What section wire to use for the hot end resistor?

A supplier delivered me the 5W resistor for the hot-end with 0,6mm wires. This seems much too light to me. Should I use those of choose a larger section?

Edited 1 time(s). Last edit at 09/13/2013 07:27PM by WestMD.

I would NOT use the resistor but replace it with a cartridge heater.
[store.qu-bd.com]
Resistors NOT really designed as heaters.

Notice wires on cartridge heater!

High temperature wire braid,
If you insist on using resistor --- Crimp and solder wire to resistor --connection will be very near HOT.

If they are driving only 5 watts thru the resistor it wouldn't get hot enough to heat the hotend to melt PLA

0.6mm is 22 gauge wire which should be able to carry 5 amps at 12v
I would use 16 or 18 gauge stranded wire ---- it moves around and flexes a lot.

Also consider beefer wire on your heated bed (12v 40w)

Resistors are not as durable as cartridges, but they are acceptable if something is used to improve heat transfer between the resistor and the heater block.

Not to be contrary, but 5 watts is enough to work with ABS which needs more heat than PLA. I've printed several pounds of it with a 5 watt resistor.

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Yvan

Singularity Machine

Mounted correctly, wirewound resistors are just as reliable as cartridges. The mistake why some are failing is, they're glued with "thermal" silicone, which is a poor thermal conductor, or even held in place by a grub screw.

Heaters should be glued in with fire cement. The same stuff heater cartridges use.

To the initial question: the wire has 0,28 mm², current is (probably) 12V / 5.6 ohms = 2.14 A, so you have about 7.6 A/mm². Not exactly low, but should work. In case you see signs of melting on the insulation, replace it with a thicker one. Also, thicker cables make the heater a bit more powerful, due to fewer losses in the wires going there.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

I just turned my printer on for the first time. Tested the hot end temperature in pronterface with the delivered 0.6 mm wires and the resistor and it works just fine. the wires don't seem to get very hot. The resistor is just 'loose' in the nozzle with no thermal compound or whatsoever. I don4t have any. Should I get some and how bad is it to use it without?


While calibrating I have just faced another strange problem with the Z and Y end-stop. While hitting the end-stop on the Y or Z axis, printrun will notify me (echo:endstops hit: Z:23.00) but I'm not able to move the extruder in the opposite direction but only in the direction which is already jammed into the end stop. Makes me wanna think I have installed those end-stops at the wrong end of the axes.

The X axes is working just fine but I don't know if it supposed to hit the end stop each time when in home position.

Pictures here: [imgur.com]

The resistor has an unpredicable life span without some kind of thermal bond to the heater block. I ran one like that for a couple of pounds worth of ABS without problems. Now the same resistor is embeded in automotive type exhaust cement and still working fine, several more pounds of ABS later.

If you can easily replace it in case of a failure it's not that big of an issue, but the sooner it is cemented in place the better.

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Yvan

Singularity Machine

Traumflug Wrote:
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> Heaters should be glued in with fire cement. The
> same stuff heater cartridges use.


Of course in the US we call it something different....

It's called "furnace cement" or putty over here and some areas it's harder to find than others. You can use the afformentioned "muffler putty" that is good to 1000* C typically. Any auto parts store will have it. In the US Permatex is a pretty prevalent brand and is known as MP1.

I have just bought some exaust repair gum named Firegum. [www.holtsauto.com]

Should this be a good heat conductor? It also hardens when heated, isn't that a problem when the resistor needs to be changed?

Edited 1 time(s). Last edit at 09/15/2013 11:45AM by WestMD.

I think that is what I've got. Should work well. I haven't had to take out a resistor yet...

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Yvan

Singularity Machine

Does anyone know if these "furnace / Exhaust pastes" are insulators or heat transmissive?
I would think a compound with some metal in it would have good heat transmission
but also may short out resistor. The stuff with copper in it should be real good
but you must insulate the bare leads with good high temp wire insulation.

Use a heater cartridge -- and no worries.

The exhaust cement is heat transmissive, that is why it's one of the accepted methods of seating the resistor in the heater block.

I had originally considered high temp. silicone, but that is not a good thermal conductor.

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Yvan

Singularity Machine

Where is the information on the exhaust cement and its heat transmissivity?
Is there a URL that shows its transmission of heat?

Tnx

cozmicray Wrote:
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> Where is the information on the exhaust cement and
> its heat transmissivity?
> Is there a URL that shows its transmission of
> heat?
>
> Tnx

I would love to see that too! It's used because people seem to have found it it works through trial and error. I seem to vaguely remember maybe Forrest Higgs playing around with stuff like this about 7 years ago?

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Yvan

Singularity Machine

Believe me, I have searched for it but couldn't find anything. Only thing it says is that can handle temperatures up to 1000°
But things seems to work fine now. I should have measured power consumption of the resistor before and compare with current values to see if it's more efficient now.

Edited 1 time(s). Last edit at 09/16/2013 04:46AM by WestMD.

I think it will have a similar conductivity to the body of the resistor so if you have the hole about the right size so that is thin then it will have a negligible temperature drop compared to the resistor itself. Much better than an air gap and also much better than silicone.

I would guess a conductivity around 1 like glass. Metals are one or two orders of magnitude better conductors and plastics at least an order of magnitude less.

I have never had a resistor fail when cemented in with exhaust putty or glass rope glue.

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[www.hydraraptor.blogspot.com]

Here are numbers: [de.wikipedia.org] and here is a diagram: [en.wikipedia.org]

Thermal silicone maxes out at 1.05 W/m/K according to yet another source, while concrete ("Beton") has 2.8 W/m/K. Air (resistor without any glue) is even worse than a poor glue.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

There is exhaust goop and there is exhaust paste?
What is it made of? Lots of differences?
Probably propriatary compound of manure and unobtainium?

Maybe I should try to see whats in cartridge heater? Nichrome wire, ceramic, aluminum shell
What is the ceramic stuff --- thats what you'd want to use with your resistors
or
Find out what resistor is coated with?