Ok Gladiators! So we’ve decided we need a DC power source on or around the mounting plate of the scope. This is because we know of at least one device that requires it and that is the OS Bus. The focuser, while it has an AC option, will also require it because we have decided we don’t want to take a chance having a bad European to US AC conversion fry the focuser. I can think of at least one more device that might need it and that is a powered usb hub. At any rate we don’t want to have a bunch of extension cords creating a birds nest around the scope as they wind their way to the nearest AC outlet! So DC power is somewhat foreign to me since I have done imaging mostly from permanent sites or close enough to the house to be able to use standard plugs. The good news is there are a TON of resources to help us with this project, including some of the astronomy community I live in now. The other good news is that the equipment we need for this is readily available and inexpensive.
Let’s start with a couple of resources right off the bat. I happened to come across this video from the YouTube “Astroimaging Channel”. Go here. Then scroll down to the video entitled “cable management in astrophotography” About midway through the video, the set up for DC power is explained. This is an excellent video highly recommended. Basically there are a couple of items you keep hearing about in this context. One is this device called a “RIGrunner”.
Think of it as a DC power strip. There is a power source that plugs into it on one end and you plug your devices into the other ports. Each device has 2 inputs, one negative “black” and one positive “red”. The RIGrunner is small, about 3 x 6 inches and weighs only a few ounces. This can easily be velcroed somewhere on the mounting plate of the scope. The other item you will hear about is “Power Pole”. This is a contemporary connector that is used with this system. They snap together like Lego’s!
The rectangular black and red plastic pieces are what connect to the inputs and to each other. The silver pieces are the key though. The wire from your leads fit into the cylindrical opening and is then secured by crimping (or soldering which thankfully you do NOT need to do with this system!). The secured wire then snaps into the red or black housing. This video does an excellent job of explaining this set up in detail. You need to look at that video several times before attaching anything!
The final piece is the power source. We will use a transformer that converts AC to DC and from there can run cabling to the RIGrunner.
This is the transformer, about 6″ square and weighing a few pounds. All the equipment you need you can find in a lot of places. I used this site where I found it very easy to find stuff and very good support.
Ok so lets go through the steps we need to take:
- You first will need a multimeter. This is a device that can measure voltage and sort positive and negative wires. They are pretty easy to use and easy to find. I got this one from Amazon that I thought was very good
- You will need to learn how to use your multimeter and familiarize yourself with it. Test it on a AA or 9V battery. Watch this video a few times
- Now what they don’t tell you. I think most of the stuff we are using has a power cord with some kind of AC adaptor on it. They typically look like this:
I could not figure out how the heck you measure positive or negative voltage if there is no power source available e.g for a wire like this in the picture! That’s because you can’t! There are basically 2 steps to the process. First you need to find out which wire goes to which part of the plug i.e center or side. Then you have to determine which pair is positive. ** Do NOT rely on word of mouth from someone telling you the center of the plug is positive! This information should be explicitly documented in the equipment manual or you should test with the device plugged in! (see below)
- To check which wire goes to which part of the plug, you have to measure resistance. Set your voltmeter to the resistance setting. Touch the one lead to the center of the plug and one to one of the 2 wires. If you get any reading at all, typically it fluctuates then settles out around 0.2-0.8 ish, then that’s your wire! If you get 0.L, that is NOT your wire. 0.L means the resistance is too high to measure. You want LOW resistance which means the 2 points are connected. **Since initially posting this page I have come to realize that the absolute full proof way to figure out polarity of the plug is to measure the voltage with the device plugged in. So before I cut off the AC adaptor I should have measured it with it plugged in and THEN cut the end off. In my case I got the wrong information from the manufacturer and only discovered that after I reconnected the wires and plugged it in with AC power! When I measured the voltage with red lead in the center and black on the side it was negative and not positive!
5. Once you know which wire goes to what part of the plug and you have checked with the manufacturer what part is positive on the plug, you are ready to assemble your wires! Now go to that video I linked at the top which shows you how to connect your power pole connectors! This is a superb video which really explains how to do it. ** One thing on the connector sizes. In the video the 3 sizes are explained, 15,30, 45. Don’t worry about the numbers. Lets call them “small, medium and large”. The point is you need to be able to fit the wire into the cylinder. Now the Powerwerx starter kit comes with 30 amp connectors for the wire which is 12 gauge. In the video they tell you what wire gauges supposedly go with what connectors.I swear only half the time I was able to fit the 12 gauge into the 30 amp without getting a strand or 2 stuck outside the connector, so I used the 45 amp. Worked fine! You don’t obviously want the wire tip swimming in there but after you crimp the wire if it doesn’t pull out it will work.
6. Set up the Rigrunner for the devices you are going to power. You will need the provided 12 gauge power extension cord from the transformer to your Rigrunner. Determine the length by checking your set up. Where are you going to put the Rigrunner on your scope? Where is the transformer going to sit etc etc? The cord from the transformer goes to the “DCIN” port on the left. My transformer runs at 30amps max so put a 30 amp fuse in there. The Rigrunner came with a 40 amp fuse so I downsized. Then plug in your devices from highest amperage on the left going down to the right. Use a fuse about 1.5 times the amp draw on the device (check with the manufacturer).
7. Turn on the transformer. Remember to set the switch on the back for the correct AC voltage (US or Europe). It tells you how in the directions . Now meter your output at every step beginning with the transformer
8. Measure the output at the end of your extension cord from the transformer. Make sure it’s consistent
9. Now connect the power extension cord into the “DCIN” port of the rigrunner. Measure the output voltage at the terminal(s) you are using
10. Take your assembled power cord with the 2 power pole connectors at the end where you had the cut off wires (remember we figured out which end was positive and put the red connector on that, black on the negative) and plug those into the Rigrunner in the first terminal to the right of the one labeled “DCIN”. Make sure you have the right fuse in there.
11. Now with the transformer turned on, check the output voltage at the plug that will be going into your device
Congratulations! You have now set up your 12 volt power supply!