NiChrome input voltage/ amperage (Prusa)

Hey guys, was wondering if anyone knew offhand the voltage and amperage inputted into the 6 Ohm length of NiChrome? I need to mock up my hot end to see if it actually works without buying a RAMPS setup... Thanks!

It's meant to run on 12V, so that works out to 2A. It's usually under PWM control though, so with 2A through it it will probably get a bit to hot.

Incidentally, nichrome is a bit dated. It does work, but has a tendancy to be fragile, depending on what you use to attach it. What did you use?

The newer thing is the ceramic wire-wound resistor - 6.8Ohms was chosen as it won't burn things up (too much) if the heater gets stuck on - which is what you'll be doing to it if you just hook it straight up to 12V.

---

--
I'm building it with Baling Wire

i ordered some insulated NiCr from makergear and it should be here soon. where can i get that resistor? is it a better bet?

Here is data on ni chrome wire.

[en.wikipedia.org]

a few issues
First the ni chrome gets to over 1400C before it fails. Meaning if it is on all the time it has the potential to burn down a lot of things besides plastic.

It does not heat evenly. a small section can get all the heat energy and melt apart

It does not solder so you will need to use crimps, and it oxidizes copper wire.


Also there is a specific power needed to heat your extruder head. it is something like 20-30Watts . 12v*2amps=24watts.


You can calculate power used by taking current *voltage. You can get current by taking voltage and dividing it by resistance.
power is P=V*I (voltage * current)

This web site i looked up can do conversions for you for ensuring the proper power. One of my sins is I like using higher voltage than 12volts.

[hyperphysics.phy-astr.gsu.edu]


I still use ni chrome for some of my extruders but I always am in the room when they are running. The 6.8ohm wire round resistors, or two 5ohm resistors seem like good form. I've also never burned a resistor one out. BTW you can find wire would resistors at radio shack and some hobby stores.

My first hot end was actually made with nichrome wire wound around a threaded nozzle using Adrian's design. It lasted for 3 months before the wire broke at the crimp terminal. I had enough to wind a second one so I took a 1/2" diam aluminum rod (~15 mm long), tapped a hole for the nozzle and drilled a hole for a thermocouple along it's axis, and wound nichrome wire around it with kapton tape to hold it. That one worked great until the PTFE insulator started leaking. So, you don't need to throw out your nichrome wire. I do recommend using a heating block (rod) since it makes it easier to mount the thermistor/thermocouple and it gives more accurate reading.

I've assembled two hot ends with ceramic resistors since then and it is a little easier to put together and disassemble and it seems to be more durable.

Thanks guys, i was wondering if a standard resistor (radioshack version) was the same as what i need at it appears it is. on a side note, will ANY 100k thermistor work?

No you need a vitreous enamel resistor to handle the high temperatures and you need a thermistor rated for 300C, most resistors and thermistors are NOT suitable for these temperatures.

[uk.farnell.com]

[uk.farnell.com]

---

[www.hydraraptor.blogspot.com]

ugh im confused. so if i need a specific resistor it seems im better of trying to get the nichrome to work unless i can get the resistor and thermoresistor from the same supplier

These are the type I recommend

[www.vishay.com]

The specific values I use are

10 Watts 5.11 Ohms 1%

I think the part number goes something like RH0505R11F... or RH1005R11F

Anyway, DigiKey has the following possible candidate

[search.digikey.com]


Others may apply too, but I only know enough to be dangerous.

Ultimachine.com sells the thermistor and resistor. It's convenient if you're getting other supplies from them anyway. They sell the big thermistor though. It would be better to use a smaller one with a heater block, like the one in the wiki. Anyway, you can also buy both from most online electronics supplier.