Dual Battery install and questions

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J

Jan-78FJ40

Joined
Sep 6, 2002
Threads
243
Messages
3,587
I put a dual battery system into my HJ60, and have some questions. As a system I used to Mobi-Arc Isolator (http://www.perfectswitch.com/isolator.htm), for the following reasons:
It is built locally
I saw the factory and got a great demonstration of the part
No amperage loss
No heat generation

I need this to power gadgets like fridges and lights, without drining the starting battery.
I put a second stainless battery tray in, and added a deep cycle battery. This connects to the isolator, which connects to the starting battery, which connects to the starter.
The input from the alternator and the fusible link connect to the axiliary side of the isolator.
The aux battery connects to a fuse box inside the cab, which powers outlets in the back of the truck. Like this the starting battery never drains, even if the aux runs completely empty.

Here are my concerns: In my setup, the fusible link connects to the aux battery. So if I drain it completely, things like the starter relay, or the glow circuit would not have power anymore. So even if the starter has a full battery as it's disposal, it would not kick over. This obviously defeats the purpose of the setup.
To solve this, the fusible link should connect to the main battery, but the alternator output should connect to the aux side of the isolator, to be able to charge both batteries.
I don't know how to do that, since the alt first goes into the voltage regulator, and then over 10 other circuits (looks like the in the wiring diagram) to the battery.
Also, in the wiring diagram it looks like there are 3 leads going to the battery, but I have only 2.
couod anyone advise me on how to do this correctly?
thanks
J

here are the pics:
starting battery
aux battery
relocation of washer bottle
 
Last edited:
Here's the fuse block, and the outlets in the back.
 
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Looks to me like a question for the manufacturer. In my setup I use the aux bat to run everything but the starter. My headlights, stereo, inverter and all other accessories come off of the aux battery, then the starter and the rest of the factory wireing comes off of the main battery (not counting headlights).
 
Jan-78FJ40 said:
I put a dual battery system into my HJ60, and have some questions. As a system I used to Mobi-Arc Isolator (http://www.perfectswitch.com/isolator.htm), for the following reasons:
It is built locally
I saw the factory and got a great demonstration of the part
No amperage loss
No heat generation

I need this to power gadgets like fridges and lights, without drining the starting battery.
I put a second stainless battery tray in, and added a deep cycle battery. This connects to the isolator, which connects to the starting battery, which connects to the starter.
The input from the alternator and the fusible link connect to the axiliary side of the isolator.
The aux battery connects to a fuse box inside the cab, which powers outlets in the back of the truck. Like this the starting battery never drains, even if the aux runs completely empty.

Here are my concerns: In my setup, the fusible link connects to the aux battery. So if I drain it completely, things like the starter relay, or the glow circuit would not have power anymore. So even if the starter has a full battery as it's disposal, it would not kick over. This obviously defeats the purpose of the setup.
To solve this, the fusible link should connect to the main battery, but the alternator output should connect to the aux side of the isolator, to be able to charge both batteries.
I don't know how to do that, since the alt first goes into the voltage regulator, and then over 10 other circuits (looks like the in the wiring diagram) to the battery.
Also, in the wiring diagram it looks like there are 3 leads going to the battery, but I have only 2.
couod anyone advise me on how to do this correctly?
thanks
J

here are the pics:
starting battery
aux battery
relocation of washer bottle
Click to expand...

Hi Jan,

It seems odd to me that the alternator would connect to the aux side of the isolator. You want the starting battery to have charging priority at all times. If for any reason the isolator opens (separating the batteries) you would otherwise be charging only the aux batt.

To my knowlege most RV type power systems distinguish between chassis and "house" power. That is engine charge, start, and run circuits are in one power domain, while the fridge, welder, lights, pumps, etc. are in the other.

As long as your chassis electrical system is in good order, I don't think you would have a problem with inadvertently discharging your starting battery. I recommend keeping your wiring simple and not to try to wrangle with which side of the isolator to put engine and chassis circuits. Just leave them as-is.

I have to caution against using sollid state isolators. While the MOSFET type is better than a simple diode isolator, it will still result in voltage drop. That means that your aux battery will never be fully charged. This can lead to premature failure. If the isolator ever shorts (MOSFETS are notoriously static sensitive), both batteries could fail explosively.

For what its worth? :cheers:
 
Mountain Goat said:
Hi Jan,

It seems odd to me that the alternator would connect to the aux side of the isolator. You want the starting battery to have charging priority at all times. If for any reason the isolator opens (separating the batteries) you would otherwise be charging only the aux batt.

To my knowlege most RV type power systems distinguish between chassis and "house" power. That is engine charge, start, and run circuits are in one power domain, while the fridge, welder, lights, pumps, etc. are in the other.

As long as your chassis electrical system is in good order, I don't think you would have a problem with inadvertently discharging your starting battery. I recommend keeping your wiring simple and not to try to wrangle with which side of the isolator to put engine and chassis circuits. Just leave them as-is.

I have to caution against using sollid state isolators. While the MOSFET type is better than a simple diode isolator, it will still result in voltage drop. That means that your aux battery will never be fully charged. This can lead to premature failure. If the isolator ever shorts (MOSFETS are notoriously static sensitive), both batteries could fail explosively.

