See live heater PWM duty cycle

oliverracing

I'm having a play with making my own version of something similar to a SuperVolcano hotend (with a fair few tweaks of my own) to push my flow rate up a bit when making large car parts and want to see if I can find what the live PWM/duty cycle being used for the hotend to help judge heater element power requirement, idea is to test the setup with what I've got and uprate the heater if I'm going above 80% duty cycle.

The hotend will be run in a ~60C heated chamber and I've got a few 40W and 50W heaters that my very rough maths says the 40W should be absolutely plenty, but I'm trying to work out why E3D spec a 80W heater! Will be printing ASA/ABS/PA so not hotter than 280C, and can't see me pushing above 60mm^3/s. I suspect the silly heater is due to the high top-end heat they spec but also know they do their research and make great kit!

A Former User

best approach is to use an oscilloscope (with a math function) as you'll get the most accurate result.

the average voltage is proportional to the duty cycle, so with a little variance between meters you should be able to get a good idea based off measuring the voltage, you could also manually set the duty cycle to verify what voltage corresponds to what duty cycle, but as the duty cycle might change faster than your readings will update its not gonna be very accurate unless the flow rate is constant

if you don't have any instrumentation, maybe you could record the LED, and compare the brightness to known levels (i.e. first manually set the duty cycle in some steps, then compare to when the heater is being controlled by PID)

dc42

See https://duet3d.dozuki.com/Wiki/Gcode#Section_M573_Report_heater_PWM.

baird1fa

@oliverracing I cannot address your actual question, though I see it was already answered by DC42. But the heater requirement of 80W for the super volcano does make sense as not only are you trying to melt the plastic but you are also fighting the cooling from the surface area of the heater block.

For example, I have a volcano running the 40W heater and it works just fine to print upto 300C (without the silicone sock) and it even does fine with the part cooling fan full on. But if i try to heat the extruder past 300 say upto 400C, It won't reach that temp with anything more than 10% part cooling.

So the supervolcano at 80W is likely more to do with reaching the advertised temperatures of 450-500C than it is for volumetric flow. Also if you think 80W is overkill, have a look at the Typhoon extruder, it uses 400W and it only boasts a little over double the volumetric flow of the supervolcano.

Best of luck.

oliverracing

@dc42 Thanks - that's perfect, I'll have a play and see where I am!

@baird1fa Ok thanks that'd good info, Yeah the large surface area will probably be a factor but will be insulating it in a similar way to the E3D version so hopefully that will reduce that issue. Yeah, that Typhoon is crazy!