Dual battery wiring tutorial (and why)

[loopkiller 10+ year member]

Let's say I am going to run both of my batteries up front under the hood.. then wiring up the negatives together should not be a problem but do I even need to do that? is there different wiring diagram if I have 2 batteries up front?

Actually the same exact wiring would still apply, it would just be that WIRE 2 and WIRE 4 would be much longer. Also, the distribution block would become more logical with a multi amp setup.

I plan to fuse everything just like you showed/explained in the picture.. I am going to use 1/0 gauge wire so I guess I should have 300A fuse on all of the fuse holders? I will be powering a kicker zx2500.1..

Yes, most 1/0 awg wire I have seen is rated to 300A, so all fuses on 1/0 awg wire should be 300A fuses. The only time this would change is if your wire was rated something other than 300A.

this is a off topic question- I am wondering if you could tell me which size fuse should I use to put in the wire between my 250A HO alternator and front battery's positive post? should it be 250A or should I just get a 300A because 250 might be too close and it might blow if the alternator produces more power somehow?

First things first, always fuse based on the wire capacity rating. You choose the wire based on the current draw, then fuse based on the capacity of the wire. So in your case, you have a 250A alt, you will need 1/0 awg wire, and 1/0 awg wire is usually rated up to 300A, so you will need a 300A fuse.

There are some differing opinions on fusing the alt charge wire. I usually choose to play things safe and fuse every wire that connects to a POS+ battery post. For this wire, I would fuse as close to the battery as possible. An additional fuse at the alt end is another possibility. We have had some discussions here on the board about that extra fuse and we have not found a sound conclusion IMHO. That topic is still up for discussion.

 

[JarvisB 10+ year member]

no problem, at least I will have that wire fused at least once..

many thanks for the clarification, I will be shopping for 300A fuses then.. also I will be needing another 2 inline fuse holders (4 in total).. will order them from knukonceptz tonight, so thank you for the info

 

[jco1385 5,000+ posts]

no problem, at least I will have that wire fused at least once..
many thanks for the clarification, I will be shopping for 300A fuses then.. also I will be needing another 2 inline fuse holders (4 in total).. will order them from knukonceptz tonight, so thank you for the info

you are welcome //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

 

[JarvisB 10+ year member]

I just reread what you said in the OP..

are you saying that adding a ground wire between the battery and amp for grounding is neccessary for 2 battery set up..

so if I end up getting just one HC2400, then will I be able to just ground my amp to the chassis in the back? rather than running another long wire back to the front to connect to the negative terminal of the battery?

 

[smoka 10+ year member]

Now the other issue here that is frequently overlooked is that as you begin to draw more current over a conductor, the impedance will actually rise. So simply measuring the resistance of your chassis without a current draw is pointless.

Good post //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

DC doesn't have impedance since there is no phase angles involved (just AC). I think you mean to say resistance.

Also I don't think measuring the resistance of your ground is pointless. Resistance is a good way to measure the quality of the conductor. If your ground is passing through several welds then it will have a higher resistance than a run of 1/0 OFC wire. (You will probably need a good meter to notice the difference though)

But I see your point, if someone bolts their ground but doesn't scrape off the paint, then the resistance will be low initially since the bolt is well grounded, but when running more power the bolt will become a bottleneck to the electrical system.

I just think its not pointless to check the resistance, but it can be misleading to some.

 

[smoka 10+ year member]

WIRE 1 should be at least 1/0 awg wire. The reason why is that when batteries are connected together, they will instantly equalize in voltage. This can be hundreds of amps of current that is passed. Anything smaller than 1/0 awg wire is likely to be too small to transfer these high currents.

I would disagree about the 1/0 wire size minimum. But most people don't need a second batt unless they are pushing alot of power which makes smaller wires pointless. But there is no reason you can't use a smaller wire as long as you fuse it correctly.

'Hundreds of amps' transferring between batts would probably kill one or both batts is my guess. I've never connected a dead batt and a full batt so I can't be positive on what happens. But most people charge their batts using less than 20 amps, so I imagine that any charging at over 40-50+ amps would be damaging the batt/shortening its life.

 

[bigbangtheory 5,000+ posts]

Nice write up, however I have been running different named batteries for years with no isolator with no problems whatsoever.

I know what you are saying, just never have had that problem with a dead battery and what not. Hell my cutlass I had, had 1 redtop up front and 4 yellow tops in the back and no isolator and ran them for 2 years and hardly ever got that low.

I have actually never ran the same battery, age and model# ever, lol!

Also I never fused before the back battery, just after the battery. //content.invisioncic.com/y282845/emoticons/frown.gif.a3531fa0534503350665a1e957861287.gif

 

[loopkiller 10+ year member]

Good post //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif
DC doesn't have impedance since there is no phase angles involved (just AC). I think you mean to say resistance.

