rambaut

Good idea about the zener diode - an easy addition. In my case the power is going into a ZWO ASIAIR Plus which then does the power distribution to the mount, camera etc. ZWO website suggests it has over-voltage protection (won't turn on above 15v). Probably best not to test this and a zener would make the whole thing a bit more general purpose.

Hi Alan, Thanks for this. I think buck-boost converters have improved a lot and are very cheap and efficient so I would be interested in how this compares in terms of efficiency. Running a higher voltage over the long cable has the advantage of significantly reducing power loss due to resistance (which would then be traded off by the efficiency of the converter - if you used an old regulator you would probably loose even more). This solution was certainly easy to throw together over a weekend using bits off Amazon. Andrew

I thought this might be of interest to others who want to run a low voltage DC power cable into their garden. I wanted an alternative to long AC extension cords and issues of weather proofing. The issue with DC cables are that unless you go for seriously large diameter cables you get significant voltage drop due to resistance in the cable (a 50m cable has a 100m round journey). The other issue is that you can't compensate just by having a higher voltage at the start because the voltage drop is dependent on the power being used which will vary. So the solution is to start with a higher voltage and then use a power regulator at the telescope end to get exactly 12V. I packaged this in a waterproof box with a volt/amp meter to keep tabs on things and a cigarette lighter socket to connect the power to my mount. This allows me to have the cable out in my garden all the time, tucked away in the hedge without worries about it being cut and I just pull it out when I need to use it. Total cost was about £100 with stuff from Amazon, but you could probably do it cheaper. Details are posted here: https://github.com/astrogear/12vdc-extension I would be very happy to have comments on how to make this better/cheaper (you probably don't need the in-line multimeter - but it is fun). You might be able to get away with cheaper cable (smaller diameter, more voltage drop) but I was erring on the side of caution (I used automotive cable with a 1mm diameter). I am not sure about the relative efficiency of running at 24vs vs closer to 12v given loss in the cable against the efficiency of the DC converter. Has been working very nicely and saves me time setting up.