Hi everyone - I need some help trying to determine what transistor has blown. I saved a cheap Chinese battery lawn mower from landfill and was advised by the previous owner that the battery would not charge. I tried a few times to no avail and when I pulled apart the circuit board,it looks like a transistoron (on review probably a MOSFET) near the large diode has fried. When I tried to desolder it, it crumbled away and I have no markings to try and find a replacement from Jaycar. Entering the circuit board number in Google came up with no results. Anyone have any idea on what it could be or where to start. The unit is only a few years old and would like to save it from landfill.
Will try and add pictures shortly
Last edited by Bobby Slogger; 26-09-20 at 06:57 PM. Reason: add photo links
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If it is that 8 pin chip, it is probably a FET like this commonly used in protection boards for lithium ion batteries. You can buy these boards on e-bay. Take a look at what is being sold and the part numbers and spec sheets. I think it is a common part, you need to consider the current this 40 V battery will deliver in selecting the part.
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"Have Spectrum Analyzer, - Will travel".
Thanks - no luck yet on finding circuit but will try Mosfet. Battery is only around 1300mAh - the Jaycar one might do the trick. Also need to clean up the tracks a little - it did a good job in burning it
That is an IC and probably a dedicated charge controller.
Do a search for LI-ION Charger Circuits.
LI-ION protection circuit fet
Last edited by Johnno; 27-09-20 at 01:38 PM.
I'll try but the chip damaged the circuit board and some of the pads (most all of them). Will try and clean as best as possible and post later.
Here is a link to the photo. The board looks pretty damaged. It looks like the pads could be common but can't tell. That's about as clean as I can get it.
Last edited by Bobby Slogger; 27-09-20 at 12:33 PM.
Had a closer look and it is marked Q4 so the mosfet or transistor array guess is correct.
Bobby Slogger (27-09-20)
I'll need to fix a few tracks as well.
I've looked at the circuit board of the Ryobi 40v battery - theirs is a 2 x batteries x 10 for around 2600mAH whereas mine is just 10 batteries @2000mAh.
Based on what I can see, I need to do a new track to D9 and New pads for the 3 that are missing that appear common. Does this sound right? I have copper tape so it should be easy to do. Have never had to do new tracks before.
Appreciate the help so far.
Check that diode D9 where the burnt track terminates, make sure it ohms out properly. As far as the chip, look at the spec sheet for that package to verify which pins are common.
You probably want to get the highest inverse / breakdown voltage rated chip due to the inductive motor load.
Probably similar to your Ryobi parts.
After you get it electrically repaired, you may want to bond that chip to the PCB with some epoxy to draw heat away. There will be some heat dissipation to deal with during prolonged use,
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Last edited by RFI-EMI-GUY; 28-09-20 at 04:09 AM.
"Have Spectrum Analyzer, - Will travel".
wotnot (28-09-20)
Can't see enough of the circuit to divine the purpose of the fet ; charge on/off switch? If it's p-channel I'd probably think is a TPC8118 or such
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