Help me wire my fridge! (1 Viewer)

[nhs15]

1995 FZJ80.
Just installed dual battery setup using the HuddExpo kit. All went well. Aux battery is a flooded marine deep cycle. Taller but still fits.
Want to run power to the rear for a small camping fridge and charging outlets. Trips are typically long weekends with the truck driving daily.
Bought 4awg to run from aux battery positive to a bluesea accessory panel 4366 for the rear area that has a voltmeter and a built in 15 amp circuit breaker.

Questions are:
1) I assume I can run a negative ground wire from the accessory panel to a metal panel in the rear. What gauge wire to use?
2) Do I need to have an inline fuse leaving the aux battery positive terminal towards the panel?
3) Any other recommendations?

Thank you!

 

[AirheadNut]

Where is your secondary battery mounted? If it is in the engine bay or anywhere not adjacent to the accessory panel then you will need a fuse at the battery, sized according to the expected load the panel can provide and slightly less than what 4awg cable can support. Your ground should be the same size as the positive cable, I would recommend a chassis ground (or do a dedicated ground back to the battery).

 

[nhs15]

Thank you. Yes auxillary battery is in engine bay. 4 gauge wire from that to the rear with a 125 amp fuse at auxiliary battery positive terminal. That wire goes to a blue sea mini busbar in the rear of truck. Then 10 gauge positive wire from busbar to blue sea accessory panel in the rear neat busbar. 10 gauge negative wire from accessory panel to metal panel in rear. Hope that makes sense and is safe and efficient.

 

[e9999]

personally I prefer to have a return ground wire to the battery rather than relying on the body. Less uncertainty. There was a discussion about that here someplace not too long ago.

 

[TreadingLight]

1995 FZJ80.
Just installed dual battery setup using the HuddExpo kit. All went well. Aux battery is a flooded marine deep cycle. Taller but still fits.
Want to run power to the rear for a small camping fridge and charging outlets. Trips are typically long weekends with the truck driving daily.
Bought 4awg to run from aux battery positive to a bluesea accessory panel 4366 for the rear area that has a voltmeter and a built in 15 amp circuit breaker.

Questions are:
1) I assume I can run a negative ground wire from the accessory panel to a metal panel in the rear. What gauge wire to use?

As others mentioned you ideally use the same gauge wire as you used on the positive side. And you'd want it grounded to solid metal, like the frame.

However ... for a fridge and some chargers 4g cable is overkill and a sheet metal ground would work fine.

2) Do I need to have an inline fuse leaving the aux battery positive terminal towards the panel?

A fuse or a circuit breaker. Up to 80a roughly if you use 4g cable and a solid ground.

3) Any other recommendations?

Thank you!

Use this as an opportunity to inspect/upgrade your grounds. If you ground your aux panel to the frame in the rear, you also want to have a good ground cable from the frame to the aux battery up front also. Using the frame spares you from having to run a long length of 4g neg cable from the battery to your fusebox. It also eliminates the risk of putting your accessory grounds in parallel with the main grounds.

Then have the main battery grounded to the frame on the same bolt or one nearby. At the same time you can replace the shoddy oem body/engine ground combo cable on your main battery.

 

[FrazzledHunter]

personally I prefer to have a return ground wire to the battery rather than relying on the body. Less uncertainty. There was a discussion about that here someplace not too long ago.

There's a lot of folks with 2nd batteries or are contemplating adding them so I'll throw this out.
I have a 2nd AGM battery powered/charged by a REDARC BCDC1225D.
That creates 2 independent power sources.

So I followed these 2 rules:

1. If the circuit originated on the starter battery side I would run the neg wire back to the starter battery neg or use the chassis.
   1. The choice for the neg wire on chassis or not was made based on convenience, ability to run the wire and concerns over corrosion on chassis connections.
2. If the circuit originated from the 2nd battery the ground always goes back to the 2nd battery neg no exceptions.

I did this because I THINK that you can get bad ground loops if you don't isolate secondary power sources. It's my understanding that you do this when adding additional alternators - something that I almost did and during consultations with the alternator vendor was counseled to keep all circuits on that 2nd alternator isolated. However, I never did the 2nd alternator, I just upgraded the OEM unit.

I am also not sure what the ECU will do if more current returns than is sent out by the alternator. Might it throw some sort of code? I'm too cowardly to try it and I'm speculating that it might be an issue. I could be over thinking it but everything works so far with the approach I've taken.

