Another motor wiring question

Hi.

I have a parvalux motor I want to use on the wheel head of my workshop constructed tool & cutter grinder. The motor has the following information on it:-

No. 11A.M/234124/6M

V 200/220

V DC shunt

A 0.7

HP 1/8

RPM 3000

Rating Cont.

There are four wires coming out of it, two red & two white.

I measure 84 ohms between the two red wires & 2.5K ohms between the two white wires,

Looking on the Parvalux web site I found a wiring diagram showing one red & white wire connected together to one leg of the supply & the other red & white wire connected together to the other leg of the supply.

The web site seem to suggest the supply could be AC or DC. I've tried AC put the motor runs very roughly. Does DC shunt mean the supply should be DC? If so would just a bridge rectifier be the answer.

Thank you.

Ian

Ian,

Have you tried actually talking to Parvalux ? When I had a similar problem a few years ago , I found them extremely helpful.

Trevor.

Hi Ian,
Shunt motors do not work properly on AC due to phase differences between the CURRENT in the field and armature windings caused by the inductance of the windings. Although the construction of a series (Universal) motor is very similar to a shunt motor the fact that the field and armature are in series means that the CURRENT must be in phase. You should be able to use the motor with just a bridge rectifier from the AC supply. (No smoothing capacitors required.) The 84 ohm winding will be the armature ant the 2.5 K winding will be the field. To reverse the motor just reverse the connections to ONE of the windings. If you wanted to slow the motor down you would need to reduce the voltage to the armature but not the field.

Les.

That's a very useful summary Les.

MichaelG.

It would however work better with a smoothed supply. The field winding (2.5 k) voltage can be kept constant, you could consider feeding the armature from a speed controller, such as a KB Electronics one. Some of these also have the rectifier to drive the field winding.

Hi all.

Thanks for the advice. A trip to Maplins to buy a bridge rectifier and now the motor runs well.

Ian

An electroliyic capacitor across the DC would help smooth the out put, say a few hundred uf, up to about 1000 uf, with at least 300v rating, although a smooth out put is more important if the motor is a permanant magnet type, the rough DC can tend to de-magnetise the magnets. Ian S C

Rectifying the mains which if you are in th UK is most likely to be 240v will give a peak voltage of nearly 340v applying smoothing will bring the DC voltage well above the 200/220 the motor is rated at. It may run happily for ever on this supply or may shorten its life.

Mike

Hi Ian (SC),
If a reasonably large capacitor was fitted the DC voltage produced would be almost 325 volts. (230 v x root 2 = 230 x 1.414 = 325.22) You would need a capacitor rated above 325 volts and the motor would be running well above its rated voltage. Even without capacitors the current in the field winding would be reasonably smooth due to the inductance of the field winding. The inductance of the armature would not be high enough to provide much smoothing but there would be an averaging effect due to the inertia of the motor.

Les.

Sounds like you should run this motor in series for AC and in shunt for DC, if you connect one red and one white together , and put the supply to the other red and white it will be running in series.

Something that strikes me here is we could do with a "sketch" facility on these sites, as well as a text box, Is that possible moderators?

Phil

also should have said from the readings it looks like ehite wires are the field and the red are the brushes/armature, to reverse swap over the field connections

The motor is rated at 200/220V DC. 240V rms provides the equivalent heating effect of 240V DC. To apply smoothing will raise that DC voltage. 340V is the peak voltage so depending how much capacitance is used will decide the ripple on the supply, some big caps could push the DC towards 300V

Mike

It is stored in the capacitors and supplied to the load when the supply voltage drops below the charge voltage of the caps.

Mike

A full wave rectified 240Vrms sine wave will vary from 0V to a peak of 340V if I store energy in a capacitor and maintain a voltage with a bit of ripple that does not drop to 0V I will have a waveform that is no longer a rectified sine wave but a slightly rough DC at a voltage above 240V DC and Below 340V DC

Mike

So is Ians motor being overstressed by a 240V full wave rectified supply? I think it is a bit and to add smoothing will make it worse and also watch out for the current pulse to charge any smoothing caps damaging the rectfiers.

Mike