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JamesF

JamesF's observatory build

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I have mains out to my garden pier, which is properly terminated in suitable enclosures, never had any issues with the power....

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I was having thoughts about running 12V out to the piers on 2.5mm T&E and then switching to something more flexible at the pier.  Need to compare it with heavy duty low voltage cable though.

James

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1 hour ago, Dr_Ju_ju said:

For high current DC, you need to use a multicore conductor cable

What's the reason for this?  I don't recall reading it anywhere, though I may just have forgotten.

James

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I use 16.5A low voltage cable.

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2.5mm T&E in large diameter trunking, especially when that trunking is in the open under the observatory where it's cool, should be good for at least 20A.  Quite possibly nearer 25A.  I think it's generally rated at 27A in free air.  I'm not going to be pushing that much down a single cable.  Resistance is effectively the same as for AC given that skin effect is irrelevant for household wiring and over a distance of a few metres will be tiny fractions of one ohm, so any heating should be the same and voltage drop should be negligible.  Where I'd be running it there'll be no need for any movement of the cable either, so multi-core isn't a requirement for that reason.  I'm just struggling to think of a reason why multi-core would be required unless there's something I've not thought of.

James

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Talk of wiring reminds me...

I went to dig out a reel of cat5e from the loft of the workshop this evening and whilst fossicking around came across a lock that I wish I could have used on the observatory.  I'm as sure as I can be that it came from the house many years ago and was fixed to the internal face of a door.  The case for the mechanism measured at least 6" x 4" and operated a single deadbolt at least half an inch thick and about an inch and a half deep.  Sadly there was no key with it, though I do have a collection of old keys, so perhaps it might be amongst them.

James

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The main reason to use stranded, is down to cable movement, i.e. if there's a chance of repeated cable movement then use stranded. But if everything is fixed, and won't move then solid should be ok.

Personally, I'm always moving stuff around, hence I use ultra flexible stranded.

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As I have posted in another thread, I'm struggling to come to a decision about 12V power to the piers at the moment, so as a temporary arrangement I'm going to use my existing 7A power supplies which means I can run all the cabling and test it out.  On that basis last night I put in all the power cables for the pier with the longest run.  I'll try to do some more this evening.

James

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I ran 7 amps through Piers Morgan. It didn't work my mount but it did make me feel better :-)

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All the power cabling from the warm room to the piers is now done.  Need to start thinking about the data cables, the first decision being what I actually want.

James

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Cat5\6, everything else can then run over wired network

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just don't go with the cheap CCA cables, they ain't Cat anything even tho they claim to be. They do work but exposed to big temp changes they aren't reliable long-term and not so good if you want to use PoE

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James, go for Cat 6, the difference in speed is quite dramatic and the cost is minimal.

 

Steve

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Yep - I have Cat 6 cable from house to observatory.  Runs at gigabit speed.

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I have at least half a kilometre of cat5e already run around the house and it quite happily carries gigabit ethernet, so I'll stick with that.  It's much simpler to make my own cat5e cables up, too.

I'm toying with the idea of sticking in an HDMI cable and a USB cable though.  They'll be easier if I pull them through first because of the connectors.

James

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Forget the USB leads, as unless you want to run local hubs, the distances are probably too great for reliable operation.

The same may also hold true for HDMI, which in theory can have longer runs, but it will be dependant on signal type e.g. 480p, 720p as opposed to 1080pamd higher, due to the higher frequencies of the signals and their attenuation along the cables....

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When I was planning my obby, I drew out every piece of equipment and what they would need in the way of cables. As everything goes underground, a draw wire is in the duct too, just in case. Cat5e ethernet cables are also happily running at GB speeds with no issues and as you say, they are easy to make up.

I added a second ethernet cable to each dome, firstly the conductors can be used for part of the security system and also if I have an issue with the data, as a spare.

Adding a USB and HDMI sounds worthwhile, just in case you need them in the future. Easy to install today, more difficult later... Perhaps needless to say, just make sure any AC mains cables do not share the same cable runs as signal cables.

Good luck

Gordon.

 

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With cables and plugs being constantly "updated" it might be safer to dig a tunnel.

Then you can crawl [or walk through] and just clip the new Cat 19.9 and USB 23+ cables into trunking on the walls as you go. :)

It makes my tatty old, mains extension cable feel so inadequate. :blush:

Is it an age thing?  :biggrin:

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At the moment I do have an old mains extension cable :)

I should perhaps have used slightly larger trunking to make running more cables easier, but it's hardly the end of the world.

