Seeking advice on DC motor speed control

[NormanV]

I am hoping that someone can advise me on this. I have obtained two 180v 2.5A 1/2HP DC permanent magnet motors. I wish to control the speed of them and have found this on ebay:-  http://www.ebay.co.uk/itm/161069549443?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649
To my limited knowledge it looks as if it would do the job, I aim to use the motors on a lathe and a milling machine. Could anyone tell me if they think that this controller is suitable.
thanks in advance.
Norman

[John Rudd]

I see no reason why it won't work.....
In fact I have one exactly the same......

PM sent...

[philf]

Norman,

I would add another resistor in series with the speed control pot to limit the output as at 220V output it could well damage your motor.

Beware that you may also get clobbered for VAT which isn't too bad at about £7 (on the value of the goods plus postage) but Royal Mail will charge £8 on top of that for collecting it (and to add further insult to injury they'll charge VAT on the £8). You may end up paying around £51 in total. If you're OK with that then fine. It seems to be the luck of the draw as to whether the carrier will try to get the VAT out of you.

Phil.

[John Rudd]

Norman,

I would add another resistor in series with the speed control pot to limit the output as at 220V output it could well damage your motor.


Phil.

Ooops, yes I omitted to point that factor out......my bad..

[NormanV]

What size resistor?
Phil, as to the VAT on the service(?) from Royal Mail I had a similar problem in a previous life. I used to be a wine maker and there was excise duty to be paid on it and then VAT on the duty! Taxing the taxes, they do it on petrol also.

[John Rudd]

The way I would do it is as follows......

Connect the speedo up to a 100 watt light bulb in place of the motor.
Connect a voltmeter across the bulb.
Now, add another pot by connecting it in series with the one supplied.
Turn both pots to max,then adjust the second pot until the meter reads 170-180v dc....
Switch off and remove your second pot,measure the resistance, that is the value needed....should it be an odd value then go up to the next preferred value available.....


Pm sent.....

[NormanV]

Thanks John, that sounds straightforward enough. Only problem that I can see is getting hold of a 100 watt bulb!
Norman

[philf]

What size resistor?
Phil, as to the VAT on the service(?) from Royal Mail I had a similar problem in a previous life. I used to be a wine maker and there was excise duty to be paid on it and then VAT on the duty! Taxing the taxes, they do it on petrol also.

Just got back from a walk and see that John's beaten me to it. He's given a more than adequate reply.

I have noticed that some Chinese sellers put a lower than paid for value on the customs slip so hopefully you'll get away with it.

I found a DC speed control whilst tidying my workshop but with no documentation and no identifying marks. It's gone in the bin. Permanent magnet brushed motors seem to have plenty of torque at low speeds which makes them very suitable for small machine tools. I use them on my vertical head on my Aciera Mill and on my watchmakers lathe.

Good luck.

Phil.

[Bluechip]

Thanks John, that sounds straightforward enough. Only problem that I can see is getting hold of a 100 watt bulb!
Norman

100W RS lamps are still available 'cept the buggers are often E27 rather than Bayonet Cap...   

http://cpc.farnell.com/ge-lighting/00091227/rough-service-100w-es-200-250v/dp/LP02281?in_merch=Products From This Range


OK to use 2 x 60W in parallel.

Dave

[John Swift]

Hi Norman

depending on where you live try
http://www.bmstores.co.uk/products/4-pack-100w-bulbs-283188
or
http://www.wilko.com/light-bulbs/general-electric-heavy-duty-light-bulb-60w-x-2/invt/0244465

  John

[velocette]

Hi Norman
Several posts with suggestions to reduce the voltage appear to be to drop the voltage of the Alternating Current from 220 volts.

Be very aware that this is a Direct Current Motor and will require a Rectifier of some description to make it work properly.

Using a Resistor to reduce the speed will reduce the power of the motor so at very low speed would not pull the skin of the proverbial rice pudding.

http://www.surpluscenter.com/Electrical/Motor-Speed-Controllers/90-180-VDC-SPEED-CONTROL-W-POT-11-2269.axd

is a link to an excellent AC to DC motor speed control. They can be tuned to the motor a bit tricky to set up but give good control over a wide speed range plus overload protection.

My workshop machines all all run with AC to DC speed controls. 

Eric



. 

[John Rudd]

Velocette/Eric,
The resistor referred to is effectively in series with the speed control pot and not with the motor....

Thinking about this, the speed pot itself needs to be reduced in value, such that the original value is not changed....Ergo, if the speed of the motor were to be halved then the value of the pot needs to be halved but the total resistance of the lot and the resistor adds to the original value....

[philf]

Thinking about this, the speed pot itself needs to be reduced in value, such that the original value is not changed....Ergo, if the speed of the motor were to be halved then the value of the pot needs to be halved but the total resistance of the lot and the resistor adds to the original value....

John,

I'm not sure about the need to keep the total value the same because if you look at the pictures only 2 connections to the pot are being used. (The wiper and one end are shorted together at the terminal block). Depending on how the circuit works you may only adjust the minimum voltage rather than the maximum. I would go for adding resistance for starters.

If you have the same controller are there any internal pots for setting max and min speeds?

Phil.

[John Rudd]

Phil,
Not had the lid off...



but peering thru, I can't see anything adjustable...

Might have look today if I get chance....SWMBO has some tasks for me.......

[John Rudd]

I can report back success.....

I connected a motor to the output and with 240 mains connected the max output to the motor is circa 150v dc max.....
There is a small pot inside the unit that looks connected to the external pot, to provide some sort of min/max setting.
As this looks factory set (dab of paint/sealant or whatever) I was reluctant to twiddle....
Suffice to say the controller should power Norman's motor without risk of burning out....