An inverter for a 3 phase Myford plus 3 Phase suds pump

[Andrew TinsleyParticipant @andrewtinsley63637]

[Andrew TinsleyParticipant @andrewtinsley63637]

Hello all, Thanks for the response to my query abourt a reliable inverter for my 3 phase powered Myford.

However I completely forgot about the small 3 phase powered suds pump (Standard Myford pump and resevoir). I was not looking at the inverter as a means of frequency conversion. So my query is can I run the suds pump motor from the same inverter powering the lathe motor?

Regards,

Andrew.

[Speedy Builder5Participant @speedybuilder5]

You could run the pump off 240volt if the pump is dual voltage (440/240). Use the 240 volt legs.Put a capacitor across 2 of the legs, and live / netral from one end of the capacitor and the spare leg

I got this information from J.Olsen:-

I don't have a method for calculating a precise value for the capacitor, but a rough calculation suggests that something of the order of 33 microfarads would be about right for a starting point…it may be happy with a bit less or it may need a bit more. It must be rated for 240 volts AC continuous operation. Some motor start capacitors are not rated continuously since they have a switch in the motor.

Ok, last thing, remember to be careful, especially while you are trying things out!

[KWILParticipant @kwil]

There is no reason why you should not run the suds 3 phase pump in parallel with the spindle motor, the power demanded is low compared with the spindle motor and you only need the suds when you are running the machine anyway. I have this available on my lathe and mill.

[Andrew TinsleyParticipant @andrewtinsley63637]

Thanks for the replies. I wasn't sure if there was some form of feedback to the inverter and trying to run two motors would confuse the feedback (if any?). Even if ther were feedback, I would assume that the demands of a small suds pump would not make much difference. However I wasn't sure so safer to ask!

Just another query, both 3 phase motors have 4 wires coming out of the flexible conduit. The 3 red phases and earth. So I assume the motors are connected in delta (i.e. no neutral connection). I have not yet checked at the motor connections themselves to see if they can be connected in star or delta. Assuming that the connections can only be made in delta (big if!). Can you use an inverter in delta, or do you have to be able to connect in star for inverter use? My 3 phase electrical theory was last use 40 years ago and is to say the least, a little rusty!

Regards,

Andrew.

[Chris HembryParticipant @chrishembry84309]

Hesitated to reply on this one as it is not recommended to have switchgear between the motor and the inverter. However, if you always switch the suds on or off while the main motor is stopped you will have no problems whatsoever. The inverter will not see that there are two motors connected to it.

I have a M280 CNC where the coolant can be computer switched via a 3ph contactor. Switching on causes no problems but switching off occasionally causes the inverter to trip out and show an overcurrent error. I guess I could alter the parameters to allow the fault but since switching the coolant off usually precedes switching off the spindle, no real problem occurs.

You can use an inverter in star or delta but if the motor is not changed over it will be running on 240V per coil instead of 415V and you will thus lose a large amount of power.

Regards,

Chris

[Martin KyteParticipant @martinkyte99762]

You can connect 3phase motors in Star or Delta without bringing the star point out of the motor. The system is balanced and does not need a neutral connection.

You have the suds pump perminantly running and add a bypass to the pipework so that when fully open you get no sudsThis would act conveniently as a flow adjustment.

If you are using variable frequency drive to control lathe speed you will slow your suds down too.

[Andrew TinsleyParticipant @andrewtinsley63637]

Thanks Chris and Martin,

Not all that au fait with inverters, but I assume that they rectify and then chop the DC volts to get a sine wave. I realise it is more complicated than that! However it will do for a start. If I am vaguely correct, then the 3 phase supply will be 240 volts per phase? So do I need the motor connected in star or delta. I seem to remember that a star configuration will be required if it is simply 240 volts per phase. However it is a long time ago since I did any 3 phase stuff. I don't even know where my old textbooks are!

Regards,

Andrew.

[Chris HembryParticipant @chrishembry84309]

Martin,

You need to connect the motor in delta to give full power on 240V.

Between any two phases there will be only one winding so it will see the full 240V. In star you have two windings between any two phases so each will see half the supply voltage.

Regards,

Chris

[Martin KyteParticipant @martinkyte99762]

Yes I know Chris, my remark was about the Star point and not needing neutral connections which sometimes confuses people.

"You can connect 3phase motors in Star or Delta without bringing the star point out of the motor. The system is balanced and does not need a neutral connection."

However you are perfectly correct that the duel voltage motor needs connecting in Delta. I could be pedantic and say that each coil would see 1/root3 or 138.56Volts but I won't.

Regards Martin

[Chris HembryParticipant @chrishembry84309]

Sorry Martin, reply was directed at Andrew.

Chris

[john fletcher 1Participant @johnfletcher1]

Regarding Cap size for the colant pump its more likely 4 Micro farads. I have done this for my friends but cannot remeber the exact value. When the motor sound right and not getting hot then you have the best value, so its a bit hit and miss. Connect Caps in parallel to increase value, in series opposite.Ex fluorescent lights are good. Old 5 foots fluorescents were fitted with 7.5 micro farad. Ted

[Andrew TinsleyParticipant @andrewtinsley63637]

Thanks Everyone for all your help. I now need to get stuck in and get my Myford on the road!

Regards,

Andrew.

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