Duel powerer supply 12/24 volt

ziggymanpopo

So heres one i would like to bounce off everyone.
I am running a cr-10 s5. Being an electrician for 30 years my thoughts were to convert to 24 volt.
My desires are to escape the painfully long bed heating cycle i currently have everythin hooked up to a 12v supply i would like to isolate the bed and connect it directly to the 24v suppy using a mosfit
My questions are two fold.
First im concerned about backfed voltage fome the 24v supply into the duet control board most likely from the heat triger wire to the duet....is ther also a possibility of an issue if both 12 and 24v volt gound wires are not bonded together i would think so if the ground was lost on one of the supplys
I would think that a diode placed between the duet and the mosfet trigger would protect the boad from undesired voltage back fed from the 24v supply. And bonding the negative terminals together so that we have abcommon ground. I was thinking would be the right approach

Second question has to do with the bed itself.
Ofcourse the unit was shiped with 4 solder pad on the heater element itself. only the outside two are being used. I would assume that there are two heater windings and only one is being used. Can the bed be rewired to 24v if the machine was origanaly sent as a 12v model .
Any suggestions or input would be greatly appreciated

JoergS5

@ziggymanpopo A different approach would be using an SSR (there are multiple threads in this forum about how to use and wire it), then you can even use 230 V AC with a matching bed heater. You care about safety, and I think using SSR and separating the heat bed current from the rest is a good approach.
There are DC-AC and DC-DC SSRs, so with the DC-DC SSR you could switch a 24 V DC heat bed on and off also.
Additionally, there is a wiki about this option: https://duet3d.dozuki.com/Wiki/Choosing_a_bed_heater#Bed_heater_driven_using_a_Solid_State_Relay

ziggymanpopo

Is the only option to lose the existing heating pad and puchase one for 24v. ?? Or is it rewire-able or ready kowing manufacturing it wouldn't surprise me. Where would someone find out what the other two solder pads are for or are they redudnent Is there a second element to wire in series?? it would be nice to know for sure. "Without dissembling the whole bed ..... twice"
Thanks for the isolation idea it would solve the feedback loop issue....i happen to have some i think might work depending on volage drop across the ssr

nhof

@ziggymanpopo Check the resistance across the pads vs the rated power to figure out if the extra inputs are for 24v input (they could well be)

ziggymanpopo

Thanks again

dc42

@ziggymanpopo said in Duel powerer supply 12/24 volt:

Ofcourse the unit was shiped with 4 solder pad on the heater element itself. only the outside two are being used.

Odd, that sounds like a dual voltage 12/24V bed wired for 24V i.e. the two halves of the split element are wired in series, not in parallel. What is the resistance of each section?

ziggymanpopo

Im not sure i willl have to disassemble it and post my findings when I know.. it will be a day or 2 before im willing.... as soon as i know
Thanks for the suggestion