Top Balancing "How to"
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Ampster
Renewable Energy Hobbyist
I used a 3.6 volt 50 Amp power supply to parallel top balance my 48 LF280 cells. It took five days before the current started tapering. Even then there was some difference in voltage because of the different resistance of the bus bars. Some were Copper and some Nickel plated steel. After assembling them into my 3P16S pack I used a 2 Amp Heltec active balancer to finish the balancing. I don't take the pack above 3.45 per cell.
EDIT:
I will move my post to a new thread so your post won't get buried.
They tend to not be high quality, and in the example you linked, I wouldn't run it more than 80% of the rated capacity for an extended period.
curiouscarbon
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derating, multiplying the rating by a number less than 1, good idea with that type of dc/dc converter. heat dissipation important
usually 80% or less (<0.8*max)
OK to connect to the BMS and charge in series. If you get to 13.8 volts with no overvolt issues the cells can be placed in service and simply limit your charging voltage to 13.8 volts. If there are over volt issues at the cell level you can reconnect in parallel and charge the remaining amount. Or possibly bleed off power from the high cell or boost charge the low cell.
curiouscarbon
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13.8 Volt / 4 cell = 3.45 volt per cell ? pretty full
if manually interested, with a resistor (must calculate appropriate Ohm value) resistor current bleed can be very effective with voltage monitoring
keep BMS monitoring visible with each cell voltage for manual bleed off with resistor
3.65 V on any cell means stop
Hedges
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BMS will shut off battery pack output if any cell gets too low, or diverges too far.
A relay with appropriate 12/24/48V coil powered by battery/BMS output could be used to complete circuit of one resistor discharging one cell.
That gives BMS protection. Not meant as discharge end-point; your target is same as voltage of other cells. But it would be protection.
Be patient Glasshoppa!
Rome was not destroyed in a day, these things take time. patience.
Just think of how satisfied you will feel at the top balance, if you do not go over the top and damage the cells.
They can still have different self discharge rates. The longer they are idle, the more likely they need balancing. Try charging them as a pack first and see. The "how to top balance" resource here tells you how to charge in series and then parallel top balance using a BMS. It is likely the top balance won't take long since they won't be far out of balance.
Top Balancing LiFePo4 Cells using a low cost benchtop power supply.
To get the paper, click on the orange at the top of this page. This is a tutorial with detailed steps on how I top-balance my LiFePO4 Cells using a low-cost benchtop power supply. To get the tutorial, click on the orange "Download" button...
diysolarforum.com
The section labeled "Pre-charging the cells to get them ‘mostly’ charged.".
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TomC4306
Solar Obsessive
In this DIY environment, you should ALWAYS top balance. Even if only to confirm what you THINK you bought. (matched)
UNLESS you are stupid rich and don't give a f*** about possibly throwing away several thousand dollars.
If you have a BMS with decent balancing current (JK with 2A for example), you could get away with just throwing the pack together and have it balance over time. It will take a while to get there though...
I am from the alternate universe and think if the voltages are very close, the cells can be assembled in series with the BMS and put in service. Best to keep the top charge voltage closer to 3.450vpc and see how the balance is. If needed the low cells can be boosted individually or the high cells can be bled down individually while still assembled. If nothing goes over volt, all is fine and the BMS will very slowly improve the balance over time.
Post the results.
If the cells are capacity matched, they should be within a few amps of each other and the BMS can be used to balance them. It shouldn't take long even with a low amperage balancing current. By keeping an eye on the BMS you will be able to see if anything is out of wack. Personally I would not parallel top balance a set of capacity matched cells.
When I received my cells the voltages were all pretty much the same. Capacity was not. If buying cells not capacity matched then parallel top balancing is probably a good idea. I won't complain for what I paid for my cells, but I will never buy non capacity matched cells again.
This works well and I had to do it even after a successful top balance...
