Another motor wiring question

[ianjParticipant @ians]

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

[ianjParticipant @ians]

Parvalux motor

[Trevor Drabble 1Participant @trevordrabble1]

Ian,

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

Trevor.

[John RuddParticipant @johnrudd16576]

Do you have a link to the website with your motor?

[Les Jones 1Participant @lesjones1]

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.

[Michael GilliganParticipant @michaelgilligan61133]

That's a very useful summary Les.

MichaelG.

[John HaineParticipant @johnhaine32865]

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.

[ianjParticipant @ians]

Hi all.

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

Ian

[Ian S CParticipant @iansc]

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

[Mike PooleParticipant @mikepoole82104]

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

[Les Jones 1Participant @lesjones1]

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.

[Phil WhitleyParticipant @philwhitley94135]

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

[Phil WhitleyParticipant @philwhitley94135]

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

[jason udallParticipant @jasonudall57142]

Ah
.if you think 240 Vrms fullware rectified and smoothed gives you 240 x 1.414 etc
Ie 340 v you are right but….expecting to see that power you will be disappointed and that is what would upset you motor
.as a 240 vrms motor is already rated for that peak voltage …or have i missed your point

[Mike PooleParticipant @mikepoole82104]

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

[jason udallParticipant @jasonudall57142]

Mike…that would suggest that recified/smoothed ac will have the heating effect of say 300V …This would suggest you have got energy from nowhere. ..neat trick

[Mike PooleParticipant @mikepoole82104]

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

Mike

[jason udallParticipant @jasonudall57142]

Rms root mean square…basicaly means for sinusoids same heating effect ie. 230 V rms will do the same work as 230V dc..you can get no more energy out by rectifying and smoothing ..in real world you get less due to losses in dielectric of the capacitprs and bandgap drops of the diodes

[Mike PooleParticipant @mikepoole82104]

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

[jason udallParticipant @jasonudall57142]

Yes and the ripple will depend on the current drawn and the capacitance used. .if the load is for first approximation R and the capacitance C the “decay” from peak votage will follow v=vpeak (1-e^(RC/t))..assuming RC large enough that the voltage doesn’t follow the sine wave…thus for 32% ripple or less RC must be greater than one quarter period of the mains ie1/(50*4) or 5 mS ..so for 1 amp 300 V we get 300 ohms equivalent load…which leads us to 5ms/300ohms or 16micro farads )

[Mike PooleParticipant @mikepoole82104]

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

[jason udallParticipant @jasonudall57142]

Ians motor is what is call shunt wound. If it says 200/220 ac/dc then 230/240 rms would be a bit rich..the rectify -smooth issue makes no difference..it does of course increase the voltage and hence the voltage rating required (insulation)..but in practice since mains motors are insulation tested/designed for 500 volts , that is not going to be the problem. .

[jason udallParticipant @jasonudall57142]

You know ..reading the question is always a good idea… futher up this post, les1 nails it ..this is a dc shunt motor…the motor will not run well or with anything like the power expected , on ac.

[Les Jones 1Participant @lesjones1]

I do not think a shunt motor will be rated to work on AC as well as DC. Regarding the effect on the motor of running it on 340 volts DC (If large smoothing capacitors were fitted.) the heat produced in the field winding would increase as the field current is only controled by the resistance of the field winding. So on 220 V DC the heat produced would be (220 * 220)/2500 = 19.36 watts. With 340 V DC this would inclease to (340 * 340)/2500 = 46.24 watts.

Les.

[jason udallParticipant @jasonudall57142]

quite

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