Also I don't think measuring the resistance of your ground is pointless. Resistance is a good way to measure the quality of the conductor. If your ground is passing through several welds then it will have a higher resistance than a run of 1/0 OFC wire. (You will probably need a good meter to notice the difference though)

But I see your point, if someone bolts their ground but doesn't scrape off the paint, then the resistance will be low initially since the bolt is well grounded, but when running more power the bolt will become a bottleneck to the electrical system.

I just think its not pointless to check the resistance, but it can be misleading to some.

Sorry, resistance is the word I should have used. But I still maintain that measuring resistance without current draw is pointless IMO. I don't think anyone here would argue that welded steel is a better conductor than copper wire. So I still stand by my reasoning, even if my terminology is off a little.

I would disagree about the 1/0 wire size minimum. But most people don't need a second batt unless they are pushing alot of power which makes smaller wires pointless. But there is no reason you can't use a smaller wire as long as you fuse it correctly.
'Hundreds of amps' transferring between batts would probably kill one or both batts is my guess. I've never connected a dead batt and a full batt so I can't be positive on what happens. But most people charge their batts using less than 20 amps, so I imagine that any charging at over 40-50+ amps would be damaging the batt/shortening its life.

You are right that you could use smaller wire if properly fused, but you would certainly have a voltage drop due to the smaller wire. If you have the need for a dual battery setup, you obviously are pulling a lot of power. 1/0 awg wire is probably going to be necessary anyways.

As far as batteries transferring hundreds of amps of current, you are right, two batteries alone would never pass that much, but larger banks might.

Nice write up, however I have been running different named batteries for years with no isolator with no problems whatsoever.
I know what you are saying, just never have had that problem with a dead battery and what not. Hell my cutlass I had, had 1 redtop up front and 4 yellow tops in the back and no isolator and ran them for 2 years and hardly ever got that low.

I have actually never ran the same battery, age and model# ever, lol!

Also I never fused before the back battery, just after the battery. //content.invisioncic.com/y282845/emoticons/frown.gif.a3531fa0534503350665a1e957861287.gif

Yeah and many people have sex without a condom and never get AIDS....

But then again, millions of others have AIDS //content.invisioncic.com/y282845/emoticons/crap.gif.7f4dd41e3e9b23fbd170a1ee6f65cecc.gif

Roll the dice if you want, I am simply pointing out the right way to do it.

 

[Buck 5,000+ posts]

Loopkiller.

When I hook up 2 batteries in the rear, should I use the 2 runs I have and connect 1 battery to one run and the same with the other? Or should I use a bus bar?

 

[Enellz 10+ year member]

This is an overall good right up. Even do some dont agree with the 1/0 gauge wire size, I say over kill everything when it comes to current.

 

[jco1385 5,000+ posts]

Sorry, resistance is the word I should have used. But I still maintain that measuring resistance without current draw is pointless IMO. I don't think anyone here would argue that welded steel is a better conductor than copper wire. So I still stand by my reasoning, even if my terminology is off a little.

what if you measure both (wire vs chassis) and there is very little, to no difference in resistance? the point i'm trying to make is it's way cheaper to use a common ground (chassis) if the resistance isn't crazy high, or even much higher than a 1/0 run of OFC. as we know 1/0 is not cheap, so if you can save $30-60 on a run of wire, most people want to do that.

 

[jco1385 5,000+ posts]

Loopkiller.
When I hook up 2 batteries in the rear, should I use the 2 runs I have and connect 1 battery to one run and the same with the other? Or should I use a bus bar?

i'm not following...?

2 runs from up front? 2 pos? or 1 pos/neg?

 

[Buck 5,000+ posts]

i'm not following...?
2 runs from up front? 2 pos? or 1 pos/neg?

My bad. 2 runs positive and 2 runs negative.

 

[jco1385 5,000+ posts]

My bad. 2 runs positive and 2 runs negative.

and 2 batteries out back? probably be easiest to use bus bars to connect all of that. unless you have some pimp ass battery terms

i just re-read that post. i'd def go with bus bars. then the 2 batteries out back are connected together and to the front, rather than each one connected individually to the front. see what i mean?

 

[Buck 5,000+ posts]

and 2 batteries out back? probably be easiest to use bus bars to connect all of that. unless you have some pimp ass battery terms

I have a couple of possible issues. The batcaps terminals are like set in, which means I would have to bend the bus bars to be able fit them down in the terminal. You see what I'm saying?

Edit: re-read your post. But I could just run a short piece of 1/0 connecting the 2 batts.