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...

[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.

[Darren]

BTW, I've got transformers coming out of my ears here, along with variacs, transistors etc etc.

I can make nice power supplies from low voltage to 4.3KV at 5amps. Used for some big valves !!

But forget all that, sometimes it's hard to make something simple. Bit like what Bogs said about once you start doing something precise it's difficult to just knock something up.

What you think about the series pot, I've never tried it, I'll see if I have something suitable tomorrow.

[Darren]

Or like you said,

Use a dimmer switch to a 12V transformer followed by a rectifier, (never tried a single diode, but half wave should be fine) That should do it?

Dimmer switches are easy to find, as are 12V transformers.

[John Hill]

Re the pot,  12V at 4A is 48 watts so to run your motor  on that supply would need a 48 watt pot!  That would look like one of those old resistance coil things they once used to control stage lighting!

Do you have any nicrome wire?  Perhaps the heater from an old clothes dryer?  As an experiment just stretch a single wire, a foot or so, between two nails in a bit of wood and use a couple of battery clips to put more or less in series with the motor, that will give you a feel for what a pot control would be like.

[John Hill]

Half wave means higher voltage for the same amount of power, more easily overcomes inertia etc at low speeds (I think).

Not all dimmers are the same but I think that would be worth a try.

[Darren]

Yes, quite right, low voltage = high current, hence using a dimmer on the 240V side. Far far lower current there.

BTW, I wasn't thinking of using a pot on it's own but in series with a resistor to take the load.

I do have nichrome wire, in the form of some very large ceramic tubes as variable resistors, but these are not very practical 

[John Hill]

Yea, but a pot in series with a resistor is just a pot with less than full travel!  Whenever you use a resistor, pot, or something like a transistor in voltage follower mode you have to dissapate a lot of heat so the components have to be big.

I think the easiest for those who dont want to mess with electronics would be the lamp dimmer, low voltage tranny and the rectification diode.  Providing of course that it works!  I have not tried it!

What is the requirement for a mill feed anyway? A steady slow, controllable, speed?

[Darren]

But we don't need the full pot control as we are looking for about a 3-5V variation and the amperage then drop considerably

Duh, sorry John, my mistake, just realised, using a series resistor the voltage will certainly drop but the current won't alter 


I do have some CB radio power supplies that use a 2n3055 output. I'm just thinking remove the voltage setting resistor and replace it with a pot.
That might be a very cheap and easy option. These power supplies can be picked up for a fiver or so. A pot is pennies.
This way you even have a tidy case to put it all in.

[Darren]

Then use a DPDT switch for forward/reverse, a couple of micro switches to limit bed travel, these could even be adjustable with the mill bed stops.

[mickn]

Hi Darren,
You guys certainly know more about electronics than I do.My speed control was via a small dc control unit from Maplins

Panel Mounted Speed Regulator Module


Order Code: RN41U

This I use on the horizontal table feed. Its fed by one  the yellow 12volt supply leads from my old PSU to the windscreenwiper motor. Another 12volt lead supplies the vertical slide. This is purely up and down and saves winding and does not need regulating its on the fast terminals in the other windscreen wiper motor.Sorry I cant be more technical

Mick

[Darren]

Thanks Mick, that clarifies things a bit...

The Maplin module can be found here http://www.maplin.co.uk/Module.aspx?ModuleNo=30310&TabID=1&C=SO&U=strat15&doy=search

It's £15.00 + P&P and it's rated at 3amps with a 5A peak. Whilst it would work fine at lower speeds (the current draw drops significantly) it might be on the edge at 12V and deff higher.  Just bear this in mind if you decide to use this and keep those speeds down a touch.

ATX power supplies look good at 30A for a 500W unit, more than enough to power 3 motors at the same time !!! Not that you would want to...
With 3, 5 and 12V outputs the choice is mind boggling. I'm assuming you can series connect them?? I'd have to try this to be sure.
But this could give you 3,5,8,12,15,17, 20V speeds on a rotary switch without using a variable power control.
If the unit will let you reverse connect (it might not) there is potential for 2, 3, 5, 7, 8, 9, 12, 15, 17, & 20V Three extra speeds. That would cover all speeds you would ever need. Don't forget the motor also has two speeds as well.
All without any complicated circuitry.

Not sure if I have an ATX power supply unit spare.

[Darren]

Can I ask if anyone is finding this interesting as i seem to be rambling on a bit here....as usual...

If you want me to carry on I'll knock something up and do a "how to" post to clean the thread up a bit..

[telstar]

please carry on , I am waiting to see the end result

dave

[Darren]

OK, I found a CB transformer power supply and an ATX supply.

I decided to start with the CB unit as this is about the simplest "proper" way to do this that I can think of for those that are not proficient with electronics. This is mainly because most of it is already done and you only have to make a small change to the circuit.

By proper I'm referring to a regulated supply, that is one that will not fluctuate in voltage even if the mains does. It will also keep the electricity supply company happy by not introducing noise into the mains supply.

The power unit

Oops, I seem to have lost a picture, you know what they look like I'm sure. If not have a look on Ebay. You will need one that is rated for 5A or more. That way we know the circuit will be the right sort.

Here it is opened up, nothing much inside. Just a small transformer and a circuit board.



The bit you need to look for is the voltage setting device. This will be a resistor or a zenier diode (auburn coloured glass)

You can see it here pointing vertically.



Closer view



We need to disconnect this and take it out. Replace with a variable resistor of about 5 - 10K value. I used a 10K as it is what I had to hand.
You can see two wires soldered to the board, these are connected to the variable resistor (pot). Doesn't matter which way round the wires go. On the pot connect these two wires to the middle and one outer connection. Again doesn't matter which outer connection you use. One connector on the pot will have nothing connected to it. we don't need to use this.



