Zermelo

I see there are already accounts within these pages of several, very accomplished power tank projects, hence the title of this piece. The other reason that this was a ‘modest’ project is the intended purpose: servicing a SkyWatcher Star Discovery 150i – an EQ6 it is not. But I thought it might be worth documenting in case anyone else was in a similar position. Context We have recently upgraded from an entirely manual first scope to the 150i, which has tracking, goto and wifi control. The default power option is an internal 8xAA battery pack delivering 12V. Unwilling to keep buying alkalines, I’ve resorted to NiMHs, but these give only around a total 10.4V fully charged, and that’s on warmish summer evenings. Opinion suggests that the mount’s goto accuracy can be impaired if the voltage drops, so I wanted to get off the internal batteries. As an alternative, the Star Discovery mount has a 12V power input socket, and I had already bought a cable with the standard car cigarette lighter plug at the other end. Apart from powering the mount, the other requirements are currently uncertain, but possibly include an electric dew heater or 12V hair dryer for the same purpose, which I assume will probably connect to a cigarette lighter socket. Also, given that the scope control relies on a phone app rather than a handset, a USB charger outlet would be useful for emergencies (and other gadgets might well also run off USB). The one thing we won’t be doing is running a laptop all night, which is what seems to really burn the juice. Choices So we needed, at minimum, a 12V power source with a cigarette lighter socket, and ideally a second socket and one or two USBs. The offerings from astronomical suppliers seemed expensive, and often included gadgets we didn’t need. Standard car batteries were on the heavy side, and would need adapting and connecting. Car jump starters were a bit cheaper than astro kit, but were optimized for short, heavy loads. So I decided to have a go at making a bespoke power pack, where I could choose the physical size, capacity and outlets. The basis would be a smallish sealed lead-acid battery. I settled on 9AH as a reasonable compromise between weight, cost and capacity, but the design allows this to be doubled if necessary. I considered buying a ‘deep cycle’ battery more suited to the observing usage pattern, but decided on a cheaper, standard model for alarms, UPSs, etc. Time will tell if this was false economy. For the casing, I used a 5 litre plastic crate from the Really Useful Box range. I chose these because (a) they are quite robust as boxes go, and (b) they are more nearly rectangular than most. The 5 litre box comes in two versions – I bought the ‘XL’, the only difference being a taller lid. The battery will live at one end of the box, but there will be a similar space at the other end for another if needed. For sourcing the electrical outlets, I found a number of sellers on eBay and Amazon that offer essentially the same range of instrument panels that run off a 12V supply, for installing in cars/motorbikes/boats, at reasonable prices. In particular, I found that a 2-by-2 panel of these instruments just about fitted onto the side of the plastic crate. I ordered one of these sets that included a cigarette lighter socket, twin USB charger, LED voltmeter and on-off switch, though I ordered a separate, second lighter socket to substitute for the switch. All of these sockets and instruments seem to be standard sizes and can be swapped in and out of the panels. The sockets also come in weatherproof versions that have integral rubber plugs, which is ideal. I thought the voltmeter might be useful to show how the battery was dealing with the load (an ammeter would also be useful, but I haven’t seen one that would fit this panel). Usual caveats apply to ordering online, there’s a lot of variation in vendor reliability. And a caution about the voltmeters – red now seems to be the hardest colour to find, most seem to be bright blue (not ideal). Build I chose the particular plastic box because the battery fitted lengthways across it quite nicely, but I knew I’d need to do something to stop it slipping sideways when being carried. My first thought had been to glue in some stout plastic sheeting to create internal compartments, but these boxes are polypropylene, so good luck trying to get anything to stick that. Instead, I decided to create a separate internal frame that would slip inside the box and wouldn’t need to be glued to it. This would create compartments for the batterie(s) and also stiffen the sides where the outlets would go. I had a piece of 6mm ply that was about right – thick enough to do the job, but it still fitted around the battery. I cut out four pieces to create the frame, all of which are 10cm deep (I would have reduced this a bit if I had not been using the 'XL' version of the plastic box, as there's less head room). As the box isn’t quite a cuboid, the longer ones are actually trapezia (or trapezoids if you’re reading this from the US) measuring 28.5cm and 29.5cm on the shorter and longer lengths. The shorter cross-pieces are 15.2cm long. The other pieces are softwood I cut up to brace the joints; there’s no way 6mm ply is going to be joined at right angles without some help. At this point, I used the instrument panel facia to mark out the position of the socket and screw holes on the long side of the plastic box, and cut them out: I then used the holes to mark the positions onto one of the long frame pieces and cut those out. With hindsight I think it might have been better to cut the frame holes, assemble it and then mark and cut the plastic box. I did find it quite fiddly – you need to be careful with the frame, because the outlet holes have to be big enough for the sockets, but if you make them too big there won’t be enough for the securing nut to purchase on later. The holes in the box aren’t so critical because nothing depends on them and they get covered by the facia. Also, assembling the frame inevitably shifts the positions of the holes slightly, causing them not to line up any more. Anyway, in the order I did it, the pieces were assembled in stages, measuring up to ensure there was enough space in the end compartments for the batteries. The softwood pieces form the corners for the ply, so you need just one good 90 degree corner on each one. I used PVA, panel pins and some very small screws (pilot holes to avoid splitting). A picture frame clamp proved useful to keep corners square. When the clamps were removed, the frame was checked for fit inside the box and I gave it a couple of coats of paint. It won’t win any beauty competitions, but it won’t be seen. The four devices can now all be inserted, passing through the facia, the plastic box, and the frame, and secured from the other side with the large plastic nuts (careful not to cross-thread). I added some rubber O rings of the right size that I had, so that the nuts didn’t take the paint off; large neoprene washers would be even better. These devices will hold the panel securely as it is, but the four screws that are supplied for the facia are worth fitting (and also for aesthetic reasons). Right sized pilot holes required so as not to distress the ply. I found the screws to be too long by about 6mm, so cut off about 3mm and then as I screwed them in I held a small rubber grommet against the inside of the frame to receive the tip and brace it still further (a small fibre tap washer would work well) but actually it bit surprisingly well into the ply. All four of the devices in the panel need 12 volts, so they need wiring in parallel, both positive and negative, which needed some thought. One option would have been terminal block strip, but I wanted to use fairly chunky cable as I wasn’t sure how much current might be drawn in future, and that didn’t lend itself well. Instead I created a couple of multiway connections using ring terminals connected by small nuts and bolts – I used locking nuts and spring washers to keep the joints tight – these were all bits I had lying around. The instrument panel kit came with spade connectors and insulators. The result is quite compact. An in-line fuse holder is a must – I managed to short out the battery terminals fairly quickly. At the moment I have a 2A fuse fitted (I put a multimeter on the 150i mount and measured the current at about 0.6A on maximum slewing speed) but I’ll review that according to future use. With the cabling attached, the box looks like this: For now, the other battery compartment is empty, but I used “piggy back” terminal connectors on the battery leads so I would need only to run two wires across the top of the box to add a second battery in parallel. And here it is all working: The lid overhangs a bit, so provides some extra rain protection for the panel. It cost about £40 altogether, half of which was for the battery.

