Sciencemadness Discussion Board - stepper motor power supply

stepper motor power supply

Magpie - 27-5-2015 at 15:28

Presently I power my stepper motor with a 12vdc supply salvaged from an old computer. I'm assuming this is a steady and smooth voltage. It works well.

However, I suspect that this is not so true with a car battery charger. Its voltage is likely a square wave with narrow gaps of no voltage. There would also be some ripple I think.

Can a car battery charger be used as a power supply to a stepper motor?

edit: corrected my terminology

[Edited on 28-5-2015 by Magpie]

[Edited on 28-5-2015 by Magpie]

smaerd - 27-5-2015 at 15:37

I'm not sure what you mean by a battery charger?

I use a "wall-wart" (Not this exact one but something similar - http://www.ebay.com/itm/like/191532316781?lpid=82&chn=ps) for my steppers rated for 2A draw. I never use the 2A's but I assume (probably wrongly) that this gives me more lee-way for source noise.

Pretty sure a computer supply will be one of the smoother options out there. A lot of the really cheap wall supplies have some pretty serious voltage ripple. This is one of those topics where I will almost always end with saying "I wish I had an oscilloscope".

papaya - 27-5-2015 at 16:00

An Electrolytic capacitor can reduce ripple, however most likely you don't need that. Btw., stepper motors (multi-phase things) are quite different from classical DC motors(with permanent magnet and rotor), I don't get why you use them interchangeably?

m1tanker78 - 27-5-2015 at 16:15

A car battery charger? It can't directly power the stepper motor but it can be switched to run the motor. Car battery chargers tend to have poor filtering (high ripple) but so do most hobbyist stepper motor drive circuits. It can be cleaned up some with a big capacitor but probing around the circuit, you'd see a lot of switching noise from the IGBTs or whatever you use in the driving stage.

If you mean a camera battery charger.. probably not. They're pretty wimpy by design. They deliver energy over a greater time but would almost surely choke even with a small stepper at low advance rate.

Magpie - 27-5-2015 at 17:18

I'm sorry, I mean a car battery charger. And, yes, it's a stepper motor, not a "DC motor."

I would think that for the "12v" setting the output is likely around 13.5v - but I'm just guessing. It's a very old charger likely about 1970 vintage - it's a Woodward-Schumacher "Electromite," 4 amp.

I suspect that it probably puts out a fairly rough voltage and that is why I asked if it would be suitable for a stepper motor. I would be willing to try it if doing so would not risk damaging the stepper motor or the driver circuit.

Smaerd, I agree, once again "I wish I had an oscilloscope."

-------------------------

Measured voltages: 7.6v for the "6v" setting, and 12.6v for the "12v" setting.

[Edited on 28-5-2015 by Magpie]

[Edited on 28-5-2015 by Magpie]

neptunium - 27-5-2015 at 17:53

now you know . . . . oscilloscope arent expansive budd this one cost me a wopping 20 bucks...

neptunium - 27-5-2015 at 17:55

its a hill hopping kind of signal not super steady and probably not great for a stepper motor

battoussai114 - 27-5-2015 at 17:55

What kind of battery charger exactly?

Quote: Originally posted by smaerd

Pretty sure a computer supply will be one of the smoother options out there. A lot of the really cheap wall supplies have some pretty serious voltage ripple. This is one of those topics where I will almost always end with saying "I wish I had an oscilloscope".

For something like checking for ripples from your power supply you could try an arduino or PIC based scope. Or even a Lcsoft Mini Board if you're not up to programming a MCU, getting components yada yada...

neptunium - 27-5-2015 at 18:00

Quote: Originally posted by battoussai114

What kind of battery charger exactly?

wal mart crap

Magpie - 27-5-2015 at 18:08

Quote: Originally posted by neptunium

now you know .

Wow, that's worse than I expected. Thanks for showing that.

My charger is bottom of the line at the time. I bought it at a Holiday gas station in Minnesota. A charger is essential equipment for that state.

neptunium - 27-5-2015 at 18:12

what are you running with a stepper motor anyway?

[Edited on 28-5-2015 by neptunium]

Magpie - 27-5-2015 at 19:18

An overhead stirrer:

http://www.sciencemadness.org/talk/viewthread.php?tid=41539&...

I'm currently limited to 12vdc using a salvaged computer power supply. I would like to increase this voltage to 24vdc. I had a wild idea to link in series the computer power supply with the car battery charger. But based on the replies here that doesn't look too promising.

