How many amps can each channel handle? It looks like the MOSFETs can handle way more than most dew heaters, but I'm not enough of a electrical engineer to know where the other limits might be.
Between my C8, the refractor I've got piggybacked, my guide scope/finder, eyepieces for each, and a hand controller warmer, I've got a need to handle 7 heaters. The eyepiece ones are for 2" eyepieces (0.35 amps each) and the hand controller one is (0.21 amps).
I'm less worried about temperature control for the eyepiece and hand controller, especially since they don't draw much power anyways.
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The real limit is not dependant on the MOSFETS - it is going to be the PCB tracks being able to handle the currents involved without melting away.
I have made the power tracks for the MOSFETS and Dew Channels larger, I would think each channel could carry up to around 3A without issue.
The 10A10 diode is rated at 10A and the Fuse is 10A. So we have around 8A easy to use before getting into any issues. Assuming of course that the MOSFETS use heatsinks and the case is ventilated.
So 4 channels of 2A each - power is PWM'd - it would be possible to run 2 channels higher and 2 channels lower for a period of time. And if you needed say 4A worth of heat then I would recommend using ch3 mode to mirror ch1 or ch2. Then you get two dew straps (say ch1 plus ch3mode set to ch1) worth 4A of heat.
If things get too hot we would have thermal runaway so if you were planning to run things towards max output then you would want to use a cooling fan to extract hot air out of the case.
I've got an older Kendrick Astro controller that I use today, I could use that for the smaller heater but I was sort of hoping I could avoid running another wire for power. I've got a pretty good rats nest of cable going on already :)
The Kendrick Astro heater for my C8 objective is about 1.6 amps.
The Dew-Not heater for my little refractor is about .6 amps.
My Dew-Not 2" eyepiece heaters (2 currently) are about .35 amps each, and the hand controller is about .21 amps.
Heaters for the finder/guider and the eyepiece would be about another .75 amps total.
Ideally, I'd like to run each scope (objective and eyepiece) on it's own channel, which would lead to this:
Hi Tom
One point to consider is that the output is PWM - hence the current draw is always going to be less that calculated maxium output.
In addition, it is unlikely that the channels would run continually at 100% output all the time, as the power algorithm is stepped to try and provide the optimal power output required to prevent dew from forming. If 100% output was required then there are safegards in the firmware to try and throttle that back after 2 minutes.
If you were requiring 100% output all the time to keep dew from forming then I would suggest you need something better than a dew controller - perhaps a blow torch or flame thrower might be the order of the day?
A review of the logging data should be able to provide you what is happening in relation to dew channel power output. The myDCP4ESP32 has such logging capability.
regards
Robert
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How many amps can each channel handle? It looks like the MOSFETs can handle way more than most dew heaters, but I'm not enough of a electrical engineer to know where the other limits might be.
Between my C8, the refractor I've got piggybacked, my guide scope/finder, eyepieces for each, and a hand controller warmer, I've got a need to handle 7 heaters. The eyepiece ones are for 2" eyepieces (0.35 amps each) and the hand controller one is (0.21 amps).
I'm less worried about temperature control for the eyepiece and hand controller, especially since they don't draw much power anyways.
Hi Tom
The MOSFETS have a maximum rating of 30A
The real limit is not dependant on the MOSFETS - it is going to be the PCB tracks being able to handle the currents involved without melting away.
I have made the power tracks for the MOSFETS and Dew Channels larger, I would think each channel could carry up to around 3A without issue.
The 10A10 diode is rated at 10A and the Fuse is 10A. So we have around 8A easy to use before getting into any issues. Assuming of course that the MOSFETS use heatsinks and the case is ventilated.
So 4 channels of 2A each - power is PWM'd - it would be possible to run 2 channels higher and 2 channels lower for a period of time. And if you needed say 4A worth of heat then I would recommend using ch3 mode to mirror ch1 or ch2. Then you get two dew straps (say ch1 plus ch3mode set to ch1) worth 4A of heat.
If things get too hot we would have thermal runaway so if you were planning to run things towards max output then you would want to use a cooling fan to extract hot air out of the case.
I would be tempted to use the dew controller for the main scope and the guide scope.
I would probably use a different method of controlling the eyepieces and hand warmer - such as
https://www.ebay.com/itm/12V-24V-8A-Switch-Dimmer-Brightness-Controller-Power-Save-for-LED-Strip-Light/324352740670
regards
Robert
Thanks for the reply Robert.
I've got an older Kendrick Astro controller that I use today, I could use that for the smaller heater but I was sort of hoping I could avoid running another wire for power. I've got a pretty good rats nest of cable going on already :)
The Kendrick Astro heater for my C8 objective is about 1.6 amps.
The Dew-Not heater for my little refractor is about .6 amps.
My Dew-Not 2" eyepiece heaters (2 currently) are about .35 amps each, and the hand controller is about .21 amps.
Heaters for the finder/guider and the eyepiece would be about another .75 amps total.
Ideally, I'd like to run each scope (objective and eyepiece) on it's own channel, which would lead to this:
Channel 1: C8 objective + Eyepiece heater = 1.95 amps
Channel 1: Refractor + Eyepiece heater = .95 amps
Channel 3: Finder/Guider + Eyepiece = .75 amps
Channel 4: hand controller = .21 amps.
The only channel that might be close to the limit is channel 1.
I could move the eyepiece heater to any other channel to get a little head room on channel 1.
Any flaws in my logic?
Last edit: Tom Hayko 2020-12-24
Hi Tom
One point to consider is that the output is PWM - hence the current draw is always going to be less that calculated maxium output.
In addition, it is unlikely that the channels would run continually at 100% output all the time, as the power algorithm is stepped to try and provide the optimal power output required to prevent dew from forming. If 100% output was required then there are safegards in the firmware to try and throttle that back after 2 minutes.
If you were requiring 100% output all the time to keep dew from forming then I would suggest you need something better than a dew controller - perhaps a blow torch or flame thrower might be the order of the day?
A review of the logging data should be able to provide you what is happening in relation to dew channel power output. The myDCP4ESP32 has such logging capability.
regards
Robert