Hello thank you for this video! Would this work for eyepiece strips also? I'm a novice so unsure how that many less resistors will affect the build, i mean would it over heat? Thank you for the video again!
An eyepiece strip wouldn't necessarily overheat but you wouldn't need the 3 watts of heat this produces. Using the formula of Ohms=(voltage^2)/watts for a one watt heater, you'd need 144 ohms. Use three 47 ohm resistors arranged around the eyepiece to get 141 ohms which would be close enough (you'd get slightly more than 1 watt of heat). Use half watt resistors and you won't have to worry about causing them to burn out.
Love your video. I have a 12” Newtonian , it’s about 42” around . How many resistors would I need ? And also for the secondary mirror ? I have a Thousand Oaks dew heater controller . Thanks
I'm not sure how much voltage is put out the the Thousand Oaks dew heater so that's one factor. With a Newtonian, unless it's open tube, you probably don't really need a dew heater for the primary. It takes a LOT for condensation to reach that far down the tube. But if you do need one, you're probably looking at a 6 watt dew heater. For the secondary, you can probably get away with a 1 or 2 watt heater. To calculate the resistance you'll need, use the following formula: Ohms = Voltage^2/Wattage So if you've got 12 volts, to generate 2 watts, you're looking at 72 ohms. To generate 6 watts, you're looking at 24 ohms. Now figure out the circumference and come up with how many resistors can fit in that space. Divide the total number of ohms by that number to get how much you'll need per resistor. On the primary of a Newtonian, don't use the diameter of the tube but the diameter of the mirror. The dew heater will go inside the tube because you want to get it as close to the glass as you can. I hope this helps. If you have more questions, please feel free to ask!
Very well explained sir. Thank you for the video. A small question though (I am a novice on electronics), what is the approximate heat generated by this?
The only reason you'd need to be concerned with orientation is because you're using the color bands as a way of measuring the spacing between the resistors. You could measure from any point of reference on the resistor but you want something that is consistent from resistor to resistor. I hope that clears it up.
if i wanted to run a 2 watt heater off a 16650 battery, am i right to assume that i would need resistance roughly equaling 6.85 ohms? if i went to say, 7 ohms it would just make me a slightly less than 2 watt heater right? the only other thing i'm confused about is what benefit i have changing the watt rating of a resistor. i thought that was their rated consumption but that can't be correct.
From what I can see, the 16650 battery puts out 3.7 volts. So, yes, for a 2 watt heater, it would come to a total of 6.845 ohms. That's going to draw slightly more than ½ amp. So a 1 amp hour battery would last about 2 hours. You might make a ring of 7 resistors each at 1 ohm. Each resistor would have to contend with 0.286 watts so ½ watt resistors would work well. The watt rating on the resistor isn't the determining factor of how much current it can draw. It's a matter of how much it can draw before it pops. If you put 1 watt of power through a ½ watt resistor, you'll burn out the resistor. As for the formula for determining how much resistance you need for a specific wattage output, it's Ohms = Volts^2/Watts. The number of resistors was based on the rating (say ½ watt) and the number of watts (3) then I'd want to use a minimum of 6 resistors so I wouldn't overload the rating. To be on the safe side, I might go with 8 so each one would generate 3/8 watt. I might do a follow up to this video to explain the math behind all of it. And I apologize for the delay in replying. Computer troubles.
Nice. Do anyone know the math behind the ammount of resistors? Think ill give this a try, sucks to have no electrical skills tho haha. I happen to have a ton of resistors at hand and i find the dewheaters to be way more expensive then they should be, could be fun to try build something instead!
First, figure out how much heat you need to generate. An 8" Cassegrain like I have takes about 3 watts to keep clear. A finder scope or smaller objective might be as little as 1½ watts. Then determine the resistance you need based on your power supply. The formula is: Ohms = Volts^2/Watts In my case, it was (12 volts)^2/2 = 72 ohms. From that, find a value for each resistor, such as 6 ohms and divide to get 12 resistors. As for the wattage rating, make sure that the total combined wattage for each resistor is greater than the number of watts you hope to generate. In the example above, each resistor would generate ¼ watt of heat so using ½ watt resistors gives me a bit of a margin for error. I hope this helps. Sorry for not replying sooner. Computer problems.