[Edited on 28-5-2015 by Magpie]

battoussai114 - 27-5-2015 at 19:59

Quote: Originally posted by neptunium

now you know . . . . oscilloscope arent expansive budd this one cost me a wopping 20 bucks...

Really depends on where you live, a whopping 20$ from ebay plus over 9000 shipping if you aren't in continental US or Canada isn't so good. There are still other options but they'd certainly get the electronics purists (the sort of people you met on eevblog forum) cringing.

smaerd - 27-5-2015 at 20:27

If anyone knows where to find one for $20 let me know. That's all I have to say.

Ya battoussai114 I've seen those cheapy variants I actually made a thread about one variety of them which I was excited about but never made the plunge. http://www.sciencemadness.org/talk/viewthread.php?tid=30483#...

Anyways, Magpie why are you trying to double the voltage?

Magpie - 27-5-2015 at 21:23

I want more speed. Right now I'm limited to 221 rpm. I thought that would be plenty, but when I made salicylaldehyde it was marginal.

neptunium - 28-5-2015 at 05:02

Quote: Originally posted by smaerd

If anyone knows where to find one for $20 let me know. That's all I have to say.

this was at a garage sale in Georgia 10 years ago...along with a frequency counter and function generator..keep digging you`ll find one too

neptunium - 28-5-2015 at 05:09

what about 2 car battery in series with a variable resistance to regulate the voltage?

like this old rheostat
http://www.ebay.com/itm/Biddle-Lubri-tact-Slide-Tube-Rheosta...
or a disc kind
http://www.ebay.com/itm/Wirewound-Ceramic-Potentiometer-Adju...

Magpie - 29-5-2015 at 10:18

I placed a 6v lantern battery in series with my 12vdc (salvaged from a computer) power supply giving 18vdc. With 18vdc the stepper motor rpm ran at 320 rpm with good torque. This compares to 221 rpm max speed without the added 6v. Torque fell off badly at higher speeds (up to 800 rpm).

This was a proof-of-principle test. If I had another 6v battery I would try for 24vdc.

smaerd - 29-5-2015 at 13:26

So I know you have a 12V line on your old computer PSU, but don't you also have 5V and 3.3V lines? Why not hook those puppies together and pull out 20.3V? It's not 24V but it should be stable, still one plug/supply. Edit - nevermind probably not the best idea, something tells me this will burn a supply.

Alternatively you could buy a second computer PSU and hook up two of the 12V lines.

[Edited on 29-5-2015 by smaerd]

aga - 29-5-2015 at 13:43

The waveform on your 'scope is that of a Half-rectified transformer output.

Car battery chargers generally have a crude germanium diode stack with lots of cooling fins between (open it up and have a look).

The transformer is OK.

Just replace the germanium thing with a 35A Bridge rectifier and a stack of capacitors after it and the voltage will be more than steady enough for a stepper/stirrer.

[Edited on 29-5-2015 by aga]

Magpie - 29-5-2015 at 14:45

Smaerd, I don't think that would do any good. The PSU taps have a common ground.

I bought a 2nd cheap lantern battery and placed it in series with the 12vdc PSU and the other 6vdc lantern battery. This gave me 410 rpm with good torque. A crude measurement with a dca meter having gradations of 1 amp indicated ~ 0.5 amp draw.

Then I filled a 1 liter beaker with ~ 300 ml of water and stirred it with the 24dcv power. It rotated at a smooth 900 rpm!

The steady load gave much smoother speed settings.

The above tests were for the advancement of science. I would likely need a source capable of more amp-hours for an extended stirring time, say 1 or more hours.

[Edited on 29-5-2015 by Magpie]

Zombie - 29-5-2015 at 15:00

Quote: Originally posted by Magpie

I'm sorry, I mean a car battery charger. And, yes, it's a stepper motor, not a "DC motor."

I would think that for the "12v" setting the output is likely around 13.5v - but I'm just guessing. It's a very old charger likely about 1970 vintage - it's a Woodward-Schumacher "Electromite," 4 amp.

I suspect that it probably puts out a fairly rough voltage and that is why I asked if it would be suitable for a stepper motor. I would be willing to try it if doing so would not risk damaging the stepper motor or the driver circuit.

Smaerd, I agree, once again "I wish I had an oscilloscope."

-------------------------

Measured voltages: 7.6v for the "6v" setting, and 12.6v for the "12v" setting.

[Edited on 28-5-2015 by Magpie]

[Edited on 28-5-2015 by Magpie]

I only read this thread to this post (so far)

You can buy an O scope for 40 bucks now on Fleabay.
They have hand held versions similar to multi meters, and they are as easy to use.

