Solenoid or battery isolator

System · March 2007

What are the advantages or disadvantages to a solenoid or battery isolator for separating the discharge to my starting battery and my battery bank in the back of my truck ( 8- 6 volt 220AH AGMs ) ... I've had my installer tell me one thing and another inverter expert tell me something else - any feedback greatly appreciated

niel · March 2007

Re: Solenoid or battery isolator

pez,
i will generalize with my electronics knowledge on the subjects, but understand that i do not have any experience with either in automotive areas and i may lack some knowledge on specifics for products available. in general both are meant to charge more than just your starting battery. we had already established that the alternator will not allow full charging of your batteries in any case.
for the isolators they use high powered diodes to stop the flow of current from going between the starting battery and the additional batteries in question from occurring. this is important for if your battery bank is 50% discharged you don't want your starting battery to discharge into the other batteries bringing it down to about the same 50% discharged state. simply put, it stops the starting battery from charging your battery bank and your battery bank from charging your starting battery. this works great except that there is roughly a half of a volt loss on the outputs of this system and there isn't any adjustment to bring it back up. this means that instead of 13.8v you will have roughly 13.3v so both will be further undercharged.
the solenoid i view like a high powered relay and can work if the driving voltage to operate the solenoid isn't too simple as to allow the solenoid to stay energized when the vehicle is turned off and thus discharge your batteries through the energizing of the solenoid. the trouble with doing it this way is that if your battery bank is 50% discharged, then so is your starting battery as they were paralleled and you are then committed to continue this until a more sufficient charge is given or you won't be starting your vehicle. on the plus side this allows the maintaining of your 13.8v.
now this is an uncommon thing, but seperate alternators and regulators would work best for the starting battery and your battery bank. this gives a more natural isolation and the maintaining of the 13.8v. the other 2 systems you mention are worse for all batteries involved. now 2 alternators are not always able to be physically mounted in a vehicle. i am not a big automotive or rv guy so i don't know what all is available. i'm sure others will have something to say on the subject.

crewzer · March 2007

Re: Solenoid or battery isolator

Pez,

They each have their pros and cons.

On the pro side, the diode isolator is relatively inexpensive and has no moving parts. If sized correctly, it should work satisfactorily for many years without requiring any maintenance. On the con side, the typical voltage drop across the diodes is ~0.7 V or so. This may not seem like much, but it will affect the quality of the batteries recharge and their life. When used with alternators whose sense line is connected to the battery, the alternator will increase it’s output voltage to compensate for this drop. However, this may cause the alternator to run hotter than normal, which would in turn reduce its output current and/or shorten its life expectancy. Also, there's a fair amount of power lost in the isolator. For example, if there's 50 A running through each diode and there's a 0.7 Volt drop across each diode, the power loss will be 50 A x 0.7 V x 2 = 70 W.

See: http://www.boatersland.com/gubais.html

The voltage drop across the relay type isolator is minimal, so that’s a pro, and so's the fact that some of these isolators allow users to manually connect the two battery banks fairly easily, if needed. However, I believe they’re relatively expensive, they contain moving/active parts that may require service, and they switch high-current DC loads, so the relay contacts may suffer damage from DC switching arcs during both break and make actions.

Here’s a link to a relay isolator that might be worth further investigation: http://www.xantrex.com/web/id/104/p/1/pt/8/product.asp

HTH,
Jim / crewzer

System2 · March 2007

Re: Solenoid or battery isolator

What I used to use was a heavy duty knife switch, to disconnect the positive of the "camping" battery from the vehicle when the engine wasn't running. Didn't cost a fortune and worked very well - - I just had to remember to open and close the switch as required. It served me well for the several years I used it and gave me great flexibility of use.
Wayne

mike95490 · March 2007

Re: Solenoid or battery isolator

Wow,
Some interesting thoughts here. It should be fairly trivial to come up with a Power FET, in conjunction with a Diode type isolator, to allow nearly 13.8V charging, as you increase drive voltage to the FET, I believe the forward drop becomes less, approaching zero.

niel · March 2007

Re: Solenoid or battery isolator

i like your idea mike.

