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philjdowns

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  1. Finally! Got an evening where it's worth setting up (apparently ?) so here's my completed heater installed, connected and running at 750mV (0.04W) to keep the primary a little above ambient as the temperature drops - fingers crossed. Not expecting to get much imaging done, for a start my NB filters still haven't arrived - two months overdue ? and as I've re-located my primary going to have to spend a while finding the correct focus point again. I've got an elasticated weather seal bag for the bottom of the OTA but again that still hasn't arrived so I'll be getting some air flow up the tube at
  2. @KevS Don't think were supposed to post links to other sites here, but if you search for it (using your favourite search engine ?) you'll find it quickly enough. Phil.
  3. Just a thought, anybody here donating unused computer cycles to the MilkyWay@home project, or any others? We could start our own team ? Phil.
  4. Quick update, I have run a test with the mirror assembly removed from the OTA, and in my workshop. Ran the heater at 3v for 30 mins, then switched off for 5 mins, then on at 250mV for 150 mins, logging the mirror temperature every 5 mins. Started at 16.1°, after 30 mins it was at 17.6°. A larger temperature increase than I wanted, but still safe. Setting the heater at almost the lowest setting (250mV) the temperature gradually fell over the next 2.5 hours to 16.5° So I now know that 3V is too high for the initial heat for my mirror, so the next test will be at 2.5V, and I'll up the the steady
  5. @KevS Thanks Kev, very interesting. though I'm not using fans to cool my mirror (it's kept in an unheated outhouse so it's always at ambient or very close) it's given me an idea of the radiant heat loss from my mirror. I'll be actually heating my mirror to about 1° above ambient then hopefully maintaining that temperature, my lowest setting for my heater grid (200mV) in theory equated to 0.00015W sop that's looking promising. My plan is to set-up and then set the heater to 3v? for 20 mins (I'll be checking the temperature all the way at first) I'm looking for a guide voltage that will give me
  6. @Jkulin Hi, yes I agree that my heater is capable of outputting way more heat than I'll ever need, I just wanted to make sure that if it accidentally got connected at full voltage (12v) it wouldn't go up in flames. I'm going to start at about 0.8v (if I ever see the sky again ? ) so that's calculated at 0.05W total (0.001W/in²), I'm not sure how to work out the rate of heat loss from the mirror but it's likely higher than 0.001W/in², so I need to find the voltage that matches the heat loss and keeps the mirror above the dew-point. It's going to take a while to calibrate things I know, but I'm
  7. Hi All, Well, no-one commented that I shouldn't so, I've mounted the lattice to a 1mm PVC sheet, and mounted the controller as well. Then fitted the unit into my primary mirror housing. (you can see where the original fan and connection points were) There will be a small plastic cover over the controller when it's all back together and tested. The added weight of this is only just over the weight of the removed fan so that's good. Now to fit the mirror, and re-install the housing into the OTA, re-collimate and find my new focus point as the mirror is 4.5mm closer to the front of the tube. I'v
  8. Information on my home built Dew heater posted here Forum | Backyard Astro Hope that works ?
  9. Hi All, After some re-thinking, finally built the first (well second really - won't mention the first one ?) operational version of my heater for my 8" Newtonian primary mirror. As you may have seen from earlier posts, I have serious dew problems! Soak testing here at 12.2v (0.912A - 11.4W) been running for a couple of hours and it's about as hot as I can stand on my fingers. Doubt very much if it'll ever be running this high for real, but I need to know it will not have any issues if accidently left on max output (though I doubt this much heat will do the mirror any favours!) Based on a sta
  10. OK, so I've had a dig about and found enough components to make a flat plate heater for my 8" primary without buying anything - Thats a result! I've done a few tests and have the following data (hope this works, a copy/paste from Excel!): 10W seems the maximum around for an over-the-counter 8" mirror heater, what I have gets me to 12W, though I'm expecting to be using the lower (green) levels as I only have to warm the mirror to 1°(ish) above ambient and then match the heat loss of the mirror to keep it there. Does anybody have figures that they use - as in W/in² ? Or how many Watts they use t
  11. @petedevon Hi, yes I have a "SkyWatcher F4 Aplanatic Super Coma Corrector" it's optimised for f4 which matches my OTA. Getting started I thought I could get by without for a while but even before I had my imaging train fully completed, I was seeing some truly horrible coma which was also causing me problems focussing, and only the centre 1/5 of the image was even passable. So jumped straight for the Aplanatic. There are cheaper ones out there but you get what you pay for. Stars are now nice little points so it's doing it's job well, as far as I can tell at this stage. It was a bit of a pain ge
  12. I've got an Orion Astrograph 200mm, just the one scope, almost got everything I'll need ? Got the primary out at the moment, building a dew heater.
  13. Thanks, thought I might get away with it as my primary has a fan on the back blowing ambient air over the back of the mirror, so looks like I need to change tack. The dew heaters I have found are mostly the strap kind that fits round the outside of the tube, so that's going to be 1/2" from the edge of the mirror. Would it be better to warm the mirror directly? I'd have thought that providing a small amount of heat to the edge of a large circular mirror will only warm the outside edge, as the mirror will dissipate the heat quickly, leaving the centre 1/2ish still liable to condensation. Would i
  14. Hi All, I'm having a problem with moisture / dew on my Newtonian mirrors and was wondering if anyone has a working solution. Today I got set-up and before dark took 100 Flats, then after dark 100 Darks, went to uncover the scope for my Lights, and it was running with water, within 5 mins of taking the cap off I had condensation forming on my primary, so gave up and covered it all up. Now I was thinking of using some Baader TurboFilm (Clear) to seal the front of my tube, then bagging the bottom round the primary and adding 1/2lb of desiccant to absorb any moisture in the tube (drying the desicc
  15. After much messing about, I finally assembled it all - looks good to me but what do I know! Spent last evening fine tuning my polar alignment (then removed the polar scope) and getting to grips with the robot focuser (auto focus in APT was getting nowhere, need to increase the steps as this is uses tiny steps!) Got the cameras rotated to match, autoguider focussed (that was a pain) Waiting to fit the NB filters to the wheel (I've only got a IR/UV cut in there for now) they still haven't shipped yet - Ho Hum.... Everything should be remote now (apart from the cover and caps!) running two cable
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