Hotend heater cartridge

[Spanners]

I recently purchased what I thought was a 24V 40W heater cartridge for my hotend but when I measure the resistance it comes out to be about 4 ohms, I’m thinking I have been supplied with a 12V cartridge instead.

Thanks in advance for any info.

So that I don't damage my board and to be clear, on the Duet 2 Maestro do I need to use a 24v 40W heater cartridge or will a 12V heater cartridge do?

[deckingman]

@Spanners If my maths serves me correctly, a 24V 40W heater cartridge should have a resistance of about 14.4 Ohms. Your 4 Ohm cartridge would draw about 6 amps at 24V which is about 144 Watts, so NO - don't use it on a 24V system.

[jens55]

@Spanners said in Hotend heater cartridge:

So that I don't damage my board and to be clear, on the Duet 2 Maestro do I need to use a 24v 40W heater cartridge or will a 12V heater cartridge do?

The voltage rating on the heater cartridge needs to match your power supply voltage which could be either 12V or 24V. You definitely have received a 12V cartridge. I have had the same misfortune of ordering a 24V cartridge and receiving a 12V cartridge but I was not smart enough to measure resistance before I installed it ... and boy oh boy does it heat up fast

[droftarts]

@jens55 said in Hotend heater cartridge:

and boy oh boy does it heat up fast

That's the danger of fitting a 12V heater cartridge. If something on the hardware fails (eg MOSFET fails open) or firmware hangs, and fails with the heater on full, it will get really hot; hot enough to melt the aluminium of the hot end. And possibly set fire to filament. There are reports of 3D printers burning and creating a lot of damage, particularly when left printing unattended. It's up to you if you want to take that risk.

However, as far as I'm aware, thermal runaway protection works well on the Duet, and I don't particularly know of a case where it's gone to that extreme. You can run the hot end at 50% PWM (there is another thread about this), but it does mean that the heater cartridge is still drawing a lot of amps 50% of the time, and stressing components on the Duet while doing this.

I would always advise getting a heater cartridge which matches the voltage supply. It's just not worth the risk.

Ian

[jens55]

Besides the fire risk, there is also the issue of overshoot. The swings are too much to handle for the PID system and you end up with noticeable oscillation of nozzle heat. It 'can' work but will stress the mosfets and generally be less than optimal so it just isn't worth it. I complained to the ebay seller and just got my money back.
Oh, I think that the PWM figure will end up around 20% as the a 40W 12V cartridge will put out 160W at 24V.