System2 · March 2007

Re: Solenoid or battery isolator

Yes, and some of the FET's used in inverters are high amperage too.
You can also hook them up parallel, for even greater amperage.
Something interesting - I've in the past bought a couple of cheap MSW inverters just to strip out the FET's - found it the cheapest and quickest way to obtain them here.

System2 · April 2007

Re: Solenoid or battery isolator

8-) Thanks so much for the replies everyone ... I want the least amount of things to worry about, so I'll be going with the bigger alternator from the website recommended and I also found this on that same website... http://www.balmar.net/page20-Duocharge.html

...Seems like the all-in-one solution (hoping )

Grateful for your input,
Pez

mike95490 · April 2007

Re: Solenoid or battery isolator

The 30A Duo Charge remember, is to charge the starting battery, and the alternator direct charges the huge bank.
This can present an odd harness to get the big battery, at the trailer hitch, to charge, you don't want your beefy alternator to melt the wires.

System2 · April 2007

Re: Solenoid or battery isolator

"The 30A Duo Charge remember, is to charge the starting battery, and the alternator direct charges the huge bank.
This can present an odd harness to get the big battery, at the trailer hitch, to charge, you don't want your beefy alternator to melt the wires" ....

Thanks Mike, yikes, are you talking about the battery on my trailer hitch which provides power for the trailer brakes? If you are, I didn't know the truck's alternator charged that battery...

If you're not talking about that battery, the battery bank I'm trying to charge is in a toolbox in the truck bed... I have a completely separate battery bank in the trailer which will be getting charged by 4 130watt solar panels ... sorry if I'm not understanding you

crewzer · April 2007

Re: Solenoid or battery isolator

And, here's a link to some "automatic charging relay" (ACR) products I stumbled across recently: http://bluesea.com/category/2

HTH,
Jim / crewzer

System2 · April 2007

Re: Solenoid or battery isolator

"The 30A Duo Charge remember, is to charge the starting battery, and the alternator direct charges the huge bank.
This can present an odd harness to get the big battery, at the trailer hitch, to charge, you don't want your beefy alternator to melt the wires" ....

This is something similar to what I want, but in reverse.

My motorhome has a 200 amp alternator, which probably derates to 170 amps when hot. Does fine with my 2x 900 CCA start wet cells and 4x golf cart wet cell deep cycle.

But I am in process of adding solar, and have replaced 4x wet cells with 8x AGM batteries.

Here is my problem... Eventually I will deplete the AGMs to 50% charge or so. When I do, the 200 amp alternator will fry because it is not current limited. It will pour it's guts into the AGMs which will be demanding 400, 500, perhaps more amps, for a few minutes.

I need a current limiter. The Balmar Duo Charge above could do the trick, except it is only 30 amps, and I need something on the order of 100 amps.

I cannot use any of the other Balmar chargers because they require an alternator with an external regulator (to give access to the field winding), and I have a stupid alternator with internal regulator, no access to the field winding.

System2 · April 2007

Re: Solenoid or battery isolator

And, here's a link to some "automatic charging relay" (ACR) products I stumbled across recently: http://bluesea.com/category/2

HTH,
Jim / crewzer

Thanks so much crewzer

... it's getting more complicated than I expected but somehow I'll figure out which method will serve my needs best

Posted by: garryp
Insert Quote
"The 30A Duo Charge remember, is to charge the starting battery, and the alternator direct charges the huge bank.
This can present an odd harness to get the big battery, at the trailer hitch, to charge, you don't want your beefy alternator to melt the wires" ....

This is something similar to what I want, but in reverse.

My motorhome has a 200 amp alternator, which probably derates to 170 amps when hot. Does fine with my 2x 900 CCA start wet cells and 4x golf cart wet cell deep cycle.