I'm guessing someone pointed this out already.

I'll read the rest of the thread.

Magpie - 30-5-2015 at 07:53

After getting the astounding 900 rpm from 24vdc stirring water I tried it with 18vdc. Here again an astounding, smooth 700 rpm stirring water.

This is a much better solution than buying a different NEMA 17 stepper motor.

The Chinese offer a 2a, 24vdc power supply with 120vac input for $17. Free shipping, but it comes on a slow boat.

I am tempted, instead, to buy a more expensive but versatile power supply that could be set at constant amps or constant volts. This would be multi-purpose with the intent to some day do some syntheses using electro-chemistry.

I would also like to buy an oscilloscope. I can't justify these toys unless I can forsee occasional use. I ran out of storage space long ago. I now compete with my wife: she buys yarn, I buy lab toys.

-------------------------------------------

Could this work for a stepper motor?:

http://www.amazon.com/LEDwholesalers-Power-Supply-Under-Coun...

I realize that this is a "switching" power supply and is different from a "linear, regulated" supply.

[Edited on 30-5-2015 by Magpie]

Bright Spark - 30-5-2015 at 12:55

Could this work for a stepper motor?:

Yes as long as the motor and its driver add up to less than 48W (2A*24V)

What is the wattage of your motor?, a car battery charger outputs more than 12V just like an alternator, it has to be higher than the battery voltage in order to drive some charge into the battery, its like a trickle charge

I am unsure why you had the trouble you did but I think the motor could be too much power and hence it dragged the power down, it most certainly should be a solid DC source with no square wave like look where theres periods of no voltage, this is the sign of a defective supply or internal protection is kicking in and out

A switching power supply is better in everyway except for reliability, for the user of equipment the difference between switching supply and linear supply is unimportant just as long as it delivers the power required

Magpie - 30-5-2015 at 22:12

I don't know the watt rating of my NEMA 17 stepper motor. I salvaged it from a Savin copier.

Can the negative terminal of the SMPS be tied to an earth ground?

aga - 31-5-2015 at 00:51

Simplest way to find out is to measure from the 0v rail to the case of the PSU.

Chances are that it already is tied to 'earth'.

Much safer to say '0 volt rail' than 'negative terminal' when talking about PC power supplies.

They normally have +12, +5, +3.3, -5 and -12 volt outputs so the black wire can't really be thought of as the 'negative' lead anymore.

Bright Spark - 31-5-2015 at 04:00

I don't know the watt rating of my NEMA 17 stepper motor

Measure the curent when its running, I would power it from something beefier to do this, it will give you a good idea

Can the negative terminal of the SMPS be tied to an earth ground?

I suppose it could but I must ask why you want to?, its probably an isolated supply so you lose the isolation if you do this (it becomes earth referenced)

Chances are that it already is tied to 'earth'.

I very much doubt it, in fact I would be amazed, they use HF transformers to give isolation because it is a safety requirement for many markets

Magpie - 31-5-2015 at 05:27

Quote: Originally posted by Magpie

Can the negative terminal of the SMPS be tied to an earth ground?

Quote: Originally posted by Bright Spark

I suppose it could but I must ask why you want to?, its probably an isolated supply so you lose the isolation if you do this (it becomes earth referenced)

My stepper motor driver circuit gets its pulse circuit power from the 5vdc tap on my salvaged computer power supply. This has an earth ground.

I have not bought an SMPS yet. But if I do, I want to know where to terminate the negative lead.

NedsHead - 1-6-2015 at 03:06

Could you not just use the -12v and +12v on the atx power supply to obtain the 24v? I'm sure I've read of this being done

Edit: I've found an instructable that combines 2 computer power Supplies to make 24v that may also be useful to you. http://m.instructables.com/id/Two-ATX-PSU-One-juiced-24-V-DC...

[Edited on 1-6-2015 by NedsHead]

[Edited on 1-6-2015 by NedsHead]

Magpie - 1-6-2015 at 20:47

I guess I do have a -12v tap on my PSU as well as the 12v tap. But I understand that it is only suitable for up to 0.3a so this may not be useable for driving my stepper motor.

Getting a 2nd PSU looks like an option. The downside would be all the table space required.

Thanks for getting this information.

