I thought this would be a good place for this question.

I just noticed that the Ender 3 hot end heater cartridge that I was using in my Spare Parts Printer is labeled “12V” and as it’s just a resistor, I’m wondering if there would be a problem using it with a 24V power supply.

My initial thoughts are that a 24V heater cartridge would have twice the resistance of a 12V to keep the initial current at a reasonable level.

Just doing a bit of research and checked the resistance of the heater cartridge that came with the Ender 3 hot end is 14 Ohms (13.9 actually). I looked at all the other heater cartridges I have and they’re all 14 Ohms except for two - one is 3.9 Ohms and one is 19 Ohms.

Looking at this article:

It looks like the Ender 3 is probably a good choice to start with as it provides 40 watts with 24V and since there is a PWM on the power control I shouldn’t get wild temperature swings. Of course, these are famous last words.

Sorry could you explain what your saying a bit more?

I’m not sure why you’re saying that “4 times the current is that going to be molten metal?”

The current through the cartridge with 24V applied will be twice that when 12V is applied and, when you look at the link I included, the 14 Ohms will mean that roughly 40 Watts (41.14 Watts actually) will be dissipated by the heater cartridge.

I am not an electrical expert, but there are only 2 equations needed to answer the question.
V=IR and P=IxIxR. So voltage equals current x resistance and power equals current squared x resistance.

So: for the 24 volt heater we know resistance is approx 14 ohms
24=I x 14. Rearrange and get 24/14=1.7= current
So; power: 1.7x1.7x14= 40.46 watts

Now do same for 12 volt heater - you measured yours at 3.9 ohms.
So: 12v=Ix3.9 Rearrange and get: 12/3.9= 3.08 current
So power: 3.08x3.08x3.09 = 37watts (should be 40, but rounding and measuring errors add up, typically a 12 volt 40 watt measures 3.6 ohm)

NOW USE THE 12 volt heater, but apply 24 volts and what is power?
So: 24v= IxR. R= 3.9. So rearrange and 24/3.9=6.15amps
Power: IxIxR so: 6.15x6.15x3.9 = 147.5watts

So if you use your 12 volt heater with 24 volts, according to ohm’s law, YOU WILL GET 147.5 WATTS which is enough to melt your aluminum block the heater slides into. Also, it would heat up very fast, and shoot right past your desired temperature, then drop below, then shoot right past again - a real pain.

Using these equations it appears that the 19ohm that you measured is likely for a 30w 24 volt heater.

Sorry punctuation is bad. So from your article a 30w heater in failure mode will reach 300°. serious but not that big a deal. but it says 40w heater in failure will be enough to melt the aluminum heater block. Aluminum melts at 660c i think this one failing would heat to close to 1000°c though

The rod heaters ive bought were rated by watts at voltage. I Recently received one that was 1500watt at 120V but was supposed to be for 240v and was mislabeled. It got red and shook the wires in about 3 seconds when put it in the metal melter it was for and turned it on.

If you think the one you have is mislabeled only power it up in the block and be prepared to kill it right away if it overheats I guess.

I know the newer boards use a pwm controller. I don’t see them as being very robust and will it cope with the extra current? though my only dealing with then was on my recent SKR2 adventure

I guess I wasn’t clear, but the Creality heater cartridge I have is labeled “12V” but is 14 (13.9 actually) Ohms and would be a 40 Watt heater (as both Filek and I have calculated) which seems completely reasonable. When I say “Creality”, it came from a Creality box with an Ender 3 direct drive hot end/extruder assembly - it is genuine Creality.

Going back to the supply of heaters I have, I have a bag of three 40 Watt heaters that are also labeled “12V” but are all approximately 14 Ohm. These came from Aliexpress and were ordered as 24V, 40 heaters (I found the invoice). I have no idea why they’re labeled “12V”.

If I apply 12V to these heaters, they’ll produce 10 Watts of heat which isn’t reasonable for anything other than jello.

I would never consider using the 3.9 Ohm cartridge - at 24V it’s basically an incendiary device. It’s not labeled as to what voltage should be applied.

The 19 Ohm cartridge at 24V is a 30 Watt device. It’s not labeled as to what voltage should be applied.

I’ll try the current cartridge (which should be 40 Watts with 24 Volts) and either report back here or call the fire department. I’m somewhat emboldened by the fact that the other 14 Ohm cartridges I have are labeled “12V” when I did order “24V” devices.

For this test, I’m using the Ender 3 hot end default PID values. The hot end heated up very quickly with a 7C overage the target temperature.

Clearly the resistance of the heater cartridge is an important consideration and I’m comfortable with Glenn’s and my math that indicates that the resistance should give the expected heat and no surprises.

Honestly, I didn’t think there was any reason to be surprised - inside the heater cartridge is simply a coiled wire. I’m guessing that the reason why the voltage is specified is in case somebody who doesn’t understand Ohm’s law tries to use the kit.

One last thing, I did a quick search on the Creality kit and found this:

This is the part that I took the heater from for the Swiss Micro direct drive hot end and you can see on the page it says that it’s “Output Voltage” is 24V which confirms my conclusion above.