TheSkySearchers

yobbo89 wrote: ↑Sat Jun 17, 2023 5:23 pm is that right 0.9 omhs at 10 v = 11 amps on the controller, i don't think i should do that, it's max is 8 amps ..

Graeme1858 wrote: ↑Sat Jun 17, 2023 4:30 pm

yobbo89 wrote: ↑Sat Jun 17, 2023 1:05 pm So I got 0.5m of nicrom wire at about 7ohms, it runs a little to hot 95 deg c with voltage controller on low 6-7volts, should I add a resistor toward the output of the controller and if so what ohm resistor?

If your wire is 7Ω and you have 7V across it, then
I = V/R
I = 7/7
I = 1A

And:
P = VxI
P = 7x1
P = 7W

At 12 V it would be:
I = V/R
I = 12/7
I = 1.7A

Then:
P = VxI
P = 12x1.7
P = 20.5W


Your temperature is too high at the lowest voltage, so try adding another 7Ω resistor in series to reduce the current flow.

Then:
I = V/R
I = 7/(7+7)
I = 0.5A

So:
P = VxA
P = 7x0.5
P = 3.5W

On full at 12V:
I = V/R
I = 12/(7+7)
I = 0.86A

And:
P = VxA
P = 12x0.86
P = 10.3W

If that gives you a temperature that's too low then change the 7Ω to a 3Ω resistor in series. I don't know if you can get 7Ω and 3Ω resistors, but you get the picture.

Then on low at 7V
I = V/R
I = 7/(7+3)
I = 0.7A

So:
P = VxA
P = 7x0.7
P = 4.9W

On full at 12V:
I = V/R
I = 12/(7+3)
I = 1.2A

And:
P = VxA
P = 12x1.2
P = 14.4W

Hope that helps a bit more than my last post!

Graeme

Graeme1858 wrote: ↑Sat Jun 17, 2023 7:21 pm

yobbo89 wrote: ↑Sat Jun 17, 2023 5:23 pm is that right 0.9 omhs at 10 v = 11 amps on the controller, i don't think i should do that, it's max is 8 amps ..

I = V/R
I = 10/0.9
I = 11.11

P = VxI
P = 10x11.11
P = 111W

You must be getting quite a temperature! What resistance would you get with 3 in parallel? And how are you insulating the wires from each other?

Graeme

yobbo89 wrote: ↑Sat Jun 17, 2023 9:28 pm oh , i was thinking that running parallel would would lower resistance thus lower heat, i got it, lower resistance = more heat with this ohmic material. it gets very confusing since a normal circuit with copper would be that a higher resistance would produce more heat.