diy "universal" charger power suply : need advice.

kaiz47

1 mW
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Aug 29, 2019
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For some time I have been accumulating 18650 cells from recycling in order to make batteries for all types of projects.
I've already made myself a microwaveoven-based spotwelder, which works, but I haven't startedthe battery assembly because I have nothing to charge the packs, and don't want to buy x chargers: one for a pack of 12v, another for 24v, a 3rd for pack of 36v, 48v, 52v, 60v ....

at worst I would make up my mind and fall back on a gophert or something like that but before, for the fun of diy, would it be viable to try something based on this kind of module on aliexpress to transform the 12v from a pc power supply at the desired voltage
https://fr.aliexpress.com/item/4001...916559866542346511e18f4!10000015567880156!sea

then add a small voltmeter / ampmeter module to visualise the right output settings
https://fr.aliexpress.com/item/1005...416559862851945272ea64f!12000016794313270!rec

and to finish the assembly with this module which I already have, to cut the load at the desired threshold.
https://fr.aliexpress.com/item/4001...d16559918616303322e7822!10000014203182133!sea

ideally it would just be the boost module and the voltmeter to buy to make a "universal" power supply / charger because I already have plenty of pc power supplies that give many amps on the 12v rail, recovery fans also, and the module to cut the load past a certain threshold:

is there a way to get something ok with a pc power supply as 12v source ? enough to charge - not necessarily quickly, but at least safely - any diy battery between 8v and 60v for example?

i know there are better ways to do it, more expensive also, but can i just get something functionnal with my 30$ idea ?
 
One need a balanced -charger (hobby chargers), or a BMS, to safely charge batteries with cells in series.

But, if you prepared to take the risk, various DC-DC modules that also provide current limiting, can be used as battery -charger.

Or pull out all cell-group, and put them all parallel, at 4.2v fixed, or use a tp4056

Nowdays there exist BMSs as IC, I have asked around here, but nobody knows..
 
of course defuso.
but assuming i equip any diy battery pack i make with a suitable bms according to the nb of cells in series and paralel, i can't see a major risk. :?:
and again, if i understand correctly, this module https://fr.aliexpress.com/item/4001077695749.html?spm=a2g0o.productlist.0.0.56275209JOyBMg&algo_pvid=7f17cafa-f955-46b7-b1f1-d6673d6c77f7&algo_exp_id=7f17cafa-f955-46b7-b1f1-d6673d6c77f7-3&pdp_ext_f=%7B%22sku_id%22%3A%2210000014203182133%22%7D&pdp_npi=2%40dis%21EUR%21%213.17%213.17%21%212.2%21%21%402100bddd16559918616303322e7822%2110000014203182133%21sea allows me to stop the charge (at 4.1v for example for a single cell or 80% for a pack to preserve longevity) before the full charge.

am i missing something ?
 
Yes, if you say so, Il like new energy, "universal" charger good name.
(Im Debian -Linux user, - the universal operating system)

Actually I have the buck-boost dc-dc thingy you 1st linked to, the one 1000W.
(dono why not buck-boost is more wildly embraced)

The second link you provided, ehe. I having hard to believe a sheep Ampere -meter module, will be any accurate.
(Il used to have a boat, and that Amp&volt -meter cost 100x more, and used a half meter shunt..

I dont know what wurst.. say, if a BMS only have 1 function what would that be, and the least..?

https://www.ti.com/tool/BQ76920EVM
 
ok not many reactions + i think i have difficulties to understand your last post defuso (i'm french), so i will reformulate :

is there a way to create a safe "universal" battery charger (for example : 4v to 60v, 2 to 5A), starting from a computer power supply 12v rail, based on aliexpress modules and for a cost really inferior to a solution plug and play like the gophert ?
of course i plan tu equip each battery packs with a bms.
if yes, can someone point me to the "good" items on aliexpress ? there may even be better choices than the ones i linked ?
thank you.
 
The computer power supply is not a charger. It's not sensing or programmed to what the battery needs. If you're feeding that into a BMS that can take a fixed voltage and decide how, when, and how much to charge with it that could work.

The specs you list are close to the newest USB PD spec, 48v @5A through a USB-C cord and charger. Might be worth looking into if it's something you want to develop. The really nice thing about the newest spec is they have a power supply mode that can output fine voltage adjustments and 50ma current step adjustments (not all chips or power supplies have to have this though.)
The downside currently is you can't find 240w spec power supplies (you can find "240w" but is spread over a few ports, not a single port.)
You also can't really find any pd chips or other circuit components that can function over 20-ish volts yet.

I built a ucpd STM32G071 board for a different project of mine to see how hard ucpd is to use. If that goes well on my other 2 projects I'm going to translate that into a true bms board that handles everything battery related (charge, active balance, current monitoring, etc.)
 
it should work, I use boost or buck converters to charge all my lithium battery packs. I have used the boost converter you are using and it works good, its basically a CC/CV charger, and I also used the cheap LED volt/amp meters and they are fairly accurate for me, you can calibrate the volt/amps if needed.
But something I would definitely add would be something to monitor individual cell voltage while charging, especially on a homebuilt battery pack.
The last item on your list is not needed but you can use it as a deadman switch in case the boost converter fails. Thats what I use overvoltage protection relays for. But if a cell goes out of balance and bms fails the overvoltage protection wont help much, thats why I prefer to monitor the cell voltage in realtime.

This a small 4 amp charger i built to charge a 10a lifepo4 pack. Basically a smaller version of what your building.

a boost buck 10a.jpg

I been using these LCD monitors to see the cell voltage while charging, these are 6s, you would need several for larger packs.
a out of balance.jpg

These tenergy lipo checkers can also be used to monitor cell voltage while charging, they are only 6s. I use these also because they are the only ones that an sound an alarm if the cell voltage goes above 4.20 volts.
tenergy checker.jpg
 
jonyjoe303 said:
But something I would definitely add would be something to monitor individual cell voltage while charging, especially on a homebuilt battery pack.
The last item on your list is not needed but you can use it as a deadman switch in case the boost converter fails. Thats what I use overvoltage protection relays for. But if a cell goes out of balance and bms fails the overvoltage protection wont help much, thats why I prefer to monitor the cell voltage in realtime.

until now i believed the bms integrated into the battery pack itself was supposed to take care of this. and cut the charge(or discharge) off if it detects something out of balance during the charge AND discharge periods. was i wrong ?

bms inside battery packs : can they detect individual cell problems or only problems inside a serie group but cut he charge /discharge regardless ?
 
I have a homemade charger. My homemade charger uses a shunt overload detector on the input AC line. IF any current falls low, or goes high, from a set current ( expected), from the line, in.. the charger immediately breaks all current flow out on relay and shuts off. This means it also shuts itself off ( breaks output DC current flow) when the charge is completed.

The hardware is a single transistor and a hall sensor shunt. This shunt is metering the input current to the supply.


I can charge up to 3000w, 24v-250v.
 
I don't trust the bms to work everytime. I once had a bms that allowed a cell go above 4.25 volts and was still climbing. When I buy a new bms I always tests them to ensure it will cutoff during charging at the appropriate voltage.
Your charging system is the first line of defense against overcharging, the bms is there to protect if the charger fails, and the overvoltage protection relay is the last line of defense if everything else fails.

You can also make your own led cell voltage meters. You can use the cheap mini LED voltage meter, all you need is the appropriate bms balance connectors. During charging of a new battery pack I always have to check the cell voltage in real time, that will tell you if you have any balancing issues.

This is a picture of an LED cell meter I made for a 4s lifepo4

a lifepo4 grp 4 case 2.jpg
 
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