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Darwin Power requirements

Posted by Robin Patenall 
Darwin Power requirements
December 12, 2007 02:33AM
Does anybody have any concrete figures on the power requirements of a Darwin type system. Unfortunately, I don't have a suitable PC PSU to mess with (I do have a really nice server Hot-Swap supply which seems to be intelligent enough to tell me to go away) so I'm sort of looking at buying a power supply specifically for my RepRap work and I'm wondering what sort of current capacity I actually need.

I'm looking to current limit the stepper motor drives and the data-sheet for the ST5709S1208 says that you should only use about 0.85A per bi-polar coil which gives me a maximum of 5.1A for all three. I make it 1A for the extruder heater and perhaps 0.5A for the motor. Add another for the electronics and I make 7.6A. Thus a 8.5A or 10A should do fine, right?

There's a nice 15V 10A one I have my eye on as this should make the steppers work a bit better as I understand (faster rise time) and reduce the current required for the heater. I'm also tempted to reduce the current to the steppers a bit (15W dissipation per motor does sound a bit much).

Although writing this it occurs to me that a 12V 8.5A supply would do nicely to power the three main axis and I could use a separate PSU for the extruder / head (I might start off with my Dremel first).

Anybody have any comments or suggestions ?
Re: Darwin Power requirements
December 12, 2007 11:18AM
What electronics are you using as the V1.0 electronics don't have current sensing so increasing the voltage will increase the current, I believe there is software control for this but be careful.

The RepRap only moves 1 motor at a time but as with most steppers will over-drive the motor with peak current up to 2A I think.

In summary I would go with the Dremel if you have it and just watch the voltage for any drop, I would be very surprised if there was any.

Robin Patenall
Re: Darwin Power requirements
December 12, 2007 06:43PM
As I'm only currently aiming for a bootstrap system and don't have the kit to create PCBs (yes, I can buy them but where's the fun in that), I'm not too worried about matching the electronics exactly (although I do want firmware compatibility for the PIC stuff) so I was going to stuff a L6506 current controller in the system between the PIC and the L298 (with which it is designed to work) to give me better control (especially as there was a possibility at one point that I'd be running off 24V with a cheap surplus PSU)

Of course you pointing out the V1 electronics doesn't have current limiting, implied that the V2 electronics did, so I checked out the state of the V2 electronics and might just use them instead.

The comment about the Dremel was that initially I might not be running an extruder but using my Dremel with some sort of router bit (to make PCBs perhaps?) so I wouldn't need the couple of Amps that the extruder required and thought that a more modular system (extruder with it's own PSU) might be easier to work with
Re: Darwin Power requirements
December 17, 2007 01:35PM
i've been using a generic power supply that i took out of a Dell computer. if i recall correctly, its 200 watts. i havent had any trouble at all, and i've been running everything off it.

i'm not 100% sure, but if you go with a nicer power supply, it probably wont make much of a difference. of course if you plan on driving stepper motors with higher voltage it will, but other than that i think any old PSU will do.
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