Thread: 3ph motor/VFD no torque

I'm probably doing something stupid/obviously wrong, however:

I bought a drill press that had been installed on a fixed/hardwired 3ph line. Motor is a GMF, plated 400/440V, 1.2A, 0.5HP, 1400rpm, 3ph continuous duty. I hooked it up to a 2 horse rated 240V VFD, dialed in all the parameters for a 50hz motor, and the motor runs at its rated speed, but has f-all torque. Motor appears to be delta. I can rub a bit of timber against the rim of the main pulley and stall it.

Am I missing something here? This formula has worked on my other 3ph conversions, I feel like I must be missing something really obvious.

Also, related: Every time I've done a 3ph->1ph conversion, I've noticed that the tool suddenly needs chassis grounding - in the case of this drill press, despite being grounded to the motor casing, touching the tool body anywhere when the motor is running will give you a mild AC shock, until the tool body has a separate ground added to it. I must be missing something, again, really obvious, because it doesn't make sense to me - the motor body is conductively connected to the rest of the tool, surely the case ground should also ground the rest of the tool? If I'm getting a shock off it, why isn't it tripping the RCD?

If its a 400/440 V Delta OR Star it will only output 0.25hp at 240V.

The motor has to be configurable to 240V DELTA to output its full power..

If it doesn't say it can be done on motor name plate then it cannot usually be done just in the motor junction box.

If it is a 440.440V delta then you are SOOL.
If it is a 400/440V Star it may be configurable to 240V delta by a motor rewinder or someone who knows how to did out the common point and make the connections.

Well, I'm SOL. That was silly of me. Thanks Bob.

Guess I'll wait for a cheap foot mount 3ph fractional motor to pop its head up.

Do you get a shock when you touch the motor?

If you get one from the drill press and not the motor then this would indicate that they are not connected properly. Connect them together with a jumper lead and see what happens. I would think that all machines should be grounded seperately from the motor.

Dean

Originally Posted by Precious Mettle

the motor body is conductively connected to the rest of the tool,

Are you sure it is? If adding a separate earth solves the problem I suspect the motor to chassis bonding isn't effective.

Originally Posted by Precious Mettle

If I'm getting a shock off it, why isn't it tripping the RCD?

The fault current may not be exceeding the 30mA trip current of the RCD.

I would'nt be using it if you get a shock...no matter what!!!
something is wrong..get a sparkie or someone who knows what they're doing to check it out

Originally Posted by Precious Mettle

Also, related: Every time I've done a 3ph->1ph conversion, I've noticed that the tool suddenly needs chassis grounding - in the case of this drill press, despite being grounded to the motor casing, touching the tool body anywhere when the motor is running will give you a mild AC shock, until the tool body has a separate ground added to it. I must be missing something, again, really obvious, because it doesn't make sense to me - the motor body is conductively connected to the rest of the tool, surely the case ground should also ground the rest of the tool? If I'm getting a shock off it, why isn't it tripping the RCD?

There are any number of reasons why you might get a shock. I have investigated quite a few shocks. I strongly suggest you contact a good elecrician and get them to come around and do some testing for you. Alternatively, your supply authority might be charged under legislation with such investigations and your electrician may well refer you to them.

When was the last time you tested your RCD? are you sure that it works? I seem to recall that they should be operated by the test button every 3 months?

Cheers

The Beryl Bloke