24V to 12V Heater

Hi I tried with 24V DC Power Supply, The problem is, I have 12V ceramic heater which need to work with 24V, so I thought to use a buck dc converter
I measured the current in the heating element (ceramic heater) It is 6.5 Amps I could not find any buck converters that can be used for this high current

Tried LM2956 a ready made one http://www.ebay.com/itm/1pcs-DC-DC-Buck-Converter-Step-Down-Module-LM2596-Power-Supply-Output-1-23V-30V-/251066005460 but gets too much heat and doesn't work well !

can you help me in building circuit or an alternate option

Thanks in Advance

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The obvious alternate option is to buy the proper 24V heater. If you are referring to the hotend heater, they are $6.99 US or less.....

Thanks Vreihen, me too think this is the best option so far but I want to explore on another aspect too !

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Explore changing the heater duty cycle in firmware. I know there's a duty cycle setting for heated beds that others are using to run a 12V heated bed from 24V.....

There is no such thing like a "12V"-heater. A heater is a heat-withstanding resistor, no more, no less. You can apply any voltage as long as you manage to deal with the produced heat.

If you apply 24V instead of 12V, you quadruple its power. 20 watts before -> 80 watts after, so expect a much quicker temperature rise. To countermeasure you can limit the PWM the firmware generates, effectively reducing the supplied voltage. Marlin has a MAX_PWM setting for this. All firmwares can limit PWM when using bang-bang with appropriate PWM_ON and PWM_OFF settings.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

Just a note here:

PWM only limits the power you draw, and NOT the instantaneous current drawn. This is because PWM is digital (pulse width modulation) and is all about switching something on/off enough times to approximate the amount of "power" that you would get with a lower voltage. As this is the way the MOSFETs are expected to work in all our electronics circuitry (on/off), it's the only real way to drive the outputs. It's also (generally) fairly efficient.

This means: You still need to have wiring (and electronics) that can handle twice the current if you're using a heating element that was previously used at 12V, when using it at 24V.

The main thing here is fuses (eg: on your electronics), which may blow if they get too much current, or your PSU may not be capable of producing that much instantaneous current and shut down.

Personally, I just prefer to use a heating element that draws a reasonable amount of current at the expected voltage to give the desired amount of power. For an extruder, and for 24V, I tend to use 18 ohm or 22 ohm resistor coated in vitrified enamel (~32W or ~26W respectively), or a ceramic heater that's been specced for no more than 40W @ 24V.

Comparison: A 6.8 ohm resistor at 12V puts out ~21W, and a 5.6 ohm resistor at 12V puts out nearly 26W - and they're pretty standard values used in most hot ends.

PS: Note that if we were to drive a MOSFET with an analog method, we'd require a much more complex circuit, everything would be much less efficient, and we'd have a lot of excess heat in the MOSFETs as a by-product.

@Traumflug: Yes I have heard from a heater manufacturer saying, heaters which he supplies can work from 5V to 24V DC
why I have this question is, I saw a heater became red hot when connected with 24V Dc, in other hand it works fine at 12V DC

In Bang bang mode, i am afraid that the heater may not produce the constant heat with precise control which will result in Print quality!

Edited 1 time(s). Last edit at 07/07/2014 02:49AM by GowthamJGR.

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Quote
Cefiar
This means: You still need to have wiring (and electronics) that can handle twice the current if you're using a heating element that was previously used at 12V, when using it at 24V.

If you had written "voltage" instead of "current", then yes, I'd agree. Current, however, is usually limited by the warming of the involved wires/components and PWM pulses are way to short to warm something up with a single On period. As such, 2 amps with 50% PWM equal 1 amp with 100% very well.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

Traumflug: I've had fuses blow in much less than a second when drawing more current than they're expected to carry, especially if they're fast-blow types.

Sure, PTC fuses may take this (but then again, I'd not run them at 24V since some of the ones people put on boards aren't rated for use above 16V), and slow-blow fuses should be fine too, but whether a fast-blow fuse will go depends entirely on the PWM and the amount of current drawn and to some extent just how fast a fast blow fuse it is.

Specifically, if you're already close to the current limit of a fuse and then try doubling it while using PWM to "limit" the max current, I would expect the fuse to blow pretty much every time. If you were no where near the limit, then you might be fine, but I know I'd prefer not to take a risk.

Quote
Cefiar
Traumflug: I've had fuses blow in much less than a second when drawing more current than they're expected to carry, especially if they're fast-blow types.

The slowest PWM doable by average ATmegas is 62 Hz, so the maximum length of a spike at 50% is 8 milliseconds.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY