Wanting to build a CNC
cgi.ebay.com/3-Axis-CNC-Stepper-Motor-Dr...&hash=item4cf30c72bf
We're planning to use an Oxygen/Acetylene torch for now, and so motor speed (and thus maybe a large power supply) is not needed. If we find that the Oxygen/Acetylene torch turns out to be insufficient, then we will likely go for the plasma cutter (and maybe then we would need better drivers).
Thoughts?
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That board has opto-isolators and plug-in power ICs, which will make things much easier to fix if something does go wrong. I found a similar (possibly identical) driver from Allegro in the PLCC package for $8.
The manual is excellent (which makes a huge difference).
Going by the advert and manual, that actually looks like it is probably a good choice. The pictures show a much higher quality board than the one I had my indifferent experience with.
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I'm guessing you could "make things move" with an old PC power supply to start and keep your start up costs down.
John
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The steppers from Automation Direct was the lowest cost item of the build at about $30 each. Looks like they are $39 now for a Nema 23 triple stack 276 oz-in holding torque stepper.
I noticed that the current per phase is 2.8 Amps on these motors. Won't this mean that my driver must be able to handle 2.8Amps. The driver that I posted off of eBay yesterday said 6Amps maximum (3 drivers one the one board), so it's possible that 3 of these motors could exceed the ampacity of the board, right?
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What are the advantages/disadvantages to getting the Nema 17 version (which pulls only 2.0 Amps/phase) with about 1/2 the holding torque?
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I apologize that my previous post is not quite correct. The manual on the aforementioned 3 axis driver says 2.5 Amps/phase per axis. This is quite close to the 2.8 Amps/phase, but I'm assuming it's not a good idea cut it that close.
No, cutting it that close is fine.
In fact the drive will always attempt to pass the rated current through the motor. If you put that size drive on a smaller motor it will overheat the motor.
A 2.5A drive on a 2.8A motor is the conservative way round.
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Also, I'm contemplating using 2 computer power supplies in series to get my 24V power. I have quite a few of these at my disposal. I have read that I need to disconnect the grounding screw (to the chasis) on the "high side" supply. I'll probably disconnect them on both just to be safe. Any experience doing this?
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Also, I'm contemplating using 2 computer power supplies in series to get my 24V power. I have quite a few of these at my disposal. I have read that I need to disconnect the grounding screw (to the chasis) on the "high side" supply. I'll probably disconnect them on both just to be safe. Any experience doing this?
Yes. It wasn't very effective. My PSU wouldn't stay powered up (even with dummy loads on all outputs).
The best PSU is probably something really simple consisting of little more than a transformer, rectifier and big capacitors.
However, if you have the PSUs, try it.
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Were your PSU's AT or ATX power supplies? If they were ATX, you know you have to jumper two wires (I would have to look up which ones they are) to turn them on. This is not the case for the older AT power supplies.Yes. It wasn't very effective. My PSU wouldn't stay powered up (even with dummy loads on all outputs).
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Many PC PSUs will shut down if there is not enough load on the 5V line. Some require load on the 12V line too. I ended up with dummy loads on all my outputs and the PSU still faulted out after a minute or so every time.
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