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Old 12-07-2021, 06:32 PM
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Stonius (Markus)
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Advice building DC power distribution box

Hi All,


I've currently got a setup that has a certain amount of 12v power distribution via various step up/down transformers, but it ultimately revolves around having DC power to run the lab supplies. The idea is to be able to go fully mobile and get off road.



So my questions are as follows;
  • Should I install an inline fuse? If so, what amperage, and what speed (fast-blow?)
  • Since I would be running the NIC and the mount off the same source, do I need to worry about motors making the power 'dirty' via back EMF (at least I *think the effect is called back EMF? It's been a while). Do I need to do some kind of line smoothing?
  • Do I need to install some kind of voltage regulator to maintain consistent voltage as the battery starts to deplete?
  • Anything I haven't thought of?



My current setup involves a 12V lab supply that I distribute into a step-down transformer to get 5V for various USB devices where necessary. I also have a PWM controller for managing fan speed.


I *used to have a step *up transformer in the mix too, to get from 12V to 15V to power the actual mount, but I got stall issues when slewing and realised it needed more juice. It's much happier running on a separate lab supply where I can jack the voltage up to 18V (the maximum in the 12-18v range).


Many thanks for any help.


Markus
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Old 12-07-2021, 09:32 PM
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mswhin63 (Malcolm)
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Quote:
Originally Posted by Stonius View Post
Hi All,

I've currently got a setup that has a certain amount of 12v power distribution via various step up/down transformers, but it ultimately revolves around having DC power to run the lab supplies. The idea is to be able to go fully mobile and get off road.

So my questions are as follows;
  • Should I install an inline fuse? If so, what amperage, and what speed (fast-blow?)
  • Since I would be running the NIC and the mount off the same source, do I need to worry about motors making the power 'dirty' via back EMF (at least I *think the effect is called back EMF? It's been a while). Do I need to do some kind of line smoothing?
  • Do I need to install some kind of voltage regulator to maintain consistent voltage as the battery starts to deplete?
  • Anything I haven't thought of?

My current setup involves a 12V lab supply that I distribute into a step-down transformer to get 5V for various USB devices where necessary. I also have a PWM controller for managing fan speed.

I *used to have a step *up transformer in the mix too, to get from 12V to 15V to power the actual mount, but I got stall issues when slewing and realised it needed more juice. It's much happier running on a separate lab supply where I can jack the voltage up to 18V (the maximum in the 12-18v range).

Many thanks for any help.

Markus
I am doing the same thing as well, I am in the middle of re-designing the power supply functionality.

Any connection in power requires some protection. This can be in a couple of ways.
Using a currently limiting power supply like you and me but as I or we are doing to replace with battery in the future yes you will need fusing or some other protect method.
I personally will use electronic protection using MOSFET, mostly because I can. But fuses at the first point of call for any DIY job.

Even if you have a current limiting Lab power supply it is still best practice to fuse protect each output just in case one dew heater coil shorts or low resistance enough not to trip the main fuse. This usually burns out all the intermediate components instead.

Motor cleanliness should be a function that should be incorporated in the motor control unit.

For my camera, I use a linear regulator. The main reason is to maintain the camera voltage and reduce the noise generated from cheap switching regulators obtained from suppliers. Funny thing is that Jaycar has the switching voltage regulators I find dirty, yet I purchased a linear regulator from Jaycar that I was able to easily modify to get accurate regulation for my camera.

One by I found useful reducing my build requirements is an automotive 12V to USB regulator for most cars, They are cheap and gives me the necessary 5V I need for most USB power requirements.

As far as the NIC, what is the Voltage input?
If it 12V, I suppose it has its own internal regulator to maintain the voltage for the system. The specs should say what is the variation Min and max voltage input.

2 bobs worth
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Old 12-07-2021, 10:17 PM
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Stonius (Markus)
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Originally Posted by mswhin63 View Post
I am doing the same thing as well, I am in the middle of re-designing the power supply functionality.

Any connection in power requires some protection. [...] But fuses at the first point of call for any DIY job.

Okay, I'll definitely look in to that then. Still got no idea what I'm doing in terms of selecting fuses, but i assume the internet will provide.



Quote:
Originally Posted by mswhin63 View Post


Motor cleanliness should be a function that should be incorporated in the motor control unit.


True, I guess. Otherwise the Mount Control Board would get fried, I assume, so it must keep the power clean somehow.


Quote:
Originally Posted by mswhin63 View Post

For my camera, I use a linear regulator.



I'm thinking something like this It has 8A capacity, but I nothing about linearity or non-linearity




Quote:
Originally Posted by mswhin63 View Post

One by I found useful reducing my build requirements is an automotive 12V to USB regulator for most cars,



Yes, i got one of those too. It's been very reliable.




Quote:
Originally Posted by mswhin63 View Post


As far as the NIC, what is the Voltage input?




12-24V, IIRCC, so it should be happy.




Quote:
Originally Posted by mswhin63 View Post
If it 12V, I suppose it has its own internal regulator to maintain the voltage for the system. The specs should say what is the variation Min and max voltage input.

Yeah, I'm not sure if it does or not. It takes a DC plug in coming from a transformer, so I suspect that it relies on voltage regulation from the transformer since compact is key to an NIC.





Cheers and Thanks for the advice.


Markus
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Old 14-07-2021, 06:38 PM
RyanJones
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Hi Marcus,

I’ve built many of these in different iterations. So for what it’s worth my advice is as follows:

Fuse all circuits is first and foremost. My new project goes one step further and uses optocouplers to separate the switching control from the actual load side of the circuit. But this is the first time I’m doing that so it can be done without. Automotive fuses are good and easy to get hold of. They are fast blow and very tollerant of climatic conditions. I use 10A fuses. Probably slightly over kill but really all you want it to do is blow for a short circuit rather than excessive current draw which they certainly will do and quick !

As you’ve stated using automotive step downs for usb power etc work well. Automotive voltage varies quite a bit so these circuits are designed to handle that.

Any circuit that involves a DC motor such as a cooling fan etc should have a diode across the load to prevent the voltage running back when the fan switches off. Not necessary for stepper motors such as in your mount.

Voltage regulation is good simply because it keeps things consistent but most of things you’ll be connecting to it will have their own regulation anyway.

Try to mount your distribution box somewhere on the RA axis. You can mount it on the actual OTA if you like but it’s more weight which is not ideal. Mounted on the RA axis you’ll only have 1 power wire coming in and only have to worry about making sure that doesn’t snag. I run ASIair’s on my setup so I don’t even have to worry about data cables but that’s different again. Bunch your DC and usb wires into a loose loom and put a loop in it and it will be able to handle any Dec articulation. Cable management is king !

That’s pretty much it.

Hope this helps

Cheers

Ryan
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Old 14-07-2021, 10:52 PM
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Stonius (Markus)
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Ryan, my friend, *that is excellent advice and I intend to follow it to the letter. Thanks for taking the time to share your experience. As someone who only has half an idea about electronics (enough to be dangerous, basically), those were the little details I really needed to know, so cheers mate!


Markus
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