Fix shorted mosfet in portable power station

[Batoubatoubatou]

Hi everyone,

I got a battery Suaoki G500 but it doesn't switch on. I opened it and I saw that the lithium pack is perfectly fine, and fully charged. But I noticed that when I connect the pack to the power supply motherboard, battery BMS goes into protection.

I measured impedance between the mother board battery ports and there is a short circuit between the 2 PCB connectors! I visually inspected the circuit board but couldn't find anything unusual.

I supposed that it can come from mosfet, so I just did measurements and here is what I found ("number of transistor:measurement"):

- Gate to gnd resistance (in ohms):
1:43k ; 2:4 ; 3:10k ; 4:-3M ; 5:43k ; 6:48k ; 7:8 ; 8:48k ; 9:300k

- Diode test (red on Source, black probe on Drain) (in Volts)
1:0,001 ; 2:0,001 ; 3:0,5 ; 4:0,5 ; 5:0,5 ; 6:0,43 ; 7:0,001 ; 8:0,43 ; 9:0,43

What can we conclude? Is there any other test to perform?

Thank you for your help!

 

[aliarifat794]

You can desolder the MOSFET and replace it with a new one if the model number is visible.

 

[Tony Stewart]

What type of FET is it? Nch or Pch

Where are these 9 transistor readings? ( useless without a schematic to see if there is a parallel coil)

How do you know which Diode polarity is correct?

But #7 looks suspiciously low.

What can you say about the history of this unknown board?

 

[Batoubatoubatou]

You can desolder the MOSFET and replace it with a new one if the model number is visible.

I started to desolder the number 2, but here is attached a picture of the mosfet, and I can't find any similar mosfet. I don't know if there is a way to find this mosfet spec by measurement?

 

[Batoubatoubatou]

What type of FET is it? Nch or Pch

Where are these 9 transistor readings? ( useless without a schematic to see if there is a parallel coil)

How do you know which Diode polarity is correct?

But #7 looks suspiciously low.

What can you say about the history of this unknown board?

- I can't power the board with a shortcut, and without schematic I don't know how to find the channel type of the mosfet (usually we just look at the fet pin with the lowest voltage). Is it dangerous to try to power the board with a mosfet missing? With the number 2 desoldered, there is no short anymore at the battery ports of the board.
- It is hard to see where each mosfet is used in the circuit, but 1 to 5 and 6 to 9 are on different parts of the board (to measure gate-to-gnd impedance, I had to change of ground reference (for 1 to 5, I used the negative port of the battery pin, and for 6 to 9, a ground which goes into another board).
- For diode polarity, I tried to measure the integrated diode between drain and source (anode on S, cathode on D). I placed the positive probe on the source (S) and the negative probe on the drain (D). If voltage was around 0,5 I supposed it was correct and if below, not correct
- I am not sure what you mean exactly about board history? It is a portable power supply of a friend and he doesn't really know what happened when it stopped working. This board is the main board of the power supply (there is an other one for the display management).

Thank you in advance for your precious help!

 

[rjenkinsgb]

That looks like one of these:-

AP8600S APEC(Advanced Power Elec) | C380197 - LCSC Electronics

AP8600S APEC(Advanced Power Elec) $1.2721 - 80V 80A 104W 5mΩ@10V,40A 5V@250uA 1 N-Channel TO-263 MOSFETs ROHS datasheet, price, inventory C380197

www.lcsc.com

The lower numbers are date / batch / production coding, so can be anything.

 

[rjenkinsgb]

For info, these look to be a suitable replacement; same or higher voltage & current, same or lower capacitance and switching times:

https://www.mouser.co.uk/ProductDetail/onsemi/FDP4D5N10C?qs=F5EMLAvA7IAO92U50NP5Zw%3D%3D

Make sure you get the Onsemi one as linked, there are other makers & not always the same specs.

 

[Batoubatoubatou]

For info, these look to be a suitable replacement; same or higher voltage & current, same or lower capacitance and switching times:

https://www.mouser.co.uk/ProductDetail/onsemi/FDP4D5N10C?qs=F5EMLAvA7IAO92U50NP5Zw%3D%3D

Make sure you get the Onsemi one as linked, there are other makers & not always the same specs.

Hi, thank you very much, I am impressed! I will try to change all suspect mosfet, and hope it will solve the problem (I also hope that they are the origin of the problem, not just consequences of another problem elsewhere).
I didn't know what specs to aim, but I trust you on this point, I will order a few of these: https://www.mouser.fr/ProductDetail/onsemi/FDP4D5N10C?qs=F5EMLAvA7IAO92U50NP5Zw== .
If you have any other recommendation, I am open!

 

[Batoubatoubatou]

Hi, I am back,
I removed 2 not-working MOSFET, other finally look to work fine. If I order 3 MOSFET (one more in case of an other mosfet not working), it could be all fine? Or maybe the problem certainly comes from somewhere else and not working mosfet are juste consequence of another issue?
Because shipping cost are expensive, I would prefer to order once.
Thank you in advance!