diy solar

diy solar

LiFepo4 top balancing equipment recommendations

I just use this
https://www.amazon.com/gp/product/B07ML2MP9Q.

  1. Start with the batteries disconnected and set the desired end voltage and the amp knobs turned all the way down.
  2. Connect the cell(s)
  3. Turn up the current to whatever rate you want for the constant current.
  • For assembled solar batteries you will usually hit the power supply limit before you hit the charge limit of the cells.
  • If the cells are already charged, you might might not be able to turn the current up very high before the voltage limit prevents it from going higher.
At this point you need to watch the current, when it gets down to a few hundred mA, the charging is done and you need to take the cell(s) off the power supply. This is the primary difference between the power supply and a true charger. A true charger will either quit charging when the current drops off (preferred) or it will drop the voltage to a float level.
That's the one I bought for my BYD batteries on wheels. It's working.
 
That's the one I bought for my BYD batteries on wheels. It's working.
Warning: If you hook it up backwards you can blow out a diode in it. The symptom is that it shows it is pumping current but there is no voltage.
(don't ask how I know ☹). The good news is that the fix is relatively easy if you have a soldering iron.

I have debated putting a schotky diode in series with the output to protect the supply from my dumb stunts, but then the voltage displayed would be off by a few tenths of a volt.
 
It is a handy little supply. I use it for all sorts of projects from powering circuit boards to charging batteries to electro-plating bus bars.
That is probably the hardest on a PS, of all those things.
 
For top balancing without investing in a bench power supply what is the problem with first assembling the cells into the target configuration (12V, 24V, whatever), charging that battery until full and then reconfiguring the cells into a parallel configuration and letting that sit for a day or two? Is that just too slow for people or am I missing something?
 
For top balancing without investing in a bench power supply what is the problem with first assembling the cells into the target configuration (12V, 24V, whatever), charging that battery until full and then reconfiguring the cells into a parallel configuration and letting that sit for a day or two? Is that just too slow for people or am I missing something?
That would probably work just fine for most people. In fact, I am becoming less and less convinced of the need for top balancing if you have a decent BMS. The BMS will balance the cells at the top anyway so after a few cycles you will be at the same place you would have been with a top balance. (Top balancing just gets you there from the beginning)

Where top ballancing might be important is if you want to do a capacity test of the bank on your first discharge.
 
That would probably work just fine for most people. In fact, I am becoming less and less convinced of the need for top balancing if you have a decent BMS. The BMS will balance the cells at the top anyway so after a few cycles you will be at the same place you would have been with a top balance. (Top balancing just gets you there from the beginning)

Where top ballancing might be important is if you want to do a capacity test of the bank on your first discharge.
Yeah, my cells were pretty well balanced from XUBA. 3x3.279V and 1x3.278V.
I probably would have been OK building the battery, hooking up the BMS, and charging to 14.4V.
 
Re: previously shared links for: DC Power Supply Variable 30V 10A, 4-Digital LED Display, $86


Here is another option that looks like same specs /by same company/ but a lower price and slimmer profile.
Anyone notice drawbacks ?? to this one?
DC Power Supply Variable 30V 10A, (Precision 00.01V,00.01A)4-Digital LED Display , $62.

4 - Digit Display ... K3010D DC power supply (above) / slightly different from lesser LW-K3010D 3 - Digit Display (below)

DC Power Supply Variable,0-30 V / 0-10 A LW-K3010D Adjustable Switching Regulated Power Supply Digital $61


I'm setting up for my 1st DIY LifePO4 24v 280Ah set on a recently started sea ship ride from China. Question: Is 10 Amp charger good enough for initial top balance charge for a24v 280Ah x 8 set of 3.2v cells ???; or ridiculously low in amps/ so spent more for a 30 amp charger ? Seems like a likely a 10 amp charger is good enough for my initial DIY build experience ;+)
 
Since we talk about settings down to the .01 volt, I find the fine adjustment to be handy (If I am honest with myself, the display is probably not that accurate..... but it still feels right to be able to dial it in.

10A is fine.... but can take a long time if the cells start in a low state of charge. Even at 10 amps your are only getting 10A*3.65V=36.5W.

What I do is first wire the cells into the 24 V bank (with the BMS) and then charge to 29.2V till one of the cells hits 3.65. This allows me to push 29.2V*10A=292 watts. However, even this can take quite a while if the cells are in a very low state of charge. Note: Initially the charge will be limited by the 10amp limit of the supply, then it flips over to constant voltage of 29.2. Usually the constant voltage part of the cycle goes pretty quick.

Once one of the cells hits 3.65, all the cells will be mostly charged..typically. However, if one starts out way more charged than the other and hits 3.65 while the others are much lower, you can take that cell out of the series set, drop the charge voltage by 3.65 volt and continue charging till the next cell hits 3.65. (Depending on your BMS, you might have to take it out of the system if you have a non-normal number of cells. In that case you have to watch the cell voltages manually.....)

