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Open Roads Forum  >  Class C Motorhomes

 > Battery Isolator or switch?

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cudabob

Ont Canada

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Posted: 08/30/09 04:36pm Link  |  Print  |  Notify Moderator

I just recently bought a 1989 Mallard Sprinter 25" C-class motorhome w/only 48,000 miles and I am having a problem charging the extra battery.When I take a voltage off the deep-cycle in the back I only get 8 volts.Under the hood is about a 1" round steel piece with 4 lugs on it.I don't think it is an isolator(no heat sink)so I assume it is a switch?On one side of this switch(?)I am getting 14v and on the other side I am getting 8v.When I replace this thing what should I be asking for?How does this thing work?I camped overnight last night and by morning the 12v system was dead.When I fire up the generator there is 12.40v going back to the extra battery.When I plug in to 110v I get 12.75 back to the battery.This still seems a little low.I am thinking some new cables may fix this.This motorhome has sat for a couple of years and I have fixed alot of stuff but I am still enjoying it,Cheers

* This post was edited 08/30/09 04:46pm by cudabob *

pianotuna

Regina, SK, Canada

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Posted: 08/30/09 04:45pm Link  |  Print  |  Notify Moderator

Hi cudabob,

It sounds as if the house battery may be toast.

That four post thing probably is a diode based isolator. They work--but cause a 3/4 of one volt drop. So if there is 14.2 going in--the other side will have a little more than 13.4.

I'd recommend replacing the diode with a solenoid based charging system.

cudabob wrote:

I just recently bought a 1989 Mallard Sprinter 25" C-class motorhome w/only 48,000 miles and I am having a problem charging the extra battery.When I take a voltage off the deep-cycle in the back I only get 8 volts.Under the hood is about a 1" round steel piece with 4 lugs on it.I don't think it is an isolator(no heat sink)so I assume it is a switch?On one side of this switch(?)I am getting 14v and on the other side I am getting 8v.When I replace this thing what should I be asking for?How does this thing work?I camped overnight last night and by morning the 12v system was dead.When I fire up the generator there is 12.40v going back to the extra battery.This still seems a little low.I am thinking some new cables may fix this.This motorhome has sat for a couple of years and I have fixed alot of stuff but I am still enjoying it,Cheers



Regards, Don
Full Time in a Kustom Koach Class C 28'5", 256 watts Unisolar, 875 amp hours in two battery banks 12 volt batteries, Magnum 3000 watt PSW inverter.

pianotuna

Regina, SK, Canada

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Posted: 08/30/09 04:58pm Link  |  Print  |  Notify Moderator

Hi cudabob.

Now that I reread your posts and other folks answers, it may be that what you do have is a solenoid.

The solenoid is wired in such a manner that it is normally "open" and only "closes" after the alternator is producing power. It may provide better voltage to the house battery for charging purposes.

I don't do my own work, but the level of skills needed is fairly basic.

If you wish to see what I've done please surf here:

Technology

and click on "Solar Boondocking".

cudabob wrote:

I forgot to mention that the deep cycle battery is new 2 weeks ago.How do I change this system to a solinoid based system?Educate me on the reasons/advantages to the other system.Is it hard to change it over?


YC 1

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Posted: 08/30/09 04:51pm Link  |  Print  |  Notify Moderator

That round silver thing is a simple on off switch controlled by your ignition switch or other means. If you are getting 8 volts on one of the large lugs and 12.5 and over on the other, start the vehicle and see if they come to close to the same. This will at least tell you the device is working as it should. Even then there might be a 1/2 volt difference if the contacts are gettng tired.

If that voltage then comes close you really need to replace those coach batteries because at 8 volts you have some SERIOUS battery problems and you can damage your charging system or alternator trying to get that voltage up to spec.


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cudabob

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Posted: 08/30/09 04:51pm Link  |  Print  |  Notify Moderator

I forgot to mention that the deep cycle battery is new 2 weeks ago.How do I change this system to a solinoid based system?Educate me on the reasons/advantages to the other system.Is it hard to change it over?

cudabob

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Posted: 08/30/09 04:53pm Link  |  Print  |  Notify Moderator

YC 1 wrote:

That round silver thing is a simple on off switch controlled by your ignition switch or other means. If you are getting 8 volts on one of the large lugs and 12.5 and over on the other, start the vehicle and see if they come to close to the same. This will at least tell you the device is working as it should. Even then there might be a 1/2 volt difference if the contacts are gettng tired.

If that voltage then comes close you really need to replace those coach batteries because at 8 volts you have some SERIOUS battery problems and you can damage your charging system or alternator trying to get that voltage up to spec.
The voltage is 14v on the one side and 8 on the other,this is with the motor running.

Dakzuki

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Posted: 08/30/09 07:46pm Link  |  Print  |  Notify Moderator

I had my combining relay fail and replaced it with a combiner from these folks: Yandina It works both ways. When the engine is running, the house battery charges, when the house battery is charging, so does the engine battery. When no charging is taking place the batteries are isolated. I keep the truck hooked up to a battery maintainer so both batteries are ready to rock when I am.


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Cliford

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Posted: 08/30/09 09:40pm Link  |  Print  |  Notify Moderator

The solinoid should have 2 big post and wires i take it 12 volts on one and 8 on the other. The 2 little post one should go to ground and the other should be hot 12 volts when runnig the engine.
I sound to me that the solinoid in open check for the 12 volts to the little post.
I have seen some MHs that if the battery not charge up the solinoid can not close.
You should hear it click when the coil is actavated or feel it.


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pianotuna

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Posted: 08/30/09 05:05pm Link  |  Print  |  Notify Moderator

Hi cudabob,

It sounds as if the device (what ever it is) is not working. Can you disconnect one of the "8 volt" side cables and re check the voltage?

cudabob wrote:



The voltage is 14v on the one side and 8 on the other,this is with the motor running.


cudabob

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Posted: 08/31/09 09:32am Link  |  Print  |  Notify Moderator

I replaced the isolator/switch this morning and now I have 13.7 v going back to the battery when the engine is running.When I check the mallard control panel(when the engine is running)it says G (good i assume)but when I shut the engine off it says F (fair?)is this normal?It never reaches the top level "C"

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