ST charger... convert from 13S to 12S

I have an SHC-8100LD charger that came with a 13S li-ion battery. For reasons documented elsewhere, I am temporarily covering the battery to a 12S.

Here is the website for the charger:

http://www.stchargers.com/SHC-8100-chargers-pd563325.html

Resting voltage without being hooked up to the battery is 55.0-55.2V.

I was hoping to use the same charger for 12S, so I opened it up looking for a pot that I could adjust.

I see none. Photos attached.

How do they set the voltage on this thing? Via MCU?

I would guess that it is controlled via a resistor somewhere in there. Good luck trying to reverse engineer that one.

You're going to have a much better (i.e. easier) time buying an adjustable charger or one set for 12S and selling that one.

Most likely a resistor, as noted above.

Which resistor? At a guess, probably somehwere around those three 8-pin ICs in the upper left corner of the interior pics.

Best bet if you wanna change this one is to find the markings on those chips, look up their spec sheets, then start tracing out on paper what other parts (and their values) connect to them.

They may be comparator (or plain op-amp) chips, for current limiting and voltage limiting. If so, then the voltage limter'll have a tap coming off the main output, probably via a voltage divider. Changing one of the resistors in the divider will change the output voltage limit.

If you look thru Dnmun's posts about charger and PSU repairs and mods, you might find useful info on the kinds of things to look for, even if this is not designed the same way as the ones he discussed.

I guess that gives me more incentive to replace the bad module...

I was really hoping for a pot... ;$

Interesting that the info on their website says nothing more than "48v"

Yeah, it's not always that easy. I've tried to mod (or repair) some chargers and failed, and others successfully. The only easy ones have pots, and even those dont' always do what you expect. Sometimes you get smoke (you'd think if a pot was designed in, you could adjust it's full range without failure, but that's not always true).

As for "48V", well, that applies to at least two different pack types, 13s and 14s, though the higher is now usually called 52V, based on the nominal mid-range voltage of the pack.

12s is an oddity that there's not a lot of out there (some, though), other than in the RC LiPo pack world (2x 6s packs in series).

10s is usually the next step down.


For this charger, you *could* use a bunch of power diodes in series with the + output line to drop the voltage. Depending on the diode and the current thru it, it'd be around 0.4-0.7v drop on each one. You'd want to monitor with a voltmeter on the pack itself, though, so that at end of charge it isn't going too high (in case the BMS doesn't cut off for HVC like it should).

If you have a bunch of old linear (transformer-based) power supplies, or old UPS battery backup units, they probably have bridge rectifiers in them that can be used. The bigger, the better. Might need heatsinks depending on the charge current (some are designed to bolt to one). The + sign on the bridge goes to the + wire on the charger, the - sign on the bridge goes to the battery + charge wire. Charger - wire still goes to battery - charge wire.



They look like any of these:
https://www.google.com/search?q=bridge+rectifier+module&num=100&newwindow=1&source=lnms&tbm=isch&sa=X&ved=0ahUKEwiJ7Zu0uvHVAhWLjVQKHaKhAv8Q_AUICygC&biw=1529&bih=925

I thought about diodes, but I would probably need about 10 of them in line. And even then, adjusting the voltage will be difficult.

I think I better just fix the bad module and keep my battery at 13s, or just build a new battery from scratch.

Even the 55.2 volts on the charger is a little bit more than what I would like. I did notice, fully charged, several of my cells were at 4.23 volts.

I'd guess that if you let the battery sit for a while it'll drain those all down to 4.2v or less, as the BMS balances them.

It's not unusual for a charger to be a little higher than the total cell HVC limits, so that balancing is guaranteed.

A number of people have ordered these charge limiter boards recently, still waiting on the reviews.
In the meantime I have ordered one to test to see how well it works myself.

Not sure how reliable they are or other unforeseen issues but will report back in the attached link once I find out.

https://endless-sphere.com/forums/viewtopic.php?f=14&t=87562

Thanks, Captain. Other than the 3 week wait from China, not much to lose at that price.

I think I would prefer the option that runs off the charger's DC power, and not AC.