Electrical Advice, Isolator or Solenoid

[BC Bus]

Here's what I have;
GMC Buff 24 Volt system, Onan Gen, Trace 3624 Inverter which powers A/C while underway, Vanner equalizer to power 12 volt systems in bus (interior lights, running lights, ec),

I have been running the Inverter, and A/C off of the Chassis Batts so far with no problem.  Now I am installing another bank of 24v house batts.  In tying the new house batts to the bus batts, mainly to charge while underway, and to run the a/c, what would be the best hardware to do this, solenoid or battery isolator?  And what amperage of either item and where is a good place to get them? 

Right now when I am running down the road I run off the 3624, the rooftop a/c, a small 120vac fridge, 20" Plasma TV.

Thanks for your ideas,
Bill

[H3Jim]

I have a 300 amp isolator I bought from Dick Wright.  I have been very happy with it so far, and its been on there for 2 years.  24 volt on both bus and house system.  Its been totally seamless, it just charges when the bus engine runs. I always get to a location with my batteries fully charged.

The only concern I have is charging the AGM house batteries too quickly, shortening their life.  The one stage bus regulator uses the start batteries to determine charge. If they are too discharged, then the alternator will  likely put out enough current to quickly charge them, and the house bats will get it too.  Charging too fast with the resultant heat and outgassing will shorten battery life.

Having said that, my house batteries show no signs of having their emergency valves open, and after 2 years are still very healthy.  I hope to get moe than 8 years from them, so the jury is still out.

[Melbo]

I had the same question when I was doing my set up

I went with an Isolator because with a solenoid the current can flow either direction and when the charger is on and one bank of batts has a lesser charge than the other not only do you have the generator suppling power the banks of batteries try to balance each other as well.

I'm not sure how much difference this will make but it will make a difference in the life of the battery banks.

The cost of the isolator was less than the cost of one of my house batteries so the bank of four hopefully will last longer and help pay for the isolator.

Your mileage may vary.

Melbo

[Gary '79 5C]

Jim,
At what voltage is your bus voltage regulator set? I have the same set up with the reg in the MCI set for 27.6 volts, thru the Vanner that is 13.8 Volts. Which I believe is low enough not to fry the AGM's. Maybe I am missing something, which happens more frequently now.

Hope this helps.
Gary

[Stan]

Melbo: Having the ability to flow current in both directions is the reason people use a solenoid. If you have a manual switch for the solenoid, you can use the house batteries to crank the engine if necessary.

I don't understand your theory on charged batteries flowing current into low batteries while charging. If the solenoid is not energized until the alternator is charging, current will be flowing iintoeach set of batteries, with the majority of the current going into the low set.

[H3Jim]

Stan, the low batteries absorb more charge, therefore more heat,  If the heat is too great, it outgases the battery, and uptimately damages the battery.  Thats why 3 stage, temperature compensated chargers help the batteries so much.  If it gets too hot, it backs off.

AGM batteries have an emergency valve in them, so if they get so much charge it starts to outgas, the gas has a place to go rather than blow up.  but it does shorten battery life.

[Jerry Liebler]

A solenoid is my strong recomendation.  All isolators have a voltage drop of 0.7 to 1.4 volts of drop so the voltage regulators, in both the inverter charger and bus alternator must be sensing the actual battery voltage.  With most, if not all, inverter chargers this is not possibile, it can be done on the bus side with some rewiring.  Undercharging batteries seriously shortens their life in addition to significantly reducing their capacity.  Your inverter will draw about 190 amps at full load.  I'd recomend a 2-0 cable from the bus to the house system protected by a 200 amp fuse or circuit breaker and a solenoid contactor rated for 200 amps continuous duty. With a solenoid contactor you can charge the bus battery from the inverter and use the house batteries to help start the bus, neither of these options are possible with an isolator.  To fully charge your batteries you need a minimum of 26.4 volts at the battery.  If you use AGMs you'll need to set your bus regulator to the maximum float voltage recomended by the battery manufacturer.  BTW I just bought a 200 amp self reseting circuit breaker, the darned thing cost over $140 and I had a tough time finding it.  To those worried about exessive charging current when a discharged battey is connected to a fully charged one, it is a non issue with batteries that can be carried in a bus and even group 31 start batteries just because of how battery curent affects voltage.   
Regards
Jerry 4107 1120
 

[H3Jim]

just a note, I did not have to rewire the regulator.  The bus regulator senses voltage at the batteries,   so the voltage drop across the big diode is already taken into account.

I rerouted the wire from the 50 DN alternator to the center post of the isolator, no change in length due to where I mounted it.  It used to go to the post on the starter motor.  I made a short cable to connect one of the output posts on the isolator to the starter motor.  That completed the change in  bus wiring.

