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Everything posted by jambouk

  1. Does anyone have any recommendations of small wind turbines (200 to 600W I suppose) to trickle charge a 12v battery for an off-grid location? Already have solar for another battery so don't want to discuss solar here. Exposed and relatively windy location. My research suggests horizontally arranged blades are much more efficient than the lantern type (vertical) blades. Thanks. James
  2. Thanks all. So is there a way to estimate the percentage dischrage of both batteries in this scenario? James
  3. Assume I have two identical brand new 12v batteries, each with 200 amp hour capacity. One drives a 12v motor which pulls 60 amps and the motor is run for 5 minutes. The other battery is connected to a smaller motor which pulls just 5 amps but is run for 60 minutes. I'm assuming both batteries have discharged 5 amp-hours worth of their capacity (2.5%). Have both batteries really taken the same "hammering"? Thanks for any replies. James
  4. I use an old laptop power supply and it delivers 15.5v I think.
  5. The thermosphere and exosphere boundaries do not seem to be static, with changes induced by the varying pressure of the solar wind. Do changes in the strength of the solar wind result in alterations in the altitude of low earth satellites? James
  6. We have a copy of this in the Library of the Society for the History of Astronomy, 1958. It seems it was written / edited by EW Playfair according to my notes. James
  7. My set up, I adapted a laptop charger and soldered the leads together and it delivers 16v and 5amps and I’ve not had a problem with it.
  8. I would highly recommend this book, can be purchased online for under £15 second hand, a newer edition exists but is more expensive since, it really does a wonderful job talking through the basics: Back
  9. If going away from home where there is no mains power then you need batteries. Leisure batteries are best, but heavy. Work out how many watts everything needs per hour of use. Work out how many hours you want it to last for. Then I would double that number, and then ideally double that number again. That is the size of the battery you need. you need to work out how to make your connections more stable. Unreliable power supply is not acceptable.
  10. I’d get a second power lead, and cut the non-telescope end off, and attach the relevant connector(s) for the power unit you are using. Just get polarity correct else it will all blow up.
  11. I suspect you’d get £75-£150 for the mount. I wouldn’t bother with a wedge. Try wide field with it with a DSLR. Else get rid.
  12. SCT you’d need to off-axis guide. Reflector will be long and unwieldy. I don’t have experience of the other two. Have Mak-Newtonians gone out of fashion? Is this all inside an observatory or will be set up each night?
  13. If it is just for imaging I would avoid adding further optical surfaces into the mix and not use a diagonal.
  14. I suspect it could. Just need to work out the balance.
  15. Yes, really nice. Do a custom white light balance with the fitler in situ to make the colours more natural and less blue. James
  16. JP-S, invariably these things are not just the result of one issue. I think sorting out the flattener and its spacing would be a good place to start. I suspect if your PA is <1' then it is less likely to be field rotation. James
  17. Flat field and maybe some field rotation, how good if your polar alignment?
  18. Interesting. If there are no encoders, it must have some kind of marker on the gearing, but whatever, glad it is working.
  19. I don’t know this set up but things which come to mind are: Does it work with the handset (as in is there an issue with the phone software / communication side of things?) Are the leads to the RA and Dec the correct way around? Does it have any encoders? Can these be turned off to see if they are causing problems? Where does it all get it’s time, date and location from? Are these correct? Ignoring alignment, does it track, and slew as expected? If you do a one star alignment what happens? At the start of the video you said something about azimuth 360 degrees, but then said something about 61 degrees, what was that? Good luck
  20. It’s not the weight which is the issue it is the length and balancing and rigidity, and that is before you add a camera on to one end of the scope. Get it and give it a go, and if it doesn’t work, sell it on. James
  21. I recall being told some time ago that SCTs don't exhibit chromatic aberration as the last optical surface the light interacts with is a mirror before reaching the observer, which is why there is no chromatic aberration in SCTs. Thinking about this as I prepare a talk for my local astronomical society, this is rubbish, well bits of it anyway. Mirrors which are silvered on the light path side of glass have minimal (no) action in reflecting different wavelegths in different ways; I suspect traditional mirrors which are silvered on the other side of the glass and where light has to travel through the glass, get reflected and then have to travel through the glass again, may be different. Anyway, this made me wonder [again] why there is no chromatic aberration in SCTs as the corrector plate is a single [simple] lens. Is this because the refractive index of the corrector plate is so low, that the amount of chromatic aberration is just so small it is not noticeable? Or is there something else? Thanks for any replies. James
  22. Whatever order I place them all in, the lens are not tight, as though I've lost a spacing ring, which I don't think I have and which wouldn't have anywhere to go anyway. I got the eyepiece for £10, and have never used it and looking online it is dire anyway, so I'm going to pass it on to a friend who likes to tinker and see if he can re-arrange them and get it to work. Thanks. James
  23. Yes I found that thread but not convinced any of them match what I've got... James
  24. Has anyone ever taken one of these apart and know how to put it back together... luckily everything fell out onto a towel. James
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