Diy dew heater

[yobbo89]

I've had my controller for over 2 years, never got around to setting it up dew "yes pun" to not finding a suitable heating pads/straps, I have a coned shape backing on my primary and my secondary has little surface area. I think I might experiment with both the 1 watt resistors and the nichrome wire. Not Realy sure on how many resistors I need.

Looking at this guide

https://www.deepskywatch.com/Articles/n ... eater.html

[yobbo89]

well project fell short, mmy kendrick controller dosn't work.. i tested it once and put it away ages ago

[Graeme1858]

well project fell short, mmy kendrick controller dosn't work.. i tested it once and put it away ages ago

That's a shame!

Looking at this guide

https://www.deepskywatch.com/Articles/n ... eater.html

Well the project might not have worked but the deepskywatch link is a good one!

Thanks

Graeme

[Juno16]

Hi Rob,
I used homemade dew heaters for years.
I tried the resistor method. It worked, but it was troublesome to limit flexing as not to break a solder connection.
The nichrome wire/duct tape works great. I bought the wire from Jacobs Online. They sold different gauges with varying ohms/ft.
I used them for years, but they looked kind of funky and they left the tape glue residue on my tube.
I ended up buying Dew-Not straps and used them with the super cheap led lighting controllers that I bought on Amazon for about $4.

[attachment=0]IMG_5546.jpeg

I still use the cheap led light controllers (about 5 years). One setup for each scope controlling two dew strap each (I try to size the straps appropriately so that I can use a single controller).
So, if you consider going with a homemade setup, consider using a let lighting controller.

[yobbo89]

I tested all the doids, caps, resistors, Leds,resetable fuse they all are in spec. Just need some ic schematics. It's got to be a voltage regulator, mosfet or the Pic16f916 that's bad


Bodge job, never seen a product with this, didn't even hot glue the cap, rethinking buying another Kendrick..

[yobbo89]

Hi Rob,
I used homemade dew heaters for years.
I tried the resistor method. It worked, but it was troublesome to limit flexing as not to break a solder connection.
The nichrome wire/duct tape works great. I bought the wire from Jacobs Online. They sold different gauges with varying ohms/ft.
I used them for years, but they looked kind of funky and they left the tape glue residue on my tube.
I ended up buying Dew-Not straps and used them with the super cheap led lighting controllers that I bought on Amazon for about $4.

[attachment=0]IMG_5546.jpeg

I still use the cheap led light controllers (about 5 years). One setup for each scope controlling two dew strap each (I try to size the straps appropriately so that I can use a single controller).
So, if you consider going with a homemade setup, consider using a let lighting controller.

Hmm I might just do this, beats standing out in the cold with a hair dryer xd

[Lady Fraktor]

UlteriorModem (Tom) used to build dew straps for people.

I use the Kendrick controller/ straps, some of them are 15 years old and other than sewing in a new piece of the stretch material they still operate well.

[yobbo89]

Hi Rob,
I used homemade dew heaters for years.
I tried the resistor method. It worked, but it was troublesome to limit flexing as not to break a solder connection.
The nichrome wire/duct tape works great. I bought the wire from Jacobs Online. They sold different gauges with varying ohms/ft.
I used them for years, but they looked kind of funky and they left the tape glue residue on my tube.
I ended up buying Dew-Not straps and used them with the super cheap led lighting controllers that I bought on Amazon for about $4.

[attachment=0]IMG_5546.jpeg

I still use the cheap led light controllers (about 5 years). One setup for each scope controlling two dew strap each (I try to size the straps appropriately so that I can use a single controller).
So, if you consider going with a homemade setup, consider using a let lighting controller.

ok i found a controller, would know how many amps for the psu i would need roughly?

https://au.mouser.com/ProductDetail/JKL ... XoQAvD_BwE

[Graeme1858]

ok i found a controller, would know how many amps for the psu i would need roughly?

https://au.mouser.com/ProductDetail/JKL ... XoQAvD_BwE

Hello Rob

My STC has a heated dew shield and a lens heater ring. They pull 1.5A and 0.8A at 80% on 12V. Not sure which is which! 2A should suffice. So go for 3A!

Your link is broken, it says the site is temporarily unavailable.

Graeme

[Juno16]

It would depend on the size of the dew heater strip.
I found this one on Highpoint Scientific for an 8" diameter (30" long) that draws 14 watts at 12vdc (1.18A). https://www.highpointscientific.com/dew ... trip-dn009.

