24V PSU with 12V components
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Limiting power to heaters via PWM is a really bad idea. If there is a hardware failure or a software bug, the heater will output four times its rated power and will likely cause things to melt and catch fire (heaterblock and wires). Limiting to 1/4 power will work in a pinch but you really should get 24V heaters if you run 24V for your own safety.
For the fans, like deckingman I also use a separate buck converter to source 12V. If you feed that +12V into the middle pin of the V_FAN voltage selection jumper (instead of using the jumper), then all fan connectors on the Duet will run at 12V even if the rest of the board is at 24V. This works because the Duet is switching on/off the GND of each fan.
Cheers,
Ben. -
As Ben said, "1" is a very bad idea.
"2" is possible. That's what I said I do. It works for me as I have a mixture of 12 and 24v fans but you can also feed that 12v into the Duet as Ben said so that all the fan connectors run at 12v. -
Thanks for the input.
Running the +12v into the fan jumper will work great for me for my LEDs and fans.
As for the hotend, until my 24v heater arrives can I run one end through my buck converter and the other through the Duet?
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If you mean run the fans via the jumper on the duet and the heater from the buck converter, I don't see why not but stand to be corrected by anyone more knowledgable than me.
Edit. Just be sure the buck converter can handle the current. Assuming the heater is (say) 40 Watt, then it'll draw 3.3 Amps, then you have the fans and LEDS so I'd have thought you'd need in the region of 5 Amps on the 12V side (but again, I stand to be corrected).
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Sounds about right to me I'm using a 24v-12v converter 5A. Have some 24v heater cartridges now and I'm looking forward to simplifying and neatening the wiring.
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Ok so it turns out my buck converter can't handle the fans, lights AND the heater; the voltage on it drops to about 9.5V when attempting to heat. Is there some way to pwm limit the heater output for temporary use?
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Ok so it turns out my buck converter can't handle the fans, lights AND the heater; the voltage on it drops to about 9.5V when attempting to heat. Is there some way to pwm limit the heater output for temporary use?
Yes there is but then the heater most likely won't get up to temperature. You can add an "S" parameter to your M307 line. So for example, S0.5 will give 50% PWM. Try it and see.
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Even if you PWM it, the total output over time may be lower but the instantaneous output is still full current and will cause the same voltage drop.
Its hard not to conclude that its best to have 24v components on a 24v machine, I didn't at first as like most of us we've come from having 12v spares lying around, or rebuilding a 12v machine, but if this isn't an option get adequate converters. at 12v for LEDS and Fans 2A will do (unless you have a lot of LED's), hot end heaters need 5A.
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I fully support the previous recommendations and I also strongly recommend to replace the heater cartridge and not to play with 12V heaters on 24V. It's for your own safety (and possible in a worst case also that of your family) It is just not worth it.
You get one here (https://e3d-online.com/heater-cartidge-40w) at a fair price . -
I've already ordered the 24v cartridge. I am looking for a temporary solution until it arrives. I've gotten this figured out now thanks for everyone's input.
