Home Forums General Discussion Technical Questions using a megger

Showed up to a building today to do maintinace and noticed one of the elevators was running without picking the brake. Its old us equipment using a holister whitney machine. Anyway I am only getting 6 volts to the brake coil but if I dissconect one lead I get the full 200volts to the brake coil. So I ohm out the brake coil and it reads good. I next get a megger and i allways second guess myself using a megger because i rarely use one. Reading the coil to ground is open but what about reading accross the coil .

hey vince, i presume that you have a ssd-1 drive unit. if the car is running through the brake and SR relay is picking up as it should, then you probably have a problem with either the SR 2 contact or the CBK capacitor, or the RBK resistor. if the capacitor is open which is the most likely case, or the sr2 normally open contact is no good or the rbk resistor is open, then you will experience the problem you are having. As far as using a megger to read across a brake coil, this is not what the tool should be used for, the brake coil already has a low resistance across its windings, a ohm meter should suffice in checking resistance across a brake coil, compare to another car to be sure if the reading is within tolerance. if the brake coil were to go to ground or short out it would open the brake fuse on the ssd-1 drive unit. one last note, it is possible that the brake coil is open, but you indicated that it reads ok with a ohm meter. i cant be sure but i think that you would read around 50 ohms or so for that brake coil, be sure to measure only the brake coil by removing the wires from the terminal as not to get a false reading. good luck

Check for AC on the brake leads if so its the CBK cap.This will give you all kinds of crazy readings but is fairly common.

yeah it was the capacitor, I saw it on the prints but didn't give it a second thought because i just put a new one in about 4 months ago just because. One of the caps looked like it had leaked a little and then resealed itself so i replaced all of them . As soon as i took a look at the cbk cap i could see where all the electolitics had leaked out , good call.