So, like Graeme said, maybe 3A?

I bought several (I think that I have 7 total) LED 12vdc power supplies (5 amp and 6 amp that run of household power) to power my mount, cameras, focuser, all of that stuff. They are cheap and work well.
I use one dedicated to the dew heaters.

[yobbo89]

ok i found a controller, would know how many amps for the psu i would need roughly?

https://au.mouser.com/ProductDetail/JKL ... XoQAvD_BwE

Hello Rob

My STC has a heated dew shield and a lens heater ring. They pull 1.5A and 0.8A at 80% on 12V. Not sure which is which! 2A should suffice. So go for 3A!

Your link is broken, it says the site is temporarily unavailable.

Graeme

OK cheers, I have a spare 5amp,i got two of those controllers from your image , they are the same ones from mouser, I also got some replacement components for my Kendrick and another pic16, but doubt Kendrick would give me firmware to Flash it.

[yobbo89]

UlteriorModem (Tom) used to build dew straps for people.

I use the Kendrick controller/ straps, some of them are 15 years old and other than sewing in a new piece of the stretch material they still operate well.

Very nice, I'd love to see an image of one of his or someone else's they made, atm I'm just going to wrap it in duck tape..

[Juno16]

UlteriorModem (Tom) used to build dew straps for people.

I use the Kendrick controller/ straps, some of them are 15 years old and other than sewing in a new piece of the stretch material they still operate well.

Very nice, I'd love to see an image of one of his or someone else's they made, atm I'm just going to wrap it in duck tape..

I just recently tossed my home made duct tape straps! I made them just shy of the circumference of the tube/shield and used a small piece of adhesive velcro to secure it to the scope. The duct tape/nichrome wire straps worked great for years.
Be aware though, soldering to nichrome wire is challenging. Do try it on a test piece first to get an idea.

I do still use the controllers that I sent you an image of, but I like the neat look of the DewNot strips. They are not too expensive and they look and feel nice.

Good luck and let me know how it goes!

[yobbo89]

Woops, i purchased 3m ohm instead of 330ohm resistors, guess I'll try the nicrom wire

[Graeme1858]

That would be ok if you put 1000 of them in parallel!

[yobbo89]

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?

[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?

Hi Rob,

I am a super rusty on the calcs, but I would think that you would need to lower the resistance to lower the heater wattage?

Maybe make a new strip with less nichrome wire or obtain a different ohm/meter wire gauge to allow you to make a couple of loops of wire for the heater strip.

Again, I haven't done this in awhile, but what I originally did was to look for a commercially made strip for the length that I needed.

For example, for my 4" frac dew shield has about a 6" diameter. (I put the sew strip on the dew shield).

I looked up the wattage for a dew strip for a 6" scope and found this. https://www.highpointscientific.com/dew ... trip-dn007.
The wattage for this 6" strip is 9.6 watts (I rounded it to 10). So, that is the wattage that I went for.

Using the calculation V*V/P=R (vdc*vdc/power=resistance), I calculated 12*12/10 = 14.4 ohms. So I needed enough nichrome wire to total 14.4 ohms to give me a 10 watt strip.

I bought 28 gauge nichrome wire so that I could get about two wraps of wire around the length of the strip. A 6" diameter strip would be about 18" long, so I wanted a nichrome wire gauge that would enable me to use a piece of wire about 36" (3 ft).
28 ga nichrome wire is 4.25 ohms/ft, so 3 ft would give me the resistance of 12.75 ohms. I just added a small bit extra (started a third wrap) to get to the needed 14.4 ohms.
You can actually place a ohm meter probe at one end of the wire and slide it down the wire until the desired resistance is obtained and cut it there.

Extremely, extremely poor diagram.

[Graeme1858]

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

[yobbo89]

Well that cheap dimmer controller died, only outputs 12v now, switch over to my backup one as I purchased 2, it's min v range is 10v, anyway I folded my Current cut piece of nichrome wire 4 times so it's running in parrell with 4x 125mm, the connection is 0.9 ohms, the wire heats up to 40 deg at 10v and I dial it to 12v and it's 70-80 deg. Resistance/power is my weak point in electronics

This is for my secondary mirror so I need a small heater , does this look right ? well i know the scope will suck alot of heat out of the wire, i just don't want to cook anything .

[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 ..