Can i adjust the outputvoltage on my charger?

[Pfnyq]

Hi! I have a 10s6p 18650 pack, the problem is that the charger don't cut the voltage at 42, instead all the cells get charge to 4,23V and i think its to high, i rather have the charge cut at 4.18 per cell (41,8 total).
Can i mod this charger so i lower the output?

https://www.aliexpress.com/item/84w-lithium-battery-charger-42v2a-for-electric-unicycle-in-factory-price/32470538759.html?spm=2114.13010608.0.0.0zpk6P

 

[Voltron]

If your battery has a BMS, you want the voltage a little high like that on the charger.... If it only goes to 41.8, it will be too low for balancing the cells. if the cells themselves are getting that high its a different story, when the BMS is working right it should be limiting the cell voltage even though the charger voltage is higher.

 

[Jimboyr6]

You could get a cycle satiator,which has adjustments in voltage
http://www.ebikes.ca/

 

[Pfnyq]

Yes i have a bms, i left the charger on when the green light came on for like 3 hours, the bms was warm so i thought it was bleeding the cells but the charger must have kept the voltage at 4.23/4,22, now when i disconnected the charger i think it still is draining the cells and i should start seeing the cell voltages go down.
Now i cant leave the battery for charging over night and expect to use it directly, because the draining will start after unplugging the battery.

I don't understand how the cells get so high when the output from the charger is only 42.2v, any ides how to lower the output to exactly 42v? Or i think i maybe need a new charger if it doesn't go in some kind of sleepmode after the red light turns off..

 

[Voltron]

Are you measuring that voltage at the actual cells?

 

[Pfnyq]

Yes, the pack is open right now so i'm measuring directly from the groups!

I guess that i have to set a timer for the power to the charger, so it disconnects the bms and can go in to bleed mode. or ells it will just sit there over charge...

 

[dogman dan]

That one is very unlikely to have the voltage adjustment pot on the board near the DC output wire. Open it to see, but I bet it does not.

Usually there is one on the larger metal case chargers.

 

[d8veh]

Your bleed resistor transistors will switch on and stay on as long as your cells are above about 4.17v, so the same will happen even if you change your charger to 42.0v. That's the way most BMSs work. At least you know that your cells are balanced.

Some chargers are adjustable, though I doubt that yours is. If you can, open it up and look for a potentiometer at the output end.

Another thing: Is your voltmeter accurate, or is 4.23v actually 4.20v? Try another meter to see if you get the same.

 

[Voltron]

You might get lucky and have a charger you can adjust. Here's a pair of my basic plastic box chargers.




The blue potentiometer on the right turned out to do the voltage, and the one the left was the current level to shut off at. But on several other chargers I use, there wasn't an adjuster, or just one, or it turned left for more volts, or they were covered in hot glue that ripped them off the board trying to pick it off etc.


Oh yeah... On these, if you bridge the space between the two metal heat sinks with your hand while picking it up to adjust it with the cover off its a nice shocker... Live and learn

That being said, if your reading are accurate, the BMS could be a problem, but harder to fix.. you shouldn't have to be custom tailoring a charger to match a battery if the BMS is set right. I only bothered setting mine as I usually bulk charge, with occasional balance charging with a detached BMS.

 

[Voltron]

Homemade insulated screwdriver

 

[Voltron]

I was reading back about your timer idea.. if you have pretty regular usage hours, instead of setting it to cut off early in the night, you can set to come on so it's peaking right when you're getting up anyway to final check it. I had to do that with my old lame SLA pack, that would sag down overnight, which of course lithium shouldn't...

 

[Pfnyq]

I Haven't got around to open'd the charger jet but i will probably do it tonight and post pictures, and thank's for the heads up i will be careful, and tejp my screwdriver "..

The multimeter was low on power so i thought that could be a reason for a faulty reading, but i change the battery and got the same results...
If my charger doesn't have any V adjust is it possible to series a diode to create a voltage drop, so i reach my target voltage of around 42? (Or maybe its just the multi meter that's bad so nothing of this is necessary, well i need to get a new one to be sure.

Timer: But if i don't let the sit a couple of hour's after it reaches around 42, it will not have'd balanced and the process have't even stared when i unplug in?:/

 

[Ykick]

I Haven't got around to open'd the charger jet but i will probably do it tonight and post pictures, and thank's for the heads up i will be careful, and tejp my screwdriver "..

The multimeter was low on power so i thought that could be a reason for a faulty reading, but i change the battery and got the same results...
If my charger doesn't have any V adjust is it possible to series a diode to create a voltage drop, so i reach my target voltage of around 42? (Or maybe its just the multi meter that's bad so nothing of this is necessary, well i need to get a new one to be sure.

Timer: But if i don't let the sit a couple of hour's after it reaches around 42, it will not have'd balanced and the process have't even stared when i unplug in?:/

I've done that before with a rather large diode. It was rated about 5-7A IIRC? Dropped voltage 0.7V. Another time I put a 2nd diode in series which dropped about 1.4V.

Be aware, I was pushing close to 5A through em and they did get very hot.

 

[dogman dan]

First voltage pot I've seen on a small plastic charger. Hopefully this will be the trend in the future. My experience has been that chargers drop in voltage after a few years use, so being able to reset them is handy.

 

[Pfnyq]

I cracked open the charger and liked you all guessed no voltage adjust, but i tested the output with a diode IN5408/NIC and got out 41.8 , and i think that's a more suitable reading, i know the bms will not stat balancing after 42, or what do you think, let that cells charge to 42.2/42.3 then discharge down to 4,17? (it fells like i'm torturing them)

I wanted to uplode some pictures but haven' them with me now...

 

[Voltron]

Timer: But if i don't let the sit a couple of hour's after it reaches around 42, it will not have'd balanced and the process have't even stared when i unplug in?:/

As long as you did an occasional long charge to get them balanced, it would be ok. And going to 4.23 isn't a lot high esp if the pack is used pretty soon and not sitting around for weeks. It's not like 4.2 is the magic number that the cell explodes at... just a good number for maximizing the cell life vs cramming a little more charge in there.

 

[999zip999]

Maybe change the meters battery.? Just a guess.