Turning up Power Supply voltage with Duet Controller?

Hi, I have a 24v 15a LED power supply running my CoreXY printer with a Duet controller. The best my heated bed can do for temperature is 80c and it takes forever to get there. Someone suggested turning up the power supply to give the bed more oomf. I believe that the Duet can handle up to 38v.

I just want to make sure that there are no surprises if I increase the voltage. I have very heavy duty steppers (78 oz inch) 24v ceramic nozzle heater, 24v heated bed, 24 volt fan cooling Duet and that is it. I tested the power supply and it can be turned up to 31.8 volts....

How high do you think it is safe to turn this up to?? I think the riskiest item is the fan. Is that correct??? Can I just throw a resistor in line to drop voltage for the fan???

Do you have any (heat) insulation under your heatbed? That makes a huge difference.

The capacitors on the Duet are rated at 35V so that is the absolute maximum input voltage. I suggest you go no higher than 30V. Other than that, I agree that the fans are at greatest risk of damage from over-voltage. You could put a 5.6V or 6.2V 1W zener diode in series with each of them.

Also check that you will not exceed the power rating of the PSU. If it's 15A @ 24V then that's 360W, so only 12A @ 30V. How much current will your heated bed draw at 30V?

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

yes, it is insulated with corkboard.

I am using a standard MK3 circuit board heater with aluminum heat spreader attached. Not sure how many amps this bed draws when overvolted. Any calculation I can use???? I will also be increasing the potential wattage of the ceramic extruder heater.....

A believe a 24V Mk3 should have a resistance of about 4.8 ohms and will draw 5A @ 24V. If you have a multimeter, you could measure the resistance of yours.

What is the power rating of your hot end heater? If it is 40W then you could replace it with 30W.

Edited 1 time(s). Last edit at 12/05/2015 03:10AM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Quote
patrickrio
yes, it is insulated with corkboard.

I am using a standard MK3 circuit board heater with aluminum heat spreader attached. Not sure how many amps this bed draws when overvolted. Any calculation I can use???? I will also be increasing the potential wattage of the ceramic extruder heater.....

I'm surprised that you can't reach the temps - I have a Mk4 heatbed (like a Mk3, but aluminium) on my CoreXY that I run on 24v. I can easily get up to 110C, although it does take a while to get there. The temp I normally use for ABS is 100C, and I can reach that in 10 - 15 minutes with a bit of corrugated cardboard on top to help it along. My Prusa i3 has the same setup but at 12v - that can also get to 110C if needed.

The only non-standard thing in my setup is the means of switching the heatbed supply - I use an independent electronic switch triggered by the control board to supply the current. I use this on the Prusa because the RAMPS board isn't too reliable at this current, and on the CoreXY because I'm at the limits of the connectors on the Duet board. I also use cable with a high current-carrying capacity on the heatbeds (it's the stuff used for connecting batteries to the motors in R/C aircraft - 30A capacity, very flexible, and silicone insulation rated to 200C).

Have you ever measured the voltage you're actually getting at the heatbed when it's turned on? Are you actually getting close to 24v? I wonder if you're losing power somewhere along the line...

Edited 1 time(s). Last edit at 12/05/2015 08:15AM by David J.