Electrical layout for ROR observatory

[Astrokev]

4 minutes ago, JamesF said:

Traditionally one might perhaps argue that a transformer can change voltages up or down, but only for AC, and a rectifier converts AC to DC.  But "transformer" is perhaps one of those words that have evolved to include things that aren't actually what they originally meant any more.  A bit like "broadband" being used for internet connections that aren't actually delivered using a broadband signalling system.

James

Yes, that seems likely. It seems a long time since I did all that stuff in A-level physics.

[Oddsocks]

55 minutes ago, Astrokev said:

The obvious follow-on question is what is the best method of supplying power to a hub at the pier?

I really don't like hubs, had so many issues with them over the years, most use capacitive oscillator clocks which become unstable when working close to freezing, hence so many hubs work perfectly indoors, or during the day, but fail an hour or so after beginning observing on a cold night.

If pushed I would look at the Startech range, they do a couple of hubs that take a power supply of between ~7 VDC and 48VDC and include ESD protection for the connected devices, the Startech hubs use, (or used to use in the past), crystal oscillator clocks that are relatively unaffected by low temperatures. As the Startech range use such a wide input voltage range you can power them from the same 12V DC used for mount.

As you are building your observatory more or less from scratch I would suggest considering a computer at the pier, using short USB cables direct to the equipment, no hubs to fail etc. The computer does not need the monitor and keyboard/mouse at the pier, you can mount these in the warm room and use a standard KVM extender to join the two. With the computer at the pier you just need to protect it against damp and in the worst case, rain, and you would need to run a couple of network cables between warm room and pier, or back to your network switch/hub, one to use, one for spare. A desktop computer with a couple of spare expansion slots would allow you to add extra USB or RS232 ports directly when needed.

In my own dome I have a pier side industrial fanless computer (Logic Supply) which uses a laptop style 19V DC supply, so no standard 240V AC ATX power supply to short out and go bang when it gets damp. The computer I use has built-in 8 USB sockets 4xUSB2 and 4xUSB3 plus 6 RS232/422/485 sockets which more than meets my needs (but don't ask how much it cost, let's just say I'll have to get at least six years out of before I could afford to replace it).

You don't have to go overboard though, I used a cheap ZooStorm desktop tower computer at the pier side for many years and only replaced it when I needed a couple of RS232 sockets and there weren't any spare expansion slots on the motherboard. As long as it is adequately protected against the elements, and well ventilated, then a pier side computer solves so many issues that in a pupose built observatory why consider anything else?

[Mick J]

I tend to think of transformers as wirewound lumps, buck converters little electronic devices, quite light and may be adjustable.

[JamesF]

1 minute ago, Astrokev said:

Yes, that seems likely. It seems a long time since I did all that stuff in A-level physics.

Me too, though I'm getting a lot of revision done in certain topics at the moment because my son is revising for his GCSEs which start, well, next month I think.  ("Dad, I'm stuck on this question on a past paper.  Can you explain how to do it?")

James

[Gina]

I use an SBC (single board computer) at the pier head or rather on the mount in the form of the Raspberry Pi3B and USB leads are very short (and tidy).  The box containing the RPi also includes a buck converter to reduce the main observatory supply to the 5.1v required by the RPi.  So the only cable to the mount is 12v(13.8v) power and sometimes CAT6 Ethernet 1000 (WiFi works fine except for planetary and solar Ha).

[stash_old]

Dont forget the Amps - RPI3b/+ need 2.5amps else they will complain about under voltage and do funny things - plus strangely if your VNC (ie remotely connect) you will never see the display "yellow lightning"(which means voltage problem) as it is overlayed (i think) - you would have to look in the logs (dmesg).

A lot of the 12v->5v Bucks say max 3amps (15watts) but they dont provide 2.5amps correctly either unless on very very short(6 inch max)  or very thick SWG cables - in my experience ?. Better using the 12v -> 5v 10amp bucks https://www.amazon.co.uk/SHINA-DC-DC-Converter-Step-Down/dp/B00QWBN53K IMO

[Astrokev]

This is really good stuff - thanks everyone. Clearly lots for me (and hopefully others following this thread) to think about.

[Astrokev]

45 minutes ago, JamesF said:

Me too, though I'm getting a lot of revision done in certain topics at the moment because my son is revising for his GCSEs which start, well, next month I think.  ("Dad, I'm stuck on this question on a past paper.  Can you explain how to do it?")

James

I'm past that stage. I'm now getting questions like - "Dad, what's the best way of lining out my camper van conversion, and can you help me install the solar panel on the roof?" ?

[Astrokev]

For what it's worth, here's a revamp of my current thoughts... I did this before reading the replies about using a computer at the pier instead of a hub. Still need to think about that!

 

[Yawning Angel]

Mains over ethernet adapter? Is that a PoE injector or a Powerline network adapter?