I made a cable that went from the other output on the isolator to the house batteries ( through a shunt).  And I was complete.  The shunt is there so I can measure all inputs and outputs to the house bats thereby having a the equivalent of a fuel gauge for the house batteries, very handy if you use the coach a lot.

Very simple installation. 

I do have a "cheater" cable that I can  use to jump bewteen the two isolator outputs if I ever need to use the house batteries to help start the coach.

[Jerry Liebler]

BC,
    If you are taking out the bus AC then you have all the parts for the solenoid intertie.  The contactor is one that used to power the huge blowers, it's even wired so the bus generator must be delivering to energise the solenoid.  The wires and circuit breakers also can be 'recycled'. I even use the switch on the driver's side panel that used to select heat-off-cool, in the cool position it closes the solenoid if the bus engine is running while in the heat position the solenoid closes if I have shore or generator power.  Thus if I should find the bus Bartery too discharged to start the bus I can start the generator and charge it through the inverter's charger.
Regards
Jerry 4107 1120

[Jerry Liebler]

Jim,
    One of the advantages of AGM batteries over flooded cells is the fact that they can be charged with higher currents provided the voltage is limited to a value below that at which excessive gassing occurs.  This is due to the different plate alloy used and the 'starved' electrolyte construction.   Your battery manufacturer has a recommended maximum voltage  during the 'absorption' phase of 3 stage charging (probably between 28.4 and 29 volts) and a maximum float voltage for long term use (probably between 26.4  and 27.4).  If you set your bus regulator to deliver the maximum float voltage
you'll only risk not fully charging the house bank from the bus because there is never going to be more than a 1 volt difference between the sides of the isolator while charging from the bus alternator.
Regards
Jerry 4107 1120 

[Stan]

H3Jim: quote "Stan, the low batteries absorb more charge, therefore more heat,  If the heat is too great, it outgases the battery, and uptimately damages the battery.  Thats why 3 stage, temperature compensated chargers help the batteries so much.  If it gets too hot, it backs off." unquote

I understand that, but how does that cause current to flow from a more highly charged battery to a lesser charged one?

[Jerry Liebler]

All,
    Gassing of a battery is NOT due to heat.  Gassing is the electrolysis (breakdown into hydrogen and oxygen) of water and only occurs at a high enough voltage quite independent of current.  Below the gassing voltage the charging current causes a chemical reaction between the electrolyte and the plate materials, little heat is generated in this reaction but it does cause the density (specific gravity) of the electrolyte to rise. As the ingredients in the charging reaction become more 'scarce' the voltage rises eventually leading to gassing.  For typical lead acid chemistries the gassing voltage is above 2.2 volts/cell.  That's why float charging results in very little gassing.  However gassing starts when the battery is only about 85% charged and if the voltage is held at that level charging gets really slow a fully charged condition will simply never occur.  A voltage in the gassing region is needed to completely charge a lead acid battery, that's what 3 stage charging is really all about, getting the last 10% of charge into the battery.  For most lead acid batteries including AGMs the absorption voltage (in the gassing region) needs to be applied for 2 to 3 HOURS.
Most automotive battery systems simply never charge the battery fully being content with 90% of maximum capacity.
Regards
Jerry 4107 1120

[BC Bus]

Good discussion guys, as usual, everyone has there own way, that's what makes this board so good. A guy can look at all of the idea and pick the one he likes. 

How about some of you electical gurus do a review on this item:  be sure to scroll ALL THE WAY TO THE BOTTOM of the page.  It looks perfect, but......you tell me....

http://www.hellroaring.com/bic75300.php

BC

[Sean]

Well, BC, since you asked: Completely useless for bus purposes.

First off, this overhyped piece of equipment is nothing more than a 95-amp isolator combined with a 95-amp bypass solenoid, and an LED.

The solenoids and isolators we're talking about for most bus conversions start at a low of 200 amps, and go up from there.  Even the HellRoaring web site says you'll need at least two of their product even for a diesel automobile, never mind a bus.  I'm not sure where any of us could use a 95-amp anything -- starting current is much higher on a bus, and most of us have battery and charging systems that can supply or demand much more than that.

On the main topic, BTW, I weigh in on the solenoid side.  I had a pair of 350-amp isolators when I got the bus, and I ripped them out and put in a 200-amp solenoid.  I'm much happier.  No voltage drop, easy to implement "emergency start", it all just works seamlessly.  And I'm not having to dump all that heat someplace.  FWIW.

-Sean
http://ourodyssey.blogspot.com

[TomCat]

If you decide a solenoid will do what you want, a good place to determine the one you want is here...http://texasindustrialelectric.com/relays.asp
Then go to the ePlace or other net site to find it at a better price.
I found a White-Rogers 586-902 on the ePlace for $14.95 with a bent mounting tab...BARGAIN!

Jay
87 SaftLiner