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aga
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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.
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Bright Spark
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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
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Magpie
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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)
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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.
The single most important condition for a successful synthesis is good mixing - Nicodem
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NedsHead
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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]
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Magpie
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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.
The single most important condition for a successful synthesis is good mixing - Nicodem
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Bright Spark
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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]
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Magpie
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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.
The single most important condition for a successful synthesis is good mixing - Nicodem
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Bright Spark
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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]
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Magpie
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Thank you.
Yes, there is a nameplate but it isn't readable anymore.
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.
The single most important condition for a successful synthesis is good mixing - Nicodem
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aga
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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.
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Texium
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Thread Moved
22-11-2023 at 19:29 |
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