But I am in process of adding solar, and have replaced 4x wet cells with 8x AGM batteries.

Here is my problem... Eventually I will deplete the AGMs to 50% charge or so. When I do, the 200 amp alternator will fry because it is not current limited. It will pour it's guts into the AGMs which will be demanding 400, 500, perhaps more amps, for a few minutes.

I need a current limiter. The Balmar Duo Charge above could do the trick, except it is only 30 amps, and I need something on the order of 100 amps.

I cannot use any of the other Balmar chargers because they require an alternator with an external regulator (to give access to the field winding), and I have a stupid alternator with internal regulator, no access to the field winding.

Garry, I too will have a 200 amp alternator charging a bank of 8 AGMs, but it has an external regulator ... ( this is the alternator -
http://www.wranglernw.com/ProductPickerResults.aspx?year=2001&make=1&model=61&engine=114&option=0&itemtype=12 ) the Duo Charger is too small for me now too ... please keep me posted in case I run into the same problems

...Other solenoid/isolator thing-a-ma-bobs I'm looking into ...

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

... or

mike95490 · April 2007

Re: Solenoid or battery isolator

garryp wrote:

Here is my problem... Eventually I will deplete the AGMs to 50% charge or so. When I do, the 200 amp alternator will fry because it is not current limited. It will pour it's guts into the AGMs which will be demanding 400, 500, perhaps more amps, for a few minutes.

Gary, perhaps you can rely on the long wire run's own internal resistance to help throttle that charge current down. Will you be using an isolator to prevent discharging your starter battery ? If the wire isn't long enough, add another 20 or 30' till you get the resistance you need. It's kind of a odd situation, to have to increase resistance. Saving grace is as amps recede back to the 30 or 40 amp range, the voltage loss in the wire will lessen, and you can still get a pretty good charge. Also, the AGM's may not like that much charge current. must sleep tonight....

crewzer · April 2007

Re: Solenoid or battery isolator

Here is my problem... Eventually I will deplete the AGMs to 50% charge or so. When I do, the 200 amp alternator will fry because it is not current limited. It will pour it's guts into the AGMs which will be demanding 400, 500, perhaps more amps, for a few minutes. ...I need a current limiter. The Balmar Duo Charge above could do the trick, except it is only 30 amps, and I need something on the order of 100 amps.

Garry,

I doubt that this will be an issue. The AGM battery bank may me able to handle a large charge current, but the current won't be there unless the alterator has sufficient voltage (EMF) to push it, and pushing lots of current tend to increase the surface charge on the batteries. Combined with resistance and voltage drops in the motorhome wiring, fuses and connectors, A "small-ish" alternator should not be a problem except for the recharge time required. In fact, the real problem will likely be that the alternator's output voltage isn't sufficient to fully recharge the 12 V AGM battery bank (~14.3 V at 77 F at the end of charger bulk stage and during absorb stage, measured at the battery terminals).

HTH,
Jim / crewzer

System2 · April 2007

Re: Solenoid or battery isolator

For the record, I agree with Jim / Crewzer on this one.
Wayne

System2 · April 2007

Re: Solenoid or battery isolator

I unhooked my truck alternator/trailer charge line. Now I mainly use solar to charge 4 4D sized AGM ("House" bank) and 2 Group 27 ("Chassis"/Slide/leveling jack Bank).

I used the Duo charge to isolate the House/Chassis banks. I also have a 200 Amp Continuos Duty Solenoid between the two banks if I need to parallel/combine them for more juice or for faster charging of the "Chassis" bank. The solenoid is also operated through the Duo Charge which de-activates the Duo Charge when the solenoid is activated.

In the Duo Charge You can select battery type, customize low and high voltage set points, and it has an optional battery temp sensor which is important for AGM batteries. The Duo charge only actively charges the "Chassis" bank when ther is 13v or more at the "House" bank or, in effect, if the "House" is being charged.