Andrew, the link to your primer article now seems to be dead?

Hi ScouseSpaceCadet , if you have time could you identify the kit you've added here? And do you have any idea how much weight it added?

Hi, you may be interested in a thread I kicked off recently, as I was in a similar position and ended up buying the 150i: https://stargazerslounge.com/topic/356514-advice-please-choice-of-next-scope/ You can still adjust the secondary on the 150i. As it happens, when I did get hold of the scope it was slightly off collimation, but close enough not to need tinkering with the secondary, see: https://stargazerslounge.com/topic/357345-how-far-off-collimation-is-this/ As others have said, the mirror itself is the same, decent-quality parabolic that SW use in their more rexpensive models. And as you have identified yourself, if the primary doesn't actually need adjusting, then that's certainly a plus in my book. The 150 is a clever compromise to be sure; the mirror and the tripod are more than you might expect, while the focuser is probably the weakest feature; but for the price I paid, I'm happy so far. Be aware that instructions for the GoTo are a bit confusing, as those supplied are for the non-wifi version of the mount. There are many threads in these forums that are helpful with the various alignment procedures.

Update. I managed to get a test on Arcturus last night at just over 200x with my shortest EP + barlow. Unfortunately my phone camera refused at those light levels so I'll have to describe the view. When defocused, I saw approx. 6 concentric rings, inner ones dimmer and outer ones brighter. It was shimmering about a bit, but I wasn't surprised at that magnification. At any particular instant there was some random distortion in one direction or other, so I looked over a period of time at (i) the "average" shape of the rings and (ii) their "average" distribution relative to the centre. As far as I could tell, (i) they were circular, and (ii) showed no directional preference. I take this to be good news. As a more real-life test, I included the Lyra double double in the observing schedule later on. I thought it might be a good test of the mirror and alignment, as each pair would be on opposite sides of the FOV, when blown up enough to split them. (I've attempted the double double before with a small refractor, but never succeeded). Impressive. Both pairs split as perfect dots, no tails, orientations at right angles to each other. Based on these tests, I'm not going to bother adjusting the secondary. I'll just check it now and again against my original photo.

