How to increase voltage on this charger without trimpots? Identify resistor that controls the voltage? 72V to 84V

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redmouse

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EDIT: Solved! https://i.imgur.com/D2CsDUN.png



Hey folks, I got this Thundersky 20S LiFePo 10A battery charger from a chinese scooter, and I'd like to use it for 20S Lithium-ion. So I need to raise the voltage from 72V to 84V.

Unfortunately it doesn't have any trimpots inside, but I did a bit of reading up ad it should be possible to identify a resistor on the board and add a trimpot parallel to it.

Would any of you be willing to take a look and guess which resistor it might be?
Here's an album with detailed photos: https://imgur.com/a/cfPAezt

Alternatively, if I can't make this work, how stupid of an idea would be to connect it in series with a 12V powersource from a PC (PSU)? The PSU can provide up to 24A, but I have no idea how could it behave in such circuit.

L2gxiJp.jpg
 
If either the charger or the PSU is not isolated, meaning the DC side has any connection to the AC side, you could have spectacular results. :/

So check wiht a multimeter for resistance between AC input leads and DC output leads, including all grounds / shields, with the PSU and charger completely unconnected from any batteries or loads or wall outlets.
 
I'm very curious about this, read about the idea in other threads, just seems so redneck to me, but probably just due to my inexperience, I'm used to matched PSUs explicitly designed to be serial and/or parallel connected.

Setting aside the ground / common isolation issue for now, let's assume that's all OK.

So main charger is 72V @10A, so call it 720W.

Trying to get to 84V, so series-connecting an additional 12V supply @24A

So that adding 280W, we'll get 1000W total, get our @84V, and ups the current to 12A altogether?

Obviously if this was driving a sensitive electronics load, one of the supplies suddenly failing could damage something.

But if only going into a battery bank, I guess the voltage drop, in effect just stops or slows down the charging, no damage?
 
amperes same in series

10a is your bottleneck

total power as described 840w
 
Thank you guys, good advice!

What I discovered so far:

1. the charger itself is insulated from Earth (the earth wire doesn't connect to anything inside. The PSU however does have GND connected to Earth, so if I decide to go that way, I'll cut it.

2. Ripperton here https://www.diyelectriccar.com/forums/showthread.php/elcon-charger-voltage-adjust-51100.html
managed to raise voltage of a similar charger. I tried following his footsteps, and determined there are two pins on the control board that have measurable resistance to GND. Pin 3 has 1350 ohm, pin 6 is 1550 ohm. So I'm thinking if I parallel another resistor (or a trimpot) to one of these, I should be able to fool the control board into changing the voltage.

3. Also determined that the control IC is HT46R23.
https://www.holtek.com.tw/documents/10179/11842/46x23v211.pdf
I've been advised it's a general control chip, and analog input is on 8 of those pins. So that probably won't help me rule out neither of those two.

4. One big catch is measuring the actual voltage of the charger with no load. It only powers up when actually connected to a battery. That means I can't know what the end voltage is. I tried connecting a lightbulb as a load, paralelling the battery and the charger to it, and once the charger turns on, disconnecting the battery. But that didn't work, the charger stops as soon as battery is unplugged. So it apparently needs something else than just a load.
Any ideas how to fool the charger into turning on "dry"?
 
redmouse said:
4. One big catch is measuring the actual voltage of the charger with no load. It only powers up when actually connected to a battery. That means I can't know what the end voltage is. I tried connecting a lightbulb as a load, paralelling the battery and the charger to it, and once the charger turns on, disconnecting the battery. But that didn't work, the charger stops as soon as battery is unplugged. So it apparently needs something else than just a load.
Any ideas how to fool the charger into turning on "dry"?
Click to expand...
Get a zener with a similar voltage to a discharged battery. (72V?) Put a power supply across it current limited to a few ma. Now connect the charger across the zener. The zener will get very warm very fast, but that should be enough time to get a bigger load resistor connected.

You might be able to do this without the zener if you are fast enough to get the load on before the charger shuts down again.
 
john61ct said:
So main charger is 72V @10A, so call it 720W.

Trying to get to 84V, so series-connecting an additional 12V supply @24A

So that adding 280W, we'll get 1000W total, get our @84V, and ups the current to 12A altogether?
Click to expand...
No, currents don't add unless they are in parallel. Only voltages add in series. ;)

So you end up with an 84v 10A charger, for 840w total peak power (at start of charge until current begins to taper off).


Obviously if this was driving a sensitive electronics load, one of the supplies suddenly failing could damage something.
Click to expand...
Yes. Unlikely, but could--see below for a possible scenario.

But if only going into a battery bank, I guess the voltage drop, in effect just stops or slows down the charging, no damage?
Click to expand...

This works exactly like the charger by itself, except it has an additional voltage source in series with it. The charger still does everything it normally would, *except* if it is designed to sense a specific battery voltage connected to it to begin charging, it may not operate as it should.

So, if there is a failure in one of the seriesed units that causes it to short it's output, and the battery voltage is higher than the remaining voltage, then if there is no reverse voltage protection on the other seriesed unit, it could cause current flow out of the battery back into the seriesed set. If you're not there to smell the fried electronics, it could drain the battery down to whatever level the remaining unit outputs, or if the remaining unit has a low enough internal resistance at the output stage, it could pull so much current out of the battery that it overloads that one too (hopefully resulting in an open rather than a short--a short would just make the problem even worse).

But this is also true of any other seriesed units, even if designed for the purpose, if they don't have protection against it.
 
redmouse said:
Unfortunately it doesn't have any trimpots inside, but I did a bit of reading up ad it should be possible to identify a resistor on the board and add a trimpot parallel to it.
Click to expand...

There is no way you can do this without rewinding transformer secondary. Try to measure output voltage from transformer first. I will upload link later so you can see what you need to do. This requires good knowlege about electronics. Also be very carefull because you have high voltage here.
 
krlenjuska said:
There is no way you can do this without rewinding transformer secondary.
Click to expand...
Usually there is enough margin in the supply to get the higher voltage. The supply won't meet spec any more; instead of working from 95 to 264 volts AC in it may now work only from 105 to 264 volts AC input or something, but that's usually not an issue.
 
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