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I have ordered a dual hotend Chimera and it came with 2x 12 V heater elements (in my rush I forgot to order the one with 2x 24V).

Chimera dual filament hotend

Is it possible to run these 12 V heater elements in series?

I am planning on running this with an SRK 1.3 board.

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No you don't want to do that.

A 12 V 30 W heater has a resistance of about 5 Ω (2.5 A on 12 V). A 24 V 30 W heater is about 19 Ω (1.25 A on 24 V). Placing two 12 V heaters in series means about 10 Ω, for 24 V that means that the current is 2.5 A, similar to a 12 V circuit, the power will be 30 W for each heater. So it appears that this should work.

But, the problem is that being in series, both the hotends are heated. This is not beneficial for the unused core which is prone to ooze filament and can cook filament if not used for a long time (long stand-by high temperature). Typically, unused printing cores go to a lower stand-by temperature when they are not printing. Also it would be more difficult to have filaments of different temperatures in the hotends. Furthermore, which thermistor would you use? A hotend cools down by melting filament, the temperature drop is measured by the thermistor results in the control logic adding current to the heater to compensate the loss in temperature. If you only use one thermistor (basically, from a firmware configuration perspective, the setup is similar to having a single heater in a single hotend and having the filament being changed) and using the other core (without a thermistor) to extract filament, the temperature drop will not be registered and as such not controlled. There is no default firmware solution to use 2 thermistors in a "single" heating element (in this case strand of heating elements), this will probably require some modding to the source code of the firmware.

You could test this setup, but I would not use it for a long time.

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This will not work as you intend.

The heaters are designed to be independent. They do not share a thermal path between them. The thermal load on the two extruders will be different whenever one nozzle is active and the other on standby, and there is no condition when both are extruding at the same time.

The two thermistors are needed so that each nozzle can be individually controlled. Placing the heaters either in series or parallel defeats this control, and many problems will follow. You will spend days trying to understand why filament is dripping, or not extruding, or the PLA cooks in the nozzle, or the firmware shuts down for over or under heating, or a nozzle seems to ever hit the right temperature. You will waste far more time than the time needed to order and receive the proper heaters.

If you must...

IF you were trying to proceed with some testing, change the 24V supply to 12V. The stepper motors will be a bit more sluggish, but the DC-to-DC converters will probably (maybe) work well enough to power the electronics. Check your supply rails to be sure.

But don't.

It is better to wait, or find a local store to drive to and fetch them, or call a friend who may have spares.

You don't want the frustration, and uncertainty, and the possibility of doing something as a hack that causes other problems.

Order the right cartridges and wait for their arrival.

ps: Not to make this a shopping answer, but Amazon has qty 5 cartridges, 24v 40w, qty 5 for $8. Depending on where you are, you may be able to get these tomorrow and use them while waiting for the "right" ones to arrive.

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