[from previous]
Electrical Layout:
(I'm open to constructive criticism here as I've only ever studied basic electronics and do not profess to be an expert. What I came up with so far works well. )
I'll try this in text as I don't have a pretty diagram.
I'm using a 13.5V supply. This could be 12-14V, I'll refer to it as 'Source'.
Source(positive)
|
|-20A Fuse-|
|-5A Fuse-|-1KV 10A Diode-|-GX12-2 output on rear of panel-|| .... to mount
|
|-3A Fuse-|-1KV 10A Diode-|-Regular set to 5V output-|-small DC plug-|-Raspberry Pi DC jack input-||
|
|-5A Fuse-|-1KV 10A Diode-|-12V Regulator-|-DC jack 5.5mm x 2.1mm-|| ... for 12V output for a cooled ZWO camera
| |-Regular set to 7.4V output-|-DC jack 5.5mm x 2.1mm-|| ... for 7.4V output for Canon DSLR
|
|-2A Fuse-|-1KV 10A Diode-|-1.8-15V 2A PWM controller-|-RCA Socket-|| ... for dew heater, max 30W output.
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|-2A Fuse-|-1KV 10A Diode-|-1.8-15V 2A PWM controller-|-RCA Socket-|| ... for dew heater, max 30W output.
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|-2A Fuse-|-1KV 10A Diode-|-1.8-15V 2A PWM controller-|-RCA Socket-|| ... for dew heater, max 30W output.
|
|-2A Fuse-|-1KV 10A Diode-|-1.8-15V 2A PWM controller-|-RCA Socket-|| ... for dew heater, max 30W output.
Each module's negative connects back to the negative bus block.
Electrical Discussion:
As part of the design I summed all of the maximum current draw ratings of each module/device. I rounded this up if needed to determine what fuse would be required. This gave me the total maximum current drawn by the whole system. At absolute full load my rig will pull 19A, that includes 4x 30W dew heaters at full power. I expect to never see it at full load, however I've designed everything to handle full load.
The current draw also determines the minimum size wiring to use, I often erred on the side of caution and used thicker cable than necessary.
I used 1KV 10A diodes as a basic reverse current protection. Should a module short and draw high current a fuse will protect it. Should a module fail and produce reverse current, or should an attached device generate a reverse current in the system, the diodes will prevent that. It helps give some segregation to an otherwise very interconnected system.
If you are concerned of interaction/interferenece between your modules affecting your system you could consider using suitable voltage regulators through to further condition the power being supplied.
All modules are connected in parallel. The source supply is delivered to two high current 'buses'. The positive bus is the fuse panel, high current along one side with suitable fuses and diode at each module connection. The return current is via a high current terminal block. Consider the fuse panel to be an 8 way 12V power outlet.
-First fuse is the for the current into the whole system.
-Second is for the mount and connects through to the GX12-2 socket on the rear side.
-Third is to the 12V regulator. From here, I connect the 12V output to a DC socket on the box AND I connect another regulator in series to this module. The second regulator drops the 12V down to 7.4V for output to my DSLR. The 12V regulator won't handle both outlets used simultaneously, but I don't plan to connect my DSLR and a cooled ZWO camera at the same time.
-Fourth to Eighth fuses outlet to each of the 4 PWM modules. These can handle 1.8V to 15V input and output max 2A.
*Hindsights & leasons learned:
-Using the same size jacks for a 12V output and 7.4V output and putting them next to each other might be a quick way to cook my Canon DSLR. I've pugged the 12V jack using some rubber insulation to prevent a light night mis-connection. As I made my own power cables for these I should have chosen dissimilar sizes to avoid an accident.
-Try to find modules that have sufficient mounting holes to support the board. The 12V 4A regulator I used only had one hole and was unstable until I supported it.
-Having accessible blade fuses looks kinda cool and is handy but the fuse panel I used took up a lot of room in the project. It was hard to find a fuse panel that didn't have teminals on the side or top. Many automotive panels aren't designed to be so openly accessible and have exposed terminals. For MK2 of this project I intend to design my own PCB power distribution board with blade fuse sockets and low profile screw terminals - but thats for another day. If you want to keep your project slim and lightweight don't use the same kind of fuse panel I did.
-Don't leave your soldering iron on for a long time, they don't like it.
-Practice makes perfect - soldering is no exception. Keep your solder tip clean. Use solder flux/rosin. Use an extraction fan - that smoke isn't good for you.
-The 5V cooling fan I'm using can be heard during operation. Sound = vibrations and thats possibly not good. I've now connected this to a 3.3V output from the pins on the raspberry Pi to slow it down.
-I needed an 'on' LED so I found a 5V power output pin on the pi and connected a suitable LED with resistor to the rear of the panel. If it's too bright I'll put this on a 3.3V output pin.
I had a lot of fun designing and making this. It took several months all up, some components were ordered from overseas and there's only so much free time. I made some mistakes along the way so it was a good learning exercise.
I'm already thinking of ideas for MK2 and hope to include an arduino based focuser and dew heater controller (using Robert Brown's designs -
https://sourceforge.net/u/brownrb/profile/ ), but that will wait for another cloudy night.
Finally - INDI/Ekos is brilliant. Read more about it here:
http://indilib.org/ Buy a Stellarmate if you don't have a raspberry pi and can't be bothered installing it. If you have a 'pi and are happy to install it you can buy and download an install image for it OR if you're really keen you can download and setup the the applications yourself. I did the later, it was fun and 'rewarding' but I'll never get those weekends back!
Happy to answer and questions and accept constructive criticism.
Cheers.
Noel.
[Posted to CN, IIS and INDI forums].