Another Powering Question

[sailor_74]

I run my EQ6 mount and dew control via a mains extension lead plugged in the house and run down the garden. No problems so far but I'm becoming increasingly concerned at the amount of dew collecting on the extension reel. 

I was wondering therefore what others do. Would a big plastic box housing the cable reel do the trick, although my mount mains adapter would still be exposed to the elements, or do I bite the bullet and get a battery.

Only thing putting me off a battery is that the mains is so reliable and as such i obviously have no issues with mount tracing weirdness!

[Tinker1947]

You could run a low voltage cable from inside your property the dew wouldn't matter then a 13.8v PSU will show very little voltage drop over 20-30 meters , ScrewFix did supply 50m reel of 2 core cheaply....having mains power in a garden with dew about is really quite iffy....

[jnb]

Low voltage in any damp areas is the safest way to do it but will be prone to voltage drop somewhere I did have a link to table of voltage drop and it's surprising just how hefty a cable you need to avoid voltage drop issues (I think I posted that link somewhere on here I'll see if I can find it again)

Personally I use batteries but that's party because I want to be able to move my setup to different locations. For a mains driven setup I would use an RCD at an indoor mains socket and then make up my own extension cable using waterproof sockets for the scope end. Something like this http://www.screwfix.com/p/bg-nexus-13a-2g-rcd-switched-socket/91095

[kalasinman]

Current carrying capacity of wire decreases proportionally to voltage. If you are concerned about shorting, make sure you use a 3-wire cabling with proper grounding (earth) right through from panel to appliance.--Jack

[sidelight]

I do pretty much what jnb suggested, a home made extension with an RCD on one end and a waterproof socket on other.  I then run that to a plastic tool box containing transformers etc, all mounted off of the base of the box (12V sockets mounted are the only external power plugs from this). I have found that the closed box, with small amount of heat generated by the transformers being moved around internally means I have never had a trace of moisture inside the box.  My laptop I run in the shed with a couple of active USB extensions so powering the laptop is not an issue for me any more, however I used to drop a plastic box over it and found it heated the inside enough to stop dew internally.

Cheers

Ross

[stevend]

Many years ago when I had the patio laid I had a power supply cable laid into the garden and a couple of waterproof plugs installed. These do a pretty good job but after getting my scope I became more concerned with tripping over a lead as well as dew, damp, snow etc. So I went down the leisure battery/jump starter route, it has never been a problem and would recommend it. All will be fine provided you buy a battery that provides enough power, and for as long as, you require and it is regularly charged.

[Carbon Brush]

These days most UK houses have one or more RCDs in the consumer unit (fusebox).

If in doubt use an RCD at the point where the cable leaves the dry house/garage.

Place the end of the extension reel in a box. It doesn't have to be a perfect seal. Just something to keep rain and condensation off the innards.

In the box, you have two sockets, at least.

One socket is used to run a small heater, left inside the box. For example a greenhouse propagator heater, or a small tubular background heater. Or a pipe frost protection heater. It all depends on the box size and how you want to use it. This keeps the sockets and mains power supplies dry. If you think in terms of 10 watts in a shoebox going up to 100 watts in a cubic metre, that is a reasonable guideline.

The second (and subsequent) sockets power the mount.

With a bit care in construction, the box can be used to keep eyepieces dew free.

Hope this is useful.

[jnb]

Low voltage in any damp areas is the safest way to do it but will be prone to voltage drop somewhere I did have a link to table of voltage drop and it's surprising just how hefty a cable you need to avoid voltage drop issues (I think I posted that link somewhere on here I'll see if I can find it again)

Personally I use batteries but that's party because I want to be able to move my setup to different locations. For a mains driven setup I would use an RCD at an indoor mains socket and then make up my own extension cable using waterproof sockets for the scope end. Something like this http://www.screwfix.com/p/bg-nexus-13a-2g-rcd-switched-socket/91095

Finally found that link for voltage drop calculations http://www.bulkwire.com/wireresistance.asp

25m at 13.8v and 2A (which is just a drive and a few dew heaters) requires a 2mm² cable which is bigger than standard T&E. The same power at 240V would only require 0.2mm² cable which is cheaper and easier to use but does leave you running at main voltage levels.

[Carbon Brush]

There is another complication with dew heaters and a low voltage feed.

The controller switches the current on/off. The rate depends on the controller. It can be seconds, or fractions of a second.

So if you have a 5 amps heater running at 50% power it alternately takes 5A, 0A, 5A, 0A. Not 2.5A all the time.

The cable calculation has therefore to been done on the basis of all kit taking max power all of the time.

This means all heaters at 100% and a mount taking max current.

Addressing the question generically, some mounts use DC motors, others use steppers. DC motors take a high inrush when starting - or going from track to slew.

The cable needs to handle the inrush without excessive voltage drop.

Any handset or motor drive will have problems when the supply droops then recovers. A brown out. They stop working and require a full power off to recover.

A worst case (and I have seen this on an old Meade handset) is the handset memory gets corrupted and needs reprogramming.

All things considered, there are more arguments for providing into the garden 240V than against.

There is though another way.

Use any old lead acid battery to run the mount, dew heaters, etc. It doesn't need a lot of capacity. Even a motorbike battery will be OK.

Connect a battery charger in the house, run a long thin low voltage wire to the battery, by the scope.

The battery will provide the large pulses of current necessary when starting a motor, or when all heaters kick in together. At other times the charger outputs enough current to run the kit, and top up the battery.

NOT NOTE NOTE. This MUST MUST be a 13.8V regulated supply (CB radio, etc) or you will get a fried handset/mount electronics.

[thanders]

Use 240V outdoor cables. If you want heating in a box, it's ok. Otherwise just cover the wheel etc. to avoid dew accumulation directly on.  

RCD - absolutely.

Be careful, but I've used electrical power tools in humid environments for years without accidents. Even in a "dry" dock.

/Thomas

[Alien 13]

A not so cheap but safe option is to run the mains through a 240/110V isolating transformer these have a center tapped earth on the output so the max voltage in during a fault/shock condition is 55V, most equipment can run off 110V these days.

Alan