power supply - 240V to 12V

[troypiggo (Troy)]

At the moment I'm set up sufficiently, I think, to run a night or 2 at a dark site without mains supply with deep cycle batteries etc.

Trouble is, I'm not really set up to run fully on mains supply and still need to use a 12V battery for some gear. I'm looking to get a mains to 12V regulated power supply so if there's mains available I can fully run off that.

Question 1: Looking at Jaycar there's a selection of 13.8V DC regulated power supplies. I understand that 12V batteries aren't always 12V, when fully charged they might be 13.8V then drop to something like 11V or whatever. So I assume one of these 13.8V supplies is the one to get?

Question 2: What's the difference between this 13.8V 20A unit and this 13.8V 20A unit, aside from $100 or so? Would the cheaper, black one be acceptable? Not sure of the definitions or difference between "bench" and "lab" supplies. Maybe "lab" is better quality but too much for me?

Question 3: How much is enough? 20A seems like overkill for HEQ5Pro mount (couple of Amps max?), and some dew heaters (few Amps?). Maybe this 12A one would be enough?

Question 4: Got any better/cheaper ideas?

[erick (Eric)]

Troy, you might want to search the threads. There is discussion of Jaycar and Dick Smith power supplies.

I bought a Dick Smith Electronics one which is fine for me. However, I don't drive a goto mount with it, just heaters and stuff. Grabbed it on special - they come round on special at Jaycar and DSE every so often. I think it is 20A and it's probably best to get a higher current rating to ensure it has plenty of capacity to do what you need without running close to its limits. The DSE one I bought allows adjustment to the output voltage and I brought it back to close to 12V.

The only other things I had to do was to disable the light n the on/off switch and swap the bright gren LED for a faint red LED. Otherwise, it lit up half the observing field!

[peter_4059 (Peter)]

Troy,

The other issue to consider is whether you get interference in the mount control electronics from the dew heater PWM circuit if you run them from a single supply. I don't know if there is a way to test for this but I've kept my supply to the dew heaters separate to avoid this issue.

I'm using a DSE regulated 12V supply to power the mount, watec video camera and light box and a supercheap auto 12V supply for the dew heaters.

Peter

[dpastern (Dave Pastern)]

Sorry if I'm not understanding this all correctly - the devices listed here will allow you to plug mains voltage into the unit in question, and then go from that to the mount? So you can use your home to power the mount, rather than a portable 12v unit? Am I correct in my understanding?

If so, awesome. Been thinking of this the past few days, would be very cool.

Dave

[[1ponders] (Paul)]

I use this one without anyprobs

http://jaycar.com.au/productView.asp...T&SUBCATID=647

there is also a 10 Amp version that i use as well.

[troypiggo (Troy)]

Thanks guys.

@ponders - yeah, that's one of the ones I was looking at. Thanks for confirming it works fine being 13.8V as opposed to 12V.

@dave - correct. That's exactly what I'm trying to do. Have a look at the one ponders linked above, which is one I'll probably get. You plug that into mains, rig up a cigarette lighter socket type deal to the red and black terminals on the front of it there, and there you go.

@peter - Thanks mate. I know you've mentioned that a couple of times and haven't forgotten. I'm thinking of getting either the 20A and a 12A, or maybe 2 x 12A ones might be sufficient, to run the heaters separate to the sensitive stuff.

@eric - Thanks. Think the one I'm looking at it all red light already, and it'll be inside my toolbox setup anyway.

[dpastern (Dave Pastern)]

Excellent. Must get one.

Dave

[erick (Eric)]

Some info in this thread:-

http://www.iceinspace.com.au/forum/s...ad.php?t=43766

[troypiggo (Troy)]

Thanks Eric.

[Ian Robinson]

The difference being regulated 22OVAC - 12VDC regulated power supplies will show up in how well conditioned the V and I ripple voltages coming out and V and I switching transients are .

A cheap and nasty (or poorly designed) RPS will have significant ripple in either or both of V and I outputs, this can have deliterious effects on your circuitry.

http://upload.wikimedia.org/wikipedi...pple.svg/400px-

A better RPS will have very small V and I ripple , and may even he ripple tuneable to suit the needs of the devices connected to it.

Only way to know for sure is to get hold of the Spec Sheet for the RPS and look at the guaranteed max ripple in Vout and Iout , or to connect the RPS to good oscilloscope and measure it yourself.

Also important to know is how big the V and I transients are when it switches - in fact these can be more important than the ripple V and ripple I as the transients occur over very short periods and can really hurt circuits connected to the RPS.

You might see something like http://www.national.com/ds/LM/LM317.pdf

[DavidU (Dave)]

Who's going to try a PC power supply? The 12V rail seems to be <8AMP.
Cheap & fan cooled

[troypiggo (Troy)]

I didn't understand either of those last 2 posts

[Ian Robinson]

Originally Posted by DavidU

Who's going to try a PC power supply? The 12V rail seems to be <8AMP.
Cheap & fan cooled

How much ripple and how are the transients ?

May be cheap because the V and I from it is conditioned by filtering circuitry in the motherboard (which will need very well conditioned V and I inputs) else it would be cactus pretty quickly.

[Ian Robinson]

Originally Posted by troypiggo

I didn't understand either of those last 2 posts

Sorry .... airing some hard won knowledge from my second engineering degree (BE in Computer Engineering) studies .... in particular Switching Electronics stuff ( a 3rd year elective ).

[troypiggo (Troy)]

That's cool. It's all interesting stuff. I never thought I'd learn so much about electronics, power etc when I started this hobby.

[DavidU (Dave)]

Originally Posted by Ian Robinson

How much ripple and how are the transients ?

May be cheap because the V and I from it is conditioned by filtering circuitry in the motherboard (which will need very well conditioned V and I inputs) else it would be cactus pretty quickly.

I will measure it . I have a full set of gear in my garage.It would be quite easy to reg & smooth the OP at 10A.An LT1038 TO3 job with switching RFI filtering.

[mithrandir (Andrew)]

Originally Posted by [1ponders]

I use this one without anyprobs

http://jaycar.com.au/productView.asp...T&SUBCATID=647

there is also a 10 Amp version that i use as well.

I've got the other one http://jaycar.com.au/productView.asp...T&SUBCATID=381
but haven't had it long. The specs say 13.8V+-5% and ripple 150mV.

It drives a CG5 (ASGT with GPS addon) plus CCD peltier without getting at all warm. It hasn't been cold and humid enough to see if adding the 3 dew heaters makes any difference.

[Ian Robinson]

Originally Posted by DavidU

I will measure it . I have a full set of gear in my garage.It would be quite easy to reg & smooth the OP at 10A.An LT1038 TO3 job with switching RFI filtering.

I wish I had some of that kind of the good stuff.

I've nice pro multimeter that has on-screen plotting , but it's not a high impedance multchannel CRO like we got to play in Comp/Elec Engg Labs.... sigh !

[Gama]

Troy,
Your "Question 3" power supply is what i use.
Its modified, so i can plug in 3 other items to the front panel.
So when on, it powers my Mathis MI-750 mount, my QHY-8 or 9, Motor focus and hand controller to the telescope and USB hub.
Its still got a little more juice for a few other things too.
All my scope/camera, everything is from that supply.
Grab that and you wont need any other supply.

Theo.

[gary]

Originally Posted by troypiggo

[I]Question 2: What's the difference between this 13.8V 20A unit ...

Hi Troy,

A colleague recently sent us one of these particular supplies as new but it failed
after a short time of use whilst only drawing a couple of amps. Your luck might
be better.