Battery Series/Parallel connection guidance

[veggie]

Hi All,

I have four 6VDC, 225 amp deep cycle batteries that I wish to connect series/parallel to get 24 volts @ 225 amps.
The picture shows my planned wiring arrangement. BUT ... I'm not sure that this is the best or correct way.

Does this look correct ??

veggie
<click picture to enlarge>

[dax021]

There is no parallel in that diagram. 4x6V is in series to make 24V 225A.  Turn the 2nd pair around so that you don't have that long link between them.  Keep your links the same length and your feeds the same length (although it is not really an issue in a straight series connection, basically it becomes one large battery)

[BruceM]

I concur-  there is no concern for matching lead length or mismatched gauge wires in a series string.
Current in and out is identical for all cells of the series.

[veggie]

Agreed, this is purely a series connection (no parallel).
Thanks for the feedback guys.
I shall proceed.

cheers,
veggie

[mihit]

I make "bus-links" by hammering 1/2" copper pipe flat and drilling required holes. Good for a couple of hundred amps. 3/4" pipe would give you a bit more again.
You can then insulate with heatshrink or tape.

And I would make them all the same length/ gauge, but it probably isn't neccessary.

[dax021]

I make "bus-links" by hammering 1/2" copper pipe flat and drilling required holes. Good for a couple of hundred amps. 3/4" pipe would give you a bit more again.
You can then insulate with heatshrink or tape.

And I would make them all the same length/ gauge, but it probably isn't neccessary.

I do the same, 1/2" Cu pipe.  Never bothered with the heatshrink though

[BruceM]

Flattened copper pipe is great, but there is also 16 oz/SF copper flashing to consider. Amazon carries it.  I use it for HF grounding systems and connections to same, and also for high current strips and straps on power PCBs, etc.  Handy stuff.

https://www.amazon.com/Copper-Flashing-Contractor-use-Lead-Pressure/dp/B07MYMMK17/ref=sr_1_2?
keywords=copper%2Bflashing&qid=1644014251&sr=8-2&th=1

[dax021]

Flattened copper pipe is great, but there is also 16 oz/SF copper flashing to consider. Amazon carries it.  I use it for HF grounding systems and connections to same, and also for high current strips and straps on power PCBs, etc.  Handy stuff.

https://www.amazon.com/Copper-Flashing-Contractor-use-Lead-Pressure/dp/B07MYMMK17/ref=sr_1_2?
keywords=copper%2Bflashing&qid=1644014251&sr=8-2&th=1

You are 100% correct, that stuff is great, but rather expensive.  On the other hand, I have so many offcuts of Cu pipe lying around from my handyman work, that it is essentially free and would go to scrap otherwise.

As far as I know, stranded cable is still the most effecient option.  As I understand it, voltage flows along the outer sides of a conduit, so the more strands, the less resistance.  The higher the voltage the less the losses, but at low DC voltages it apparently makes a differnce.  In my case the cost doesn't justify the effeciency gain.

[ThomasEriksen]

Skin effect only applies to alternating current, so nothing to worry about before you get over the kHz range, direct current use all of the conductor

[BruceM]

+1 Skin effect is entirely an AC high frequency issue, and has no role in DC power connections.  Stranded wire (round or strap) only helps with flexibility for DC power.

I agree too that battery connection straps from flattened copper pipe are a great use of surplus copper pipe cutoffs.

For high frequency grounding, where ground strap length to width ratios of 4 or 5 to 1 are often recommended, copper (16 oz/SF) flashing sheet works nicely.   I also like to use the 20 inch wide roll material as part of the buried earth HF ground system.  Since I have leftovers I tend to use the copper sheet for lots of smaller bits.

   

[dax021]

Thanks, learnt something today

[veggie]

mihit and bruceM,

Thanks for the tips. I used both ideas.
[1] Flipped the batteries around for shorter distance between posts, and [2] made terminal straps from copper pipe.
Anyone know the amperage capacity of a 7" length of flattened 1/2" copper pipe ? 
<click picture to enlarge>

[BruceM]

https://diysolarforum.com/threads/copper-pipe-1-2-inch-what-is-max-current-capacity.11405/

One poster estimated 200A derated to 120A for safety. 

You may have to do a more rigorous calculation depending on your application.  Flattened 3/4 copper tube will have better than 3x the ampacity due to wall thickness, much larger cross sectional area and total surface area for heat dissipation. 

[veggie]

Thanks bruceM,

To be safe I installed a 200A fuse on the on the positive post of the battery bank leading to the + connection on the inverter..
A typical draw from this bank will be 80 to 120 amps.

By the way, that's a useful link that you attached.
I will monitor my copper temperature when drawing a heavy load.
If I'm concerned, I will double them up.

veggie

[BruceM]

I'm quite impressed with the accuracy of the technical content that young Will Proust has on diysolarforum.com and his youtube videos.  He't not an engineer but he thinks like one and really seems to do his homework.  His enthusiasm for LFP batteries and PV power systems is enjoyable. 

Looking forward to seeing what you're up to, Veggie.  You do nice work!