For what its worth? :cheers:
Click to expand...

cool, thank you for the advice!
the reason why the alt connects to the aux side is that the flow of current can only go from aux to starting battery, not the other way around. If I undewrstand this correctly, then the aux would never charge.

I have to look into this deeper.

thanks,
jan
 
this is the charging circuit in my truck.
do I understand it correctly that the fusible link on the left (1.0Y) is the one supplying the juice from the alternator?
Yes I know, I am bad with this...

thanks
Jan
 
Last edited:
Jan-78FJ40 said:
this is the charging circuit in my truck.
do I understand it correctly that the fusible link on the left (1.0Y) is the one supplying the juice from the alternator?
Yes I know, I am bad with this...

thanks
Jan
Click to expand...

Yes. That's correct. It protects that alternator. All current to and from the batteries will flow through this link.
 
Mountain Goat said:
Yes. That's correct. It protects that alternator. All current to and from the batteries will flow through this link.
Click to expand...

so then the two links could be seperated, with the alternator 1.0 going to the aux side of the isolator, and the ignition 0.5 one from the main battery.
like this both batteries can charge, but the ignition circuit, and everything that hangs on it (glow, radio...) would still work when the aux battery is empty.
it seems that the only thing connecting the two links is the ignition main relay, and that just allows continuity between poles 2 and 4 when 1 and 3 are energized.

thank you!
Jan
 
Jan-78FJ40 said:
so then the two links could be seperated, with the alternator 1.0 going to the aux side of the isolator, and the ignition 0.5 one from the main battery.
like this both batteries can charge, but the ignition circuit, and everything that hangs on it (glow, radio...) would still work when the aux battery is empty.
it seems that the only thing connecting the two links is the ignition main relay, and that just allows continuity between poles 2 and 4 when 1 and 3 are energized.

thank you!
Jan
Click to expand...

You could do it that way, but watch out. Those FSM wiring diagrams are way over simplified. :)
 
I'll jump in here to clarify. You are absolutely correct that there is a voltage drop, but the total voltage drop at full current is less than 20 millivolts, that's 20,000th's of a volt.....that's less resistance than 18 inches of #4 cable. As such, full charging does occur....all day, every day. With respect to static sensitivity, MOSFET's are static sensitive when they're floating, not when installed in an engineered package. In terms of shorting or failure, you're much more likely to weld a solenoid shut than short the FET's, statistically speaking. Your words of caution are well intended, but POWER-GATE is a technological departure from any other isolator out there.




Mountain Goat said:
Hi Jan,

It seems odd to me that the alternator would connect to the aux side of the isolator. You want the starting battery to have charging priority at all times. If for any reason the isolator opens (separating the batteries) you would otherwise be charging only the aux batt.

To my knowlege most RV type power systems distinguish between chassis and "house" power. That is engine charge, start, and run circuits are in one power domain, while the fridge, welder, lights, pumps, etc. are in the other.

As long as your chassis electrical system is in good order, I don't think you would have a problem with inadvertently discharging your starting battery. I recommend keeping your wiring simple and not to try to wrangle with which side of the isolator to put engine and chassis circuits. Just leave them as-is.

I have to caution against using sollid state isolators. While the MOSFET type is better than a simple diode isolator, it will still result in voltage drop. That means that your aux battery will never be fully charged. This can lead to premature failure. If the isolator ever shorts (MOSFETS are notoriously static sensitive), both batteries could fail explosively.

For what its worth? :cheers:
Click to expand...
 
I stand corrected. Thanks for the info.
 
I'd like to clarify here.
I am not complaining about the isolator at all. On the contrary, I think it is the best one out there, and I am completely happy ans satisfied that I went with it.

I would have the same problem with any system, since I don't have a designated 'in' line from the alternator.

nothing a bit wiring-tinkering can't solve.


cheers,
jan
 
So the auxillary or secondary battery is for running things like fridge, and other such devices that you have wired in the back. But I'm a little confused about how this works.

It looks to me that current can always flow from the auxillary side to the primary side, but not vice-versa. So if there is something causing a drain on the primary side, say headlights left on, then both batteries will completely drain and you won't be able to start the vehicle, even if you move the second battery over. Am I missing something?

Devices like the Hellroaring or solenoids typically allow you to charge both systems but keep them completely independent. And then with a flip of a switch you can combine the batteries. This way you can give your winch some extra juice or jump your starting battery from your auxillary.
 
Cruzerman said:
So the auxillary or secondary battery is for running things like fridge, and other such devices that you have wired in the back. But I'm a little confused about how this works.

It looks to me that current can always flow from the auxillary side to the primary side, but not vice-versa. So if there is something causing a drain on the primary side, say headlights left on, then both batteries will completely drain and you won't be able to start the vehicle, even if you move the second battery over. Am I missing something?

Devices like the Hellroaring or solenoids typically allow you to charge both systems but keep them completely independent. And then with a flip of a switch you can combine the batteries. This way you can give your winch some extra juice or jump your starting battery from your auxillary.
Click to expand...

That is correct. If I forget the headlights, bot batteries will drain. But I am not worried about that.

cheers,
jan
 
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