Goatlord
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Just to be on the safe side, I probably would have to get a power source for top balancing. On that Will Prowse video:
he top balances 16 LiFePo4 cells with cheap Amazon regulated PSU. Since I am acting with 24V bus systems, I would like to use the same PSU for testing bus equipment also. Will any 30V 10A regulated lab PSU do?
he top balances 16 LiFePo4 cells with cheap Amazon regulated PSU. Since I am acting with 24V bus systems, I would like to use the same PSU for testing bus equipment also. Will any 30V 10A regulated lab PSU do?
>snip
This works well and I had to do it even after a successful top balance...
I did too. The $60 10A Longwei power supply from amazon worked perfectly - charged all the cells in parallel up to 3.65V and current finally went to zero. It just took five days, mostly my fault, not the batteries or charger. It takes a long time to charge them at 3.65V, even longer if you start at a lower target voltage - your charge current drops off as it gets close to full, so you end up charging at less than half the rated current.
If you're going to charge them parallel from 30-40% set the CV to 3.65V and leave it till it's done.
Built the pack, once charged up on external sources I had two cells that would shoot up past the other two. I kept bleeding them down with an auto-headlight bulb and they all came into perfect balance. I was surprised how easy that was to do, just watch the bms app.
My four new Eve cells arrived in pristine condition and all at the exact same voltage down to 1 mV. QR codes etched in. They still needed to be top balanced.
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Yes as long as the voltage is adjustable. Although 10 amps will take several days to a week to top balance all the cells together in parallel. If you have something rated higher that would be OK too.
Hedges
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Yes, so long as power supply has CC mode as well as CV.
Which is where optional series-charging the cells (with BMS to protect against over-charge of any cell) may speed up the process.
After series charging to the point of disconnect because one cell reached about 3.65V, you can rewire cells in parallel for parallel top-balancing.
Or, use power supply to top off each cell individually. Would BMS try to bleed off individual cells? Maybe disconnect it for this step.
I probably should have made myself clearer as @Gazoo did. Having purchased a set of grade B cells, and two sets of matched grade A cells from Amy Woo, I strongly suspect that putting them in series with a BMS and charging them, you will find no need to top balance them.
The cheap 10 amp power supply that Will uses, I did a review on two of them. There is a reason that they are so commonly used, they are cheap and work well. Just don't use the included leads they come with, build a high quality cable using 10 gauge wire and ring terminals. It will also make a good 10 amps charger for your 24v pack.
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If you want to spend more money (right at $200) you can get a 24 amp Riden, which is cost competitive with most dedicated LiFePO4 chargers, and also makes an excellent 24v battery charger. It is also programmable using the USB port, although the extra cost WiFi interface is more trouble than it is worth. The Riden kits are limited by the (not manufactured by Riden) switching power supply that won't allow full output for a 48v battery pack.
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I like the Ridens because you really can set it to 3.65v and just wait until it finishes. Very reliable and accurate, and 24 amps is a really good output.
The cheap 10 amp power supply that Will uses, I did a review on two of them. There is a reason that they are so commonly used, they are cheap and work well. Just don't use the included leads they come with, build a high quality cable using 10 gauge wire and ring terminals. It will also make a good 10 amps charger for your 24v pack.
Cheap power supply for top balancing (tested and works well).
First, a link to the cheapest 30 volt, 10 amp supply I could find on Amazon. There are others on occasion that go on special for a dollar or two less, but this one is pretty consistently the cheapest I could find. https://smile.amazon.com/gp/product/B07512KQDW/ An alternative that is not as...
diysolarforum.com
If you want to spend more money (right at $200) you can get a 24 amp Riden, which is cost competitive with most dedicated LiFePO4 chargers, and also makes an excellent 24v battery charger. It is also programmable using the USB port, although the extra cost WiFi interface is more trouble than it is worth. The Riden kits are limited by the (not manufactured by Riden) switching power supply that won't allow full output for a 48v battery pack.
Which power supply for Riden RD6018
The RD6018W kit is offed with a choice of 800 or 1000 watt power supply. Which one is best? Is bigger better? Will the larger unit fit in the case? Thank you.
diysolarforum.com
I like the Ridens because you really can set it to 3.65v and just wait until it finishes. Very reliable and accurate, and 24 amps is a really good output.
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