Best way to hook 2 batteries together

[SolarNorm]

I have created two illustrations to provide a talking point.

Image #1 Image #2


So these batteries are wired in parallel for a 12 volt system, using 2-12 volt 230 amp AGM Batteries.

I believe the 1st image depicts the "best way" to wire, however I have been told the 2nd image will work too.

I'm guessing it's an "electron flow issue" that may make the 1st image better. Which is better and why?

EEs thoughts here?

 

[gnubie]

They are trying to match the resistance of the wire so that each battery will be called on to deliver the same current, assuming they were identical in every way.

In the 2nd option the other 2nd battery has the additional resistance of both wires going to it's terminals while in the first the added resistance is distributed by the - supply wire to the load being on the 2nd battery.

The third option would be to have a central stud for + and - and run equal lengths of wire from the batteries + and - ( the wires on + can be a different length to the wires on - ) and then to attach the load at the central studs.

A clamp meter will show you exactly where the current is flowing in all cases, and make it easier to understand.

 

[SolarNorm]

They are trying to match the resistance of the wire so that each battery will be called on to deliver the same current, assuming they were identical in every way.

In the 2nd option the other 2nd battery has the additional resistance of both wires going to it's terminals while in the first the added resistance is distributed by the - supply wire to the load being on the 2nd battery.

The third option would be to have a central stud for + and - and run equal lengths of wire from the batteries + and - ( the wires on + can be a different length to the wires on - ) and then to attach the load at the central studs.

A clamp meter will show you exactly where the current is flowing in all cases, and make it easier to understand.

Both of the Batteries are Victron AGM style 12v-230a and identical. The leads wires from the Inverter/Charger to the #1 Battery as shown are just about 20 inches in length each, including the Ceramic Fuse, the difference (as shown in image 2) is probably less than 3 inches, i.e. the Black Wire connecting Battery #2 to Battery #1. All Battery Cables are 1/0 high strand count.

 

[gnubie]

If the wires between the batteries in picture #2 are that short and that heavy there's not going to be a lot of difference. Each way of hooking up the batteries has its advantages and disadvantages. If you are happy with #2 that's good enough.

 

[svetz]

You might also find this of interest: http://www.diysolarforum.com/index.php?threads/battery-faq.200/post-1751

 

[SolarNorm]

If the wires between the batteries in picture #2 are that short and that heavy there's not going to be a lot of difference. Each way of hooking up the batteries has its advantages and disadvantages. If you are happy with #2 that's good enough.

Thank you for your inputs, I'll review the other thread and reconsider my options.

 

[grizzzman]

Here is info on multiple battery parallel connections. Here

 

[eddie1261]

If you have just 2 batteries connected in parallel, is one of them "first"? To which set of posts would I make the connection from the charge controller and to which set of posts would I take 12v to the 12v fuse block? My logical brain says with only 2 batteries it wouldn't matter. When you get into 3 or 4, yes, it might, but with 2, looking at them from either end, neither is "first".

 

[Rider]

If you have just 2 batteries connected in parallel, is one of them "first"? To which set of posts would I make the connection from the charge controller and to which set of posts would I take 12v to the 12v fuse block? My logical brain says with only 2 batteries it wouldn't matter. When you get into 3 or 4, yes, it might, but with 2, looking at them from either end, neither is "first".

Path of least resistance. If the wire has less resistance than the batteries, I expect the charge (and voltage if sized for no sag) would be the same at each battery. Shouldn't matter if there is 2 or 6, as long as the wire can carry more current without loss than the battery can absorb.

 

[SolarNorm]

If you have just 2 batteries connected in parallel, is one of them "first"? To which set of posts would I make the connection from the charge controller and to which set of posts would I take 12v to the 12v fuse block? My logical brain says with only 2 batteries it wouldn't matter. When you get into 3 or 4, yes, it might, but with 2, looking at them from either end, neither is "first".

So if I'm not mistaken, the input received thus far pretty much indicates that image #1 would be better (preferred) setup providing the wire diameter used is larger, I used 1/0 AWG wire and lugs from ACDC Electric Supply online

 

[gnubie]

Preferred but as you mentioned in another post the wires between battery 1 and 2 are only 3 inches (if I read that right). If that's the case there will be little difference in the load sharing due to the very low resistance of such a heavy piece of short wire.

 

[SolarNorm]

The ultimate difference in length (the Black wire) is probably 12 inches but again it's a 1/0 diameter wire so the loss will be minimal anyway. But pulling the + off battery 1 and the - off the second battery, its pretty much a wash anyway. I'll create an electron "flow" diagram to assist our readers.