ebike charger Component Function (for replacement)

[Vincenzo2]

I have a fancy (around $400) 72V 1500W ebike charger that was connected to a battery in reverse polarity. There were two high specs MOSFETs on large heatsinks that blew up to pieces.


I ordered the MOSFETs from digikey and inspected the few other large components near the outputs and there was still a short.

My suspects were two MOVs that were not short, 680uf/100v 3 parallel caps that measured good (capacitance, leakage, and ESR), and finally a small SMD diode that had a crack and when inspected off the board was shorted.

This diode is connected across the caps (and the output to the battery) in reverse bias. My guess is that it is put there for reverse connection protection but I am not sure. I am trying to make an educated guess to what to replace it with because consulting websites that list SMD components' symbols was not fruitful so far.

I am hoping that someone with more experience and knowledge have come across a similar situation. Any advice is much appreciated

[CapLeaker]

Re: ebike charger Component Function (for replacement)

Yep, you guessed correctly. It’s a reverse protection diode. The unit should work without that diode, but you loose the reverse protection. Diode marking PK comes back as a TVS (transient) diode at 130V. However the size of it I am not sure about. You have to measure it and check a few spec sheets.

PK = 6.0SMAJ130A Uni directional

[Vincenzo2]

Re: ebike charger Component Function (for replacement)

Thanks much.

The reason I was in doubt with my guess was that this "protection" component did not prevent the little explosion and did not protect the main switching components.

The charger owner wanted me to come up with a polarity reversal protection addition to the charger and gave me permission to drill anywhere in the enclosure if a need arises. My first thought was using one of those fuses that look like a little push button (photo attached). Then, I thought, to avoid counting on the tripping speed in comparison to the fireworks, I can just give them a large enough series diode to be connected on the way between charger and battery (with appropriate connectors, like a two-port) with a shorting switch that withstands the current so that the connection process will be two steps, one with diode, then shorting the diode if step 1 was good...just like a preliminary power connection to a circuit of unknown status through a series bulb that can be shorted out if no explosion happens with bulb.

[Vincenzo2]

Re: ebike charger Component Function (for replacement)

this is the little protection add-on that should not be larger than a matchbox (in dotted line).

[CapLeaker]

Re: ebike charger Component Function (for replacement)

Case style is affecting the wattage. I just compared a P6KE130 with the one SMD one that was in there. The SMD one was better than the through hole counterpart.

Something doesn’t add up with the owners story and what you found. The protection diode only works in conjunction with a fuse. Diode shorts, and blows the fuse, thus separating the battery from the PSU. So either the owner put a larger fuse back in or wired it directly. Anyway thats whatI think had happened. In this case a larger protection diode, won’t work much either.

[Vincenzo2]

Re: ebike charger Component Function (for replacement)

Something doesn't add up with the owners story and what you found.

I did have a similar feeling that the guy wasn't very accurate. I am not repairing it for money, it is more like a challenge. After further inspection with a meter I found a tiny (what looks to be) general purpose transistor in a small aggregate of components that look like a little sensing or protection circuit that has the central pin shorted to one of the side pins (shown, back of main board, and enlarged).

That, assuming that it IS a transistor. I use this site mostly, is there anything better or different that you use

[CapLeaker]

Re: ebike charger Component Function (for replacement)

I doubt that this little SMD transistor is bad. It all depends on the circuit. I have a saying "When in doubt, take it out" and re-check it out of circuit. In your case, I would go for the obvious first and concentrate on that. You know that the TVS diode is shorted, you know that the Mosfets are shorted.
Now you need to work on the the gate drive for these Mosfets and make sure all the components are good there. Here is why: If all 3 pins from the Mosfets are shorted, it means full power went to the gate drive circuitry. There could be a blown or out of spec resistor, a bad PWM etc.
Working with switching power supplies things go sour fast if you missed just one component on the HV or the Hot side. If something is bad on the secondary, things aren't that bad.
I (also many others that work on switching PSU's) built a Power Mains Current Limiter. Google something like "light bulb current limiter" aka known as light bulb trick. Get yourself a few different incandescent light bulbs. Like 60W, 100W and a 150W. Basically you rewire the light bulb to be in series with the Mains hot wire.
Let's say you have a short somewhere and didn't find it in the PSU, all that happens is that the light bulb will glow really bright, limiting the current and hopefully making the PSU not blow up. Don't forget that the bulb can briefly light up when you turn the PSU on (inrush to charge the caps).
Again... you have to get all the HV stuff on the Hot side of the PSU working first. Make sure you clean the flux and other gunk of the board with at least 90% or better 99% IPA rubbing alcohol and do nice clean job.
I've had a battery charger come to me, that didn't work anymore 3 days after a different person fixed it. Cause: That someone didn't clean the PWM good enough and a piece of paper towel was stuck in between the pins. Charger turned off, high humidity in the garage, that piece of paper towel got damp, charger turned on and the PWM went south again. I replaced the PWM, cleaned it and it is still working today.
As for the SMD code sources I use a bunch of different sites or go by manufacturer and look at some spec sheets / catalogue. You can use Google like "SMD diode marking PK" an you will find your TVS diode fast.

[R_J]

Re: ebike charger Component Function (for replacement)

Any protection circuit you place between the battery and this charger/power supply will likely cause this charger to not even work as it will upset the current and voltage monitoring.
Plus there is no need as it already has, this is from the manual:

The charger features a maximal safety protection,
 Reversed polarity protection on input and output
 Anti-spark on input and output even connect to 50V battery.
 Wrong battery connection protection when multi battery pack connected in series on adapter board.
 Charge time, charge capacity and battery temperature protection.
 Over temperature protection during charge at DC input and at AC input
 Over temperature protection during discharge
 Over temperature protection during balance
 Short-circuit protection on output, safer and more reliable.