View Full Version here: : Providing DC power in observatory

18-06-2016, 09:29 PM
Hi all, I have very limited electrical knowledge so would like to ask what I should be buying to provide 12volt power in my observatory under construction with two piers.

The piers will have 240v sockets on them for cameras etc. My 12 volt gear could include for each pier - dew heater, scope fans, mount of mid range size.

All these items have the cigarette lighter fittings so some sort of multiple outlet thing is what I will go with at the pier end.

My question is more around what device should I buy to provide the current. The longest run from the "warm room" would be about 6m.

A specific make and model would be great if people have that information. I am guessing that one device located in the warm room to power both piers would be the way to go.

Any help appreciated.

19-06-2016, 01:48 AM
Gooday Brett,

I use an old Amateur Radio Transceiver power supply that can deliver up to 20A at 12v.

A lot of other people use an ATX Computer Power supply, a 400W version is about $60.00 but you need electrical knowledge to wire it up. (e.g cut off all the hard drive connectors and connect the 12V portions in parallel to get the required current needed). However I am not sure how many watts are available on the 12V rail as the bulk of the 400W is in the 5V rail.

In your situation the best bet is go to Jaycar and buy one that can deliver at least 15A preferably more for insurance.

For your 6M run make sure you have thick gauge cables to minimise voltage drop across the cable. The thickness used for house wiring should be OK, they are rated at 20A before they heat up..

P.S. If you can find one with a backup battery would be good, so if you lose mains power the battery will keep you going long enough to do a shut down and park the scope etc. Nothing worse than doing a slew to a new target and then lose power, gears start crunching in the mount, especially on an EQ6.


19-06-2016, 02:24 AM
I bought a couple of 12V x 10amp transformers from eBay and fitted them with cigar sockets. I use two 4 x cigar socket hubs (available in camping shops) to power all my gear.

20-06-2016, 09:31 AM
I was advised for the Jaycar power supplies to at least double your expected draw as they are supposedly a bit under rated.

For my mobile setup when I expect to have mains available I have a Jaycar 13A power supply run in parallel with a SLA battery from a jump start pack. he battery will not run my heaters for all that long (The SCT heaters are greedy) but it does mean any mains interruptions are pretty much ignored.

20-06-2016, 11:34 AM
Andrews Optical carry good quality Manson power supplies: http://www.andrewscom.com.au/power-supplies

I use a rebranded Manson that's probably an earlier version of the SPA-8330. Running at 13.8V allows for some cable loss and my mount likes a bit more than 12V, especially in cold weather.


20-06-2016, 02:17 PM
Mine runs at about 13.7V. You do need a little fat for voltage drop on the cable, my heater controller shuts down at 12.5V.

20-06-2016, 04:19 PM
Cigarette lighter sockets are unreliable. Can I suggest you look at Rig Runner DC power distribution using Anderson Connectors.


While it may seem expensive, in reality it's a fraction of the cost of your gear.


20-06-2016, 07:35 PM
G'day Brett,
If I was to ever build an obs off my beer garden, then I would not hesitate to run the 12vDC loads from a good quality AGM battery connected permanently to a multistage battery charger. A UPS ( Uninterrupted Power Supply ) if you like.
The prime reason for this is there can be no interruption to supply as you may expect and likely get direct from a 240v to 12 volt power supply.
This gives you some considerable insurance from interruption to grid supply.
Secondly, the battery ( say around 100 Amp Hour minimum) gives you the capacity to handle peak amp loads that only a very good and expensive power supply would be able to handle.
Thirdly, the charger to battery setup provides your electronics with the best possible voltage and surge protection where the battery acts as a filter.

Good quality 10 Amp battery chargers such as Xantrex, Sterling, Victron and Ctek to name a few. Expect to pay upward of $450
Good quality deep cycle AGM battery such as Remco, LifeLine, FullRiver. Expect to pay $350 to 600.

I'm with David on the Anderson style 12vDC connection and fused distribution.
However, the lower current load devices are possibly still ok with cig type connectors.

You can even consider an inverter in this system if you wish to have your poota in the same protection loop. There are combined inverter chargers such as Victron and possibly Baintech.
Best do a bit of research here though as inverters can considerably increase system sizing and cost.
Keep all this gear as close to your pillars as possible to reduce wiring cost and voltage drops. This in not necessarily the case for gear like poota's running off the 240 side of the inverter.
A battery monitoring/management system along with solar for charging is then something you can consider a little later.

I have noted your limited electronic knowledge, but if there was a willing experienced asto guru to help you get through this in Brizzy, the benefits and the leaning experience would be very rewarding.

The brands and prices suggested above are not bottom end, but neither are they any where near top end stuff.
Hope this helps.

23-06-2016, 06:53 PM
Thanks all for their thoughts, definitely a variety of opinions on this one.


03-11-2016, 02:38 PM
Sorry to bump this thread but I'm looking for a bench power supply too.
Jaycar NZ carry several but what is the difference in these two units?



The cheaper one claims SMPS and the expensive one states "ripple voltage
150" and DC current tolerance of 5%...

That might just as well been written in mandarin to me though. :help:

Any good suppliers of other 13.8Vdc power units?

Thanks for your help!

03-11-2016, 03:39 PM
Hi Stu,

Either of those power supplies will be OK for what you need, all power supplies these days are switch mode power supplies (SMPS), including PC's, TV's etc.

The older style Linear power supplies disappeared in the 1990's because the transformers were heavy and bulky and the filter capacitors were also large and heavy to get rid of the 50Hz/100Hz ripple. THE SMPS power supplies operate at about 100Khz and therefore the filter capacitors are quite small.

The 5% current tolerance means that while advertised as a 20A supply it may provide a max of 19A to 21Amps.
The 150mV ripple is nothing to be concerned about and would be the same for the cheaper unit.


03-11-2016, 04:41 PM
Bill I don't think the more expensive one is a Switchmode model.
I have that one and from memory it's not SMode.

It's very well built and I'm very happy with it.

The cheaper one (black) is a SMode and I was told it's not as good a quality as the more expensive unit.

I could be wrong (it's been a few years ago now) but I took their advice and went for the white unit.


03-11-2016, 05:50 PM
Gaud, again, the 1st link (black smode supply) is absolute rubbish, ive been burnt by that as have many others, RB is correct, the second link (white one ) is OK, if derated by 50%.

03-11-2016, 09:34 PM
Well I apologise to Stu if I gave him misguided advise (hope he didn't buy the first one). I really should only comment on equipment I've tried and not speculate.


05-11-2016, 07:23 AM
Thanks Bill, Andrew and Fred.

I will keep looking and consider the white one if all else fails..so to speak.