I have a small problem and hoping someone can help:
I am trying to design and build a reasonably universal underwater housing for some different cameras. there is a breakout box on the surface and the housing is cabled to this box for things like a video feed, ethernet control of the camera etc.
My current problem is power. As well as onboard batteries, I also want to feed power to the camera from larger DC block batteries located on the surface. There are two inputs on the breakout box, one accepts 12v DC power + and – from a block battery and one accepts 24v DC power + and – from different type of block battery. Inside the camera housing underwater, there are two power connectors (one 12v with + and – terminals and one 24v with + and – terminals) as I would like to support the use of both 12v and a 24v camera. These power connectors are different styles to avoid connecting a 12v camera to a 24v supply!
I only have three wires left on my underwater cable to carry power so can't just hard wire the 12v input to the 12v output and the same with the 24v input/outputs as this would require four cables (this is an assumption on my part: You can't have 24v positive going down cable 1 with 12v positive down cable 2 and have them share the same negative cable 3. Please correct me if I'm wrong!).
I will only need one of these sources depending on whether a 12v or 24v camera is being used.
To solve this problem and make it the least amount of work for the user possible, I have the following solution:
inside the surface breakout box have a circuit that detects which power input has a battery plugged into it. If it's the 12v battery, use cable 1 to the housing as positive and cable 3 as negative. If it's the 24v volt battery, use cable 2 as positive and cable 3 as negative. If the user has plugged both a 24v and 12v battery, it should favour the 24v and use the logic above but isolate the 12v battery to prevent it overloading.
Down at the housing end, another circuit can detect whether positive current is coming down cable 1 (this would be the 12v battery according to the logic above) or cable 2 (the 24v). Based on this detection, it would the connect the power to either the 24v or the 12v outputs to power the camera.
I don't want to get into voltage measurement as 24v and 12v are expressed as simplifications. Actual voltages could vary (but would remain within camera tolerances). Also I wouldn't want to smooth voltage to a consistent level as the video feed from the camera includes an overlay that expresses voltage of the input power source that people use as a gauge of when to change the battery.
My questions are:
a) is this possible?
b) is there a better solution to my problem?
c) is it possible to just have voltage convertors at the camera housing end? (eg one that would take 10-30v and convert to 12v and one that would take 10-30v and convert to 24v). Overheating is a consideration for a camera in an enclosed environment but if this were a potential solution, I would accept voltage smoothing, contrary to what I mentioned above.
Thanks!
Sam
Best Answer
You can absolutely share the same ground for as many voltages as you like.
Current flows to whatever loop is closed, so as long as you don't connect both positive and negative together the batteries won't even know about each other. That would be the easiest solution:
simulate this circuit – Schematic created using CircuitLab
R1 sees only 12V, R2 sees only 24V and neither battery can ever see the other.
And you can also just connect them like this, same idea:
simulate this circuit
Just make sure the load doesn't connect between the 12V and 24V, you'll get 12V, but it will run through both batteries and cause trouble when one is empty before the other.