48V Duet3(4?) to complement future Duet Motors?

o_lampe

@jens55 said in 48V Duet3(4?) to complement future Duet Motors?:

what do you do for hot end heater cartridges.

In config.g you can reduce the power for a 24V heater cartridge to 0.5. That's what was done in early FDM days, when the 24V controller boards where new and 12V cartridges were the only available ones.

jay_s_uk

@o_lampe but thats definitely NOT recommended as you're still feeding 48v to the cartridge!!!!

o_lampe

@jay_s_uk The heater is just a resistor with a max. power value.
It doesn't care about voltage so much when the duty cycle is limited to 50%.
Maybe PID tuning is difficult?

oliof

@o_lampe Ohm's Law tells me you'd need to go to PWM 0.25 at a maximum, and I am still with @jay_s_uk that it bears considerable risk.

dc42

@jens55 it's possible to buy 48V cartridges to fit hot ends that use cartridges.

oliof

@dc42 I would still suggest to get more current on the 12V rail in a future revision, BTT boards like the Octopus allow 4 / 8 A on 12V.

dc42

@oliof we'd like to do that but it's expensive to generate 12V from 48V and also difficult to meet FCC and CE EMC regulations. I don't think any other boards support 48V input without requiring a separate 24V input to power the lower voltage components.

jay_s_uk

@dc42 thats correct. all the other boards require a 24v input to generate the lower voltages with 48v only used to drive the motors

o_lampe

@oliof I agree about ohm's law telling us to use only 25% duty cycle. My mistake!
I've use a 12V bed heater at 24V without problems using this method, but overpowering a cartridge might be a different story.
Just wanted to point out, that a resistor doesn't have a voltage limit per se.

o_lampe

@jay_s_uk
What about using a big 24V PSU and feed the motors from a DC-DC boost converter?
I'm using a few different boost converters for several tasks and they never failed me so far. ( 100W - 600W are cheaper than a second PSU)

jay_s_uk

@o_lampe that may work assuming the boost converter and PSU can handle it.
For my voron 2.4 i went with a separate 48v PSU. The LRS-200-48 aren't very expensive https://www.printyplease.uk/LRS20048?search=48v

o_lampe

@jay_s_uk
I'm using a separate 48V supply on my CNC, too. I always forget to switch it on before powering the 24V PSU. The TMC5660 drivers don't like it and quit responding.
With a boost converter, I only need one mains-socket/cable/switch...and ground-loop issues are no problem anymore.

oliof

@o_lampe the resistor does not, but the insulation may!