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Join Date: Jun 2011
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Voltage Conversion Rewinding

05/03/2012 12:08 AM

hello to all, please educate me what to do.

I am converting a craftman router rated 1/2hp, 8A with 120VAC into 220VAC. I rewound the stator winding reduce the wire size and double the number of turns.

The router when tested have a reading of 17A and the RPM is slow.

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Guru
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#1

Re: voltage conversion rewinding

05/03/2012 3:30 AM

It depends upon the value of time.

One of the options is to recycle it and replace it with one that is already wound for the voltage of application.

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#2

Re: voltage conversion rewinding

05/03/2012 4:31 AM

A suitable transformer would have prob' been cheaper and easier.
BTW I'd have expected half the amps at twice the volts.
e.g 8A at 120VAC I'd expect 4A at 220VAC.
17A at 220VAC sounds seriously wrong to me.
Del

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#3

Re: voltage conversion rewinding

05/03/2012 5:06 AM

...and 17A is more than the 13A fuse in a BS1363 plug top can stand. The thing has become a 3.8kW convector heater!

So recycle it and replace it. Before someone gets hurt and damage occurs.

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#4

Re: Voltage Conversion Rewinding

05/03/2012 9:24 AM

Any chance one stator winding is connected reversed? And you did connect 'em in series, right? Anyway, the info you give us on the motor type is NOT enough. S.M.

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#5

Re: Voltage Conversion Rewinding

05/03/2012 11:55 AM

I agree with others here, you should just buy the proper tool. Particularly since you've apparently lost all of the critical information you needed to know to make a proper rewiring. Here's a partial list of what you should have documented in your disassembly to rewind to another power grid voltage. What type of motor is this; single phase induction, shaded pole, universal, stator pole count, capacitor count and location to windings, number of windings (not number of turns per windings), starter circuitry configuration?

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#6

Re: Voltage Conversion Rewinding

05/03/2012 1:25 PM
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#7

Re: Voltage Conversion Rewinding

05/04/2012 1:23 AM

Most small routers use a Universal motor. Did you rewind the armature and turn the commutator? If it is an older tool, you may also need to undercut the commutator. Are the brushes in good condition? Did you clean the winding slots thoroughly after you removed the old wire, and did you compact the windings so that they fit snugly over the pole pieces and tie and cement them in place so that vibration can't wear the enamel off the wires?

How many poles in the motor? If any of the stator windings is connected backwards, the motor will either fail to start or will run sluggishly.

Rewinding a motor is a good educational experience, but it can cost you more than the price of a new tool. If you live close to a large public library, you will find books on the subject available. Here's an old one (out of copyright) on the internet that's free.

http://books.google.com/books/download/Armature_Winding_and_Motor_Repair.pdf?id=RIlPAAAAMAAJ&hl=en&capid=AFLRE71Px3o2AgpXkZ6iN6h6WdHDH7EIRlpuyBLZ3zYn5wGC-BReTJ3xIGzi9eLSL48fgq8bffocDz1DOepT7ELECU_aVxaqkg&continue=http://books.google.com/books/download/Armature_Winding_and_Motor_Repair.pdf%3Fid%3DRIlPAAAAMAAJ%26output%3Dpdf%26hl%3Den

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#8

Re: Voltage Conversion Rewinding

05/04/2012 8:14 AM

I haven't run through the detailed calculations but it is likely that doubling the voltage requires the number of turns to increase by square root of two as the inductance in a magnetic circuit increases with the square of the number of turns. You now have a router that could run on 480V. (don't try it though)

The main problem with what you did is that he voltage rating for the rest of the parts will still be at 120V. This means that the commutators may arc over from the lack of clearance. Is the switch rated for 220VAC? What about the rest of the insulation system.

If you used a high quality industrial tool, there is probably enough safety margin to handle the higher voltage but I would not trust a cheap modern tool to have good margins. They barely work on what they have been designed for.

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#9

Re: Voltage Conversion Rewinding

05/04/2012 10:19 AM

I would guess that this is a series motor. You will have to rewind the rotor also. With most modern motors of this type it would be very difficult if not impossible. Sorry. To rewind the stator took great skill.

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#10

Re: Voltage Conversion Rewinding

05/04/2012 10:33 AM

Your basic approach is correct, double the No of windings and half the cross sectional area of the wire as the current at 220V will be reduced approx by half say about 4amps which will produce the same density approx of magnetic flux as the original windings.

But in your case you have twice as much as the original current which would indicate a reversed field winding on one pole [ assuming you have wound the armature correctly]. The fact that you have some slow speed indicates you do not have the same No of turns on each pole [ not to big a problem so long as it is not excessive which could increase brush arc-king]. You should reverse the connections to one of the poles, take care your rotation may be the wrong way in which case reverse the armature connections or both fields whichever is easier to do.

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#11

Re: Voltage Conversion Rewinding

05/04/2012 1:53 PM

Many here are right, you need to rewind both rotor (armature) and the stator to work correctly.

As someone else mentioned, it would be better to have bought a 230 to 120 volt transformer. It would have been cheap from say ebay and quick.....

As this is a universal motor, the frequency is immaterial.

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#12

Re: Voltage Conversion Rewinding

05/04/2012 7:36 PM

After reading some very informative answers, Safety seems to remain most prevalent. Go and Buy the right tool for the job. Don't risk life, limb or fire to be cheap.

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#14
In reply to #12

Re: Voltage Conversion Rewinding

05/05/2012 3:13 PM

You are dead right except that what he has done is not cheap!!!!

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#13

Re: Voltage Conversion Rewinding

05/05/2012 3:12 PM

Many years ago in the UK I bought a heavy duty 230 to 120 transformer for 5 pounds. In most European countries, the 120 volts may only be used on building sites for safety reasons.....

Look on ebay or go to car boot sales or their equivalent where you are....

Here is what I bought, it may be even cheaper than mine by the end of the auction!!!:-

http://www.ebay.co.uk/itm/110-volt-safety-isolating-transformer-/221013452565?pt=UK_BOI_Industrial_Tools_Construction_Tools_ET&hash=item33756da715

Best of luck.

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