Have my FET's blown?

My setup is an Ezee controller and motor, and I upgraded the caps in the controller to 100v caps as I'm using a 12s Li-ion battery pack and it's just over 50v when fully charged and the old caps were 50v.

Quick question to anyone who has melted/killed a FET or two, does this sound familiar?

My motor cut out while doing a standing start on an uphill, so I guess the current was high. I an running a few more volts compared to the 36v pack the bike shipped with, so this may explain why it stopped working.

Originally I thought it was the motor (250w ezee geared hub) but I've since tested this motor with another controller and it works fine.

So, my Ezee controller seems to be the culprit.

I have yet to take it apart since it stopped working, but my gut feeling is blown FET's.

The the FET's are STP75NF75 which have a pretty high RDS on, and there are only 6 FET's in the controller. Ezee claims that the controller limits the current to 20A, but even so maybe the limiting doesn't work as well at higher voltages?

Now if they have blown, can I do a straight swap for IRFB3077 FET's? I"ve checked the specs and they seem pretty similar, but I'm not 100% sure what some of the specs mean like the timings. I wanted to be sure before ordering the IRFB3077's.

Also, Once I get the controller open, is there a way I can test the FET's once they are out of circuit?

yep, dead fets. they are rated to 75V.

dnmun said:

yep, dead fets. they are rated to 75V.

Click to expand...

Ok, I finally managed to remove my controller and get it apart and there is definitely that familiar burning smell.

However, the FET's themselves look ok, it seems the PCB is burnt, here are some photo's.





Now, I have yet to remove the FET's from the circuit, but even so is this sort of thing normal when a FET blows? I should be able to repair the PCB, but even so could this problem have been caused by the PCB as opposed to the FET's?

grrr, When I tried to post it, my longer post was deleted by the gods of internet problems. Excuse the brevity of this repeat.

1) It is hard to tell much from your photos. Try "macro mode" on your camera, it should take better closeup photos. Those photos are rather blurry.
Edit: Your photos aren't actually that bad. It was a bad first impression on my part. The glare isn't great though.

2) You might find http://www.endless-sphere.com/w/index.php/FET_troubleshooting helpful. It's method's rightup on fet troubleshooting.

3) Solving your fet problems does not gaurentee that something else didn't also blow/melt on your pcb. I'd go for careful inspection and in the future beefing up your traces [One easy way, especially with boards that are a few copper wires and excessive solder globbed, is to use copper braid on the traces. Carefully check for shorts around the fet legs after you beef up the traces. This should only be done after you fixed the rest of the borad]

Thanks for the reply, and that link does have lots of good info on FETs and testing them.

I did replace all 6 FETs in this controller last week, but unfortunately this didn't seem to fix things.

It seems that something else on the PCB has been damaged, as I get 11 blinks from the LED meaning the the controller thinks it's over temperature. I've checked the traces on the PCB, and they seem OK, but even so I'll get better photo's at some point.

I wanted to get my bike working asap, so I've now replaced this controller with a generic one from ebay, and it's up and running again, I eventually plan to get an ecrazyman controller as these can easily be reprogrammed.