Bench DC power supply for atro use.

[The_bluester (Paul)]

I thought I would split this out from the other power supply discussion to avoid annoying the OP of that thread with discussion not relevant to his problem (Here http://www.iceinspace.com.au/forum/s...d.php?t=131984 )

I mainly observe at home and near enough to my shed that I could run out a power cable to carry DV power without any significant voltage drop. My equipment is relatively hungry in that I have a 9.25" SCT and the heater belt for the corrector plate would tip in at nearly 3A when running flat out. The mount seems far lighter than that, maybe 2A when high speed slewing on both axis. Add them up for 5A combined as a reasonably worst case picture. Most of the time the current draw would be much smaller, even if I cave in and buy a heater for my finder which is useless after an hour or two, but the goto performance of my mount is good enough to ignore the finder after doing the initial alignment.

Has anyone got an opinion on the use of one of these for DC supply?

http://www.jaycar.com.au/productView.asp?ID=MP3097

I was thinking that something like that (10A continuous seems ample at double what I can reasonably foresee my gear using) AC ripple seems fairly well constrained at 120mV. I would just need to ensure my cabling did not stack up to more than 0.2 ohms to ensure that voltage drop was no more than 1V under worst case to keep my heater controller happy. Done right it would result in being able to have the power supply in the shed and out of the moisture and only some cabling out to the mount. Combined with a pre charged small SLA battery in parallel to the PSU in case of power bumps it should power my gear happily. Is anyone doing something similar?

[wasyoungonce (Brendan)]

Just a trick I have learned. Try to run a separate PSU for PWM dew control to that used on the mount/scope. The DEW controller PSU does the heavy haulage capacity, current draw wise.

Then a separate lower capacity PSU for the mount and accessories IMHO.

Those jaycar units are ok.

[The_bluester (Paul)]

That has always been my problem, running off a battery, the Kendrick controller shuts down under volts a long time before the mount stops working, but in those conditions it is a moot point as the scope dews in a flash.

For general mount use I think I would be able to get away with a single PSU given all I need is clean enough power to keep the mount running happily. No imaging to worry about in my case.

I might start with a single Jaycar PSU and see where I go from there. I have in the past had a PC PSU suggested but I can not really be bothered with working it out to trigger and make sure I set it up safely.

[wasyoungonce (Brendan)]

Funny enough. I have been using A PC PSU @12V (for years just fine) but have now converted another PSU to run @14V DC (although I can go up to @18V DC for my mount, 14~16V is enough)

Just had to find the controller IC PWM feedback network divider pin and replace it with a pot. Also replace overvoltage zeners @3.3V line @5V line (had no zeners on 12V line!) with 18V one (on 12V line, only interested in this line as this is the Vrail I am upping)...oh and replaced caps with higher rated ones on the appropriate places.

I have it running now.

I have a new metal case for it and was going add some more output filtering via capacitors and high capacity ferrite choke. This part is still in work atm. but PC PSUs are very useful for these applications.

[The_bluester (Paul)]

It may have been you who suggested it to me.

The 12V rail runs about 12.4 on a PC yes? That would give me no freeboard on the Kendrick controller before it shut down as under volts. Plus a bench supply would be handy for some other stuff I do as well, get some use out of it in daytime too.

[wasyoungonce (Brendan)]

Yeah around 12.2~12.4 max on PC PSU. That said most/alot of PSUs use either TL494 or KA7500 PWM control ICs and both of these are very easy to change the feedback Vdivider to achieve 14.4~16~18VDC out.

Of course this up's the outer Vout rails, so you need to change their caps as well. That said you can just remove this unwanted rails completely.

[The_bluester (Paul)]

Quoted from another thread to ensure things make sense.

Originally Posted by The_bluester

Thanks Brent. I split out my discussion to a new thread over here http://www.iceinspace.com.au/forum/s...d.php?t=132022 to avoid irritating the OP given my discussion is really on a different topic.

My current idea is to get a bench DC power supply able to meet my current requirements and more and use a smallish SLA or maybe even a larger car battery across the output to float me in case of outages.

I am looking at the moment into mounting the bench supply and battery in an enclosure so they can be wheeled out next to the scope and plugged in to mains via an extension cord. The battery would be separately charged before use on a proper multi stage charger to ensure it was in top condition and the bench supply would effectively maintain it.

[ZeroID (Brent)]

I'm using a PC PS for 12v & 5v DC (fan speeds) and 240 VAC for the OTA heater ( 6 watt beer mat !! ) but I'm in a permanent Ob setup so 'batteries not included.'
12 V drives the mount, the fans and the ZWO Peltier when in use. 400 watts capacity so plenty of grunt although the Peltier can slow the fans marginally when it comes on.

Actually I should run a line to the 3 kwatt UPS cos if the power ever does go off (extremely unlikely !) and the lights all go out then THAT is when I'd like to be able to carry on imaging and guiding.

[The_bluester (Paul)]

I think for the variety of uses I have I will just get a 10A bench supply for now. The most I can foresee is around 5A slewing with the heater on full blast so plenty of freeboard.

Couple that up with a little SLA I already have to pad the mount over any power bumps and help smooth any remaining AC ripple and we should be good.

I think I will build it into a box on wheels with covered AC input (And a power board) so I can have AC via an extension cord if I am out at a star party but still run off the bench supply. I will just need to arrange for some cooling air paths for the supply so I don't cook it inside the box.

UPS I might worry about if I am ever doing imaging, but like most people that would be with a laptop so it falls over to battery anyway in a mains fail.

[marc4darkskies (Marcus)]

Not 100% relevant because I have a power hungry permanent setup. But I do drive everything from a Lab PSU (Powertech 3-15V VDC 40 Amp) as part of my DIY UPS:
http://www.jaycar.com.au/productView...y&form=KEYWORD

DIY UPS drives everything:
http://www.pbase.com/gailmarc/image/126742409

Observatory Schematic here (with text underneath).
http://www.pbase.com/gailmarc/image/153621600

Cheers, Marcus

[The_bluester (Paul)]

That is similar to what I was thinking through I was not going to worry about an inverter, very easy to add one later if I wanted to though. Once I eventually have an observatory set up I would build a low power windows box, probably with an Intel NUC as they are pretty low power consumption. A small inverter off the battery stage would keep it powered for a good period (the NUC I use as a HTPC consumes about 15W on average, give it something harder to do and it might be double that.

[g__day (Matthew)]

That's what I use in my PC lab - its rated as a Lab power supply from memory.