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Bench power supply fail - do I really need to top balance?

Simi 60

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I know in the perfect world top balancing is essential
But in this not so perfect world I have been sent a dud bench power supply
Due to covid and based on how long the last one took to arrive ( I bought inside Australia) I may not see a replacement until next year.

Our home (boat) has rapidly failing house batteries.
The eve 280 purchased from Amy have arrived, all A grade matched and batched, all reading 3.31v

Would I be able to assemble, put them to use and get away with letting the JBD 200amp BMS do its thing?
 
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You will probably be fine .... especially with those cells. The only issue if they aren't balance well is that you will loose some capacity.
You can also do some manual balancing by passively bleeding off some power from the cell that his 3.65 first.

I certainly wouldn't wait a year to put them in service.
 
You will be fine, the problems only start when the first cell goes over 3.4v, so to avoid any problems set your max charge voltage lower. Ie 13.6v for a 4 cell bank.

Your only losing a few percent capacity, so it's not a major issue. Then as you say, your BMS will balance your cells over time.

Perfect initial top balancing is required when your want to get Max capacity from your bank from the start.

Hope that helps....
 
Thanks and thought as much.
We will see what the supplier of the powersupply says, hoping for a refund (eBay) and then I'll buy another closer to where we are and hopefully have it in a week.
 
I have put together one small pack, 24 volt 50 ah, and am in the process of putting together a second 24 volt pack at 280 ah. I pre-charged with solar power, and then finished off the top balance with the power supply.

My power supply was also broken, and I planned on top balancing without, but after messaging the company, I received a replacement prior to the pre-charge beint finished. Had the power supply not shown up so quick, this is what I planned for a top balance with BMS only:

BLUF: Make sure your BMS balancing is actually enabled.
GIve the BMS time to work with a low balancing amps.
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I think you could be good with the BMS, with a could of caveats. Your BMS balancer needs to turn on to balance, and is also limited to whatever the specs or setting is. I just did a top balancing with a 100 ah overkill BMS for my 24 volt cells. The BMS does not top balance until cells reach 3.4 volts And charging. These are configurable, to all the time verse just charging and the voltage per cell is also adjustable.

So, what I’d recommend is to charge your battery to a per cell average of more than when your BMS turns on. My BMS turned on at 3.4, so my charging voltage was 3.43 volts Approximately per cell. At that point my BMS displayed balancing on the cells that were balancing. If you don’t trigger the BMS’s charging, there will be no balancing.

Second, is a BMS will not balance as well as a Heltec active balancer, at least not as quickly. I don’t know the amps the BMS pushes at, so with 26 AWG wires, I assume 1 amp. That means no more than 1 amp per hour. A 280 amp hour cell mismatched will take a quite a while to balance.

If it takes quite a while to balance, You may want to consider leaving Flost at the same voltage as bulk charge and have a slight load on in the daytime.

My point would be not to use the batteries for normal day to day loads until the BMS equalizes them, which could take days or more. 1 amp per cell balancing will take a long time for bigger packs if they are mismatched.
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To give you some stats of the 280 ah packs I just balanced, each of the two batteries was 24 volts and 280 ah, so 6720 wh. Each battery took about 4.2kw on the 24 volt 15 amp SCC for a pre-charge before being moved to the 3.65 10 amps top balance. THe power supply only needed 3 hours.

My cells were also grade A and really well matched.
 
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Would I be able to assemble, put them to use and get away with letting the JBD 200amp BMS do its thing?
Yes absolutely. Best if you can limit charging voltage to avoid over volt shut down by the BMS. Assemble and put in service and see how it goes.
 
Assemble battery and charge. After charged connect cells back in parallel let the set overnight. This will let them all balance to the same voltage. And they should be on the same point of the curve then.
 
Think yourself lucky your power supply didn’t fail to 5.0V while you had all your cells connected to it with no overvoltage protection.

As others have said, build your battery into its final configuration, then see what happens during the series charging.

If you don’t have a single cell charger the easiest way to stop a high voltage cell from triggering the BMS high voltage disconnect is to put a resistive load on whichever cell is approaching the cut off voltage. (the LED load resistors you can get from a car shop are OK for this - bolt them to an aluminium plate)

Don’t stress, you are better off missing out on the parallel top balance.
 
Assemble battery and charge. After charged connect cells back in parallel let the set overnight. This will let them all balance to the same voltage. And they should be on the same point of the curve then.

No, they shouldn’t - and they won’t.
 
Think yourself lucky your power supply didn’t fail to 5.0V while you had all your cells connected to it with no overvoltage protection.
Useless thing didn't even get connected
Could not select a voltage lower than 6v

As others have said, build your battery into its final configuration, then see what happens during the series charging.
Still have "some" time - noalox has not arrived yet, can't be bought in Australia

If you don’t have a single cell charger the easiest way to stop a high voltage cell from triggering the BMS high voltage disconnect is to put a resistive load on whichever cell is approaching the cut off voltage. (the LED load resistors you can get from a car shop are OK for this - bolt them to an aluminium plate)
Living on a boat, actually cruising so if it ain't coming by post to our next port I can't get it.
Are load resistors something I can get on eBay?
Don’t stress, you are better off missing out on the parallel top balance.
Yeah, not sure about that - seems to be an often mentioned thing to do.
 
Yes you can get the load resistors off ebay. Look for “LED load resistors, 8ohm” Use 2 in parallel for more current bleed but be prepared for them to get hot after a while.

Parallel top balancing is frequently mentioned, the risks involved and total lack of need for them less so.

If you get stuck for NoAlox, i have a large tube and can squeeze out enough for a couple of systems and post it to you - PM me if you are keen.
 
This is the method i use to quickly lower the voltage of a big 280ah cell.

 
I have used about 45' of #14 wire and alligator clamps. Pulls about 30 amps. String it out to dissipate heat because it gets warm.
IIRC a 25' piece of #16 will pull 20 amps off a single cell.
 
Thanks everyone for the replies
Yes you can get the load resistors off ebay. Look for “LED load resistors, 8ohm” Use 2 in parallel for more current bleed but be prepared for them to get hot after a while.
Thanks
Parallel top balancing is frequently mentioned, the risks involved and total lack of need for them less so.
Yep, but as this is full time cruiser, no marina/shore power I would like to start out right if I can
If you get stuck for NoAlox, i have a large tube and can squeeze out enough for a couple of systems and post it to you - PM me if you are keen.
And thanks for the kind offer.
DHL shows it landed in OZ so I would like to think it will be here soon.
 
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