Gallery, Projects and General > Project Logs
Mill Power feed
Darren:
Inspired by Mickn in his post in the introductions section, and by Ralph flashing off his garage door motors I purchased a car windscreen motor.
This one came from Ebay priced at £5.00, it's Saab 900 GM 9-3 Front Windscreen Wiper Motor
Here you can see I've opened it up to have a look inside. I'm using one of my bench power supplies to test it.
After fully stripping it down to look it over it was obvious that it was well built. All the wiring was a hefty gauge as you would expect with low voltage devices. (low voltage = high current for a given power, so wires need to be beefy) The insulation also looked to be in good order.
I tried voltages from 0-30V DC, the 12v motor is quite happy from 1.5V to 30V, I left it running for about 20 min continuous at 30V and no problems were detected. This is well over what it would be expected to do on a mill. At 1.5V it did seem to still have plenty of power, I certainly couldn't stop it by hand but the real test will have to be on the mill.
BTW, it's real slow at 1,5V and 30V would give a nice quick tram to shift the table over.
I'm lucky, I have all the power control I would need it the unit you see above. That's a 0-30V at 20A supply. I can barely carry it, I'm not sure that I can any more ::)
Oh the motor runs at 4A at 12V, I'll test the current draw at other voltages tomorrow as we need to know this if building a power supply (PS) from scratch.
Mick, how did you sort the variable speed? Did you use a pot as a shunt? If so what value?
The motor has three wires, this I assumed meant three brushes. I had a look inside and sure enough there they were. Two opposite each other, the main two, and one offset. I assume this was some sort of second speed control. But for the life of me I couldn't get it to do anything no matter how I connected it. I'll try again tomorrow as I've just had another idea. It could be useful.
Also on this unit fitted to the large plastic wheel is a copper plate, this is some sort of counter trigger, maybe speed or maybe just a counter. There are sprung contacts on the cover plate that connect to this disc. Maybe someone can think of a use?
Darren:
A little Googling and it seems the copper "counter" plate is for an auto park mechanism. Ie stops the motor is the correct position.
But we could poss do something else with it.
The three wires are for two speeds, One is earth and two are lives. one for fast and one for slow. But I could only get one to work. I'll try again tomorrow.
Darren:
Right then, I have now got both speeds working, you don't want 30V, ignore what I said before as that was on the slow speed.
Fast speed is much faster and 12V is prob too much. At around 6V you can switch between the two speeds and this seems to be a good compromise if you don't want to make a variable voltage circuit. maybe a 6V bike charger will do?
I need to get my rpm tester out tomorrow and see what it is really turning at.
later... :thumbup:
John Hill:
Darren, I suggest looking for the circuit diagram of the donor vehicle. That would give an indication of how the three wires were used and hopefully would give the value of any resistors etc, I assume they are related to speed control.
If you are going to use a pot as the speed control it would need to be a high wattage, low resistance kind, I would suggest pulsing the motor for speed control. But if a simple pot control is required use it with a pass transistor, 2N3055 maybe?
One possibility would be a low voltage lighting or old electric blanket transformer (not a switch mode power supply kind). They will give you AC but that motor (if it has a magnet in it) will require DC, easily provied by just one diode which will give half wave rectification. In electrical terms that would be a very 'rough' output but ideal for motor use. Then use a light dimmer to supply the transformer.
Wiper motors are great in that they can be set to do one revolution then stop, that opens up interesting possibilities.
But really, there are more ways of doing this than skinning a cat.
Darren:
Hi John,
I've got a circuit I made up some time ago using a 2n3055 controlled by a Lm317 I think, but it may be some other chip.
I'm thinking that whilst I can do this there must be something simpler for the other chaps. What about just putting a pot in series with the motor. We are not looking for finesse power supplies here and whilst the pot may be wasteful energy wise we are using the mains and not a battery. So less important in this scenario.
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