So, I;m trying to help a friend fix his 60V scooter. The battery had been drained and left that way for some time,... I took the battery from him, and brought the charge back up to about 60V and returned the battery. The scooter had been running fine before the battery died (months ago). He reported to me that while his charger now worked, and that the battery was fully charged (about 67 V), the scooter would not work. I did a basic investigation of the scooter.... all the connectors, and the battery again. When the battery was unplugged, the output read the correct 67 V.... but as soon as it was plugged into the controller, the voltage suddenly dropped to around 11 V (measured at the battery's output connector both connected and unconnected). So... I removed the controller, and attempted to investigate further. I followed the instructions for testing blown mosfets on ebikes.ca (http://www.ebikes.ca/documents/BlownMosfets.pdf
) as well the similar instructions http://www.lsdzs.com/en.php/article/show/id/50.html
When measuring the reistance between the 3 phase wires and GND... the Green and Blue phase wires measured ~10k Ohm... while the yellow measured 8k Ohm. (I beleive that means yellow's bottom bridge mosfets may be having problems)
When checking continuity between positive power and the phase wires, all 3 had 0 continuity... which I thought meant ALL the top brideg MOSFETS were broken.
These results seemed to make sense to me, considering the voltage drop when the battery was connected to the controller... and a have a relatively large number of good mosfets laying around, so I figured I might as well replace the 15 stock mosfets with the new, better ones (The stock ones were Si Tech S80N10R.... planning to replace them with CSD19536KCS FETs).
I began by taking the controller apart, and removing all the current FETs (luckily I have a a Hakko FR300 solder sucker.... made this much easier/cleaner/quicker). After removing them, I used a transistor tester device I have to check each individual FET.... while I planned to replace all of them, I figured I might as well keep the good ones.... BUT... ALL 15 FETs tested fine... this seemed odd... so I then tested most of the FETs manually with a simple DMM.... same results, all fine. I investigated the rest of the circuit board, and the pieces the FETs mount to, etc.... couldn't find any obvious problems at all... surprising the controller, while rather simple, is very clean and in pretty good condition.
I'm now very confused at what has gone wrong.... where I messed up in the tests.... and also, I need to figure out what is actually wrong, causing the battery to drop to almost nothing when plugged into the controller, and why the scooter will not work at all. My only though right now is, I took the controller from my friends place, back home to fix it here, but I don't have the scooter or battery on hand. When I found this voltage drop, the controller was still connected to the motor (at the very least the phase wires, but I believe more than that). I'm now worried that I should have tested everything, once disconnecting the controller from the motor completely. Also worried that the actual issue could be the motor now. I'm really not sure, the FETs seemed to make the most sense to me... but I've literally triple checked them, and can't find anything wrong with them. I'm likely still gonna replace the FETs with the better ones (I have quite a few CSD19536 around), but I 'd like to figure out what actually is wrong, and fix it... before putting the FETs into a controller that may possibly never work again. I suppose there's also a small chance that there was an issue with the FETs, but removing all of them, and reinstalling could have unintentionally fixed it... tho I find that somewhat unlikely. I'm still quite confused at the tests results from checking the resistance/continuity between the phase wires and neg/pos power wires, before I even opened the controller.
Anyone have any advice?... anything I should look into next?... also pointing out my mistakes may be useful,hopefully I'll be less likely to repeat them next time.... any and all help is very welcome. It is definitely annoying not having all the pieces together at my place to make things easier... but I could not get the rest of the parts (scooter/battery) between the apartments at this time, so for now I can only have the controller... would like to see if there is anything else I can find wrong with it today, then get it back together... supposed to return to my firend's with it tomorrow, and if lucky have the scooter fixed with the fixed controller... if not so lucky, will have to attempt to troubleshoot/fix whatever is still broken when I am there.
EDIT: BTW, just check the Phase wires resistance between the pos/neg power wires again.... still getting 10k, 10k, and 8k (green, blue, yellow to neg power).. and infinite resistance between blue/yellow and pos power, and jumping between infinite or jsut REALLY high resistance between green and the pos power.... more or less same results when the FETs were installed, but this is with them completely removed. Not sure if that's exactly as it should be, or if that means something. The yellow being 8K seems strange, as well as the Green not being completely infinite, while the other 2 are seems a little strange, tho maybe it is normal.. I don't know... figured it was worth mentioning... not sure what to do next... would like to run more tests before reassembling, but not sure what I should be doing.