The clip leads are connected to the original power output of the unit and connected to the motor.

That's it...all we need now is a reversing switch, I'll do this later and fit it back into the case.

Here is a video, not very clear, sorry, but you will get the idea. Notice when I unclip one cable and the motor speeds up, we could add a push switch here for quick transverse of the mill bed. Hold your finger on to power, let go to revert back to the pot setting speed.

The digital meter is showing the Amperage, not voltage. I found that on the motor the high speed used much lest current (amperage) than the slow speed. I really don't think we need to be bothered with the slow speed.

Hope you enjoy the video, it's rough......

I will fit it all in the case later....

[Darren]

Now time to put it all back in the case,

This is the reverse switch, it's a DPDT center off. ( Double Pole, Double Throw, Center OFF ) Meaning it switches both positive and negative with three lever positions. on-off-on.

Note the black and yellow wires and how they are connected. The center is the feed from the power supply and the two outer positions both go to the output terminals/motor. Only one side works at a time.





Drilling the hole for the direction switch, another was drilled for the speed control pot.



From above, the whole internals where moved back and extended wires made up for the LED on/off light.



And finally here it is with it's lid on.
The only thing I would like to add is a momentary switch for the rapid tram control. That way the desired speed setting can be left alone.



Hopefully this vid will demonstrate it working....



There, a simple but very versatile power supply from very inexpensive parts, or the junk pile in my case......

Now then, fitting the motor to the mill.....or lathe or rumbler.....now there's a thought......!!!

[ja2on]

Great job and a very informative write up 
Cant wait to see it working on your mill.

[John Hill]

Good work Darren
Like I said, more ways than skinning the old moggie!

However, are you happy with the resistance replacing the zenor?  The zenor is a constant voltage reference, how about this variation?



The red lines are the new bits.  This will retain the voltage regulation whereas just putting the pot in place of the zenor converted your voltage regulated circuit into a variable resistance circuit where the pass transistor amplified the function of the pot. 

[Thats all assuming of course I understand what I am talking about!]

[Darren]

I don't think that would work John, you are keeping the 12V zener and paralleling a resistance to it. This would only serve to lower the output voltage as it's the reference to the transistor. You might not be able to get 12V output.

The zener is only a reference device, most of these circuits use a resistor instead. But the zener is more stable than a resistor and you can get them in many voltages. 12V zeners just happen to be handy to the manufactures of the circuits as they are always accurate. Resistors rarely are.

I think if you look at the semiconductors PDF files they will show a resistor and not a zener. The pot is just a variable resistor as you know. Therefore it varies the reference voltage to the transistor.

At the end of the day it's only a simple amplifier circuit.

I use this sort of set-up on my audio valves heaters where quality is paramount. The last thing we need here is noise getting into the circuit to be amplified along with the audio signal.

For this sort of use for powering machinery it's pure overkill. But it also happens to be convenient 

[Darren]

John, I should have said, on this circuit the zener was not regulating the output transistor but instead the smaller transistor before it.

I've no idea which one it is, didn't look, and the output transistor is a BD142, similar to the 2n3055 but rated at 15A not 35. More than good enough in this application.

I've been playing with the ATX power supply this evening. Interesting, never really considered them before.

You can't add or subtract the voltages as the protection circuit kicks in and switches the whole unit down,
So really stuck with 3,5, and 12V outputs all with good heavy current capabilities. The 3V can only be used with the slow speed circuit on the wiper motor. For some reason it won't work with the high speed. I don't know why there should be more than enough current as it's stated as 14A.

And on my unit the 12V is only 10V. I don't know if this is typical?

It works, and is probably good enough for powering the mill bed.

If anyone wants me to demonstrate please shout up. You lot are so quiet on this thread I'm wondering if the world has come to an end whilst I've been locked in the cellar 

I do hope someone has benefited, cos I didn't really need one, but it will be used now its been made 
If anyone is still confused speak up....

[bogstandard]

Darren,

Don't be worried, we all have our own specialities, mine ISN'T wiggly amps and electric string, and also, I've got my feeds sorted already.

You just might be way above most of us, and we are just sitting back waiting for the punchline.

Bogs

[John Hill]

Darren, if the 'top' to the zenor goes to the base of a small transistor you may find the collector of that transistor is connected to the base of the big transistor,  this is a Darlington pair configuration and the small transistor is amplifying the base current for the big transistor and allows the use of a smaller wattage zenor.

The zenor conducts while the top end is  equal or above its zenor point the end result being that the top of the zenor is kept at a constant voltage.  Connecting the pot as I showed is a voltage divider across the zenor, so, wind the pot contact to the top and the full zenor regulated voltage is applied to the following circuit, in this case the base of the smaller transistor in the Darlington pair, the pot in that position is the same as the original circuit disregarding whatever current there is through the pot (which should not be much). Wind the pot down a little and you are tapping off a voltage less than the zenor voltage which means less voltage on the base of the Darlington pair.  If you want a voltage higher than the original then change the zenor for a higher voltage one, or you can add a diode to the zenor (in series) or a string of diodes each one increasing the voltage by about .6V. 

My own bench power supply (which I made back in the '70's) has 32 diodes carefully soldered in series around a 32 position switch which provides a voltage from about 1.2V to 20V which is applied to the bases of four parelleled 2N3055s, in those days the switch was much easier to find than an integrated regulator!  Though technically very crude such a circuit is simple in concept and is relatively 'smoke tight'.

The ATX power supply wont let you series the different voltages because they all share a common earth, the best you could do would be to take one of the positive voltage and 'add' it to one of the negative voltages but in most cases the negative voltages will not handle much current so it is not worth much for our purposes.  If you are really keen there are dozens on pages on the web showing how to modify and make use of these power supplies. But to drive an electric motor I doubt it is worth the bother.