Cheap chargers with customizeable end-of-charge voltage

today I found something I looked for since quite a while: cheap notebook style chargers with customizeable end-of-charge voltage:

the description is in german and basically says for most of those charger: there is a poti inside, that allows you to fine tune the end-of-charge voltage which is AWESOME for batteries without a bms.

if you check typical discharge curves, in this example from 2 very familiar cells:

you notice how the cells working interval appears to be probably around 3.3-4.0V, i.e. the small tip from 4.0 -> 4.2V doesnt hold too much capacity and below a certain voltage (probably really around 3.2-3.3V), the voltage also drops really fast (again not too much capacity in that area).

now reducing your end-of-charge voltage has a 2-fold effect: firstly youll be able to prolong your battery life without much downside really -> quoting batteryuniversity: most Li-ions charge to 4.20V/cell, and every reduction in peak charge voltage of 0.10V/cell is said to double the cycle life. For example, a lithium-ion cell charged to 4.20V/cell typically delivers 300–500 cycles. If charged to only 4.10V/cell, the life can be prolonged to 600–1,000 cycles; 4.0V/cell should deliver 1,200–2,000 and 3.90V/cell should provide 2,400–4,000 cycles.

and secondly (and the reason why Im so keen on it): it allows you to essentially run without a BMS for a long time, because even though cells might or might not drift: the headroom for a drifting cell to reach a value beyond 4.2V or below 2.5V is quite large in a safe custom interval like 3.3-4.0V!

and you get these 2 things without much of a downside really - just some capacity loss, which, if you look at the plot, isnt a really big deal. sure, if you got very small batteries like 200Wh and less, you probably cant really afford lower end-of-charge, but people with 400Wh+ should consider it imo!


I like this comment! Might change the way of charging 18650 's

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Nevermind my comment - just checked and my comment made no sense when you look at the charge currents.

just wanted to comment and then you already edited it: kinda unfair to compare 4-5A chargers for 70€ with a 1A charger for 40€ :joy:

groetech also has a 1A charger for <40€

Yeah just checked again and saw the same thing. Sorry for that - already edited my comment again but you were quicker this time :slight_smile:

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groetech has also these smart BMS that can be customized - particularly interesting for me this one:

if you configure it as balancing while idle, you can just stick it on a battery and after a few hours it will be balanced. if one of my 10S battery will ever show some drifing, Ill buy that module and just stick it on every now and then - no need to have it onboard. :slight_smile:

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I’m going to try and find 12s :open_mouth:

Shit check out the 12s4p for 339

The base price is for US18650V3 cells however. They have a 10A discharge rate = not enough at 4P. Changing them to high discharge rate batteries costs 2€ per cell = you need to add 1242€ = 96€ to make it ready for esk8s.

Ah , so the 18650 batteries @barajabali built me are 20 amp? I know they are 12s4p which would equal out to ten amp unless it’s a different 18650 cell

He is probably using samsung 25r with a 20A discharge rate.

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Check these out, pretty penny. With this recommended from @whitepony

Whitepony I have a 42v charger similar to your Evolve charger. You mentioned yours charges to 41.4V I believe ?,…mine charges to 42.2 …if i leave it to fully charge . I wonder if i can modify it to charge to 41V ??

Thanks for this writeup @whitepony ! I’ve looked a few times for configurable chargers and BMSs. Charging to 4.1V has the added benefit of reducing the risk of the full battery/regen shutoff that VESC is prone to. It looks like the BMS is configured at the factory and made to order, but the small chargers are user-configurable.

About the chargers (translated): The final charge voltage can be adjusted at a potentiometer inside the unit to between about 40.5 and about 43.0 volts . If necessary, also to 46V , please inquire. Opening by removing the rubber pads of the feet . Caution : Such manipulations done but at their own risk , may be done only with appropriate expertise ; also voids the guarantee.

my charger arrived, 4A 42V version for 70€ which I now “modded” to 40.5V!

basically you remove the rubber feet, open the 4 screws and youll find a small potentiometer, that was covered in some form of loctite to fixate it.

i then had my half empty spud battery and connected it - 4A charging is really fast - I quickly got to 40.5V and started dialing the potentiometer. apparantly you turn it right for lower cutoff and left for higher cutoff. I slowly dialed right until the charger led switched to green, unhooked battery again, hooked the charger up, it kept green. unhooed battery again, dialed cutoff a tiny fraction larger, hooked up battery and 5min later led switched from red to green, still at pretty much 40.5V.

then I covered the poti with some loctite and put the charger back together.

Im really happy about this!! :grinning:

charger hooked up to battery, measuring voltage parallel, led just switched to green!

reapplied some loctite:

manufacturer is “modiary”, maybe someone finds it cheaper on alibaba or so:

p.s.: this seems to be the one I got:


That is great ,… my charger overcharges to 42.2 V so this is a great option !

Is 4A charging for your 10s4P ?

? Link does not mention Ajustable max Voltage ?

i assume its this one from alibaba after opening up the one I bought here:

you cant really advertise it as “adjustable” imo. adjustable for the average joe consumer means there is a knob on the outside enclosure. this is more like a mod thats not meant to be, but possible because markus gröbe from groetech tried it out.

he is a superchilled guy btw, we talked for 30min over thw phone about batteries and he said that he has no bms in his batteries either. basically we gave each other mwntal high fives the whole time. :joy:


Thanks bud !!,…makes me wonder if all chargers have a poti iside for the manufacture to fine tune final Vomtage ??

Think i will open mine just to check ??

Another method to charge your batteries (for bulk charging with BMS) is to buy a MeanWell (or Chinese ripoff power supply) and modify it by adding a potentiometer. It’s sometimes called the R33 mod. Here’s an old forum link:

I’ve done this with the Chinese clones; it’s a different resistor but it works just as well.

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