Telescope Reviews: Re: Write up for peltier cooling an SCT

I like your idea for a switch Jim. I have thought about adding one switch that turns off the Peltier, but continues running both fans. I have noticed that peltiers briefly get warm on the cold side when you turn off the power. Keeping the heatsink fan running should help minimize that.

I too am a relative newbie to these peltiers, but I've learned a few things so far with the 2 models I've experimented with now, and from what info I've read online.

I'm modding my C11 very similar to how Paul Haese did his C14 since mine's an SCT. I'm going to use an M-size, panel mount, coaxial power jack by just drilling a larger hole into the back of the cell. It plugs into my switching PS perfectly. I'm still on the lookout for a similarly sized push button switch (Radio Shack had nothing I liked). I'm thinking right there in between the C11's metal handle is the perfect spot for them. Then my wires will mostly be inside the OTA, except right there at the cooler, and the mirror temp. sensor.

I'll also say that as far as I can tell the total peltier heat generated is a bit less than the wattage of the TEC (amps times volts used) plus the rated Qmax (energy transfer from cold to hot side). Peltiers will try to draw their rated amperage, so you really need a switching power supply that is at or is exceeding the peltier's rated amperage (don't forget about the few hundred milliamps for the fans).

I imagine some of the rated wattage isn't dissipated as heat, so it'd be a bit less than this. For example I've decided to use a 72w 6a peltier @ 12v. It's Qmax should be about 50w @ 12v. So it will be roughly 110-115w of total potential heat generated on the hot side. This is right at my chosen heatsink's (Swiftech MCX775-V) heat dissipation rating with a 37.5cfs 80mm fan. I'll also give the heatsink the benefit of the doubt that is has a bit more ability to dissipate heat in a cool outside environment since the heatsink isn't going to be cooped up inside a PC case like its designed for (recirculating hotter air diminishes efficiency and it was designed with that environment in mind). You'll want a bit of overhead like that. The main thing to remember if you're assembling a peltier system from parts, like I am doing, is to make certain you chose an adequate heatsink or you will have a runaway buildup of heat that will eventually lead to fire/meltdown (as the 168w 10a peltier I tested on this heatsink tried to do). I'm pushing it really close to the limit, but I think it'll work out just right. At some point the experiment has to include the mirror cell to really know how efficiently it'll suck heat out of cell (it may not meet Qmax level of efficiency which would be better), so the actual modification is my next step.

I will try to visually document stages of my mod to share here. It might still be a few weeks, depending on my free time next weekend.

One last frame of reference. Paul tells me his peltier units are about 80w @ 12v together for the C14, and they are working good judging by his Jupiter shots. I'm going to use just a bit less at 72w @ 12v and I think it should be more than adequate. This should give you guys a basis on which to choose the power of peltier(s) to use on a given SCT size.

Post Extras