How to modify a set voltage on a battery charger

[leffex]

Now I'm working on a ev- charger with a relay and a set 520ohm resistor next to it. The output voltage of this 72v 8a charger is 88v.

I want to lower the output voltage on this charger so I'm pondering about how to do it. If you have any idéa to get me on track, please let me know.

My plan right now is to lower this resistor value to 70% or 0,7 x original and then se how the charger reacts, if it reacts at all. Why 70.

I have opened up some chargers and repaired some with success and I'm always learning.

Now it seems I have come to the place in life when you really do have a need of your school electronics course. Yay. Hurray.

I want to but the basics ,replace mosfets, resistors and maybe the big coil that also microwaves owens have but that of course is smaller on the chargers. Maybe. But that is when I get the hands on the safety and security about how to handle these stuff while dismantling and repairing these and the latter I think I'll hold on from attempting in the nearest future as I have so much other things to learn before that.

I started checking and repairing in the end of 2021 I guess. I don't count or remember "trivial" stuff. I just head forward as fast and safe as I can.

Please let me know if you can help. Any help is appreciated.

 

[E-HP]

Do you see a trim pot on the circuit board?

 

[leffex]

Do you see a trim pot on the circuit board?

No trim pot.

Something like this I like to do but now I'm going backwards and also I like to keep as high current as possible following the modification. But right now the major modification I like to do is set output voltage to 74,5 - 75 volt DC rather than what it is now at 88v.

Output caps must be at least the voltage you want to charge plus extra for reliability
Feedback resistor . What is that? What happend when it changed from 2k to 1k with the voltage?

 

[leffex]

It looks like I have this one. You can se some components but not all on the photos:
https://www.aliexpress.com/item/1005004388099812.html

Very similar to this board:
https://www.aliexpress.com/item/4001156842057.html

 

[BH4SKM]

You must first understand which model of the switching power supply IC is. If it is TL494, then you are lucky, because it is very easy to change the voltage of TL494. I posted the 24V MEAN WELL modification tutorial on YouTube. I successfully modified it to 0-30V. If you only reduce part of the voltage, it is easier (no need to install a 12V auxiliary power supply)

?si=VxuubML2N0k1B3-J

 

[leffex]

xie xie

thank you

Have you eaten? Are you well?

For me what stage I am at for "modifying" my charger it is a little bit of a test and I can afford the failure but the failure rate is dropping or the rate at which I can't repair broken chargers so soon I may be able to repair them all if I have time and that my effort is worth it in the end for me of course.

So my understanding is good to read the data sheet and the map of electronics but I can't calculated the voltage or understand what happens after a resistor exactly. Because I do need to know exactly what happens if I want to build something myself.

I will do easier projects for a start. I just realized I already have chargers available for me so I can try and change the voltage on a 42v charger more easily as well.

I would like a small factor 10-15a charger in the volume of 1 liter or a brick. The weight should also be as light as possible and also the safety rating should be CE or as close as possible.

From the Huawei 4850, 4875 they should also have one called 4810 or 4815 which should be in that region capable of about 1kw of power if I am not misstaken also at a very small size and volume.

 

[leffex]

It seems to be easy to change a charger to give out a little different voltage that its original.

When you want to change it more than a few volts it gets trickier.

Caution is needed as it is dangerous. Very.

Broken components may also brake so called internal fuses or voltage draining parts which kind of works like fuses draining down for example capacitors.

I'm currently doing research and youtube videos is very explanatory and gives a lot of details. It feels like it is very easy as you get to understand more and more.

I recommend you to, if you think it's too hard that your guesses may be in the wrong. It is easier than it looks. Still needs some thought and following examples to get the best and fastest knowledge process.

 

[leffex]

I tried changing a resistor near a 12v relay and the output. Original value was about 540hm. tried with paralleling another resistor and also lower to a total 140ohm but no real change. Maybe this resistor is affecting amperage power and as I only measured the voltage in these instances there was no other possible change to what I could se.

I have a smart bms that cuts the power but I want the voltage of the charger to be maximum 75v and not 88v as it is now as to increase safety while charging.