Dew heater band PS has died after only one month.

[Rusted]

Many thanks for your continuing, expert support.

I am treating my observatory as a corded power tool as far as it is fed with a flexible, 2-core cable. 30m x 1.5mm^2.
The 2-core cable is not connected deliberately to any metalwork nor the earth rod.

If I install a normal domestic socket in the obs. it becomes a new installation with legal requirements to use a qualified electrician.
So I use wandering, 2-pin multi-sockets in the obs. to feed the individual PSUs to the all 12V equipment.

Note that the pier and dome are all of wood or plywood. Only the mounting itself and the telescopes are metal.
These are earthed with the rod. As are the cases of the [British] AWR Tech drive boxes.
Their PSU is also 2-core cable to a 5A black brick.

The earth rod was an attempt to kill a "tingle" I was feeling when I brushed my fingertips on the telescope metalwork.
Reversing a 2-pin plug indoors is standard behaviour in Denmark.
It can help to eliminate "tickles" from metal cased sewing machines and washing machines.
In my observatory the tingle remains but at a less dramatic level after plug reversal.
The obs. floor is of wood so should not provide a ground route shock.

There is probably a potential danger in touching something live while in contact with the metalwork.

[fifeskies]

Yes that tingle is the exact problem with earths not at the same potential that can arise from these types of installation.

The wood floor is a good extra level of protection (as long as it is dry).

More a nuisance than a proper threat unless there is a major fault.

 

I try to run as much as possible from my 12v supply , lights etc all at the 12v end and avoid mains under my open roof.

[Rusted]

Thanks.  Weather and dome leaks are a worry. I shall have to fibreglass the dome next year when it is warm enough.

If I mount the MW RS150 in a non-metallic, fan ventilated, weatherproof box it can safely supply the drives and the dew heater bands.

The Laptop and monitor remain separate with their own PSUs on a protected, outdoor 2-pin, multi-socket.

From what you are saying: I should not use the earth terminal on the MW RS150-12 to connect to the mounting + earth rod?

[fifeskies]

Probably not unless you install a local RCD 

It would prevent the tingle problems but compromise the protection unless you use a local RCD.

 

Your domestic installation actually ties together earth and neutral at source , but its probably best not to tie N and E at the PSU

 

All fine as long as you place it inside an insulated box. fan ventilated is best.

 

 

 

[fifeskies]

If you have access to a 3d printer , thingiverse has templates for fan cooling this module

 

 

 

[Rusted]

Many thanks. 

I am most grateful for your patience and thanks, of course, to the other contributors.

Hopefully the information shared here will be of use to anyone considering an observatory.

Safety first!  If in doubt ask!

Regarding mounting the cooling fan: I have access to lots of scrap metal.
I have a couple of old computer fans knocking around somewhere.

[fifeskies]

Bigger diameter fans run quieter   😜

[fifeskies]

If you have an old PC case around you can mount the PSU inside it and use the case fan mountings positions before putting it all into an external box    🤔

 

[Rusted]

Thanks to your coaching I can claim success.
Two x 6" aperture Astrozap bands, via the HitechAstro, 4 x controller, drew 1.7A at full throttle.

I added the AWR drives and they worked fine but I haven't checked the current yet.

Thanks for the case idea, but the PC cases are scrapped. I just kept the fans and HDDs.
One little 12V fan whizzed but then went still. Couldn't make it work after that.
I'll order a 2-wire fan online. Hopefully I can find a slow and quiet one.

[fifeskies]

Glad to hear you are back up and running.

 

Just been reading your amazing thread about your self build scopes and mounts , seriously impressed.

You have some incredible instruments under your belt, custom instruments have such a great look to them.

[Rusted]

Thanks. I like the "industrial" look.

It avoids having to obtain and maintain a very high quality finish.
Commercial instruments must be pretty to seem like they offer real value for money.
Cosmetic perfection means high wastage or highly skilled workers.
I do not have that need. Function before appearance every time.

My main tubes are secondhand, galvanized steel, extractor ducting from a furniture factory.
The lack of the usual spiral seam avoids dust collection potentially leading to a fire.

They are incredibly stiff but thin. About 0.3mm from memory.
Making them easy to drill but they offer no material thickness to take a screw thread.
So it's a lot of arm stretching to reach nuts inside the tube! Which means baffles won't slide!

Provided I align the single, longitudinal seam with the tube ring hinges these tubes are fine.
They are certainly no heavier than any other normal tube material and cost me only small change.

I was surprised to discover how little variation there was in main tube weight with material choice.
CF is not lighter unless it is made as a foam sandwich with light weight in mind.
Seamless aluminium would need to be much thicker for the same stiffness.
Rolled and seamed aluminium not stiff enough without serious reinforcement.
PVC ducting is a heavy and rather flexible material. Particularly as it warms.
PVC drainpipe is worse on both counts.

The lightest refractor tube I ever made was thin, aircraft birch ply. 5" f/15.
Which was wrapped and laminated around, thin structural, plywood baffles.
That was decades ago and I used Cascamite glue and cut down, inner tube, "rubber bands." 
Today I would use epoxy and ratchet straps.

This was the 5" on an experimental, plywood equatorial.
Far too much friction despite the PTFE and Formica.

 

[Rusted]

Just to complete the thread:
I finally have the MW 12V 12.5A PSU safely housed in an inverted, snap-on lid, food container.
Part of a nested set from the supermarket at a ridiculously cheap price:
Once closed, the white lid/base is so difficult to remove it needs tools!

A 40MM cooling fan keeps an airflow going over the unit inside the box.
Ventilation holes were drilled in the lid/base at the far end from the terminals for safety.
I intend to fit some rubber feet and hang the unit off the pier.
A compact "marine" fusebox uses blade-type fuses to protect the kit.
The airflow has reached only 63F inside the box after running for several hours.

Thanks to all who responded with advice and entertainment.