Diy dew heater

[Graeme1858]

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

[Juno16]

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

Excellent Graeme!

[yobbo89]

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

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.

i will grab some alligator clips and test a long length of nichrome

[Graeme1858]

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.

You can think of any (well almost any) resistor or conductor as a current limiting resistor. For a fixed voltage, the higher the resistance, the less current can flow because they are inversely proportional to each other. And if there's less current then there's less power. If there's less power there's less heat.

Graeme

[yobbo89]

ok i made a longer one,i'm at 26 deg low @ 1 to 1.5v, 70 deg max 12v, ambient air atm is 20 deg. wire length is about 980mm long 13.4 ohms , about 10.8 watts max i think

[yobbo89]

That should make life easier . btw I've got 25 hrs on a target,night sky is on a clear streak atm so maybe a few more nights on some oiii

[Juno16]

Sounds great Rob.
After you mentioned the voltage that you were seeing across the controller, I measured mine. Same result.
About 12vdc wide open and about 10vdc at a lower setting.
For me (and sounds like you too) this kind of works like a medium and high setting.
As long as you correctly size the wattage output of rhe strip you should be good.
Good for you about the weather. Mine is garbage as it has been foe several months.
Best of success collecting OIII!

[yobbo89]

I ended up glueing the wire on the secondary, I use mobile phone glue for glueing lcd screens in place works well, it's like a silicon soft glue., the scope disepates alot of heat away , I'm running it max settings and the seconday is lukewarm, I'll probe it with a temp gage during the week, I might lower the resistance just a little bit, atm star defractions are a little off, maybe because I bumped the seconday or the wires running on the spider vane might be a little too thick, I'll recollimate for my next target

[yobbo89]

update on my kendrick dew heater,took the pic16 off, read the fw ,chip is ok but i flashed the fw onto another pic and soldered it back onto the board in case some of the pins were not working on the old pic16,replaced the mosfets on the input aswell, still no luck, the pic16 has a clock signal, i can get power to the board ,the leds will light up when i short p1 (dew heater rca) to ground,hmm maybe the fw is corrupted on the old chip,

edit: emailed kendrick for fw details.

[Juno16]

I sure hope that you get good support and can get that Kendrick back on line soon.
You are certainly giving it a heck of a good try!
Let us know how it goes.

[yobbo89]

well they email me the fw no problems, i'll do a check on it