LiFePo4 Charger - bang! Repairable? 204V AC clearance on PCB? - Page 1
Forum section: electronics / repair

author: migry
author_rank: Regular Contributor
timestamp: August 21, 2025, 08:02:22 pm
content: My 2 year plus old Nexpeak LiFePo4 charger went bang the other night when I was charging a 50Ah LiFePo4 at the highest 20A rate. I might not have used this setting before, as I usually charge on the middle 10A setting. I'm a bit upset because the unit has done a great job and it has travelled to both the USA and Cyprus with me, working at both 120 and 240V AC. My only initial "concern" was that the output wires to the croc clips looked a shade thin for the highest current.So with it not switching on, I took it apart[ Specified attachment is not available ]The above shows the main PCB. I have removed the not so large heatsink and bent up the two packages. The part on the left is a CHM31N60 presumably MOSFET and is shorted across all pins. The surface mount resistor (next to the 8 pin smd IC) above appears to have exploded and left a trace of the outline of the transistor. Note that I cannot find any data on this transistor, so currently cannot find a replacement. I also noted the slightly melted insulation on the lead from the PCB to the front panel display (or circuit board) caused by the current shunt on the lower right hand side. The other bent up device below the transformer is a dual diode. There are two smaller SMD diodes just above and one looks unusual. I am not sure if it has blown or it simply has residue from when the PCB was populated.[ Specified attachment is not available ]The image above is the bottom of the PCB. The 240V AC mains comes in via the connector on the top right hand side. The top pin passes through a MOV(?) and the red circle shows virtually no clearance between it's other pin and the other mains input pin. It made me wonder what is the minimum recommended clearance, as that PCB trace gap is less than 0.5mm (at least they slightly chamfered the corners) . I am not sure but I wondered if the wide traces on the 240V AC side were wider than strictly necessary. At the bridge rectifier again the gap between the PCB pads seems quite narrow. The middle two pins are the AC input.I suspect that it might be repairable, but it depends whether the damage is more than just the MOSFET. Perhaps someone might suggest a possible replacement (same package, high current, low on, etc.) MOSFET?I was also intrigued by the small clearance on the 240V AC side (just as bad on the top PCB for the high voltage DC traces), and wondered if apart from likely bad practice, it might be illegal in some countries?It's a shame, so many good things about it, but let down by a few issues, which probably wouldn't be too difficult to solve. I have observed this in other Chinesium products.In the time being I have ordered a new unit which is almost identical but from a different manufacturer. At the time I bought it, it appeared that the same identical device came with different front panel printing with different manufacturers names.Sorry I think I have made a mess of in-lining the images.

author: Gyro
author_rank: Super Contributor
timestamp: August 21, 2025, 09:17:41 pm
content: Sadly, the same old far eastern crap that we see time and time again! It has clearly never been through any sort of safety testing or approval - there's no way that it could carry alegitimateCE or UKCA marking.More important that the (yes, non-compliant) primary side clearances is the pitiful Primary - Secondary creepage and clearances and that's without looking at the way the transformer is wound. From what you say, the primary side MOSFET was sharing the same, non earthed, heatsink as the secondary side rectifier. Also non compliant.Short answer, it's not electrically safe and never will be, so definitely not safely repairable, even if you start changing parts. Buying an "almost identical" replacement may not have been the best of ideas unless you got very lucky with the different manufacturer.

author: migry
author_rank: Regular Contributor
timestamp: August 22, 2025, 05:13:41 pm
content: So I unsoldered the two big 3 pin devices. Both were showing shorts.The "transistor" which I think drives the high voltage primary of the transformer is a CMH31N60 by a company "Cmos" (not helpful for googling!). It might possibly be an IGBT. Every pin is shorted to each other.The other device is a dual diode (MBR40150PT Dual Schottky), and one side is a complete short, whereas the other side gives a 0.25V reading on the multimeter diode setting.Having removed the dual diodes I tried to power up the low voltage side from a bench power supply, but the screen did not come to life and there was almost no current draw. TBH this did surprise me.

author: Kean
author_rank: Unknown
timestamp: August 22, 2025, 05:30:08 pm
content: Possibly a clone of the obsolete IXYS IXGH31N60 - you can find some potential substitutes on Digikey search.I'm in agreement with Gyro regarding safety, and not sure this is worth repairing. Also you should probably review your replacement unit to see if they have improved creepages and clearances before use.A dangerous charger effectively negates the safety aspects of using LiFePO4 batteries.