Once the cells are mostly charged, take the bank apart and re-wire them all in parallel and then charge them to 3.65V till the current drops to near zero. (This will typically be quite a bit faster than it took to initially charge them in series. )
 
Last edited:
My 4 cell pack of XUBA 280AH starting at 3.298V in parallel.The first 1.5 days I was only pushing 5A because I misunderstood the outputs of my 3 channel power supply. When my mistake was pointed out, it was a "I know that" moment. Thanks to some people here I got that worked out and was pushing the full 10A. Another day at 10A and once it went over 3.4V it started picking up steam and topped out at 3.65V in about 6 hours.

As for the PS meters. They're fine for setting the max amperage output of your PS. For the voltage side, use a good DMM to set the max voltage. Don't trust the voltmeter on the PS, until you have checked it with a DMM. Mine is off by 0.5V on the PS. But it doesn't matter if I set the output with a DMM.
 
Last edited:
Since we talk about settings down to the .01 volt, I find the fine adjustment to be handy (If I am honest with myself, the display is probably not that accurate..... but it still feels right to be able to dial it in.
....snip..
It would be interesting to see an accuracy chart for the meters in a PS.

My old 3 1/2 DMM is 0.5% for DCV
My newer 3 1/2 Clamp/DMM is 0.05% DCV.
I used both of these when I built my battery and there was a difference between them in the 0.0XXDCV range

The used Fluke bench 5 1/2 DMM is 0.005% DCV.
I got this one off eBay after I built my battery. It is what I'll be using in future builds.
 
Whether you are using the PS display or a top-end Fluke, being able to fine tune the value is handy..... so I like having the extra knob.
I agree. My setup just has 1 volt and 1 amp knob per channel. It takes a real light touch and a little luck to get the volts set just right.
What I give up there, I gain the ability to have 2 different channels set to different voltage and amperage. Go parallel to double the amperage and series to double the voltage. So I have 30V at 10A, 60V at 5A, or separate channels at 30V 5A.. The 3rd channel is a fixed 5V 3A, too...

A single channel 60V 50A would be nice for charging and to test DC-DC chargers and SCC, on the bench...
 
So after days and days of slowly charging my battery bank and getting everything top balanced I was finally able to fully assemble my battery today. The 4 groups of parallel cells all showed either 3.600 or 3.601 prior to making the series connections. I’m still waiting on my bms to arrive prior to doing the final tourqe down and there installing the lock washers. Once connected my meter showed 14.4V. I can’t wait to capacity test the battery after the bms is installed. It feels good to be making progress though.
View attachment 8391

What BMS did you end up getting? I'm considering a similar battery configuration.
 
I just use this
https://www.amazon.com/gp/product/B07ML2MP9Q.

  1. Start with the batteries disconnected and set the desired end voltage and the amp knobs turned all the way down.
  2. Connect the cell(s)
  3. Turn up the current to whatever rate you want for the constant current.
  • For assembled solar batteries you will usually hit the power supply limit before you hit the charge limit of the cells.
  • If the cells are already charged, you might might not be able to turn the current up very high before the voltage limit prevents it from going higher.
At this point you need to watch the current, when it gets down to a few hundred mA, the charging is done and you need to take the cell(s) off the power supply. This is the primary difference between the power supply and a true charger. A true charger will either quit charging when the current drops off (preferred) or it will drop the voltage to a float level.
I went with this for $20 less/ has similar specs. Seems good enough to me for lite weight use. https://www.amazon.com/gp/product/B07M9N73YQ/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
 
I went with this for $20 less/ has similar specs. Seems good enough to me for lite weight use. https://www.amazon.com/gp/product/B07M9N73YQ/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

so you may wind up spending a few more bucks on some real leads -- or make your own .. i have one of these Amazon things also and the 2 things you will notice is - If you get 6A out of it you will be blessed ... and the leads were really designed for about 4A .... BUT overall I am happy witht these little chargers...
 
My 4 cell pack of XUBA 280AH starting at 3.298V in parallel.The first 1.5 days I was only pushing 5A because I misunderstood the outputs of my 3 channel power supply. When my mistake was pointed out, it was a "I know that" moment. Thanks to some people here I got that worked out and was pushing the full 10A. Another day at 10A and once it went over 3.4V it started picking up steam and topped out at 3.65V in about 6 hours.

As for the PS meters. They're fine for setting the max amperage output of your PS. For the voltage side, use a good DMM to set the max voltage. Don't trust the voltmeter on the PS, until you have checked it with a DMM. Mine is off by 0.5V on the PS. But it doesn't matter if I set the output with a DMM.
Any chance you could share with me what you did differently to get your power supply to charge at the full 10a? I’m trying to top balance my 8 280ah cells and it is taking forever!

I’ve got it set for constant voltage at 3.6v currently...
 

Attachments

  • 1440DE64-D088-4023-9296-F0446B6236DA.png
    1440DE64-D088-4023-9296-F0446B6236DA.png
    472.5 KB · Views: 17
Any chance you could share with me what you did differently to get your power supply to charge at the full 10a? I’m trying to top balance my 8 280ah cells and it is taking forever!

I’ve got it set for constant voltage at 3.6v currently...
If it is not taking the full 10A, the cells are starting to get charged. However, with 8 cells it could still take a *long* time to complete because even at 10A, you are only pumping 36W.

Check out the tips in this resource about wiring them in series first:
https://diysolarforum.com/resources...ls-using-a-low-cost-benchtop-power-supply.65/
 
Back
Top