 

[TreadingLight]

I just saw your update from this morning so I'll amend my response a bit.

It's a little bit odd that you've run a 4g cable for the positive side and a 10g cable grounded to sheet metal for the negative. Its just a bit asymmetrical. If you wanted to make this more rugged and have room for future expansion, I'd add a nother bus bar grounded to the frame with a 4g cable, similar to your positive run. Then follow my previous notes on the rest of your grounds.

As far as safety, my only concern is the 10g run from the bus bar to the fusebox. Right now that circuit is fused for 125a which is a lot for a 10g cable should something go wrong. I would either:

1) put a small fuse, 30a or so, on the 10g wire OR

2) replace the 10g wire with a 4g wire. That won't burn up before the 125a fuse pops.

Final note, 125a is on the ragged edge for a long 4g run. I'd fuse it at 80 or 100a personally but I tend to be conservative about circuit protection.

 

[e9999]

^ he said there is a 15A breaker on the panel, so the 10 ga is protected by that I assume.

 

[nhs15]

Great info. I can change the 125amp inline fuse from the aux battery terminal to a 100amp. Yes the blue sea accessory panel has a 15amp breaker on it.

Only reason I added that positive mini busbar was it was hard to find a 4g female disconnect terminal. So I used a 10g wire from the busbar to the accessory panel and then matched that with a 10g negative local ground.

 

[TreadingLight]

I see. It looks like the blue sea USB/cig lighter panel has a built-in 15a breaker and has a 1/4" male spade terminal for power. Makes sense that you wouldn't be able to put the 4g cable on it directly.

I am wondering though, why the 4g cable for a 15a load? Do you plan to expand to include high draw devices (inverter, amp, etc)? If not you could use a 14g wire and leave out the bus bar. Cheaper and simpler.

If you do plan to expand that rear circuit, then consider the frame grounded bus bar and look at your main grounds as I mentioned earlier. Most of the 80s I've looked at had very ratty corroded battery grounds.

 

[nhs15]

Yeah I guess I could have run a smaller wire but I figured do it once and then its more future proof.

I'll check out all my grounds.

 

[TreadingLight]

Future proofing. Makes sense.

 

[ntsqd]

Something to keep in mind with long wire runs is the voltage drop can get quite significant. This is particularly a problem when trying to charge batteries at that distance. When charging batteries what decides the wire size is no longer simply the max amps expected, it is the max acceptable voltage drop at that max amperage.

With dual battery systems I ground both battery's to the same bolt. None of my vehicles require a DC-DC charger. I think that I would float the aux battery entirely if/when I do have to deal with a 'stoopid' alternator. The vehicle would get a floating negative bus system that all aux battery loads were grounded to.

 

[jgranthevagrant]

I have a dual battery system, but not grounded to the same bolt. What is the rationale behind grounding to the same bolt?

 

[ntsqd]

When they are connected together and not grounded to the same bolt there is a tiny resistance in the ground path. between the - battery terminals. Since two batteries are never exactly the same SoC this means that one battery is slightly higher voltage and it will try to charge the other battery. That tiny resistance dissipates power as heat, which causes the SoC's to see-saw, ultimately killing both batteries and limiting them to a very short life-span.

This is really more of a problem when it is two batteries that are always connected than when there is an isolator between them, but after living that nightmare for a while with a factory-wired dual battery system before figuring out what was going on (both batteries grounded to the engine block, but not to the same bolt) I consider it best practice even with isolated batteries to ground to the same bolt. Subsequent experience has shown that the batteries do live longer when grounded to the same bolt, even when there is an isolator in the system.
Best practice with two batteries always connected in parallel and no isolator is to connect + to + and - to - with heavy cables, and then connect the ground at one battery and power at the other. Even then, they are effectively grounded to the same bolt.

 

[jgranthevagrant]

Good to know. I will take a look and see if that is possible. I don't really want to redo the entire cable if I can avoid it, but something to think about for the future. I'm hoping to upgrade the house battery to a LiPO4 within about 6 months.

 

[ntsqd]

The rules change a little with LiPo or LiFePO4 (which is safer for an RV house battery type of use). I'm not as conversant about them, but I suspect that the presence of the BCM usually coupled with the use of a DC-DC converter/charger to charge it might mean that grounded to the same bolt isn't nearly as important. In my own eventual use of a LiFeO2 house battery I plan to float the grounds from the vehicle. Essentially I will wire the house battery like is done with a fiberglass boat.