Connecting multiple heated beds to Duet 3 6HC

Zerocool1703

@fcwilt I plan on printing very big objects that will take a long time (days, possibly a week) and want to save on power costs when I do not need the full 500x500mm area.

Plus the bed heaters take >30 Amps as they are (I don't want to mess with mains power) and I don't feel comfortable going much higher than that, which would be the case with a 24V 1300W heated bed.

Phaedrux

@Zerocool1703 said in Connecting multiple heated beds to Duet 3 6HC:

(I don't want to mess with mains power)

I'd be less willing to mess with the wiring requirements for 30A loads.

Zerocool1703

@Phaedrux Is 24V 30A "worse" than 230V 2.83A? As in "kills you worse"?

I mean, I have already bought the hardware so I will probably go with it, but I'm still curious to know.

Anyway, do you have some advice on my original question as well? I would really appreciate it.

hackinistrator

i would control each bed from different out , each with own thermistor .

Phaedrux

@Zerocool1703 said in Connecting multiple heated beds to Duet 3 6HC:

Is 24V 30A "worse" than 230V 2.83A? As in "kills you worse"?

Well it's more fire risk than shock you risk. The wiring required for carrying 30A at 24v would be thicker and stiffer. Not really an issue if you take proper precautions with the correct gauge wiring and strain relief and cable chain for bend radius management if the bed will be moving.

But the AC voltage risk can also be mitigated with proper grounding, fuses, cable separation, and ground fault interrupters.

Either way there are risks you must mitigate.

@hackinistrator said in Connecting multiple heated beds to Duet 3 6HC:

i would control each bed from different out , each with own thermistor .

This might be the simplest way. It would complicate the slicer being able to turn the bed on automatically. But you'd have to flip a switch manually anyway. At least this way you just manually set the temp on the heater you want to use.

fcwilt

@Zerocool1703 said in Connecting multiple heated beds to Duet 3 6HC:

...want to save on power costs...

If cost is an issue than 3D printing may not be something for you to invest in.

The amount of money I have spent on filament dwarfs the cost of running the printers.

I suggest you follow the advice to connect both to the board via the SSRs and use a separate temp sensor for each one.

I would also suggest you re-consider using line voltage units.

Good luck.

Zerocool1703

@Phaedrux
"Well it's more fire risk than shock you risk. The wiring required for carrying 30A at 24v would be thicker and stiffer. Not really an issue if you take proper precautions with the correct gauge wiring and strain relief and cable chain for bend radius management if the bed will be moving."

I use 10 awg copper wire for everything that has 30A and I do plan on using cable chains. That should be fine, right?

"i would control each bed from different out , each with own thermistor ."

This sounds like I misunderstood something in the Duet 3 6HC documentation. I thought the board only has one out for a heated bed?

Phaedrux

yes there is only one dedicated heated bed terminal, but you can use other lower current outputs and control a relay or dc-dc SSR to switch the high current.

Zerocool1703

@fcwilt "*if cost is an issue than 3D printing may not be something for you to invest in.

The amount of money I have spent on filament dwarfs the cost of running the printers.*"

Hehe yeah, that's probably right, but I'd rather save on power than on the filament

"*I suggest you follow the advice to connect both to the board via the SSRs and use a separate temp sensor for each one.

I would also suggest you re-consider using line voltage units.*"

I suspect when you say "connect both to the board via the SSRs" you mean to do it a different way than the one I laid out in the original post? Could you please elaborate on how I would go about doing that?

Is there a line voltage unit you could point me to for 650W heated beds?

Sorry for all the questions, this is my first build...

Zerocool1703

@Phaedrux Oh, that makes sense. Sorry.

Does the output I use for this have to be PWM capable?

fcwilt

@Zerocool1703

I have used Keenovo line voltage silicone heaters for all my printers.

Here is a 120VAC 750 WATT unit

Then all you need is a good SSR that can handle the load of the heater and whose control inputs are compatible with the outputs from the Duet.

SSR

You would connect them much the same way as in your diagram except instead of powering them with DC power supplies you would have connections to line voltage and there would be no "plug with switch".

You would want to have a device like these for safety

Frederick

Zerocool1703

@fcwilt said in Connecting multiple heated beds to Duet 3 6HC:

I have used Keenovo line voltage silicone heaters for all my printers.
Here is a 120VAC 750 WATT unit

Ah, I live somewhere with 230VAC so I guess that one wouldn't work for me, but I see what you mean now (Sorry, I thought a "line voltage unit" was a PSU since english isn't my native language).

Thank you for all the Info, I will have a look at it, however I am afraid switching to mains power won't be an option immediately due to budget considerations (I already bought the 24v hardware).
However I will keep it in the back of my head and contemplate whether I like fire risk or shock risk better
For the time being I will definitely keep a fire extinguisher handy just in case.

fcwilt

@Zerocool1703

You may want to purchase some silicone insulated wire to run power to your 24 volt heaters.

Such wire is generally going to be quite flexible compared to other types.

Here is an example

Frederick

Zerocool1703

@fcwilt said in Connecting multiple heated beds to Duet 3 6HC:

You may want to purchase some silicone insulated wire to run power to your 24 volt heaters.

That's what I bought I use 10AWG silicone wire for everything in the heated bed circuit (except for the input side of the SSRs, since those are low Voltage and amperage).
I'm trying not to set anything on fire haha

hackinistrator

i think you should test how much (steady state) current is needed to maintain your max expected bed temp with your bed config .
if the current is anywhere near 30A , i would use double 10awg wire , as 10awg wont be enough for hours of printing + hot bed .
you can basically use any pwm capable out as another bed heater if its going through ssr anyways .the simplest is to use one of the extruder heaters (if not in use).

for slicer setting ,simple solution is to configure the second bed as "chamber heater" (if you don't use one anyways) , then just activate it in slicer setting if needed .

fcwilt

@hackinistrator said in Connecting multiple heated beds to Duet 3 6HC:

i think you should test how much (steady state) current is needed to maintain your max expected bed temp with your bed config .
if the current is anywhere near 30A , i would use double 10awg wire , as 10awg wont be enough for hours of printing + hot bed .

By my calculations for 1 meter of 10 gauge copper wire carrying 30 amps the voltage loss would be around 0.2 volts.

That seems acceptable to me.

Frederick

Zerocool1703

@hackinistrator said in Connecting multiple heated beds to Duet 3 6HC:

if the current is anywhere near 30A , i would use double 10awg wire , as 10awg wont be enough for hours of printing + hot bed .

I made a mistake in my previous posts, since 30A is actually what the PSUs can put out, but the 650W 24V heated beds should actually "just" pull a maximum of 27.08A.

The Extruder heater is powered via another PSU so it won't add anything to that.

for slicer setting ,simple solution is to configure the second bed as "chamber heater" (if you don't use one anyways) , then just activate it in slicer setting if needed .

Yes, I have read about that, too. In that case I would connect one to the OUT0 and the other to OUT 1, 2 or 3, right?

But I have also read that SSRs can't really handle PWM signals, because it's at too high a frequency and you should rather use a "bang-bang" mode?

fcwilt

@Zerocool1703 said in Connecting multiple heated beds to Duet 3 6HC:

But I have also read that SSRs can't really handle PWM signals, because it's at too high a frequency and you should rather use a "bang-bang" mode?

You can still use PWM you just have to use a low frequency.

Here is my setting:

M950 H0 C"bedheat" T0 Q10 ; create bed heater output on bedheat and map it to sensor 0

Notice the Q10 which specifies the frequency - it works fine with my SSRs.

Frederick