Motor speed controler,

[snowcat]

A while back I posted up about making a rotary welding table, well iv managed to scavange a big old dividing head which is ideal for the job, I can easily couple a motor to the input shaft and bob's your uncle.

Now comes the tricky part which I have very little idea about, I need to be able to control the motor speed,
Which voltage should I use 12v D/C, 240, or 3 phase?
If I use 12V then i will need to step the voltage down, the pickhills give me a 12v A/C strap for battery chargeing, Can i rectify this to D/C?
Is the circit reletivly straight forward to build?

Thanks for any advice.

 

[irondarren]

Snowcat i must admit although i havent got round to sorting it out yet i have a single phase to 3 phase controller unit which allows for speed control. Its ment to go on the forge blower motor when i do a rebuild. but it is supposed to be very constant in its speed control, having said that you need a motor with gearbox attached to lower the speed, if i remember the rotary turntables go from 0-20 rpm

 

[snowcat]

Snowcat i must admit although i havent got round to sorting it out yet i have a single phase to 3 phase controller unit which allows for speed control. Its ment to go on the forge blower motor when i do a rebuild. but it is supposed to be very constant in its speed control, having said that you need a motor with gearbox attached to lower the speed, if i remember the rotary turntables go from 0-20 rpm

Seting the ratio on the input end shouldnt be too much of a problem I have gearboxes, sprokets and pulleys, galore, RS do off the shelf units but they are £££ they do just what i want. A freind of mine has one on a small lathe and it is <>infinatly variable. I think as there is no real loading ever on the table I shouldnt need to bugger about too much with lots of gearing.

 

[rtbcomp]

Try getting an old vacuum cleaner (skip, Freecycle) with a variable speed motor. This will give electronic control and with gearing (belt & pullies?) you may get what you want. Use the gearing to get close and the electronics to fine tune.

Just a thought.

 

[MarkMG]

Or how about a cheap electric drill, the rechargeable ones normally have variable drive, should be easy to re-use

 

[cobminor]

Are you sure you have 12v AC for charging? AC charging is a good way of wrecking a battery. If it is AC then it is really easy to rectify it to DC but you would wind up with more volts, up to 15 dependant on the rectification type.

 

[MrFluffy]

Im (shortly going to be) using a 3phase vfd (variable frequency drive) that powers a 1.5cv 3phase motor. It allows you to regulate the speed from 0-1000hz, giving any speed you want.
The thing to remember with a vfd is that the motor will produce the same torque no matter how fast it is spinning up to its design rpm rating unless it has some very fancy feedback circuitry and extras, torque != power, so at half speed, it makes the same torque hence half the power. Normally you would gear the motor so say 30rpm = 1000rpm / 1500 rpm motor spindle speed depending on the motor and use the vfd to slow it down to whatever speed you want. You could also reverse direction by swapping two of the motor wires with each other using a switch.
I paid 60e for my vfd and I think it was cheap because it was 3phase in 3phase out, so bargains can be had...

 

[Drains]

Mr F, you're going continental for sure.... 1.5 cv??

 

[Drains]

Snowy, motor wise i'd use a windscreen wiper motor or similar and appropriate gearing. For speed control, erm, maplin does a motor speed controller which can go up to 20A...

A 12v supply is easy, if you buy it, but I would imagine your 12v battery charger welder would do, for starters.

Others here will be better able to say if the above will work.

 

[irondarren]

windscreen motor, or welder wire feed motor out of an old busted welder (not an sip). the wire feed motor on my thermal arc looks eactly the same as a windscreen wiper motor, plus either unit is already relatively slow running any way. Must admit snowcat i have two motors (probaly 1hp +) with gearboxs already mounted on them with a chain sprocket on the gearbox, so to make a turn table would just need speed controller and a chain drive unit worked out, they came off a racking system where it used to move the racking around.

 

[bill_gj]

A friend of mine wanted to control the speed of a 900W drill over quite a large range (almost standstill to almost full speed) and I bought one of these for him:

http://www.velleman.be/ot/en/product/view/?id=9075

Maplin used to sell them but I couldn't find them in their current catalogue. You'd have to hunt around for a UK supplier, but you can buy them from the Vellman web site.
Vellman stuff is really good quality. It took me one evening to put it together.

Result was excellent. Controlled drill just as required, using one rotary potentiometer.

 

[snowcat]

Snowy, motor wise i'd use a windscreen wiper motor or similar and appropriate gearing. For speed control, erm, maplin does a motor speed controller which can go up to 20A...

A 12v supply is easy, if you buy it, but I would imagine your 12v battery charger welder would do, for starters.

Others here will be better able to say if the above will work.

Thanks all, I think that little cheep kit will do the job just nicely, I was already thinking of winscreen motor size , The head already is geared slow from the input shaft, soo I think i can couple direct to the shaft, Hadnt even thought of maplin going to be easy to get a transformer for the job as well, I have a cunning plan for the table, its not for welding at the mo, more will be revealed later

 

[rtbcomp]

Choose a wiper motor where the shaft rotates rather than oscillates !!!!!!