what you read.

...
Sean, I wished that I could also monitor at least the voltage running through the solenoid, but amperage would be even better. Please explain how you are using a shunt and ammeter to monitor the solenoid? I assume that by 'inter-tie' you are referring to this.

I happened to have a 200-amp, 50 millivolt shunt lying around, and I put this in the line leading from the chassis system to the solenoid.  I bought a surplus 50-millivolt bi-directional meter that reads "0-10" (25 mv deflection) in one direction, and "0-20" in the other.  Since it's a 200-amp shunt, I just multiply the meter reading by 10 to get amps flowing in the intertie and through the solenoid.  I hooked it up so that the 0-200 side of the meter measures current going from the chassis system (alternator) to the house system (batteries and inverter), and the 0-100 side measures the other direction.  This comes in handy when manually over-riding the solenoid to allow the charger in the inverter to charge the chassis batteries, but, of course, it pegs if I need to use the house batteries to "jump" the chassis side.


(Pardon the dust -- never-ending projects.  Also, it's hard to take flash photos of gauges.)


Shunts and meters are available from many suppliers on-line.  You want a shunt rated at least 200 amps; 500 amps is another common rating.  Most shunts are 50 millivolts, meaning that will be the amount of voltage between the terminals when the full rated current is passing through the shunt.  Most meters have their full-scale deflection also at 50 millivolts, but different meters will have different numbers and graphics printed on them.  Ideally, with a 200-amp shunt, you would want a meter that reads "0-200" on the face, but one that reads "0-2," "0-20," or even "0-2000" would work fine, as long as you know to multiply or divide as appropriate.  One that reads "0-10" or "0-100" would also work, but I find it harder to know at a glance when I need to multiply by 2 or 20 vs. just moving a decimal place.

-Sean
http://OurOdyssey.BlogSpot.com