Motor Star / Delta question

Duncan Munro · 2006-11-15T13:52:16+00:00

One of the million and three projects I have on the go is to convert the old ML7 over to 3 phase using one of those new fangled inverter things.I picked up a 3 phase 1/3 horse motor off Peter Neill at the weekend (thanks Peter!) and have been having a look at the windings on it, the motor having three windings which are strapped to operate in star mode. The motor in question is a Brook Gryphon and is marked for voltage as 220/240 & 380/415.Looking at the specs on inverters, they all seem to output three phase with no neutral at all, so I need a bit of advice from those who have toyed with the inverters.* Can the motor be left wired as star but no neutral connected? This should in theory still give the right voltage/phase to the windings.* Should the strapping be removed and the motor wired with all the windings in delta? Just thinking this through each winding will see 415V instead of 240V. Are they rated to handle either voltage or am I going to run into trouble?Also any tips on the inverters themselves, I've seen the Telemecanique ATV cheaper ones in RS, they can take a speed pot and start/stop buttons and won't break the bank.Any advice or recommendations on the above welcome :-)

Nov 15, 2006 26 Replies

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Robbus 19 years ago

I've just completed this very task. I won a 2hp inverter from Drives Direct on fleabay for =A3105, got him to provide a forward/off/reverse switch and a speed pot. My motor is a very old Brook Gryphon 1hp that I've just had rewired to Delta and given a refurb by my local rewind place. The instructions with the inverter are amusing in their lack of detail, I basically figured it out from the rough diagrams included. Pretty straight forward to wire it all up and job done. Just waiting for an IP56 junction box thing to arrive through the letter box so I can mount the switches neatly and I'll be all set! If you'd like to see some pics let me know and I'll get the camera out.

Cheers, Rob

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John Blakeley 19 years ago

John...I don't what they are paying you but it's not enough!

Thanks for the explanation.

John B

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Duncan Munro 19 years ago

Thanks to all for their help and advice with the motor and inverter questions.

A Telemecanique ATV 11 turned up from RS this morning and I have spent the evening connecting it all up on the bench to test. It runs nicely so I will box up the speed pot + switch and stick it all on the ML7 tomorrow.

There's one thing I noticed and that's the inverter will trip the house RCD on switch-on from time to time so it will probably get left on all the time.

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Ian Ph 19 years ago

Duncan

I hope leaving it on all the time works for you!

I used to leave my Siemens VFD on all the time because it too regularly tripped half the power in our house when switched on. What was worse though is when I left it powered up constantly it frequently still tripped the RCD, seemingly randomly, but usually middle of the night, middle of the day, and whenever else it felt like it.

I have got round the problem in the short term by plugging the VFD into a socket wired into the non RCD protected side of the consumer unit but would really like to get to the root of the problem.

Ian Phillips

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Andrew Mawson 19 years ago

inverter

regularly

Inverters, like switch mode power supplies, have a high leakage current due to capacitive effects and the high frequencies that they switch at.

AWEM

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Tim Leech 19 years ago

Often made worse by built-in EMI filters. The makers often say that they shouldn't be used through an RCD, or only be used with a particular type of RCD, which works with DC as well as AC.

I have an ABB inverter for which the manual recommends disconnecting parts of the internal filter for use with an RCD. They say to contact ABB for instructions. Needless to say, they were initially baffled when I asked! It would trip the (80mA) RCD every time, but now it's fine with the filter partially disconnected.

Cheers Tim

Dutton Dry-Dock Traditional & Modern canal craft repairs Vintage diesel engine service

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Steve 19 years ago

I have a Teco 1HP inverter for my pillar drill and the manual says any RCD must be >200mA and operation time >0.1sec. I think this is probably quite insensitive, I recall we had ones at work in an office that were

30mA for 30ms and they had to change them to 80mA. Maybe you just plug in a different RCD module ??

But then I don't have an RCD consumer unit - so no problems for me.

Steve

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