Paralleling 3 batteries in a balanced setup

Hey Doug,

You are familiar with 380-volt systems and Fairbanks-Morse prime mover motor-generator systems. I salute you!

My learning experience was through a salty senior MCPO who in turn spent three years as COB of a Gato class boat.

Just an interesting bit of information. With three batteries wired as they normally are, that is equal jumpers from pos to pos to pos and neg to neg to neg with output from opposite ends, as the batteries become better the middle battery supplies less of the total current. That is as the battery resistance decreases the middle battery supplies less of the total current. As the battery resistance approaches zero (I know it can never reach zero) the middle battery current approaches zero! If they are wired in a balanced manner all three will provide equal current. While this can not happen it shows that as batteries become better (lithium ion)balance becomes much more important.

lenr wrote:
" If the analysis is for fun then more information is needed for electrical engineering nodal analysis."

It is fun but also useful for those that want balanced wiring. What other information is needed for a complete analysis. Seems that all need information is there.

doughere wrote:
"This is not actually balanced, and is used usually as it is a pretty good system. If you want to perfectly balance it, double the length of cable between the jumpers farthest form the power take-off, or increase the wire size of the cables closest to the take-off."

That is exactly what I'm saying! The easiest way to increase the wire size of the cables closest to the take-off point is to put another cable of the same length and size in parallel with it. To balance the resistance of the cables closest to the take-off point needs to be 1/2 the resistance the cables farthest from the take-off point.

pianotuna wrote:
Hi,

I've been known to draw 276 amps. I'm fused at 350.

doughere wrote:
Unless you are using some BIG batteries, or some HUGE draws this will work fine.

The most important thing is still CABLE SIZE AND CONNECTIONS.

Doug

My brief Naval career was on a WWII diesel/electric sub; yours are not HUGE draws.

Doug

Hi,

I've been known to draw 276 amps. I'm fused at 350.

doughere wrote:
Unless you are using some BIG batteries, or some HUGE draws this will work fine.

The most important thing is still CABLE SIZE AND CONNECTIONS.

Doug

doughere wrote:
Jumper the 3 pos together (one to the next to the next), jumper the 3 neg together (one to the next to the next). Take pos from one end of string, take neg from opposite end of string. As MEXICOWANTERER sort of pointed out, good connections all around are just as important as the wiring itself.

Doug

This is not actually balanced, and is used usually as it is a pretty good system. If you want to perfectly balance it, double the length of cable between the jumpers farthest form the power take-off, or increase the wire size of the cables closest to the take-off.

Unless you are using some BIG batteries, or some HUGE draws this will work fine.

The most important thing is still CABLE SIZE AND CONNECTIONS.

Doug

“Jumper the 3 pos together (one to the next to the next), jumper the 3 neg together (one to the next to the next). Take pos from one end of string, take neg from opposite end of string.” This is the most common way to wire them. However they are not balanced (if you are into balanced wiring). To balance the wiring all that is need is to add another cable of equal length and size across the cable already there from battery one to battery two + connections. Also another cable from battery two to battery three negative connection. You can use the same bolts so there are no more connections needed to balance three batteries.

VintageRacer – I don't agree with your analysis. You may be correct, that is why I started this thread, to get feedback and discuss it."

Well, Ohm's law and thousands of battery bank installs in telephone company CO's and other UPS systems kind of says you're wrong and I'm right. Sorry. It's just the way it is.

Sorry to disagree with you, but it is what it is.

Brian

The obvous needs little if any elaboration by me...

Serious systems where there may be 24 individual cells, and perhaps four parallel banks are magnitudes more sensitive to imbalance than a bevey of three batteries. When I read elaborations regarding connection architecture and not one word about something ten times as important I give a shrug. I have seen properly divided batteries just as imbalanced by corrosion as I have end string connections with the caboose suffering inadequate charging which in practice is THE ONE AND ONLY characteristic of a non-inverter system that affects along parallel string. If enough time is alloted for charging even a caboose battery gets fed it's due. Milliohm connections coupled with milliohm bridge wiring only becomes a concern when a long tabulation of milliohms are added up. But limited TIME CHARGING and high applied discharge values demand equal resistances battery to source.

But AGAIN, 100 to 1 I have seen slightly oxidized connections toss complex wiring architecture into the rubbish bin. And again this is directed at high rate charging and discharging systems.

Bumpyroad wrote:
“I thought that the "best" would be to hook all +s to a large buss bar with as short a cable as possible of equal lengths and do the same for the -s. your first diagram seems to mimic that.”

First diagram does mimic that. It is balanced. I'm saying that the second diagram is also balanced.

Bumpyroad wrote:
“don't know what advantage your second diagram gives other than makes it look more complex.”

12thgenusa wrote:
“If one were to assume you could wire as in method 2 with equal length wire, what would be the reason for doing so over the much simpler method 1?”

piantuna wrote:
“Even if the second way were balanced what would be the benefit?”

smkettner wrote:
“^^^ and no mention of bus bar. Just attach at each end of the stack.”

And smkettner wins the gold star! Diagram 2 really is simpler to implement.

With diagram 1 you need a connection point for all the cables from the + battery outputs and a connection point for all the – battery outputs. These connections are sometimes done using bus bar, not so easy to implement.

With diagram 2 you wire them as doughere writes:
“Jumper the 3 pos together (one to the next to the next), jumper the 3 neg together (one to the next to the next). Take pos from one end of string, take neg from opposite end of string.” This is the most common way to wire them. However they are not balanced (if you are into balanced wiring). To balance the wiring all that is need is to add another cable of equal length and size across the cable already there from battery one to battery two + connections. Also another cable from battery two to battery three negative connection. You can use the same bolts so there are no more connections needed to balance three batteries.

VintageRacer – I don't agree with your analysis. You may be correct, that is why I started this thread, to get feedback and discuss it.

wa8yxm wrote:
“-GC2+-GC2+ = 3 group 24 in parallel
That said, Balancing is a tad over rated”

Agreed balancing is over rated! But if you want balance what if you have six GC2 batteries?

hershey wrote:
“Is there really a "real world" need to go to such an extreme to balance the setup?”

I don't think so but a lot of others do so I'm trying to make it easier.

MEXICOWANDER wrote:
“Of course with the slightest bit of infintesimal corrosion all this theory turns to mouse-milk.”

One star for that, it is true. Could have been two stars if you mentioned that is a problem no matter what method you use to connect batteries.

I'm disappointed that with your experience and knowledge that you choose not to give a more useful critique.

Still need more useful feedback on method 1 vs method 2.

Hi hershey,

4 six volts it doesn't cost a dime more to wire in a balanced manner.

With six jars it becomes a chore

With eight it doesn't cost a dime more--but almost no one has eight.

It looks like LI has finally come of age now, too, so this may be moot in the near future. After all, if going LI is cheaper then it would be nutty to stay with lead acid.