The USB runs will probably be too long for USB3, but USB2 is fine for keyboard and mouse for example, or even a remote USB DVD unit, and I shouldn't be going over 5m which is the specified limit for USB2.  HDMI should be fine over a similar distance too.  I don't need stupidly high resolution.  It just means I can have access to a console in the warm room if I need one.  Makes it easier to keep an eye on things if I need to reboot or reinstall for whatever reason.

James

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Last night I ordered a weatherproof box for each pier to house the electronical bits that don't like getting wet.  In the end I went for a 350mm x 250mm x 150mm ABS box with a clear door from ebay:

https://www.ebay.co.uk/itm/WEATHERPROOF-IP65-LOCKABLE-ABS-ENCLOSURE-WITH-METAL-BASE-PLATE-CLASSIC-WALL-BOX/112869512272

The seller isn't totally convincing, but I struggled to find anything similar elsewhere in a suitable size so decided I'd take the risk.  Boxes with solid doors are easy.  It's just that sometimes it's reassuring to be able to see the flashy lights :)

Today I drew a 5m HDMI cable, 5m USB2 cable and a pair of cat5e cables through the ducting for the furthest pier into the warm room, in that order.  Actually it was far easier than getting the power cables through despite the plugs on the ends.  All my other spare HDMI cables are too short, so I've ordered a couple more in appropriate lengths as well as a 3m USB2 cable for the pier closest to the warm room.  As the HDMI cables have the largest plugs I want to pull them through first, then the USB ones and finally the cat5e.  Bonus points to the cat5e supplier for actually having it wound on a proper reel rather than just having a dispensing nozzle on the box.  Minus points for not printing the lengths on the sheath (every other reel I've used has had the distance from one end marked every metre, which makes it so easy to cut off, for example, eight metres of cable).

The Met Office is teasing me with forecasts of a few hours clear sky tonight but they've not exactly covered themselves in glory so far today, so I'll believe it when it happens.

James

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  At Lowell's half-meter telescope, we've got a pair of 5 m USB 3.0 extenders which just barely reach from our computer shelf to the mount. One is dedicated to the mount itself, while the other is connected to a 12-port hub up by the telescopes. This works quite well, though we've seen issues with some devices if the extender is connected to a hub closer to the computer -- daisy-chaining USB hubs is generally not a good idea, so don't do that. The reason for so many ports is that we have two telescopes on the mount with several cameras along with focusers and other instruments. Not all will ever be operated simultaneously, however, so bandwidth isn't an issue.

  I had no previous experience with USB extenders, but so far I haven't seen any down side to using them.

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Hi James,

the IP65 boxes will be more than enough to keep the electronics dry. The problem will be the cable entries you need - a rubber grommet is not enough to maintain the IP rating. Little plastic cable glands like the link below will maintain the rating. To help, try and only drill through the bottom if you can and gravity will then help you.

Gordon.

https://www.ebay.co.uk/itm/IP68-BLACK-CABLE-GLAND-NYLON-WITH-NUT-PG7-PG9-PG11-PG13-5-PG16-PG19-PG21-PG29/282622655872?_trkparms=aid%3D555018%26algo%3DPL.SIM%26ao%3D1%26asc%3D57923%26meid%3Db6547d16968f4f4f9e74a2debcbb6273%26pid%3D100005%26rk%3D4%26rkt%3D12%26sd%3D401751103669%26itm%3D282622655872&_trksid=p2047675.c100005.m1851

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I have to admit that I'm not too panicky about the whole electrics getting damp thing.  It's not as though the roof is going to be open in the middle of a torrential downpour.  Really all I need to protect against is a few splashes of rain before I get the roof closed and a heavy dew.

Today one of my new HDMI cables and the 3m USB cable arrived.  That meant I could run all the cabling for another mount, which is pretty much all I've got done today.  The weather has alternated between sunshine and stair rods at a moment's notice, so it's been a bundle of joy to be outside.

Last night I actually managed to use the observatory "in anger" for the first time, having noticed the Moon hanging about to the south west-ish, I stuck the 127 Mak and 450D on the HEQ5 and quickly ran off some subs for a lunar image.  It's not great -- all a bit rushed as I wasn't really prepared, but I posted it in the imaging section to celebrate my return to imaging.

I also spent a lot of time faffing with PHD2 to drift align two of the mounts.  I've never used it before so it was something of a learning experience and it probably took far longer than it should have.  I think the key might be to have everything set up the same every time, so the corrections that have to be applied are the same every time.

James

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2 minutes ago, JamesF said:

I have to admit that I'm not too panicky about the whole electrics getting damp thing.

It might be worth considering the effects of 100% humidity inside the observatory. Condensation can be as harmful as water ingress. In England I found that this (inside my water-tight garage) caused things to rust and connectors to corrode.

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