Teco Westinghouse VFD

[BillSct]

I've been studying the manual for my new Teco-Westinghouse FM 100 series VFD (from Dealers Electric) and clearly (or maybe not so clearly) the unit includes an overtemp protection feature. What's confusing is the block diagram shows a thermal overload relay in a box outside of the VFD box and located in between the VFD and the motor. But the manual talks about programing the built in thermal over load function. Anyone else running one of these units who can explain this to me?

[mhubler]

I have a TECO VFD, and I agree that the manual is hard to understand. This same product is also supported by Bodine Electric and their manual is much better. Here is a link:
http://www.bodine-electric.com/pdf/micro.pdf

Hopefully this will answer some of your questions

[mbensema]

I couldn't download the manual from TECOs website, but the external overtemp is a thermistor that is imbedded in the motor windings. The VFD or another device measures the resistance of this and when it excedes a certain value, it trips indicating the motor is too hot.
The internal method on my Toshiba determines what the motor can handle and adjusts the output current at the low frequency range to prevent the motor from overheating due to lack of cooling. So at say 20 hz you may only get 70% of your motor rated current. You should have a selection for an inverter rated motor and standard motor, the inverter rated motor can handle more current at lower speeds, so it's derating is less then the standard motor.

[BillSct]

The Bodine manual is better. The diagrams show no external thermal protection. My question is how exactly does the internal overload protection work? Is the VFD measuring current in, current out and making some assumptions (reprogramable?) about loading on the motor? As far as I know the motor I will be running off this VFD has no external protection device such as the aforementioned thermistor. Also, what's the deal on EMI? The Bodine manual mentions an optional filter. Finally, who actually makes these particular VFDs, TECO, Bodine or someone else?

[rklopp]

The VFD computes a theoretical temperature rise based on current and speed history. The current gives the heat input and the speed (if the fan is on the motor's rotor) gives the heat out. There's a different setting if the fan is independent, like a small boxer fan.

EMI from VFDs can be terrible under certain circumstances. I had a case in the lab at work where we were trying to run a power steering pump with a VFD-driven 3-phase motor so we could control the speed. We couldn't keep the 30 kHz chopper noise out of the strain gage amps no matter what we tried, including shielding, and connecting the amps to separate, clean, isolated-ground power. We had to give up and bypass the VFD and run at 60 Hz. On the other hand, I don't usually have troubles with radio or TV and VFD nearby.

[mbensema]

rklopp, many times changing the carrier frequency will get rid of the noise. I had a couple jobs where the carrier frequency interfered with bearing RTDs and adjusting the frequency to a lower value solved the problem. Sometimes the electrical items that are having the problem act as antennas and once you get out of the frequency range they are sensative to, the noise disappears.

[JimGlass]

Hi Bill;

I just installed the same VFD. I read the manual the same as you and installed an external motor starter with an overload relay. I called Dealer Electric and they explaned there was an internal overload and the one I installed was not required.
If nothing else the motor starter serves as a disconnect. I think I'll download the Bodine manual anyway.
Jim

[BillSct]

The thing that confused me about the drawing in the TECO manual is that it's my understanding (having read it here and possibly even in the TECO manual) that there shouldn't be any switch between the VFD and the motor or at least not one that you switch on and off with the VFD powered up. The drawing in the Bodine manual shows no external motor protection device. My application is going to require a switch to retain the two speed feature of the motor on the drill press but I'm going to install the switch on the side of the machine where I won't be tempted to grab it by mistake while the drill is running.