How to Run 12V HotEnd with 24V Duet2?

dc42

@snowcrash said in How to Run 12V HotEnd with 24V Duet2?:

@elmoret said in How to Run 12V HotEnd with 24V Duet2?:

DC to DC converter, power it directly from the printer power supply, positive from the DC-DC converter goes to the heater lead 1, negative from the Duet goes to the heater lead 2.

The Duet will switch the negative side to achieve temperature control, and the hotend will see 12v maximum assuming the DC-DC converter does not fail.

Thanks for the suggestion, @elmoret!

If it was linear voltage, I wouldn't think twice about it and indeed use a dc-dc converter. My concern, though, is these converters tend to be relatively slow and as you point out the Duet uses pwm for controlling the voltage input to the heater. Hence, I worry a converter may not always be quick enough to do the job.

Any opinion on this, guys?

What @elmoret is suggesting is that you use the DC-DC converter to provide +12V power to the positive heater lead. Not to power the converter from the PWM output, which would be a bad idea.

DjDemonD

Yes using it the way elmoret suggested works great and I have done so many times.

Do not PWM it down from 24v. Most people would set 50% which is actually still 2x the max power, it would need to be 25% PWM max to get a rough equivalent, but even then its just 25% duty cycle of 24v ON, 0v, 24v On, 0v etc... You're still running your heater at 4 times its rated power output just only for 25% of the time, assuming nothing (like a mosfet) fails and runs the heater at 4 times power for the few minutes/seconds it would take to melt and/or catch fire.

SnowCrash

Thanks for the clarification, @dc42, that indeed makes sense (sorry @elmoret for not fully grasping your suggestion till now).

And thanks for confirmation @DjDemonD, and the additional explanation!

Just to make sure I've got it right, this is the converter I intend to use:

And here's how what I take the setup to be:

Is this right?

dc42

Yes that's right.

SnowCrash

@dc42 said in How to Run 12V HotEnd with 24V Duet2?:

Yes that's right.

Thanks, @dc42!

SnowCrash

Hi,

Apologies for reviving this old thread, but I'm re-designing the PCB containing the above circuit for running a 12V hotend off a 24V power-supply, and it occurred to me that it might be a good idea to add a protection diode like so:

I'm aware that these types of diodes are typically added in series with inductive loads (like we do in the case of fans), whereas the heater is resistive, but perhaps there would nevertheless a benefit in adding the diode here? or is it completely redundant?

Thanks!
SnowcCash

SLKittie

Wouldn't it be easier using a mosfet?
im not sure if i am right or not though.
Plagiarism picture incoming? (edit:- clean up picture a bit)

I'm not sure if it would work like this but from my understanding it looks like it?
Don't quote me on this though. lol. i may not be right haha. just a thought

fcwilt

@snowcrash said in How to Run 12V HotEnd with 24V Duet2?:

Hi,

Apologies for reviving this old thread, but I'm re-designing the PCB containing the above circuit for running a 12V hotend off a 24V power-supply, and it occurred to me that it might be a good idea to add a protection diode like so:

I'm aware that these types of diodes are typically added in series with inductive loads (like we do in the case of fans), whereas the heater is resistive, but perhaps there would nevertheless a benefit in adding the diode here? or is it completely redundant?

Thanks!
SnowcCash

It would serve no purpose since, as you pointed out, the load is resistive.

It wouldn't hurt anything other than to reduce the voltage going to the heater a bit but why would you want to do that.

Frederick

SnowCrash

Apologies for the late response. Either I didn't get notification for the posts for some reason or I managed to somehow totally miss them.

Thanks for the clarification, @fcwilt

@latexcupcake, given that conventional MOSFETs have only 3 terminals, and your drawing contains 6 connections for it, I can't really see how it can work. However, if by MOSFET you meant a MOSFET-based power module (and an optocoupler) similar to this one

Then that could potentially work depending on the type of built-in Mosfet (I tests a number of these modules in practice and some worked but others didn't).

That said, a simple diode setup is much more economical, no?

dc42

@snowcrash said in How to Run 12V HotEnd with 24V Duet2?:

That said, a simple diode setup is much more economical, no?

No diode is even more economical.