Nichrome wire Ohms clarification

Hi All:
Under the guide "none rapid prototype mechanical parts" the Nichrome wire Ohms are called out as 8 Ohms while under the guide "extruder control board" the Ohms are called out as 6 Ohms with the use of Tip110 @ 2A.

What is the correct value in Ohms for the Nichrome wire sold through RepRap. org when used with Tip110 @ 2A?

Also what is the correct quantity for Tip110? only one is shown on the extruder board while three is specified in the "BOM"

Hello,

I believe that Adrian lowered the requirement to 6 ohms on the nichrome. Either will work, but 6 ohms gives you more wattage on your heater. If you're in doubt, go with the value on the wiki (or ask here!)

As for the TIP 110, the universal board is capable of driving 3 TIP 110s. only one is currently used on the Thermoplastic Extruder controller. I'll change that on the BOM. I'm currently working on re-vamping the BOM generator, so once thats done, I'll change all the wiki pages to be referencing it, and then it will be easy to keep these things up to date.

I think it started at 12 ohms, went to 8 and now 6. I made mine when 8 was recommended and it rapidly gets to 200C, and would get hotter if I left it on, and that is without any insulation, so I am not sure why it needs to be as low as 6. I think Forrest's Tommelise has 6 but that has a large plate at the top end acting as a heatsink as well as no insulation.

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[www.hydraraptor.blogspot.com]

Thanks Zach, That clears things up a bit better.

Power law voltage squared divided by R is power. Lower R and raise power
Example 8 ohms @ 12vdc is 144/8= 18 Watts, for 6 ohms 144/6= 24 watts

Yes I too had been assuming 18W for 8 ohms as I use MOSFETs for switching but actually the UCB uses a darlington with a 2.5V max drop at 2A. If we assume a more typical figure of 1.5V then that reduces the power to: 14W @ 8R and 18W @ 6R.

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[www.hydraraptor.blogspot.com]