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Author Topic: 48v battery bank with 24v take off point - feasible?  (Read 1659 times)
Joeyboswell
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« on: September 28, 2019, 05:13:23 PM »

Greetings!
In a battery bank of four 12V batteries connected in series to make 48V is it possible to connect a 24V device to part of the bank? Say across the middle two batteries? Or is there a better method, I am sure someone has done this already.
Thanks in advance. Mike
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Tinbum
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« Reply #1 on: September 28, 2019, 05:33:51 PM »

No is the short answer. The long answer if you did, and not recommended, is to use a battery balancer.

You would have to use a 48v to 24v converter.
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Scruff
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« Reply #2 on: September 28, 2019, 08:26:13 PM »

DC-DC Converter.
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Joeyboswell
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« Reply #3 on: September 28, 2019, 10:09:02 PM »

Ok thanks guys, suspected as much. Not a problem just at the planning stage now. Cheers
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pj
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« Reply #4 on: September 29, 2019, 03:42:33 PM »

Or alternatively...
Yes, electrically this is an OK thing to do (take 24V from half the bank). But the problem is it leads to an imbalance in SoC between the two pairs of 24V (2x12V) batteries, which would eventually kill one pair of batteries. If the 24V load is very light compared to the 48V load, then it may take many cycles for the imbalance to be a problem, and before it gets to be so, you could swap the 24V load onto the other pair. Only you can say if this is an acceptable approach. Alternatively, an active battery balancer will keep shuffling the needed charge between the pairs.

On the otherhand, a DC-DC converter is a much cleaner hands off solution, as suggested above.  Smiley
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Scruff
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« Reply #5 on: September 29, 2019, 04:51:34 PM »

It's only acceptable with balanced loads on both taps ie. Practically never.
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nowty
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« Reply #6 on: September 29, 2019, 08:50:14 PM »

Agree with the DC to DC converter option as an unbalanced battery bank is a BIG no no.

I re-used a 24v DC disconnect relay when I upgraded to a 48v system. I either had to buy a new 48v relay or use a 48v to 24v DC to DC converter or use a resistor. The DC converter was much more efficient than a resistor and soooo much cheaper than another relay.

You can see the converter in the picture, its the silver box.

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Joeyboswell
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« Reply #7 on: September 29, 2019, 10:38:02 PM »

Thanks, I will be going for the 48V/24V DC converter route.

Thinking up my next questions now.  Smiley

Cheers Mike
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Fionn
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« Reply #8 on: September 30, 2019, 10:29:50 PM »

I've been using one of those silver china special down converters for a long time too and it's been great.
Mine is a 12V 20A model and it's proven very effective, decent surge capacity compared to the one it replaced too. Must measure the idle current out of interest, I suspect it's negligible.
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