Charging lithiums is interesting and a lot to learn. Recently I put 2 x 12V drop ins in parallel(\\) for 24hrs. Only a few mA still flowed. After charging the 1st one to reach 14V at a starting current of 17A the current dropped to 3A after 1.5hrs. Then doing the same with the 2nd one it took 3hrs to reach 14V. I expected the time to be similar.

Thanks everyone for the responses, I didn't expect so much feedback!

While I was going to try the light bulb/resistor option, I now realise that I do have some buck converters that do CC/CV which I should be able to use. I bought these when my solar was DC only and was using these to convert the 24V (from deep-cycle at the time) down to 12V to use with lighting, router etc:

CMU DC/DC BUCK/LIPO CHG 1.25-36V - Communica [Part No: CMU DC/DC BUCK/LIPO CHG 1.25-36V]

So maybe it would be better for me to use this on the low cell? I could then set it to 3.6V and the current to 3-5A. Has anyone set current on these before? The website says I should set my multimeter to current and put it in series across the output...would that not just be a short circuit and damage the multimeter or the buck or would the current protection on the buck then kick in? (I think I've have seen people measure the current output of solar panels in this way - but I always worried that something would get damaged).

1. 10A current with a multimeter measuring the output short circuit current file (directly to the two leads to the output can), while adjusting the constant current potentiometer allows the output current reaches a predetermined charge current value;

 

41 minutes ago, Lindsay said:

Thanks everyone for the responses, I didn't expect so much feedback!

While I was going to try the light bulb/resistor option, I now realise that I do have some buck converters that do CC/CV which I should be able to use. I bought these when my solar was DC only and was using these to convert the 24V (from deep-cycle at the time) down to 12V to use with lighting, router etc:

CMU DC/DC BUCK/LIPO CHG 1.25-36V - Communica [Part No: CMU DC/DC BUCK/LIPO CHG 1.25-36V]

So maybe it would be better for me to use this on the low cell? I could then set it to 3.6V and the current to 3-5A. Has anyone set current on these before? The website says I should set my multimeter to current and put it in series across the output...would that not just be a short circuit and damage the multimeter or the buck or would the current protection on the buck then kick in? (I think I've have seen people measure the current output of solar panels in this way - but I always worried that something would get damaged).

1. 10A current with a multimeter measuring the output short circuit current file (directly to the two leads to the output can), while adjusting the constant current potentiometer allows the output current reaches a predetermined charge current value;

 

This one may be a little bit better suited, the one at communica seems a little light in the pants

Ignore, my suggestion was bad advice not applicable to this solution

Edited July 29, 20223 yr by WannabeSolarSparky
correction

1 hour ago, Lindsay said:

Thanks everyone for the responses, I didn't expect so much feedback!

While I was going to try the light bulb/resistor option, I now realise that I do have some buck converters that do CC/CV which I should be able to use. I bought these when my solar was DC only and was using these to convert the 24V (from deep-cycle at the time) down to 12V to use with lighting, router etc:

CMU DC/DC BUCK/LIPO CHG 1.25-36V - Communica [Part No: CMU DC/DC BUCK/LIPO CHG 1.25-36V]

So maybe it would be better for me to use this on the low cell? I could then set it to 3.6V and the current to 3-5A. Has anyone set current on these before? The website says I should set my multimeter to current and put it in series across the output...would that not just be a short circuit and damage the multimeter or the buck or would the current protection on the buck then kick in? (I think I've have seen people measure the current output of solar panels in this way - but I always worried that something would get damaged).

1. 10A current with a multimeter measuring the output short circuit current file (directly to the two leads to the output can), while adjusting the constant current potentiometer allows the output current reaches a predetermined charge current value;

 

This buck module should not be able to output more than 5A before it starts to limit the output. It would thus be safe to connect the multimeter on 10A scale to the output terminals. Beware of heat built up so perhaps try it at a 4A current limit. Some of these modules can only provide the spec current if fan cooling is used to assist cooling.

Yeah, even at a couple amps they seem to get very hot, so will attach a heatsink, or will point a fan at it  

Just make sure you use a isolated source, like a spare battery to power the buck.  You get some nice cheap little converters with a display and indep voltage and current adjustment, which make topping up a cell pretty straightforward.

Ian

7 hours ago, stok said:

nope, they cannot balance as it can only connect one cell and one cell will always be in balance with itself. To balance you need one cell as reference and another that must balance to achieve the same state of charge.

it acts like a voltage switch that limits voltage to between a min and max setpoint. it will switch on (let current flow through it) if it is above a certain voltage (usually 2.5v) and remain in that ON state until it reaches its upper limit (3.5 - 3.75 depends on manufacturer0 then it will switch off again and remain in the off state until the cell's voltage drops below the threshold (recovery voltage is about 5 - 20 Millivolts lower than cut off) or in a low voltage disconnect situation it will cut at 2.5v and remain off until a charger is connected or some of them self recover at a set voltage. 

you will still need a  power supply to charge the board(cell) with or you can use a cc/cv buck converter/bench power supply set to 3.6V

yea i was sthinking of the protection boards that just add resistance to a peaking cell when multiple cells are chartging ie the charge does not flow through them

while i meant charger board as the ones that though you give it a different voltage modulates it to the desired voltage for the cells and kick in and out at the correct voltages 

 

verbelising what i'm thinking ain't my strong suite