Wiring up a dual battery question (1 Viewer)

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Looked through a number of threads and I think I have a plan in mind. I won't use the Slee kit that would have a solenoid to link the batteries for a jump start - on the off chance I ever have a dead battery, I'd just jump the cables from the aux one. So I'll use a VSR.

Had a few questions, hope someone can throw some light.

1. The diagram below does not show any fusing. I feel like every single one of these + wires should have a fuse right next to the battery + post and right next to the VSR module. Makes sense? (I could maybe avoid one set of two fuses if I put the VSR right up against the main battery with a very short cable run straight to the battery, but still, the concept remains).
2. What fuse rating should I use, and what wire gauge should I use? I am thinking 4ga wire across all paths, and 4x 100A fuses at each end?
3. Do the negatives really need to be connected in this diagram, or can I just ground each battery straight to the nearby frame?
4. If I ever do need to jump the main battery - do I need to disconnect the aux battery FIRST and THEN jump cables, or can I just hook up directly and boost?


1685972184296.png


Thanks!
 
I fused mine just on the battery positive ends, so two. Then my aux fuse panel handles the fridge and other accessories.
 
Look below your post at the bottom of the screen, a few similar threads with one being more recent with several links.
- A fuse next to each battery would be smart but not necessary. Consider an accessory panel like mentioned in post 2
- Consider taking the original frame ground and adding a properly rated 4 post BUSS bar. and extend Ground feeds of this. If you planning dual battery and accessories, its likely you will want to add more later.
- 4AWG sounds small. Size your cable per the fuses or 80 amp alternator feed. 100amp fusing would work so I would look at 2 AWG(~115) or even 1/0(~150) if you ever upgrade you alternator. I would at least match the existing alternator cable size which I believe is 1/0.
- I would disconnect the house battery when jumping but just seems smart. Why take a chance to blow your accessory fusing if you don't have to. chances are slim...
I would assume what ever isolator manufacture you go with would have this detail with the product. If not call them.




 
Look below your post at the bottom of the screen, a few similar threads with one being more recent with several links.
- A fuse next to each battery would be smart but not necessary. Consider an accessory panel like mentioned in post 2
- Consider taking the original frame ground and adding a properly rated 4 post BUSS bar. and extend Ground feeds of this. If you planning dual battery and accessories, its likely you will want to add more later.
- 4AWG sounds small. Size your cable per the fuses or 80 amp alternator feed. 100amp fusing would work so I would look at 2 AWG(~115) or even 1/0(~150) if you ever upgrade you alternator. I would at least match the existing alternator cable size which I believe is 1/0.
- I would disconnect the house battery when jumping but just seems smart. Why take a chance to blow your accessory fusing if you don't have to. chances are slim...
I would assume what ever isolator manufacture you go with would have this detail with the product. If not call them.




Nice. Thank you. Of course, the related threads come up AFTER I post a dumbass question. :D But I appreciate your reply.

- I'm somewhat worried that, for example, in the case of a frontal collision, the long run off the aux battery may crimp and short, and unless there's a fuse right next to it, nothing prevents it from making a bad time worse. I think you're right that I shouldn't overdo the fusing since the VSR will serve as a fuse block (I think?), so assuming the VSR is right next to the main battery, I think I'll fuse the long run to the aux, but leave the VSR to function as a fuse on its own.
- So you're saying I should run minus to minus and then to frame ground near the main battery without grounding the aux battery to the frame? As opposed to aux minus->frame nearby, and main minus->original frame mounting point? (essentially using the car frame as the connecting ground between the two)
- You're right, I looked at the wiring again. The OEM wiring is 4AWG as best I can tell, but it's barely 50cm to the alternator, so there's no voltage loss, whereas I'm looking at doing a ~2m run across the front of the car, so I definitely need to upgauge. 0ga it is.
- Noted. Indeed, probably best to do that - thanks.
 
regarding the -ve cable question, Yes auxillary battery must be ground to the frame and engine. They do not need to be 'tied' together like the diagram but grounded sufficiently
If you do not ground properly it will not get the full voltage and that battery will have a short life

I ground my aux battery to the Air Con bolt and one to the body mirroring the starter battery
 
regarding the -ve cable question, Yes auxillary battery must be ground to the frame and engine. They do not need to be 'tied' together like the diagram but grounded sufficiently
If you do not ground properly it will not get the full voltage and that battery will have a short life

I ground my aux battery to the Air Con bolt and one to the body mirroring the starter battery
Ah okay, I was wondering why there were two grounds on the OEM minus. Makes sense, that's how I'll ground it then.
 
This is the diagram I used, it was sourced from @NLXTACY

I do have a breaker installed next to the Blue Sea ML ACR. It is not connected as of yet because I have yet to determine my layout for the wits end 1/4 panel mount.

