Electronic Circuits and Projects Forum

Listen well to cachehiker ! Shaft/bearing currents can be a real problem when using high frequency PWM drives. I am currently replacing bearings every 3 months on my furnace fan motor.

pilko

"I am an insomniac, but I don't lose sleep over it!" ---- LOL Love it

Originally Posted by pilko

I am currently replacing bearings every 3 months on my furnace fan motor.

I'd be embarking on a quest to find a better fan motor.

There is simply such a thing as motors that have been optimized (cost reduced) for strictly pure DC or 50/60Hz AC applications. Bearings in such motors will simply not stand up to use with inverter/PWM drives when the motor frame is grounded. There are times when even isolated mounts and shaft grounding brushes aren't enough.

The biggest thing to remember about rectified line voltages is both supply rails end up hot. With 230VAC, the positive one will settle in at +160VDC relative to ground and the negative one at -160VDC. The processor will likely share its negative supply rail with the rectified line. Pushbuttons, displays, potentiometers, and such that are connected to the processor will be shock hazards unless they're optically or otherwise isolated. Disconnecting the processor from the mains for a while (depends on how fast it discharges) before connecting it to the USB port or your computer for programming is MANDATORY unless you have and abundance of computers at your disposal. Connecting a grounded computer to a hot rail will let the magic smoke out. You might be able to salvage some drives or some memory, but the motherboard will likely be roached. This makes debugging a major pain so concentrate on writing robust or easily testable code the first time.

Thanks cachehiker,
I am starting a new thread so as not to hijack this one. --title "Motor Shaft Currents".

pilko