I’m trying to understand how some old equipment from Lenze is working. I have schematics for the circuit boards, but it does not contain any information about the parts. Can you please help me identify these varistors? The photo is attached.
This is off of an OLD VFD.
http://www.tenmilecreek.net/forum/php/download/file.php?id=333&sid=c63afb249956f4c854cb89b20e3bf534
Brandon,
It appears that you have 200 volt and 340 volt varistors. The two letter/number combinations at the bottom are likely date codes. The clamp voltage is higher than the rated voltage. When devices like this go bad, they are usually pretty obvious from the outside. These all look like they are in good condition. Since this is part of a frequency convertor for a motor control, they are mostly used to clamp any back EMF pulses from backing up from the transformer/motor coil to the electronics and taking out the output stage drivers.
If you are having trouble with this controller, look to replace all the electrolytic caps. Most often you will see some bulge in the case of the caps that are really bad. I am going to bet you have issues with running the output under load.
A word of caution… This is not a device for amateurs to troubleshoot. It contains high voltage when connected to the mains and caps can hold their charge for quite a while. It requires special techniques and tools to troubleshoot devices that mains operated.