Extruder Resistor

Hey folks.

I'm wondering if i can use a 3,3 Ohm 3 Watt wire wound resistor as a heater for my extruder ? or is it too low on Ohm ?

Thanks in advance

That's about 43W if you're using 12V (draws about 3.6A). If you are using a higher voltage, then you might be pushing it too much.

Some printers have issues with hot ends over 35W (depends on just how much current you pull, and whether the fuse on the board is rated to handle that). You might do fine though as most of the heater cartridges are around the 40W mark.

Note: Just make sure that the resistor is one of the wire wound resistors that is covered in ceramic (usually green in colour). The standard painted ones can get damaged (paint scratches off), leading to the resistor shorting to the hot end, which could be a problem (especially if there is more than one short).

PS: The max I tend to recommend with a resistor is 3.9 Ohms at 12V. It's not often that a hot end is large enough to really require a 40W heating element in it, though the stainless steel nozzles are more likely to require more power to get them up to temp.

Hey Cefiar

Im using a Resco Hotend, so its an all metal hot end. and its the green ceramic one I'm using.

Maybe i should try it out, what could blow up ? the fuse and the resistor ? not the arduino board ?

Since you're using RAMPS, all that could happen is that the 5A PTC fuse would trip after extended use.

PTC fuses take a while to trip when experiencing over-current situations (20-30 secs is not uncommon).

The fuse controls power to the Arduino Mega, the Hot End and also to the stepper motors. so you want to try cycling your x/y/z/e axes back and forth a lot to make sure that it doesn't trip out on you, otherwise it'll probably fail when you're using it for a print job.

Note: You can always replace the PTC fuses with real fuses that have a higher current rating (eg: 7.5A), as that should be more than enough. They will also blow faster if there is a fault, which helps protect things when there is an issue.

Hmm, maybe i should look for another resistor then. Because my psu os bolt 350 wattage and i Got a heatedbed too.

Im not done building my reprap so i Can still consider my options

Thanks again for your answar

If you have an ATX supply that's rated for 350W, that's way to small. If it's an industrial 12V supply, then it's good for about 29A (which is plenty).

It's cheaper / easier / better to get a ceramic heater cartridge than do a wire wound resistor. They are way more rugged and much easier to work with.

Uncle_bob:

Its an server psu thats rated at 350 and im going to get a heated bed and the mentioned resistor.

What if the resistor are 20 ohm instead? Thats the closest i Got.
Else i have to buy some heater cartridges.

Edited 1 time(s). Last edit at 12/27/2013 10:43AM by TRoager.

A normal ATX supply that will work with these printers needs to be rated for 600W or so if it's going to have a chance. An industrial supply that only puts out +12 and nothing else rated at 350W is adequate to run one of these printers. Spend the $45 and get a good industrial supply.

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Power into the hot end is going to vary directly with 1/resistance. Increase the resistor to 20 ohms and the power into the hot end goes down by about 10X. That's not going to be enough for most hot ends and most filaments.

Hmm i see. then i have to get another one i guess. ill get an industrial when i can afford one in the new year, right now every penny is gone for this year

The new PC power supplies that are "Haswell" compatible completely removes all
the question marks that plagued older ATX power supplies. For instance the Corsair
CX430 is capable of supplying a very small 12V load only. The internal architecture makes
the old demand of minimum loads on all voltages obsolete.

Snipped from the data sheet: +12 V max 28 A, +5 V max 20 A, total load max 430 W.
A fan using 80 mA on the +12V as the only load gives voltages on all outputs that are all within spec.
(3,33 V, 5,10 V, 12,14 V, -11,61 V and 5,02 V on "flea power")

It's quiet and cheap too and you get all the other output voltages for free.
There's an external control pin for on/off like on all PC PSU's.

Quote
Dala.horse
The new PC power supplies that are "Haswell" compatible completely removes all
the question marks that plagued older ATX power supplies. For instance the Corsair
CX430 is capable of supplying a very small 12V load only. The internal architecture makes
the old demand of minimum loads on all voltages obsolete.

Snipped from the data sheet: +12 V max 28 A, +5 V max 20 A, total load max 430 W.
A fan using 80 mA on the +12V as the only load gives voltages on all outputs that are all within spec.
(3,33 V, 5,10 V, 12,14 V, -11,61 V and 5,02 V on "flea power")

It's quiet and cheap too and you get all the other output voltages for free.
There's an external control pin for on/off like on all PC PSU's.

Do you have a link to it ?

Tonight all I get is a german version of their (Corsairs) page for CX430, you can surely find a better version.
In swedish currency I payed 60 USD for it but we are fortunate to have 25% VAT so most countries should
have a lower price.

The Corsair CX430 costs more than a dedicated industrial supply ($45 for the industrial) $45 to $55 for the Corsair unless you catch a deal at $40. While I personally have had good luck with Corsair supplies, you can find a *lot* of posts from people who have had poor luck with the low power end of the line.