OK, I was a bit prematurely worried then. I'll try to do a star test tonight, and depending on the result (and how brave I'm feeling) I'll give it a tweak.

Thanks John, but is that a secondary adjustment, or primary (which I can't do on this scope - at least, not unless I try to emulate the factory process)?

150mm F/5 Newt, as received new, view down eyecap collimator (no adjustments attempted by me): I've read a couple of intro guides, so I'm led to believe that the off centre image of the secondary in the primary is normal for a fast reflector. The whole image of the primary in the secondary seems to be reasonably central too. My concern is obviously that the black dot from the collimation cap is not within the "doughnut" centre marking from the primary. I've tried here to superimpose a circle with centre lines, but I'm not sure if I've got the circle itself correctly positioned (I'm not sure what I should be lining it up against): Now, the interesting thing is that it's one of those jobbies with a sealed, non-collimatable primary. But I believe the secondary has all the usual degrees of movement. Does it look likely to be far out? I can try a star test tonight (first time for that too).

Thanks all, for the replies. The "saddle" I have is actually integral to the mount, it's one of these: https://www.firstlightoptics.com/skywatcher-mounts/sky-watcher-star-discovery-wifi-az-goto-mount-tripod.html so I don't think there's a way to replace it with a third party version. dobblob, the bar/puck attached to the OTA has no overhang or holes, it has an identical section along the entire length (hence my concern about its ability to slip unhindered through the mount). But your point is valid: I could probably drill and tap a single hole at the eyepiece end of the bar, insert a machine screw, and that would catch the OTA against the saddle if it did slip. It might still shake up the optics a bit though! (but the closer I placed it to the saddle clamping screw, the less it would fall).

I have a new scope on a Skywatcher mount with a Vixen dovetail type mount. The scope is a lightweight F/5 150mm Newt. The mount has a single screw that braces the inserted OTA 'wedge' against the opposite side of the dovetail recess. There is no other mechanism to prevent the inserted wedge slipping, so it's basically relying on friction (and on a single, unlocked screw) when the scope is vertical. The first time I used it, I had tightened up the screw as tightly as I dared, but half way through the session I felt the scope slip slightly when pointed upwards, and managed to catch it, but only just! I'm not very happy with this design. My previous refractor had a similar dovetail arrangement, but it had a slightly recessed area to receive the screw, which meant it was more secured against slipping out. I'm thinking of doing something similar with the new scope - countersinking a *very* shallow hole in the centre of the OTA wedge to give the screw something to bite into. An alternative (or additional) ploy might be to line the inside of the mount dovetail recess with some variety of thin, rubbery self-adhesive strip that would grip the OTA wedge more firmly than the existing, smooth metal-against-smooth metal. Is there any reason I shouldn't perform this mod? (other than voiding any warranty, obviously). Clearly I'd be establishing a "preferred" position for the OTA in the mount, so if I needed to rebalance it in future, for whatever reason, then I'd need to repeat the procedure (the OTA has no rings, the wedge is attached directly to the tube).

After another round of agonizing, I've ordered the Star Discovery 150i from FLO. (and also a Hyperflex 7.2-21.5mm zoom, which seems to be well thought of in these parts) Thanks again to everyone who chipped in to the discussion, and I apologize in advance for the obligatory spell of cloudy weather that will hit the south western UK in "approximately 10-15 working days time".

Also remember there are two "ends" to the problem. You want to try to cut out as much of the light that shouldn't be there, but you also want to let through as much as possible of the light that should be there. The characteristics of the first of those is fixed, depending on the pollutants in your environment (and as others have said, LEDs are difficult) but the second is variable according to your current target in view. You can only ever cut out light with a filter (from the target object and the pollutant), but the aim is to selectively remove the right wavelengths so as to improve the contrast between target and background, even though the image as a whole is dimmed. For nebulae in particular, a filter that does this trick best for one object may not be the best filter for a different object, because the spectra differ. People have spent a lot of time comparing lists of objects with different filters and made recommendations, e.g. https://www.prairieastronomyclub.org/filter-performance-comparisons-for-some-common-nebulae/

OK ScouseSpaceCadet, I suppose that's no great surprise at that price, and that link is useful - I'm sure I can tackle that. I've also read that thin PTFE plumbers' tape (which I already have) can help with excessive play. Thinking cap on again.

Good point Shaun, I keep forgetting about exit pupil.