IMG_1361.JPG


Blue Sea .jpg
 
FWIW, most source-load circuits need only one fuse - on the source end (battery end) of the circuit.
The only circuit I fused on both ends is the run connecting the two engine room batts. And this wasn't strictly necessary as there is a dash-switched relay inline of that circuit. So in practice, in the event of an accident that pinched that crossover cable to short, it would only blow the source-end fuse (crank batt side) unless the batteries are bound at the time of the accident (relay energized) wherein both fuses would blow (or the relay may trip first).
MRBF style fuses/holders ensure batt > fuse > circuit topography. (no pigtails between batt and fuse)
 
Sorry to bring this back to life. I was reading on SDHQ's website for their dual battery setup for the 4Runner. They talk about running a negative cable between the house battery and starting battery. When I did my install I based my wiring off the picture I posted above that I acquired from Joey at Wits End, there is no negative ran from battery to battery, is this something I should install?

"The 90” Negative Main Battery to Auxiliary Battery wire will run from the
Negative Main Battery Terminal to the Negative Auxiliary Battery Terminal"
 
Sorry to bring this back to life. I was reading on SDHQ's website for their dual battery setup for the 4Runner. They talk about running a negative cable between the house battery and starting battery. When I did my install I based my wiring off the picture I posted above that I acquired from Joey at Wits End, there is no negative ran from battery to battery, is this something I should install?

"The 90” Negative Main Battery to Auxiliary Battery wire will run from the
Negative Main Battery Terminal to the Negative Auxiliary Battery Terminal"
I would guess they do that so you don't have to put in a local ground from aux to chassis and aux to engine block.
But no, it's not strictly necessary unless their kit utilizes devices wired in such a way that takes advantage of the neg run between batts.
 
I would guess they do that so you don't have to put in a local ground from aux to chassis and aux to engine block.
But no, it's not strictly necessary unless their kit utilizes devices wired in such a way that takes advantage of the neg run between batts.
I mean the only question, I suppose, is whether the resistance of the car body is higher than the resistance of a direct cable, but even if (likely, if marginally) so I feel like it shouldn’t make a huge difference.
 
I mean the only question, I suppose, is whether the resistance of the car body is higher than the resistance of a direct cable, but even if (likely, if marginally) so I feel like it shouldn’t make a huge difference.
Right.
Strictly speaking it's impedance value between batt neg term and the body. And impedance value between neg batt term and the engine block.
A ground to the chassis at say, a trailer plug, should have the same impedance as between an engine room batt and the chassis. Or the block for that matter.
Put another way, the impedance between a wheel lug nut and a batt neg term should be same as all the values above.
If there is variance...raise an eybrow, put a mental pin in it, then find a ground w/o that variance.
 
I would guess they do that so you don't have to put in a local ground from aux to chassis and aux to engine block.
But no, it's not strictly necessary unless their kit utilizes devices wired in such a way that takes advantage of the neg run between batts.
They do the ground to the chassis/block as well. Thank you all for the insight.
 
All right. Well, for better or for worse, job complete!

- I found a decent deal on copper-clad aluminium (CCA) cable, which seems to be good quality and far more affordable than all-copper
- Basically I figured that my cable is probably not as high quality as something I could've spent hundreds of dollars on, so it seemed logical to upgauge it as far as it will go to compensate, so I went with 0ga for everything.
- I also changed the OEM grounding cable that went to the fender from the current 8ga or so copper to 4ga CCA, and I also added a 0ga frame ground because why not (this is in addition to the normal engine harness ground that's already there).
- I used a module that flips the current to the battery that needs a charge. I could've gone with a solenoid and a proper "let me boost my car from the aux battery" setup, but it occurred to me that that is overkill, and then I would _really_ need proper wiring, and never really need it - I can carry boost cables for the time I'd need it.

Here's what the setup looks like.

Aux battery side. The two fuses and wires are: the smaller blue one, 100A and 4ga wire, for the audio amp + trunk wiring. This used to run to the main battery and hang off the +ve, but this was the perfect thing to flip over to the aux battery. The large red one, 150A and 0ga wire, is to go to the main battery. I know some folks here have mentioned that no fusing is needed between batteries, but I absolutely cannot fathom why (because aux is grounded to frame, and then that would mean there's a 2m long power cable that starts at the battery and goes to the VSR module, which, in the case of a collision, or something, could potentialyl short the cable somewhere where it's not fused, and bad things would happen), so I went and did it just because.

bat1.jpg


Both the blue and the red cable run across the top of the radiator, and off to the other battery.

bat2.jpg


View of the main battery. I left the fog lights and the roof bar on the main battery, because I figured there is no chance I would ever need either one with the engine off, so I don't care to move them to the aux. Blue wire connects to the red wire through a fuse that heads out through the floor to the back.

bat3.jpg


Closeup of the VSR module.

bat4.jpg


Amusingly, I am still missing the ANL fuse for the battery-to-battery connection, so I haven't actually checked if the car will set on fire or not. Soon...
 
By the way, for what it's worth, I relocated the windshield washer reservoir without needing the Slee kit - just by using longer bolts like so:

wa1.jpg


wa2.jpg


Works fine, the bolt is not long enough to stress the screw hole from what I can tell, and it's not even that it saved me 60 bucks but it's just that I couldn't easily get my hands on it.
 
Agreed, walk away from anyone saying no fuses are required on the between-batts run. That's just irresponsible. A pinch in a collision could absolutely light a rig on fire.
 

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