Electrical layout for ROR observatory

[Startinez]

Looks good to me from an electrical engineer's perspective, I don't have enough experience with observatories. I'd say having the spare double is a good contingency and gives room for expansion.

 

Shouldn't have any issues with overloading as the only thing that has a big current draw is the convection heater. It's worth a mention about being mindful of RCD nuisance tripping on the circuit which powers the mount if you're doing this method of getting the 12V supply via the mains sockets, not that I think anything would be particularly troublesome but you don't want that happening mid session.

[Astrokev]

12 minutes ago, Startinez said:

Shouldn't have any issues with overloading as the only thing that has a big current draw is the convection heater. It's worth a mention about being mindful of RCD nuisance tripping on the circuit which powers the mount if you're doing this method of getting the 12V supply via the mains sockets, not that I think anything would be particularly troublesome but you don't want that happening mid session.

Thanks. The 12V will be supplied via a plug-in transformer power supply. As suggested earlier in this thtead, I plan to run the mount supply on a separate RCD circuit from the CU to reduce risk of it tripping if something else goes down.

Thinking some more on the plan - is a USB hub powered from a powered USB supply cable, or from a 12V power supply? (you can tell I'm not very good at electrics, can't you!)

[Startinez]

1 minute ago, Astrokev said:

Thanks. The 12V will be supplied via a plug-in transformer power supply.

Thinking some more on the plan - is a USB hub powered from a powered USB supply cable, or from a 12V power supply? (you can tell I'm not very good at electrics, can't you!)

You can get either. I use a 4 port USB powered one for my daily laptop usage but if the space is there and it's on a permanent setup then I think a standalone mains powered would be the way to go.

[JamesF]

I think I'd be tempted to have at least one spare double socket in both the scope room and warm room, just in case :)

The fascia with all the USB plugs looks interesting.  I could use quite a few of those around the house assuming it can supply sufficient power.  Do you have a link for it?

If you have an earth supplied to the house (rather than a local earth rod) I imagine the electrician will prefer to export the house earth.  As one said to me a while back: "The supplier can provide a much better earth than you can with an earth rod".  I know our earth (provided by the supplier who has to pay us rent for it) is actually three 25m braided cables buried in the ground, so he probably has a fair point.  It also may depend on whether you need to have the pier earth-bonded, since it is steel and is in the ground outside the envelope of the structure.  Worth discussing that with him.  I think wiring regs might insist upon it these days.  I am not a sparky, however :)

James

[Astrokev]

38 minutes ago, JamesF said:

I think I'd be tempted to have at least one spare double socket in both the scope room and warm room, just in case

The fascia with all the USB plugs looks interesting.  I could use quite a few of those around the house assuming it can supply sufficient power.  Do you have a link for it?

If you have an earth supplied to the house (rather than a local earth rod) I imagine the electrician will prefer to export the house earth.  As one said to me a while back: "The supplier can provide a much better earth than you can with an earth rod".  I know our earth (provided by the supplier who has to pay us rent for it) is actually three 25m braided cables buried in the ground, so he probably has a fair point.  It also may depend on whether you need to have the pier earth-bonded, since it is steel and is in the ground outside the envelope of the structure.  Worth discussing that with him.  I think wiring regs might insist upon it these days.  I am not a sparky, however

James

The USB fascia is just a clip-art picture used to illustrate that this socket will carry USB ports. The ones I've seen in the DIY emporium seemed to be 2 port fascias from memory.

For the earth, this was really just acknowledging @RayDsuggestion. My house is 100 years old and, based on the state of it when I bought it, the earth may be a rusty coat hanger for all I know. I'll obviously discuss earthing with the sparky, and put my trust in him. I'm sure he'll have a fancy bit of tech with flashing lights that will reveal all.

Spare sockets - yes, I've added a couple. I know people say - estimate and then double, but to be honest, I can't think of what else I may need (he says foolishly).

[JamesF]

1 minute ago, Astrokev said:

Spare sockets - yes, I've added a couple. I know people say - estimate and then double, but to be honest, I can't think of what else I may need (he says foolishly).

If you could think of it, you wouldn't need to add spares

James

[Gina]

My mains supply is line and neutral only with an earth rod to supply the house earthing.  In this case I had to have a separate earth rod for the observatory and feed line and neutral only from the house.  This is on a 13A plug to avoid needing the observatory main wiring officially checked.  I have an RCD in the observatory with two over-current trips - one power and one lighting.

[Astrokev]

8 minutes ago, JamesF said:

If you could think of it, you wouldn't need to add spares

James

Can't argue with that logic ?

[michael8554]

I know your consumer unit is just a generic image but just to be sure:

The rightmost switch has the supply from the house connected to it and is used to isolate the whole obs and warm room.

So circuits 2 and 3 shouldn't be connected to it. 

Those circuits should be on the switches to the left of the one mentioned above, like circuit 1.

You might want to put any lighting on a separate switch on the consumer unit so that the lighting can be left on while you work on the isolated power wiring.

You realise that those USB outlets on the socket plates are powered all the time?

Michael 

[Astrokev]

22 hours ago, michael8554 said:

I know your consumer unit is just a generic image but just to be sure:

The rightmost switch has the supply from the house connected to it and is used to isolate the whole obs and warm room.

So circuits 2 and 3 shouldn't be connected to it. 

Those circuits should be on the switches to the left of the one mentioned above, like circuit 1.

You might want to put any lighting on a separate switch on the consumer unit so that the lighting can be left on while you work on the isolated power wiring.

Thanks Michael.  The pic of the CU is clearly misleading so I’ll amend to reflect more accurate switch connections. 

Sensible suggestion about the lighting sockets being on a separate switch. 

