I don't know the answer to your question, but I note that with the
latest extruder head even the Makerbot people have abandoned using
resistors as heaters.  they've gone to the little canister elements
that everyone else is using.

Somewhere before I blew up my computer I had a link to a great website
that showed pictures of the resistor cores migrating out of the
aluminum heat sinks and destroying themselves.

I personally had problems because every time I fired the thing up the
solder would soften up and the resistors would disconnect themselves.
You're probably not running them that hot.

but generally I would (and did) use nichrome wire for heating up large
flat things, even though it's a royal pain to wire.

Thanks,

DougM

On Sat, Oct 1, 2011 at 6:44 PM, PICdude <picdude3@narwani.org> wrote:
> I have a few chassis-mount resistors mounted to an aluminum block
> specifically for the purpose of heating the aluminum block (3D printer
> extruder head). =A0Can't I run much more power (than rated) through the
> resistors, as long as I don't exceed the max operating temp?
>
> Specifically, the resistors are 5-ohm 10W, and if I power it from 12V
> (lead-acid battery) I get 2.4A per resistor, and 28.8W. =A0I would PWM
> it to reduce the average power, but with feedback. =A0So it would run at
> 28.8W until it comes up to temp (I need <150 deg-C), then reduce
> average power. =A0The resistors are rated at 250 deg-C max, so I'd be
> well within that.
>
> Cheers,
> -Neil.
>
>
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