"... a member changed the focuser to a GSO low profile one" happy-kat, do you have a link to this please, I couldn't find it.

Yes, I admit I'm wandering all over the place, Geoff! But I half expected my thoughts to be upended. It's all grist to the mill.

ScouseSpaceCadet, "The focuser is pants" - as in, not as good as on the 150P / 150PL? collimation cap - so, no need for a cheshire, even though this is an F/5? Because we only need to check the flat?

The more I look at it, the more I like the Sky-Watcher Star Discovery 150i as a lower cost interim choice. If you can look past the ABS shell and lack of collimation (or conversely, if you believe that it won't require any, then it actually becomes a bonus) then it has an awful lot going for it. And at that price, we'd still have a chunk left over for some EPs and a power tank. Use it for two or three years, and then we'd be in a better position to decide whether we want to spend our serious money staying on the visual route (perhaps move to an 8" by then) or else into imaging. And even then, the 150i would still be a nice, compact, easy to use alternative to keep around for the right occasion.

"£600 could be tricky as you stipulated GOTO as a requirement" yes, it could be, jonathan, but we can go a bit extra if we need to. I'll have a hunt for the CG-4, thanks for that steer. I agree fully with your last point, and I have been putting in some hours with my existing, (very) manual scope, so I although I class myself as a newcomer, I won't be completely at the mercy of the tech 😂

"There is a Sky-Watcher Star Discovery 150i WiFi ..." So there is, Kyle - I had completely missed that one on FLO. At £389 all in, that's comparable with the EQ3 Pro combinations and quite a bit cheaper than the EQ5 Pro. I will investigate.

I’ve been starting to think about my next scope, and knowing that order lead times are quite long at the moment, I’ve been spurred into writing by the pre-midnight appearance of Jupiter and Saturn. I’m hoping for some wise input to break me out of analysis paralysis. Here are my thoughts so far. Please feel free to rebut/add anything at all (but you might want to note my PS). Thanks in advance. Context: I’ve had a "budget" (but quite decent) 70mm F/10 refractor on a GEM for a while now, and recently have started to take observing more seriously, learned my way around a bit, and started to run up against aperture limits. My partner is also interested, but not so keen on spending long hours in the cold watching me failing to find stuff. We already have Telrad, barlow and a few extra EPs. Location: most observation is likely to be from the back garden, which ClearOutside declares to be Bortle 4 (I would say slightly generous, some nearby lighting) but we have darker skies within a 15 minute drive that we would like to take advantage of with the next scope. Likely Targets: equally interested in solar system, DSOs and doubles, so not much help on the decision there I'm afraid. Might be interested in spectroscopy at some point, but not a deal breaker. Not really keen on solar. Imaging: we are both interested to get into this “at some point” but I have taken on board the message that visual and imaging often send you down different paths, and we have agreed that we will prioritize visual for a few seasons, and consider buying further kit later if we do decide to do imaging. It might be a bit nuanced now with decisions like mounts, but ideally we would prefer to spend only what we need for visual work now, rather than going for a higher spec that would also support photography at some unknown point in the future. Budget: not particularly constrained, but ideally looking to spend no more than £600. Aperture: I know some have said good things about some 130mm scopes elsewhere, but I feel anything less than 150mm doesn’t seem enough of a step up from the current scope (and also possibly because Patrick Moore always said six inches was the minimum size for a beginner! ). I even considered a 200mm but decided against on portability (and on the heights of some of the prospective observers! ). OTA: looking to a Newt for bang/buck. There is so much choice that I’ve only been looking at Skywatcher models so far – not because I’ve already decided they’re best, but they seem to be a decent quality/price point for us and then I’ll have something to compare with if people suggest alternative ranges. So in the 150mm arena I've been looking at the Explorer 150P (F/5) and 150PL (F/8). Obviously if we were going to do imaging we’d opt for the shorter model, but for visual the F/8 is quite appealing to me with its 1200mm focal length – better contrast and magnification, more forgiving in various respects (eyepiece design, collimation, …) We’re probably not looking to spend more than £50ish per eyepiece, and may need two or three more yet, so that favours the PL. On the con side, we are obviously sacrificing some TFOV compared with the F/5, and it’s physically longer. I'm thinking a wide-field 32mm will span most DSOs with the PL. The 150P comes with a 2” Crayford focuser, the PL has a rack-and-pinion, I’ve read pros and cons for both? We’re unlikely to make use of 2” ultra-wide field EPs. Both scopes have parabolic mirrors, which I like, and I've read good things about the durability of the coatings. The PL seems to have attracted some good feedback in these pages. Mount: Getting tricky now. But GoTo (or at least PushTo) is an absolute must, because there will be one or more observers who will be wanting fast location (and even I will probably lose the will to live if I have to star hop too much). I have seen good things written about the Skywatcher AZ GTi (and it’s a keen price), but I’m advised that it’s not too stable with anything larger than a 130mm instrument. So if I went for the F/8 150 Newt, then in the Skywatcher range we’re looking at, minimum an EQ3 pro, possibly an EQ5 pro (I’m quite comfortable with equatorials). Is it worth the extra £160 for the EQ5? Would we only see any benefit in the future for imaging, or will a 1200mm tube behave better now on an EQ5 anyway? One other factor: noise. Small back garden, so motors must be quiet, and need to be able to slip and slew by hand without the GoTo losing its fix. So, where I am at the moment: For the sake of convenience, I’m still framing this in terms of the Skywatcher range (in the absence of some revelation of a better value offering elsewhere). I seem to have convinced myself of the following: - Newtonian - 150mm - GoTo (probably on an EQ mount ) - Skywatcher are a brand to beat But still undecided on the focal length. I’ve found one or two “150P vs 150PL” discussions on these forums that are interesting but haven’t been conclusive for me, mainly because I have no preference on planetary vs DSO. I think more of a factor for me on the longer focal length is just the effect on stability, and the impact of that on the mount decision. We could live with the PL on an EQ3 if it were steady enough for regular visual, even knowing that we wouldn't use the mount subsequently for photography, or even for upgrading to a 200mm for visual only. Is it just a question of living with a bit longer wait for the image to settle after focusing, for example? That wouldn't be a problem. But if an EQ3 is only marginally capable handling the 150PL, that would push us into considering either the 150P on EQ3 or 150PL on EQ5. So as I said, a bit deadlocked at the moment. If anyone can chip in with any thoughts that sway it one way or another (or unpick it and take it in some other direction), I’d be very grateful! (PS Yes, I know I’ve not mentioned Dobs. Yes, I have considered them, but as I mentioned, it’s important to me that we have a scope that finds and tracks objects. While I’m sure you can make a Dob do that, I don’t think that’s its raison d’être. Please don’t be offended, Dob lovers).

