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Battery Isolators – solenoid type versus diode type

Question:

I am considering replacing the isolator in my 1995 Coachmen Class B. Presently it has an automotive solenoid type. What are the advantages and disadvantages of both types of isolators when used in a camper to separate the coach and house batteries when you are camping and connecting them when the engine is running? How is that for a sentence?

Response:

I am considering replacing the isolator in my 1995 Coachmen Class B. Presently it has an automotive solenoid type. What are the advantages and disadvantages of both types of isolators when used in a camper to separate the coach and house batteries when you are camping and connecting them when the engine is running? How is that for a sentence?

I can’t speak to the different types, but I can tell you what I have. My original chassis/house battery solenoid started acting erratically a couple of years ago. Sometimes it would connect the batteries, and sometimes it wouldn’t. I traced the problem to a corroded ground terminal and poor design. (It was designed to ground only through the mounting screw, which wasn’t satisfactory.) Chris Bryant gave me the WWGrainger part number (6C017, about $17) to use as a replacement, and I ordered one. It turned out to be an exact replica of the OEM one, except that the new one had a separate grounding terminal — which was of course an improvement. I installed it and it has worked fine ever since. In fact, not long after that I replaced my failing main 12v house power relay (a different type) with another one just like it — and I added a third one in my refrigerator line so that when I’m running it on 12v and turn off the engine, the refrigerator automatically turns off too. They work fine and are rated for 80 or maybe 100 amps, continuous duty. GB in NC

Response:

I am considering replacing the isolator in my 1995 Coachmen Class B. Presently it has an automotive solenoid type. What are the advantages and disadvantages of both types of isolators when used in a camper to separate the coach and house batteries when you are camping and connecting them when the engine is running? How is that for a sentence?

The big disadvantage to the diode type isolators is that the several different styles of alternators each require a different isolator.  That and the diodes are subject to damage from transients, etc. the big advantage to the relay type is that in a pinch the relay can be activated to boost off a dead cranking battery using the house batteries. That one feature is definitive for me.  My MH has a momentary switch to perform this.  As a last resort you can take a jumper clip and manually energize the relay. John — John De Armond http://bellsouthpwp.net/j/o/johngd/ Cleveland, Occupied TN

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activated to boost off a dead cranking battery using the house batteries. That one feature is definitive for me.  My MH has a momentary switch to perform this.  As a last resort you can take a jumper clip and manually energize the relay.

You can always jumper around a diode type isolator as well. Not that I like them better. I have had several diode types fail due to overheating becuase, I think, they are potted with epoxy, which does not seem to shed heat well. So Next time one fries I’ll try to get a solenoid type just hbecause they should inherently be more efficient. I wonder if anyone makes a solid state all electronic switching isolator as a stand alone……hmmmmmmm MLM

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– Hide quoted text — Show quoted text – I am considering replacing the isolator in my 1995 Coachmen Class B. Presently it has an automotive solenoid type. What are the advantages and disadvantages of both types of isolators when used in a camper to separate the coach and house batteries when you are camping and connecting them when the engine is running? How is that for a sentence? The big disadvantage to the diode type isolators is that the several different styles of alternators each require a different isolator.  That and the diodes are subject to damage from transients, etc. the big advantage to the relay type is that in a pinch the relay can be activated to boost off a dead cranking battery using the house batteries. That one feature is definitive for me.  My MH has a momentary switch to perform this.  As a last resort you can take a jumper clip and manually energize the relay. John

John:  I went the relay route myself.  Nobody has mentioned this yet in this thread, but I believe you also lose 0.5 volts across the solid state isolator.  Your house batteries never get fully charged. – Sandy

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John:  I went the relay route myself.  Nobody has mentioned this yet in this thread, but I believe you also lose 0.5 volts across the solid state isolator.  Your house batteries never get fully charged.

It all depends upon where the voltage sensing is accomplished. If the system is set up for remote sensing, then the batteries *will* receive the correct charge. — D.J., N8DO; FMCA 147762 davidjosborn at sbcglobal dot net

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<< They work fine and are rated for 80 or maybe 100 amps, continuous duty. GB in NC I’d be concerned about a rating that includes a "maybe." Tom M

Response:

John:  I went the relay route myself.  Nobody has mentioned this yet in this thread, but I believe you also lose 0.5 volts across the solid state isolator.  Your house batteries never get fully charged. It all depends upon where the voltage sensing is accomplished. If the system is set up for remote sensing, then the batteries *will* receive the correct charge.

Correct.  But if I remote sense the charging voltage on the other side of the isolator, I’ll boil the starting battery due to over voltage. – Sandy "still uses 2 alternators" Nicolaysen

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<< They work fine and are rated for 80 or maybe 100 amps, continuous duty. GB in NC I’d be concerned about a rating that includes a "maybe."

LOL. It isn’t the rating that includes a "maybe" — it’s my memory. GB in NC

Response:

– Hide quoted text — Show quoted text – John:  I went the relay route myself.  Nobody has mentioned this yet in this thread, but I believe you also lose 0.5 volts across the solid state isolator.  Your house batteries never get fully charged. It all depends upon where the voltage sensing is accomplished. If the system is set up for remote sensing, then the batteries *will* receive the correct charge. Correct.  But if I remote sense the charging voltage on the other side of the isolator, I’ll boil the starting battery due to over voltage.

That’s not correct. There’s a diode between each battery and the alternator, and so each battery sees a lower voltage than is put out by the alternator. — D.J., N8DO; FMCA 147762 davidjosborn at sbcglobal dot net

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John:  I went the relay route myself.  Nobody has mentioned this yet in this thread, but I believe you also lose 0.5 volts across the solid state isolator.  Your house batteries never get fully charged.

I didn’t mention that because if you go through the hassles of identifying the right isolator, with the correct sense hookup and all, then this isn’t a problem.  Unless you’ve been mis-guided enough to have been talked into converting to a one wire alternator.  then you’re SOL….   In any event, seems like a lot of work to get around just hooking up a twelve dollar relay :-) John — John De Armond http://bellsouthpwp.net/j/o/johngd/ Cleveland, Occupied TN

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