dnmun
1 PW
i wondered if he is reading open circuit as 0V too. but no way to know.
Blew my controller. Please advise......
- Thread starter StudEbiker
- Start date
StudEbiker
100 kW
open circuit would read 0v right. No current flows on open circuit.
I am in diode mode.
This is the meter I am using. I have the meter's pointer turned to the setting two up from the bottom on the right.
http://www.amazon.com/gp/product/B000EVYGZA?psc=1&redirect=true&ref_=oh_aui_detailpage_o00_s00
I am in diode mode.
This is the meter I am using. I have the meter's pointer turned to the setting two up from the bottom on the right.
http://www.amazon.com/gp/product/B000EVYGZA?psc=1&redirect=true&ref_=oh_aui_detailpage_o00_s00
That looks like the correct mode on the meter. What does it read if you don't touch the probes to anything? If you touch the probes to each other, it should read zero.
dnmun
1 PW
yes, open circuit is the reading on the meter when the probes are not touching while using the diode tester. when you short the probes the reading should drop to 0 volts. same will be true if you measure resistance.
that is what your diode tester is evaluating when it is trying to push current out of the red probe and into the diode.
the diode will not conduct in reverse so you have open circuit on the meter,and it does conduct when your reverse the probes and that is the forward bias of the body diode at 1 A current.
so the ones you say have 0 V are ok, if that is what you were seeing on the meter, and they are the good mosfets and the ones with the .513 numbers are shorted.
that is what your diode tester is evaluating when it is trying to push current out of the red probe and into the diode.
the diode will not conduct in reverse so you have open circuit on the meter,and it does conduct when your reverse the probes and that is the forward bias of the body diode at 1 A current.
so the ones you say have 0 V are ok, if that is what you were seeing on the meter, and they are the good mosfets and the ones with the .513 numbers are shorted.
StudEbiker
100 kW
fechter said:
Hey guys, thanks for your help. It was a very busy weekend, but I had a chance to take a look at the meter. When the probes are not touching, the meter reads ".0L" with a "v" in the upper right hand corner. When they are touching it reads ".000" with a "v" in the upper right hand corner.
Like I mentioned before. I am really, really not very knowledgeable with this level of e-bike repair, but I would like to learn so I really appreciate you walking me through this so I can get my bike back on the road.
StudEbiker
100 kW
So is the .0L the open circuit reading? It still seems really odd that I could blow six fets all of a sudden like that. I still haven't tested the fets using the phase wire technique you mentioned fechter, I guess I should try that too.
It's really the same as measuring from the drain-source pins on the FETs. The drain is the middle pin. The outer pin with the heavy copper traces will be the source. Since the FETs are in pairs, if one is shorted, the one parallel to it will also read shorted even if it isn't.
dnmun
1 PW
the drain leg is attached to the phase wire for the loside mosfets and the source is connected to the phase wire for the hiside mosfets. the source is connected to ground on the loside mosfets and the battery positive B+ is attached to the drain for the hiside mosfets. the drain is always at the higher voltage, source at the lower voltage for n channel mosfets like these.
that is why you can measure the mosfets without opening the controller.
just by measuring from the phase wires and the B+ and ground wires.
it takes a while to sink in but you will get it. but it does look bad for your loside mosfets.
but verify by measuring from the phase wires and B+ and ground like richard said and that will give you a big leg up on everybody else in tech savvy.
but you will be cursing when you have to replace them.
that is why you can measure the mosfets without opening the controller.
just by measuring from the phase wires and the B+ and ground wires.
it takes a while to sink in but you will get it. but it does look bad for your loside mosfets.
but verify by measuring from the phase wires and B+ and ground like richard said and that will give you a big leg up on everybody else in tech savvy.
but you will be cursing when you have to replace them.
dogman dan
1 PW
FWIW,, a shorted mosfet is easy to diagnose. With the battery un plugged, If the motor cogs and resists very heavy, there is a short in the phases. For a geared motor, turn the motor by hand in reverse to check for cogging.
If unusually heavy cogging vanishes as soon as you unplug the controller from the motor, then the short is in the controller, and usually this is a blown mosfet inside.
Read back on this thread to see how to figure out which fets are blown.
If unusually heavy cogging vanishes as soon as you unplug the controller from the motor, then the short is in the controller, and usually this is a blown mosfet inside.
Read back on this thread to see how to figure out which fets are blown.
StudEbiker
100 kW
Thanks, that's a good tip. I replaced this controller with a new one, but I still have it around so I might check it out using this method sometime. Funny you should revive this old thread this week DD, I used your wheel building tutorial posted on electricbike.com this week to build a wheel. Great method, much simpler than the method posted in most other how-to guides. 8)
