how to convert an AT/ATX power supply for astonomy use

[oldpink]

I had a 12v - 2A power supply for my scope, unfortunately it decided to die on me yesterday

as a quick fix I took an old AT power supply from a PC and converted it to run all my 12v connections via a 3 way cigarette lighter adapter

pretty easy job to do

I bought one of the 3 gang cigarette type adapters from the local supermarket (available from lots of places

took the AT power supply and on the main plug that goes to the motherboard I took the green wire and one of the black wires either side of the green wire

and snipped them off the plug stripped them back a bit and joined them together and taped them up

they are the wires that connect to the PC on / off button, switching the supply on and off, once I finally mount the supply into a hobby box I'll connect them to a switch

next take all the yellow wires and snip them at the plugs, make sure you use them all or you won't have enough current / Amps to power the mount

snip them at the plug ends and gather them all together strip them back and join them all together this is your +12v connection

take about 4 or 5 black wires and snip at the plug ends and join them together, this is your ground or - connection

I took the 3 gang adapter and pulled the cigarette lighter plug apart (a screwdriver helps)

the positive wire runs to the center pin and the negative to the outer "Spring" clips
snip the wires off and connect them to the power supply making sure the positive goes to the yellow cables and the negative goes to the black cables

for now I have just taped them up securely but I'll solder them when I finish the project

so now I have my scope and focuser connected to two of the available plugs and leaves one for a camera power supply

[triton1]

Don,t suppose you could post some pic,s up.I got one knocking around somewhere so it would come in handy to run three things from on supply and save a few quid too.

[oldpink]

give me 5 mins
I'll post up pictures

[oldpink]

this is the finished (so far) unit

as I said its really easy just make sure you use all the yellow wires to get the full power

and join the green wire and black on the main AT / ATX plug to make the unit think its switched on

the picture shows a bridge used to test the power supply but its better to cur the wires, join and insulate them to prevent shorting

I've taped the rest of the unused wires & plugs up to keep it tidy and avoid them getting dew

[Wyvern]

Nice one "oldpink",

Now hands up all those who are scrabbling around their collection of discarded computers/parts.

Yep, that's me at number 1 

Regards and thanks,

Les

[Gina]

I use an ATX PSU to power everything but the mount which seems to need 12.5v minimum.  So I run that from a Maplin 13.8v 7A PSU.  I use 3 pin XLR connectors for my main power distribution supplying 12v and 5v.

Another ATX PSU provides an indoor bench supply for 3.3v, 5v and 12v - very useful in addition to my variable bench PSU (0-20v and 0-5A).  Many of my projects need several voltage supplies.

[oldpink]

Gina

I have a fully modded ATX psu supplying 12v 5v and 3.3v as a bench DC supply in my unit, it gets used to test all sorts of gear
or even charge phones, and a lot cheaper than a dedicated supply
the 400w one I converted tonight supplies 24A on the 12v rail which powers my NEQ6 and focuser with ease
I may go get an 800w ATX to boost the output and allow me to use another 3 gang and split the output between them

or divert more to the mount and a lower wattage connector to handle the focuser etc and also use the 3,3 and 5v as extra's

[Herbig]

Surprised your NEQ6 is happy with 12v, as Gina says they seem to need a bit more 12.5 - 13.8v?

[oldpink]

well with 24w available from the 400w it seems to be happy to run with it
I suspect the focuser is a small fraction of power drawn so the 12v has enough juice to power the mount
I may use the 3.3 with the 12v on the final build with a regulator and smoothing circuit to refine the power supply to the mount

[Gina]

You will need two separate PSUs if you want to add the 3.3v to the 12v as all the outputs have the same ground (common).

[stoffe]

I do not know if it is mention already in this thread. Some ATX power supplys need to be loaded on 12V and in 5V or any load on any outputs to start up. It could be a little resistor or a fan or something like that.

A tip!

If you have an observatory computer with a ATX power supply, you can run your mount and everything from the same source. It works very well to do that.

[triton1]

Yes I,ve dug mine out as well,many thx oldpink

[Mick J]

We did one of these a few years ago to run 12v battery chargers (not so toy cars), still going strong and now powering dew straps and things, there are good guide's on the net - I can remember it being important to make sure the power supply was fully discharged especially if you are removing the case to modify the wiring.

Very useful bit of kit and easy work,  well done oldpink