12 volt heat cartigde with 24 volt supply
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What should the line look like to run a heater rated for 12 volts of 24? In other words stretching the limits of pwm control. I route pwm signal from hotend jack from duet to the signal input from a stand alone solid state heating board intended to serve this function. Its 30 amp 12v - 72v ac or dc compatible with signal range from 1 pulse per sec to 48khz at 3.3vdc - 30vdc range.
so I just wanna supply the heater0_1559318431073_heater.txt a 50 percent pwm duty cycle rate to simulate 12vdc.
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running a 12v heater at 24 volts actually quadruples the heating power so be very careful the general advise is to spend a small amount and get a 24V Heater cartridge there not that expensive and will be a damned site safer
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@sir-printsalot said in 12 volt heat cartigde with 24 volt supply:
50 percent pwm duty cycle rate to simulate 12vdc
50% PWM is not 12v. Rather, 50% PWM is 24V 50% of the time.
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Doubling the voltage will double the current, and quadruple the power. The result would be getting a lot of heat, but putting a lot of load on the power supply and MOSFET. Definitely not recommended, but with a fuse upgrade, the Duet can probably deal with it.
So say you have a 30W 12V heater, you're now running it at 120W. Running the PWM at 50% is still 60W, and still putting the full 120W load on the PSU and MOSFET when it's on. You should also ALWAYS consider that the MOSFET can fail, and stick on. If that happens with a 30W heater, it's bad enough. If it happens with a 120W heater, the risk of fire gets rather high. There are all kinds of failsafes for thermal runaway in place, but the less I need to rely on these things, the better, as far as I'm concerned.
My Makerbot clone is still running a 12V heated bed, though everything else is on 24V, but I have a separate 12V PSU for it, and I'm just using an external MOSFET to control it. It's kind of an ugly solution, but it works. I have since purchased a 24V heated bed, but since I haven't used that printer in several months, I haven't yet installed it. A heated bed is much higher wattage than a hotend heater, and running that at 24V was absolutely out of the question.
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duet board doesn't supply the mosfet power directly to the heater. it's output is being used as signal input for a secondary heater ssr rated at 3 times the intended load.
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Look at the P paramter to M303 for tuning the heater.
