Thread: Clarifying 3ph Motor connections

I think you might have misread that, there is no problem having contactors upstream of the VFD.. the motor should be wired directly to the vfd, with no switching in between.. ( ideally that is ).

This is a direct quote copied from the corrected manual I downloaded thanks to Joe Hovel. I believe you came up with the link.

"No contactor should be installed between the power supply and the inverter to be used
for starting or stopping of the inverter. Otherwise, it will affect the service life of the
Inverter."

Box looks ok, bigger would be better.

Yes, it would. Biggest I have tho. That is the reason for the ventilation. I have just realised that bottom vents will not work. The bottom will be mostly blocked by the lathes electric cabinet. That means either front or rear at the bottom of the cabinet. Front would provide the best air flow.

That 10 ohm pot might be a bit low... 10K would be better..

Did I say 10 ohm? Are you sure.

10K it is of course. Slight slip there.

PS I'm not seeing some of your pictures? Second one is ok, first and third say invalid attachment?

Hmm. Some problems with posting pictures like others have commented on.

Why do these things keep getting changed? It worked fine already. I will correct the problem if I can.

Cheers

Dean

Hi Dean,

Yes you quoted it correctly, but it means what Stuart said.. don't switch the motor on/off using the upstream switching. Use the VFD stop/start controls.

Ray

I hope the pictures now show as intended. The frustrating part is that my edit window showed everything as normal. When I clicked on "Preview Post", it showed 2 pictures in position, but the third as a thumbnail at the bottom, which was the same size anyway, as the way I insert pictures provides only thumbnails in the body of the text.

Dean

Originally Posted by Stustoys

Nope thats what is says. But what(I assume) they mean is "don't use the 240V supply for normal control of your VSD"

If the current tests I am doing are anything to go by you might not have enough power Dean, but there is one way to find out

Stuart

I assumed they meant what I said as it refers to "starting or stopping of the inverter" as opposed to starting or stopping the motor. I am inclined to err on the safe side, as these vsd's apparently have a life expectancy of about 8 years according to what I have read from previous posts, and the fact that my vsd has been sitting in my metalwork cupboard for a couple of years already. I did not know about the gentle start up until I had already run it, as well.

Re power. There was always only one way to find out. I recognised that fact. I made a decision based on my thoughts. If it does not provide enough power then I will have to buy a bigger vsd. Sigh. I see that an almost identical version as mine is available from Osmestore for quite a bit less than I paid according to a post from the last little while.

Dean

Originally Posted by RayG

Hi Dean,

Yes you quoted it correctly, but it means what Stuart said.. don't switch the motor on/off using the upstream switching. Use the VFD stop/start controls.

Ray

Ok, I will keep that in mind. I did wonder how that would affect the life of the vsd. I am not sure how I am going to switch the power yet, but as I have lots of now unused 3pH contactor switches in the lathe's electrics cabinet, that may be the best way to go providing I can get the correct latching voltage without too much cost. 115 volts from memory.

Dean

Originally Posted by Oldneweng

If it does not provide enough power then I will have to buy a bigger vsd.

IF I recall the numbers correctly, your VSD is just fine, its the motor wiring. Getting a bigger VSD* wouldnt give you anymore power with the motor wired as is.

Stuart

*well unless you get the 415V output VSD

Originally Posted by Stustoys

IF I recall the numbers correctly, your VSD is just fine, its the motor wiring. Getting a bigger VSD* wouldnt give you anymore power with the motor wired as is.

Stuart

*well unless you get the 415V output VSD

Motor wiring, as in the method of connection? Am I looking at Ray's suggestion of double delta? Am I looking at a different motor?

Dean

Originally Posted by Oldneweng

Motor wiring, as in the method of connection? Am I looking at Ray's suggestion of double delta? Am I looking at a different motor?

Well it would be nice if the double delta works as I don't think you will get a two speed motor that will run(at full power) on 240V(though I could be wrong). So with some serious switching you might be able to use double delta/parallel star and at least have full power on one speed.

Now whether its better to run one speed wired for 415V on 240V or use the "other" speed that is wired for 240V and use the VSD to over/under speed to get to the speed you want, I'm not sure about.

I'm currently working on a motor dyno to test these very setups. The first tests would seem to suggest power from a 415V motor on 240V is even lower than the worst estimates I have seen online........around 20% but that's early on with scales that aren't exactly suitable and I'm yet to check my numbers fully. Also my hercus drill has a 2hp 415V motor running on 240V and it works ok which would cast doubt on the 20% figure. So maybe its something that is motor dependent so my tests will only apply to the motor I test.

Stuart

Originally Posted by Oldneweng

I am inclined to err on the safe side, as these vsd's apparently have a life expectancy of about 8 years according to what I have read from previous posts, and the fact that my vsd has been sitting in my metalwork cupboard for a couple of years already.

Dean, a design life of 8 years 24/7 nonstop use is roughly equivalent to 70,000 operating hours. That is about 7 times the life of a farm tractor. Or about 5 million km for a car driving at 70km/h. Not bad if you look at it that way.

Originally Posted by Stustoys

I'm currently working on a motor dyno to test these very setups. The first tests would seem to suggest power from a 415V motor on 240V is even lower than the worst estimates I have seen online........around 20% but that's early on with scales that aren't exactly suitable and I'm yet to check my numbers fully.
Stuart

If you had a 750W ( ~1hp) 415v motor, that's 1.8A (ignore power factor) drop the voltage to 240V, without changing anything else and current drops to about 1.04A, which equates to a power of 249W, or roughly 33% of the original kw rating.

Of course it's not that simple, the amount by which you can load the motor mechanically, before it stalls would be different, you could get the locked rotor current by watching the startup inrush.. when the slip is 100% ( or by stalling the motor.. )

A graph of slip% versus current and shaft torque would tell the story.

Take that into account as well as lower power factor, and 25% of nameplate rated power wouldn't surprise me.

All that aside, the results of those tests will be very interesting.

Ray

Based on what I've seen with mine I don't think you will have any issues with the size of your VFD. I work to limit the current on the input side to the nameplate rating because I figure the most stress will be on the rectifier when you run it on single phase. With a 15- 20 second ramp up time I haven't ever seen current go over 13A at high speed on the mill which has a big heavy geartrain.. On my lathe at normal sorts of speeds itsnormally 7-8A. Once working its easy to alter DOC and feed to control current but even then I've never seen it go much over 16A.

It will be interesting to see what happens with the motor unmodified... Although its counter intuitive like ray hinted you might actually see quite high current if motor cant produce enough torque and starts slipping excessively. We just went through a problem like this at work where the motor on a compressor failed and when it was replace the new motor was accidentally wired for a higher voltage. The compressor would start and run normally (albeit taking longer than normal to get up to speed) but as soon as it was loaded you could hear the motor slow and the current would skyrocket until it would trip on over current. Sparkies were convinced for a week that it was a mechnical problem in the compressor.