@@planetofmystery4787 Awesome explination, tyvm. Im sure others also will have much use for this. Ive built two bands already and they have worked very well. They ended up a tad lower powered that I expected but close enough :D
hello great video i have a question through. when you measured the spacing of the resistors why did you say to use the same mark on the same ends of both resistors but on the video you showed to have used one side black and the other resistor the red to measure the 46.25 mm? reason i am confused it because you mention to use the same band to measure the distance but in the video you are showing to use two different sides or color bands. you are measuring from black to red to measure the 46 mm. please any advice would help and thanks again
On the resistors I used, there were bands on both ends so the orientation doesn't matter (I think I mention that at some point). If your resistors have bands at only one end, you are absolutely right about making sure they have the same orientation when you measure. Good of you to catch that!
@@planetofmystery4787 AHH IC ok you mean on the same ends in this case the band all the way to the right . that would be my measuring point end to end from right end to right end. I ordered the same exact resistors on your link you are awesome sir thank you! Clear Skies! how has to heater held up to the dew? my resistors come tomorrow.
@@GalileoUAS Mine worked quite well when the weather was warm and humidity was my biggest problem. I'm preparing to make one with half as many resistors (so I'll have to use wires between the resistors) which will double the heat output from 3 watts to 6 watts. These resistors should be adequate to handle the 3/4 watt they each generate but I'm not sure I'd want to push it beyond that. Ad astra!
so the resistor code does not come down to red black black... it's a 4 band resistor with code "orange, black, black, silver with 1% tolerance (brown)"...
Hello thank you for this video! Would this work for eyepiece strips also? I'm a novice so unsure how that many less resistors will affect the build, i mean would it over heat? Thank you for the video again!
An eyepiece strip wouldn't necessarily overheat but you wouldn't need the 3 watts of heat this produces.
Using the formula of Ohms=(voltage^2)/watts for a one watt heater, you'd need 144 ohms. Use three 47 ohm resistors arranged around the eyepiece to get 141 ohms which would be close enough (you'd get slightly more than 1 watt of heat). Use half watt resistors and you won't have to worry about causing them to burn out.
Love your video.
I have a 12” Newtonian , it’s about 42” around . How many resistors would I need ? And also for the secondary mirror ? I have a Thousand Oaks dew heater controller .
Thanks
I'm not sure how much voltage is put out the the Thousand Oaks dew heater so that's one factor.
With a Newtonian, unless it's open tube, you probably don't really need a dew heater for the primary. It takes a LOT for condensation to reach that far down the tube. But if you do need one, you're probably looking at a 6 watt dew heater.
For the secondary, you can probably get away with a 1 or 2 watt heater.
To calculate the resistance you'll need, use the following formula:
Ohms = Voltage^2/Wattage
So if you've got 12 volts, to generate 2 watts, you're looking at 72 ohms. To generate 6 watts, you're looking at 24 ohms.
Now figure out the circumference and come up with how many resistors can fit in that space. Divide the total number of ohms by that number to get how much you'll need per resistor.
On the primary of a Newtonian, don't use the diameter of the tube but the diameter of the mirror. The dew heater will go inside the tube because you want to get it as close to the glass as you can.
I hope this helps. If you have more questions, please feel free to ask!
@@planetofmystery4787 thank you for the great help! Very useful information !!!
Very well explained sir. Thank you for the video. A small question though (I am a novice on electronics), what is the approximate heat generated by this?
At 12 volts DC, this will generate about 3 watts of heat.
Why does a resistor care which direction it's connected?
They carry current either way, right?
The only reason you'd need to be concerned with orientation is because you're using the color bands as a way of measuring the spacing between the resistors. You could measure from any point of reference on the resistor but you want something that is consistent from resistor to resistor.
I hope that clears it up.