Perhaps a silly question to help my learning - what voltage do the USB ports provide?

cheers

[Dr_Ju_ju]

5 volts DC, USB voltage, fast charger (for phones) up to 5.25 volts DC

[Oddsocks]

1 hour ago, Astrokev said:

Perhaps a silly question to help my learning - what voltage do the USB ports provide?

Julian has answered your question re voltage.

Personally, at the current time, I would avoid mains sockets incorporating USB charging points, in the past they have been found somewhat lacking in safety.

If you absolutely do have to have one ensure it is one from a branded major manufacturer, expect to pay at least double to triple the price of the cheapest unbranded sockets on the market.

It should be labeled to comply with BS1363-2 2016 and carry the USB devices logo on the packaging, avoid sockets labeled BS1363-2 1995, which are still legal to be sold until August this year (2019) but do not meet recommended safety levels re separation of the USB part from the mains part.

Note that these USB sockets are charging points only, they should not be used to provide power to 'live' devices such as hubs or cameras.

Further information regarding safety issues around mains sockets facias incorporating USB charging points may be found here:

https://www.electricalsafetyfirst.org.uk/professional-resources/technical-e-news/investigation-into-uk-socket-outlets-incorporating-usb-charging-points/

William.

[Astrokev]

30 minutes ago, Oddsocks said:

 

Note that these USB sockets are charging points only, they should not be used to provide power to 'live' devices such as hubs or cameras.

Further information regarding safety issues around mains sockets facias incorporating USB charging points may be found here:

https://www.electricalsafetyfirst.org.uk/professional-resources/technical-e-news/investigation-into-uk-socket-outlets-incorporating-usb-charging-points/

William.

Thanks William. 

Good advice there. I didn’t realise you shouldn’t use these sockets to power hubs and cameras. I wonder how many others use them for this purpose?

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

[JamesF]

13 minutes ago, Astrokev said:

Thanks William. 

Good advice there. I didn’t realise you shouldn’t use these sockets to power hubs and cameras. I wonder how many others use them for this purpose?

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

I wasn't aware of that either, though I've not actually tried.  I do however have a stack of RPi and similar devices permanently fed from a USB charging unit.  One of these:

https://www.amazon.co.uk/gp/product/B07CTKQFYC/

Perhaps I shouldn't be doing that either.

(As an aside, when I logged in to Amazon to look for that order there was a section that said I have had my account since 1999.  Can't believe I've been an Amazon customer for 20 years!)

James

[JamesF]

As a further aside, if someone hasn't yet made a single unit suitable for providing permanent power to a pile of USB-powered devices, it's about time they did.

James

[Gina]

I power my 5v devices with buck converters and my battery backed up observatory supply of 13.8v.

[Astrokev]

1 minute ago, Gina said:

I power my 5v devices with buck converters and my battery backed up observatory supply of 13.8v.

what the heck's a buck converter?

[Macavity]

I "standardised" on 12V *input* voltage to my observatory. That way I can 
use a deep-cycle Marine Battery... with a (temporary) mains lead charger.
I intend (one day) to dig a proper mains supply trench + armored cable? ?

If I need stabilised voltages, I have a few Laptop type switching inverters
to get a "few more volts" and feed those to sundry "home-brew" boxes
containing various "7812" etc. voltage stabilisers /  smoothing caps etc. ?

[JamesF]

Just now, Astrokev said:

what the heck's a buck converter?

It's a small bit of electronic gubbins that steps a DC voltage down to a lower DC voltage.  So you could for instance use it to step 12V or 13.8V down to 5V for devices that require a 5V supply.

James

[Astrokev]

I've probably got a bit of time to fine tune my power needs. I've tried to contact my local sparky, but as yet have had no reply. This follows me trying to get hold of my local "call me anytime you need anything doing" plumber over a week ago, and I'm still waiting to hear from him.

I've made this point before, but what d'you have to do to get local "professional" tradesmen to respond to calls for work?  Just a simple acknowledgment of a call or voicemail message would be nice. Not too much to ask, surely.

[Astrokev]

3 minutes ago, JamesF said:

It's a small bit of electronic gubbins that steps a DC voltage down to a lower DC voltage.  So you could for instance use it to step 12V or 13.8V down to 5V for devices that require a 5V supply.

James

Ah great, thanks. I'd call that a transformer, but maybe they are just for stepping down AC to lower voltage DC. What do I know!

[JamesF]

2 minutes ago, Astrokev said:

I've made this point before, but what d'you have to do to get local "professional" tradesmen to respond to calls for work?  Just a simple acknowledgment of a call or voicemail message would be nice. Not too much to ask, surely.

If only there were some sort of portable device they could carry that would allow them to respond to phone calls or messages to let you know they'd get back to you.

I'm having the same problem with Western Power at the moment.  I want to talk to them about how we get power to the barn we're going to convert to a holiday cottage.  I got as far as "We'll passing this on to our West Somerset team." over a week ago.  I've heard nothing since.  I'm wondering if their "West Somerset team" might be on his holidays.

James

[Gina]

13.8v is the voltage of a standard nominally 12v lead acid battery.  A 13.8v PSU is a good way to charge them and keep them topped up, I'm told and that's what I do.  All the nominally 12v astro gear is fine on 13.8v.  It's designed to run off a standard lead acid battery (car or leisure battery).

[JamesF]

4 minutes ago, Astrokev said:

Ah great, thanks. I'd call that a transformer, but maybe they are just for stepping down AC to lower voltage DC. What do I know!

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

[Astrokev]

7 minutes ago, JamesF said:

If only there were some sort of portable device they could carry that would allow them to respond to phone calls or messages to let you know they'd get back to you.

What a great idea. Somebody should get onto that. Sounds like it could be a really useful device with so many applications.