Bright Spark - 2-6-2015 at 15:43

Hi Magpie

I have an old computer PSU and I just tested it and the earthed case is connected to the negative rail of the PSU so the power supply is what we call earth referenced, I am no expert on computer PSU's but you can bet that they will all be like this

the SMPS you showed will have an isolated ouput, so there will be no connection between the mains earth and the output (if it even has an earth connection) so if your motor has an earth connection then yes you are correct in that you can connect the earth of the stepper motor to the negative terminal and that negative terminal to the mains earth and you make your whole system earth referenced

It doesn't really make a difference if you do or you don't but an isolated supply can be classed as superior to an earthed system because its actually quite difficult to get a shock, not that 24VDC is going to shock anyone but this holds for higher voltages, most shocks are to earth and an isolated system can't pass current to earth so its actually better

I would be concerned about the power rating you need, a computer PSU can deliver a lot more than 50W so I would say you need to measure the current draw at max output before spending any money

Can you post some pics up so I can see the motor, a picture is worth a thousand words

Regards

BS

[Edited on 2-6-2015 by Bright Spark]

Magpie - 2-6-2015 at 16:37

Thank you BS for that information.

The reason I asked about the negative lead from the SMPS (if I buy one) is that in my reasoning it would have to be terminated at some location so that the motor circuit is completed.

The stepper driver module 5v (from the PSU) is grounded to earth through the PSU as you say. That's the first thing I checked by doing a continuity check with the ground plug of the PSU mains connection.

Could the negative lead of the SMPS be just left dangling?

Here's the long thread detailing the development of my stepper motor stirrer. Page 3 has a picture of my Mineba NEMA 17 stepper salvaged from a Savin copier. As far as I know it is a garden variety NEMA 17, I just don't have much data for it as it is not an off-the-shelf Mineba but is proprietary to Savin, I think.

http://www.sciencemadness.org/talk/viewthread.php?tid=41539&...

I did measure the amps by using my oversized amp dc meter (1 amp gradations). I grabbed the shaft and held it firmly enough to nearly stop it. The reading was 0.5a, at 18vdc (or possibly 24 vdc). At any rate I think these little motors can provide a lot of torque (like 30 in-oz), likely way more than I need for stirring.

My stirring is done in small RBFs like 500 ml or at most 1000 ml. The small necks limit the size (width) of the agitator blades (I use a folding type). Therefore, I don't ever envision challenging the torque capability. Therefore, the amp draw should be low.

The picture is not the best (too dark). If you want I can post a better one.

Bright Spark - 7-6-2015 at 03:05

Magpie, I really like your enthusiasm, its impressive

In the link

http://www.sciencemadness.org/talk/viewthread.php?tid=41539&...

Is that a nameplate for the motor? its hard too see but it looks like it

If you measured 0.5A then it certainl;y sounds like its less than 50W and that power supply should be fine, you can connect the earths to the 0V as discussed but you could also leave it unearthed as discussed

Have you ever considerd making a PCB?, you have the skills and you can get software for free if you know where to look

I recommend Eagle PCB, if you are interested send me a message and I will help you out

I am really impressed and very soon I will be doing all the things I talked about, I have done some things but lately I have had a lot on so I am just educating myself, its going to take me a while for sure

Edit

I think you should buy a benchtop power supply Magpie, some are available really cheaply, they yhave adjustable output with current limiting and I think for you its what you need

$50 will get you a lot and it will come in handy for all kinds

[Edited on 7-6-2015 by Bright Spark]

Magpie - 7-6-2015 at 08:38

Quote: Originally posted by Bright Spark

Magpie, I really like your enthusiasm, its impressive

Thank you.

Quote: Originally posted by Bright Spark

Is that a nameplate for the motor? its hard too see but it looks like it

Yes, there is a nameplate but it isn't readable anymore.

Quote: Originally posted by Bright Spark

Have you ever considerd making a PCB?, you have the skills and you can get software for free if you know where to look

No, I only build these things to support my chemistry hobby. It's too easy to go off on tangents as it is.

Quote: Originally posted by Bright Spark

I think you should buy a benchtop power supply Magpie, some are available really cheaply, they yhave adjustable output with current limiting and I think for you its what you need

$50 will get you a lot and it will come in handy for all kinds

You are probably right here. Instead of buying a single purpose SMPS for $20 I should apply that money to a good power supply with controllable voltage/controllable amperage.
This would be much more versatile.

aga - 7-6-2015 at 14:11

Just pick up a used PC PSU and it will be absolutely fine.

PCs don't run too well on dirty power, and your stepper motor will be a Lot less fussy than several million transistors switching at very high frequencies.