Now if somethning goes wrong with my "House" bank I'll still have the back-up chassis bank to pull inthe slides and jacks and get out of the woods. Or, to extend the party a little longer...

System2 · April 2007

Re: Solenoid or battery isolator

Posted by: garryp
My motorhome has a 200 amp alternator, which probably derates to 170 amps when hot. Does fine with my 2x 900 CCA start wet cells and 4x golf cart wet cell deep cycle.

But I am in process of adding solar, and have replaced 4x wet cells with 8x AGM batteries.

Here is my problem... Eventually I will deplete the AGMs to 50% charge or so. When I do, the 200 amp alternator will fry because it is not current limited. It will pour it's guts into the AGMs which will be demanding 400, 500, perhaps more amps, for a few minutes.

Hi again everyone, hope you can bear with my "newbieness" again

I know you said Garry didn't have to worry about his alternator even having enough "EMF" to charge his battery bank, but I think he was worried about his alternator overworking and burning out to try and charge the AGMs, correct?

I will be getting my new 200amp alternator installed this weekend - so will I have to worry about frying this alternator which will be charging the auxilliary batteries (8x AGMs 880ah battery bank is discharged say 10%-40%) and I drive my truck for approximately 20-40 minutes to get home?

The tech specialist at Wranglernw ( http://www.wranglernw.com/ShowCategory.aspx?categoryid=770 ) seemed to think there was a possibility of melting the alternator if my battery bank was severely depleted - I tried my best to get a straight answer from him - such as, " any rough estimate as to how long your alternators can run at full power before frying " - all he could say was "it depends on how much I'm pulling from it." He recommended a digital volt and amp meter hooked to the alternator and also to check the volt meter on the dashboard of my truck... if the dashboard meter reads that the volts are dropping, then the alternator isn't keeping up and I had better pull over...

So to sum up...

-- 880ah battery bank mounted in truck will be fully charged overnite by ProgressiveDynamics 9180 Battery Charger,
-- leave in the morning for 6 different appointment stops, each appointment depleting battery bank ~ 10% (80 ah) for 1 hour
-- drive 15 minutes between each appointment then 1/2 hour drive home for a combined total of 2 hours truck driving time to make use of the alternator partially recharging the battery bank...

Posted by: mike90045
Insert Quote
The 30A Duo Charge remember, is to charge the starting battery, and the alternator direct charges the huge bank.
This can present an odd harness to get the big battery, at the trailer hitch, to charge, you don't want your beefy alternator to melt the wires.

Mike, you didn't get back to me, but I wasn't sure what you meant by "the beefy alternator melting the wires" ... please advise :-o, I don't want to make any dangerous errors! Thanks for your help

Any thoughts and suggestions greatly appreciated

PS - Any particular size wire suggestions to run between the alternator and the battery bank?

niel · April 2007

Re: Solenoid or battery isolator

if you have doubts then you could either fuse it or put a breaker on it. 150amps is a common value and put it near the batteries. it is a good idea to have a fuse or breaker on it anyway as one mistake and it's the fourth of july with any shorts and it'll be an expensive one at that. it was also mentioned about the wiring being able to limit it some with a large voltage drop under that high of a load. that holds some merit, but the wire too will be called upon to dissipate that power in the form of heat.

System2 · April 2007

Re: Solenoid or battery isolator

Posted by: niel
Insert Quote
if you have doubts then you could either fuse it or put a breaker on it. 150amps is a common value and put it near the batteries. it is a good idea to have a fuse or breaker on it anyway as one mistake and it's the fourth of july with any shorts and it'll be an expensive one at that. it was also mentioned about the wiring being able to limit it some with a large voltage drop under that high of a load. that holds some merit, but the wire too will be called upon to dissipate that power in the form of heat.