Thanks all, I won't be sending it back then. To be clear, the batteries are definitely fresh (tested with battery tester) and I was trying it out in a pitch black room. But I'm reassured that the operation seems to be typical of the brand - a logarithmic pot seems to be a good call, niallk. And Astro-Geek, the pulsar add-on looks a really neat idea, I wish you hadn't mentioned it ! There are just too many gadgets in this hobby, and not enough pennies.

I've just taken delivery of a Telrad, never used one before. I thought I'd been sent a dud at first, I couldn't see anything when I switched it on. But it seems that I need to turn the rotary switch very nearly to maximum (it has a 270 degree range) before the reticle starts to light at all. At maximum setting I can see the rings clearly in the window and it certainly seems bright enough to work with, but I have only the last 10-15% of the 270 degrees in which to set the brightness from zero to max (to be clear, I haven't tried this in the field yet, I was just testing that it worked in a darkened room. The way the weather is looking, it won't be seeing any real action for a while). My question for experienced users: is this normal behaviour for a Telrad? It seems a bit odd to configure the potentiometer circuit so that the LED fires up only at the very top end like this (I know semiconductors do have different characteristics from filaments). One concern is that I'm testing it now with new batteries at 25°C, so the voltage is unlikely to be as healthy come midnight in January - if it's only just lighting at the top end now, might it fail to at all, in more taxing conditions?

My first order from our friends at FLO arrived yesterday. Obviously things are running a bit slower at the moment with COVID, but that did mean that the out-of-stock EP became available before dispatch😁 All these items were chosen based on (multiple) recommendations from forum members. Although my Other Half and I plan to upgrade to a GoTo before too long, I figured an RDF would still be a good call in the short term. I still can't believe that the filter is our most expensive purchase to date, by some distance. You have a lot to prove, little UHC, when the darker skies return! We tried out the new EP last night on the moon. As it was a 12mm, I thought it would be nice to compare it against the 12mm stock Kellner that came with the budget 'frac we use (no specs for the stock EP of course, but I had previously calculated a 33° APOV from a drift test). Wow, very impressive - I've never viewed through an EP with a 60° APOV before. Lord knows what the view in a 110° Ethos is like, but that would be more than we were planning to spend on the next scope😂

Well, the conclusion was that last night (25th) was showing a similar forecast (high cloud only, starting from about 23.00) but I went out anyway and didn't see a trace of cloud until I finished at a quarter to 2! Brilliant night.