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damien-walker avatar image

Cable or busbar for correct midpoint voltage?

In this section of the Wiring Unlimited book, the midpoint connections are illustrated as cables. Should the midpoints be connected to a busbar like the positive and negative cables in order to get the same midpoint voltage across each series?


cableBattery Balancer
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2 Answers
Ingo avatar image
Ingo answered ·

This is the correct method. Equal length cable with bus bars at the main connections as per the Balancer manual.


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JohnC avatar image
JohnC answered ·

Good question @Damien Walker

In a perfect world you'd only need a smallish wire to help balance out minor midpoint differences. Certainly not a busbar.

In the real world a failed batt/cell anywhere could prompt high current flow between string midpoints, and you don't really want that. Better to let one batt/string fail 'quietly' than to have it cop the full stored energy of all strings together. Think 'meltdown'.

Many recommend fuses on the midpoint links, designed to blow before the wire melts, for pb's a hydrogen-explosion prevention thing. At least lowering the odds of that happening.

Then of course if you're monitoring remotely with a single midpoint reading (like from a BMV) you may never know a fuse is blown, and your bad string rolls on in the darkness..

Our imperfect world.. but I think a busbar is not the way to roll..


2 comments
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Curious.


Can you please explain why NOT to use busbars?


Thabks in advance!

@Heinzie

Personal preference plays a part, but for me it would be the chance of that 'meltdown' scenario I theorized about before. I haven't ever seen that (hope I never do), but I've seen plenty hot batts from imbalance, and that's not nice either.

I use a secondary bank of 6x 6V old batts for a 12V buffer, and I'm not game to even connect the midpoints. Only lightly loaded and charged to only 13.5V for a limited time, and I periodically run a multimeter over the midpoints to check (I removed 2x (of 8) just a few weeks ago when they didn't test well).

If you have busbars across the midpoints and a good monitoring/alarm system then it might be ok.

My real preference is to have single strings only, a major reason I switched to 48V for my main bank, which carries my serious loads..