If it's an injector, then I'd consider a small PoE switch instead, as it'll also give you additional network ports for the inevitable accretion of technology ?

If it's a Powerline, I'd strongly recommend running SWA cat6 at the same time as the mains, if you can get a route. I've come into the house next to the phoneline and dropped straight into the router. Not that Powerlines don't work, I use them round the house, I just trust hardwired more

[Mick J]

1 hour ago, Astrokev said:

For what it's worth, here's a revamp of my current thoughts... I did this before reading the replies about using a computer at the pier instead of a hub. Still need to think about that!

Are you running this in Kev or your busy sparks,  you may need to think about cable size & ring for the three sockets 5>10, 3 & 4 Convector & Dehumidifier may draw some power (you may not use the heater much).  Earth rod?  possible earth in the supply cable.

 

[R26 oldtimer]

I suggest that you use an Earth rod, even if your mains feed provides an earth cable. Those two should also be connected and I strongly recommend to hammer down that rod as far as it goes by combining 2 or 3 rods using their specific thread adapter. You should be aiming at 3m deep ( and less than 2Ω ground resistance). Practice has shown that a longer and deeper rod will provide lower resistance than 3 shallow ones combined. Don't forget your 30mA RCD.

[Dr_Ju_ju]

Like Alex, I'd recommend that you don't mix disparate systems i.e. ethernet\power, at some point it will fail & you'll be left high & dry, and for the cost of running 'external' grade cat5\6 its not worth it. 

If you are using armoured mains cable (and you should be), then a local earth rod may not be required, as long as the armour sheath is properly earthed at the house end, and the Obsy end is bound to local earth points. 

I'm not sure if your diagram shows it, but I'd make all mains cable runs, as local 'ring mains', i.e. from each RCD, 2 cables are run to the sockets, which I think you should also consider adding  3 more double outlets to 1\2, 3\4 & 11\12.

I'd always advocate local to pier PC's, Windows or Linux, as it will cut down on the headache of long USB leads, which causes most of the grief we face....

 

 

[Astrokev]

Decisions, decisions. Thanks chaps; loads more things to think about!

In answer to one of the questions, I’ll definitely be getting a sparky to do the techy work. I’ll be in charge of the shovel and hammer  .

The mains/Ethernet idea is based solely on a mate or uses one without any problems whatsoever. I’ll certainly give this more thought though. 

The cable run from the house will (I hope) be above ground (along my fence) since there are too many difficulties with digging a trench. My sparky will be able to advise on this, and on the possible need for an earth rod.

The cable run from the laptop in the warm room to the mount is about 3.5m. I’d rather not have to get another PC unless I have to. Initially, I’ll be running everything from my laptop in the scope room, and only consider moving this into the warm room when I’m more confident in the setup. I guess I can revisit this then. 

[Astrokev]

5 hours ago, Yawning Angel said:

Mains over ethernet adapter? Is that a PoE injector or a Powerline network adapter?

No idea Alex!

I need to do more research about connecting up data to understand the terminology a bit better!

[Dr_Ju_ju]

'About 3.5M' is that to device form laptop? I suspect not, especially when allowing for additional cable length, so that nothing get wrapped around the mount, proper cable dressing etc. You'll easily hit 5M or more, which is the absolute limit for some devices. If not a local computer, consider high quality, powered hubs, both USB 2.0 and USB 3.0 (which also has a much shorter cable length recommendation)....

[Yawning Angel]

53 minutes ago, Astrokev said:

connecting up data

It’ll be Powerline then. Essentially network over mains. Fantastic bits of kit, if the home cabling supports it

They do them with mains pass-through, so keeping the socket free. There are also mains faceplates with powerline built in

[Gina]

The INDI people have made setting up a Raspberry Pi with all the software required to drive mount, focussing, filter wheel and take images with an enormous range of cameras very simple.  Just follow instructions to install Ubuntu Mate and run a script that installs everything needed.  Anyone capable of installing software and using copy and paste can do this - it's not rocket science!  See my Blog :-

Setting up a Raspberry Pi for Astro Imaging and Control - Ubuntu Mate   All the usual astro devices are covered but unusual devices are often covered by third party contributors. 

You then install KStars/Ekos on your indoor computer (Linux, Windows or Mac OSX). 

All connections are made to the USB sockets on the RPi so the cables can be very short.  RPi has 4 USB ports.  Communications between RPi and your main computer can be either Ethernet (wired) or WiFi.

Any queries please ask me.

[old_eyes]

Good thread! Thanks to @Astrokev for starting it and everyone for chipping in.  You are ahead of me in the build, and this will be valuable advice and information for me to think through the electrical side of my obsy.

[Astrokev]

My sparky has been in touch and is coming round this coming Monday. The way forward will hopefully soon become clearer ?