@@planetofmystery4787 Thanks
if i wanted to run a 2 watt heater off a 16650 battery, am i right to assume that i would need resistance roughly equaling 6.85 ohms? if i went to say, 7 ohms it would just make me a slightly less than 2 watt heater right? the only other thing i'm confused about is what benefit i have changing the watt rating of a resistor. i thought that was their rated consumption but that can't be correct.
From what I can see, the 16650 battery puts out 3.7 volts. So, yes, for a 2 watt heater, it would come to a total of 6.845 ohms. That's going to draw slightly more than ½ amp. So a 1 amp hour battery would last about 2 hours.
You might make a ring of 7 resistors each at 1 ohm. Each resistor would have to contend with 0.286 watts so ½ watt resistors would work well.
The watt rating on the resistor isn't the determining factor of how much current it can draw. It's a matter of how much it can draw before it pops. If you put 1 watt of power through a ½ watt resistor, you'll burn out the resistor.
As for the formula for determining how much resistance you need for a specific wattage output, it's Ohms = Volts^2/Watts.
The number of resistors was based on the rating (say ½ watt) and the number of watts (3) then I'd want to use a minimum of 6 resistors so I wouldn't overload the rating. To be on the safe side, I might go with 8 so each one would generate 3/8 watt.
I might do a follow up to this video to explain the math behind all of it.
And I apologize for the delay in replying. Computer troubles.
Nice. Do anyone know the math behind the ammount of resistors? Think ill give this a try, sucks to have no electrical skills tho haha. I happen to have a ton of resistors at hand and i find the dewheaters to be way more expensive then they should be, could be fun to try build something instead!
First, figure out how much heat you need to generate. An 8" Cassegrain like I have takes about 3 watts to keep clear. A finder scope or smaller objective might be as little as 1½ watts.
Then determine the resistance you need based on your power supply.
The formula is:
Ohms = Volts^2/Watts
In my case, it was (12 volts)^2/2 = 72 ohms.
From that, find a value for each resistor, such as 6 ohms and divide to get 12 resistors.
As for the wattage rating, make sure that the total combined wattage for each resistor is greater than the number of watts you hope to generate. In the example above, each resistor would generate ¼ watt of heat so using ½ watt resistors gives me a bit of a margin for error.
I hope this helps.
Sorry for not replying sooner. Computer problems.
@@planetofmystery4787 Awesome explination, tyvm. Im sure others also will have much use for this. Ive built two bands already and they have worked very well. They ended up a tad lower powered that I expected but close enough :D
hello great video i have a question through. when you measured the spacing of the resistors why did you say to use the same mark on the same ends of both resistors but on the video you showed to have used one side black and the other resistor the red to measure the 46.25 mm? reason i am confused it because you mention to use the same band to measure the distance but in the video you are showing to use two different sides or color bands. you are measuring from black to red to measure the 46 mm. please any advice would help and thanks again
On the resistors I used, there were bands on both ends so the orientation doesn't matter (I think I mention that at some point). If your resistors have bands at only one end, you are absolutely right about making sure they have the same orientation when you measure.
Good of you to catch that!
@@planetofmystery4787 AHH IC ok you mean on the same ends in this case the band all the way to the right . that would be my measuring point end to end from right end to right end. I ordered the same exact resistors on your link you are awesome sir thank you! Clear Skies! how has to heater held up to the dew? my resistors come tomorrow.
@@GalileoUAS Mine worked quite well when the weather was warm and humidity was my biggest problem. I'm preparing to make one with half as many resistors (so I'll have to use wires between the resistors) which will double the heat output from 3 watts to 6 watts. These resistors should be adequate to handle the 3/4 watt they each generate but I'm not sure I'd want to push it beyond that.
Ad astra!
and is the power supply AC or DC?
DC. It's possible to use batteries to run the dew heater but due to the current drain, they'd run out pretty quickly.
so the resistor code does not come down to red black black... it's a 4 band resistor with code "orange, black, black, silver with 1% tolerance (brown)"...
Correct. Each resistor is a three ohm, 1-watt (for heat dispersion). I was able to find them online.