3 strings in battery pack, cross connect?

[daloniga]

I have three serial strings in my power pack.  Of course, these strings are connected in parallel. 

Some time ago,  I found a website (that I can no longer locate) that was talking about the merits of cross linking the strings of a battery pack.  The picture on the website showed, best I can recall, that each terminal in a string was connected to the identical terminal in the adjacent string.  Benefits claimed that the cells were not as likely to fluctuate as much as non-cross-linked systems.

Is there any truth to this?  Good idea, bad idea?

[TomW]

I do not have any actual experience doing this but it seems to make sense and I had suggested it before as an option.

It would make it a lot easier to spot a bad battery, or at least narrow it down to 3, in your case, very easily.

It makes perfect sense electrically, at least to me.

Like most stuff, it probably has valid pros and cons and deciding which is more important for each application will be the fun part.

More hardware means higher cost and more possible points of failure, too.

An interesting subject for discussion.

Tom

[russ_drinkwater]

That is an english site.
And yes the way the diagram showed the wiring of the batteries and the losses measured it was by far the best wiring config.
It looked a bit odd, but in regard to efficiency and losses it was light years in front.
I may still have a link buried somewheres.

[Westbranch]

this one ? http://www.smartgauge.co.uk/batt_con.html

[russ_drinkwater]

That looks to be it!

[daloniga]

Valuable info to be sure but this is not the website I was looking at.  The website I saw had multiple serial strings and crossconnections between adjacent terminals of each string.  I'll keep hunting until I find it, if it's still there.

My pack is not even close to what a lot of you folks have, still, I have over 4K invested in the pack.  I'm all for doing anything that can give me 1 more amp for one more day .....

[russ_drinkwater]

I am interested if you come up with some better wiring configs as I want to add 4 x L16h's to the 870 amp @ 24 volts I gave my son.
Doubling the diameter of the leads if they are twice as long should reduce resistance and losses and I stand corrected if this is not correct.
That will mean there are 3 x strings of 435amp hour batteries to connect. (12 batteries in total)
Ant takers?

[TomW]

Doubling the diameter of the leads if they are twice as long should reduce resistance and losses and I stand corrected if this is not correct?

Russ;

Well, if you double the diameter your resistance per unit length  will go down A LOT. My math sucks but you end up with way more than 2X the conductor that way. 2X Diameter not guage, however. Just my opinion.

(Area of circle = π r²) the r² bit makes the cross section go up exponentially (I think that is the term)?

Tom

[Westbranch]

there is that old RoT (rule of thumb)

to determine the wire size needed to double or halve the wire you have,  subtract or add  3 to the AWG number....

so 7AWG is ~2 x as big as 10 AWG,   and 13 is ~1/2 the size of 10 AWG wire

[sigp2101]

I have three serial strings in my power pack.  Of course, these strings are connected in parallel. 

Should not have more than two (2) strings in parallel if you value your battery bank. Having 3 is looking for trouble.

[grgdgreek]

How does 40 Rolls s-550
5 strings 48 volts , 50% dod 7 years so far...
It's all about being wired right.

IMHO
George

[daloniga]

Should not have more than two (2) strings in parallel if you value your battery bank. Having 3 is looking for trouble.

It would not surprise me in the least.  Mama always said I had the tendency to fall out of the stupid tree and hit every branch on the way down.   :-)

[daloniga]

How does 40 Rolls s-550
5 strings 48 volts , 50% dod 7 years so far...
It's all about being wired right.

IMHO
George

George,

How are these strings wired?  What does "dod" stand for?

I found a related article tonight but the pictures in the PDF seem to imply this is more geared toward battery powered tools.  The text makes my eyes cross:

http://www.freepatentsonline.com/EP1780819A1.html

[russ_drinkwater]

DOD = depth of discharge.

[grgdgreek]

this one ? http://www.smartgauge.co.uk/batt_con.html

Diagram #2

George