Oh, great idea (fuse), thank you for the suggestion niel :-)

mike95490 · April 2007

Re: Solenoid or battery isolator

Melting wires with 200A alternator:
If your battery bank is low, and your alternator is cranking out 200Amps, you need some beefy wire to take that amperage, which will likely not last 200A for long, engine RPM varys, as charge builds up, amps drop. I'd expect to have it draw 200A for no more than 5 min, then it should drop back.

What gauge wire for 200 A ?
For a 12' long run, a 6ga wire will drop 1V, a 4 ga will drop .66V 4 ga would be safer, but 6 ga should work ok
I don't have a chart past 10ga.(30 A) sorry

I'd also make sure the bond wire from the engine block to chassis frame is in good condition, it should be a very beefy wire too, otherwise return amps may flow thru transmission bearings or some other nasty path to ground.

mike95490 · April 2007

Re: Solenoid or battery isolator

BTW - don't forget a good 4 or 6 ga ground wire between trailer frame, and truck frame, you don't want to weld the hitch ball ! Again, that does not happen with 20 or 30 amps, but with a 200A alternator, and the last stop of the day when the batt's are low, you could see it.

System2 · April 2007

Re: Solenoid or battery isolator

Posted by: mike90045
BTW - don't forget a good 4 or 6 ga ground wire between trailer frame, and truck frame, you don't want to weld the hitch ball ! Again, that does not happen with 20 or 30 amps, but with a 200A alternator, and the last stop of the day when the batt's are low, you could see it.

Newbie question regarding the wire between the trailer frame and truck - do you mean any of the wires in the 7-way trailer plug which connects to the truck outlet and powers the trailer lights, signals, and trailer brakes? Oh, is there a wire that runs from the truck's chassis battery to the outlet of the 7-way plug, and do you mean that wiring? Thanks Mike

mike95490 · April 2007

Re: Solenoid or battery isolator

pez wrote:

Posted by: mike90045
BTW - don't forget a good 4 or 6 ga ground wire between trailer frame, and truck frame, you don't want to weld the hitch ball ! Again, that does not happen with 20 or 30 amps, but with a 200A alternator, and the last stop of the day when the batt's are low, you could see it.

Newbie question regarding the wire between the trailer frame and truck - do you mean any of the wires in the 7-way trailer plug which connects to the truck outlet and powers the trailer lights, signals, and trailer brakes? Oh, is there a wire that runs from the truck's chassis battery to the outlet of the 7-way plug, and do you mean that wiring? Thanks Mike

Somehow I thought your batteries were in a trailer being towed. I guess not. and so my concern is misplaced.
If one was towing a trailer full of batteries, a heavy ground wire is needed, that 18 ga in the 7 pin connector won't handle too much.

Don't forget the ENGINE ground bond wire. There is usually one from the factory to get the starter motor cranking, but it's not designed to handle continuous loads, and may be rotted out, or just undersized.

System2 · April 2007

Re: Solenoid or battery isolator

Oh, ok, shwew, one less thing to worry about ... but I will make sure about the ground wiring :-) Grateful for your help Mike!

System2 · April 2007

Re: Solenoid or battery isolator

Ooh, I found this at Balmar's website ... it has a specific setting for regulating AGMs ... haven't found out the price yet but if it's reasonable this should match perfectly with the new alternator

http://balmar.net/page15-maxchargemain.html

System2 · April 2007

Re: Solenoid or battery isolator

Just gotta say that I'm a bit concerned about passing 200 amps through a 6 ga wire.
My own experience, with my solar array, is that it will noticeably warm 6 ga wire while passing only 35 amps. (granted it involves several hours at a time)
I can easily imagine softening, or melting the insulation on that 6 ga wire if I were to pass 200 amps through it. 200 amps is major stuff for that size wire.
Just thinking out loud.
Wayne

System2 · April 2007

Re: Solenoid or battery isolator

Thanks Wayne, I will look into it and let you know

Solenoid or battery isolator

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