Telescope Power Supply
Currently, for powering my telescope, I use what is basically a car battery in a fancy box (and price tag). It’s infact so close to being a car battery that it actually has terminals on it for jump-starting cars. It does the job well enough, right up until the charge level drops below about 11v. After this point the mount can become erratic and unstable. Also, the cold temperatures encountered at night also affect the charge levels available negatively. This has an impact on not just the telescope battery, but also the battery in my camera.
More than one evening has been cancelled early due to dwindling power reserves.You can see the one I use in this photo. My mind was made up; most of my astronomy takes place in the back garden anyway, where there’s a surplus of 240v power. The tank can be stored for use when I venture out.
I want a proper power supply. One that can supply ALL of my doohickies, whatsits and do-dads. And the DSLR. And charge my phone. No, two phones. FOUR! And the dew shields! Multi channel Dew Shield control! Maybe some LED lights too! Red ones. DIMMABLE RED ONES!
Initially I started my search online and was aghast at the price of some of these supplies that barely even came close to being able to charge four phones at once. I’m not going to link any, but let me tell you, the price was high enough to necessitate locks on the windows of the upper floors on all the eight blocks of Wall Street. I mean, all these power supplies are is 240vAC to 12vDC stepping transformers, some wire, a box, and some plugs to suit. How hard could it be to build one?
Obviously stage one is ‘design’, and thanks to my exuberance with CAD I had to start there. I definitely went way over-board with the tolerances and centre lines and other completely unnecessary things for something that I was later going to go from development to manufacture with squinted eyes, a drill, solder and zero supervision.
Design sort of walked hand-in-hand with what I could actually source for as cheap as humanly possible, without having to wait a million weeks for delivery from Asia.
There was no doubt in my mind that building this was going to be messy. Boxes, envelopes and packaging to start with; then little blobs of solder all over the place. Or tiny strands of copper wire everywhere that’ll be sticking in my feet for days and days afterwards. What if I burn my table with the soldering iron!? There was nothing for it; I’ll just have to order everything for delivery for my girlfriend’s house and do it there. She will like that, me spending loads of time with her. Yeh. Definitely wont backfire…
After some intensive googling, I selected RS Online [not affiliated] as my chosen supplier, they had most of the components that I needed in stock for 3 day delivery, so that’s what I did. eBay, Amazon and a couple of trips to my local Maplin filled in the blanks of things that I forgot, or didn’t even know I needed for the project. (KFC on the way back was mandatory, really.)
There were a good number of changes on the way, some of which never actually made it into the CAD drawings. Like the Black/Red +/- power distribution blocks.
I actually purchased them, but after they arrived, I discovered the magic that is a Wago Block. Think of a choc-block that has arrived in the 20th century. Lift lever, push in wire and lever snaps shut. Perfect. I can use these linked together with jumper-wires as a rudimentary power bus!
The heart of the operation is the AC->DC power converter itself. At first I was going to buy a laboratory Bench Power Supply. They’re super accurate voltage regulators and readily available, but these quickly became an unsuitable choice when I noted that the moment you’d like one capable of producing more than about 5amps@12v their cost becomes a very large number that someone has doubled. Twice. It started to become clear why the Retail versions were so eye-wateringly pricey.
as cheap as humanly possible, without having to wait a million weeks for delivery from Asia.
Salvation came in the form of CCTV. CCTV cameras are incredibly common, numerous and require a stable voltage for many cameras; necessitating a high amperage capability. Changing “lab switched mode power supply” to “CCTV switched power mode supply” in google netted about a 70% saving over the equivalently capable lab version. Ok, the lab versions have certain fancy sounding electrickery thingies that they can do, which pushes up their costs. I’m not calling them over priced, they’re just not suitable for my needs. I needed pure muscle.
A forced air-cooled variant. [read: has a fan] 240vAC to 12vDC @ 20AMPS! 20 of them!
I need this power supply to give me the ability to power everything from this single supply. I also need it to be future proof as I don’t yet own any dew shields but I’ll be putting that future capability in the line up. I also plan to leave space on the output panel for something I can’t think of right now, but may need in the future. A powered filter wheel for example. Currently, the planned list to be receiving power is:
- Telescope Mount(12-14v)
- Guide Camera (12v)
- Dimmable LED lighting strips (12v)
- 5v USB (FOUR PHONES)
- 7.4v Camera Dedicated power (no more camera batteries dead.
- Focuser DC motor power (12v)
The future but installed now are:
- Dew shield controller (variable output)
- Cooled, Dedicated Astronomy Camera (12-15v)
And finally, the real holy grail:
- Full remote control system: unknown as yet requirements.
The first and foremost problem is me. Human error will be the single largest risk in the execution of this. My electrical knowledge starts and ends with the word electrickery. Don’t get me wrong though, I have a basic understanding of electronics; I know that if I feed 12v into an iPhone designed to take 5v max there will be some tears (mine) and a barely recognisable puddle that used to be my lolcat machine.
The scary side of the electronics (the AC side) is a 13amp cable (fused for 5amp) salvaged from an old vacuum cleaner, earthed to every metal part individually for safety.Can’t be too careful here, while it’s in the testing and building stage, I’ll be turning on and off the power supply to the box to verify correct polarity etc and I really don’t want to get a “shocking experience”.
I’ve taken meticulous care to figure out what devices use how many amps and at which voltage using a good quality multimeter so that I don’t a) fry something b) exceed the total 20amp capability of the heart and most importantly c) die the end of a 240vAC domestic supply. Where practical, I’m using inline fuses (typically 2amp) for each device output to protect against overloading and peace of mind. Where impractical the two primary distribution circuits are protected by a 10amp fast blow fuse each. There are two circuits arranged to load balance across the two main supply outputs 10amp x 2 = 20amp total.
|LED Light Strips (x3) ~9ft/3m|
Using the above table and accounting for voltage drop, I have the setting for the voltage drop I need to dial in to prevent the system dropping below the critical 11v threshold that causes issues with the mount’s stepper motors and control boards.Even when everything is at full load.
The final hurdle to … hurdle is the differences in voltage for some of the equipment, like the USB ports and the DSLR camera. 5v and 7.4v respectively. Thankfully, Amazon had my back here with a brilliant company called Drok. They make loads of handy little trinkets for boosting/clipping voltage, PWM Devices for dimming LED’s and heaters (best order two of them!) and even little screens for monitoring total power output and watts consumed, should my math be as typically rubbish as it usually is.