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Another motor wiring question

Parvalux motor

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ian j22/06/2013 21:08:38
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306 forum posts
285 photos

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

Trevor Drabble22/06/2013 23:37:37
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261 forum posts
5 photos

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 Rudd23/06/2013 09:00:28
1438 forum posts
9 photos

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

Les Jones 123/06/2013 09:06:42
2234 forum posts
153 photos

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 Gilligan23/06/2013 09:36:35
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18932 forum posts
943 photos

That's a very useful summary Les.

MichaelG.

John Haine23/06/2013 10:15:37
4172 forum posts
242 photos

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.

ian j23/06/2013 11:37:09
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306 forum posts
285 photos

Hi all.

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

Ian

Ian S C23/06/2013 13:30:59
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7468 forum posts
230 photos

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 Poole23/06/2013 14:31:49
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3071 forum posts
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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 123/06/2013 14:37:00
2234 forum posts
153 photos

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 Whitley24/06/2013 22:04:04
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1372 forum posts
147 photos

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 Whitley24/06/2013 22:07:18
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1372 forum posts
147 photos

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 udall24/06/2013 22:22:01
2030 forum posts
41 photos
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 Poole24/06/2013 23:28:42
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3071 forum posts
72 photos

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 udall24/06/2013 23:48:51
2030 forum posts
41 photos
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 Poole25/06/2013 00:11:25
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Moderator
3071 forum posts
72 photos

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 udall25/06/2013 00:59:18
2030 forum posts
41 photos
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 Poole25/06/2013 01:25:47
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3071 forum posts
72 photos

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 udall25/06/2013 02:27:27
2030 forum posts
41 photos
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 Poole25/06/2013 02:57:49
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3071 forum posts
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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

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