My tale of woe begins with me happily spending the summer ebiking to work using a new stock bl-36 system, bought this year. The bike ran at 20 mph with no pedaling, 24 mph pedaling.
I first changed the throttle to a 36v crystalite half-twist instead of the the thumb throttle that came with the kit because my thumb got tired.
I then upgraded the system to 48v by adding another 12v SLA battery. The bike ran at a plenty-fast-for-me speed of 27mph with no pedaling, 30 mph pedaling. My first problem was stripping the front dropouts and having the one of the motor wires damaged at the axle when the axle rotated in place. I tore the motor apart and brought a new wire out from the windings. And put in some wonderful torque arms from ampedbikes.com
About a week later of daily use, controller #1 dies. The voltages were good coming from the throttle, the little green light on controller changed blink pattern when twisting the throttle, but
no voltage coming out of the controller on the motor leads. I took it apart, but seeing no obvious damage, and wanting to get back on the road, I bought another bl-36 controller.
This ran fine for about a week and then it died with the same symptoms as controller #1. I tore controller #1 apart, scraping the black gunk off from everything. The FETS looked okay. The in circuit resistances for the fets wer:
for fets 1,2,5,6,9,10: gate-drain 4Mohm, gate-source 4Mohm, drain-source 20Kohm
for fets 3,4,7,8,11,12: gate-drain >20Mohm, gate-source >20Mohm, drain-source 9Kohm
These two groups seem to be the upper and lower portions of H-bridges, where one H-bridge of
4 transistors is associated with each motor wire.
I pulled FETS 1 and 3 out of circuit and they look okay, I think. The gate-drain resistance is >20Mohm, gate-source resistance >20MH. Using a diode tester, I put meter negative on the source and meter positive on the gate (to charge the gate). Moving the positive lead to the drain I then got a non-zero, non infinite number which I assume is okay indicating the FET is conducting. Putting my finger on drain and gate, the reading went to infinity, indicating the FET switched off. This was repeatable for both FETS.
I'm at (my very small) wit's end. The FETs seem plausible. Something, however, is blowing up in the controller.