Hi all,
A few years ago now I managed to snag a 40s ammeter from a sale of stuff being stripped from an old factory. It’s a huge, cast iron bodied analogue indicator ammeter designed to run off a current transformer, so detached from the main circuit. Here it is hooked up to a bench power supply to show the needle moving:
I’ve spoken to @joeatkin2 about donating/long term loaning it to the space (as I realistically am never going to have need/use/space for it) and we’re both keen to get it set up somewhere visible as a cool semi-functional piece of decor. Joe’s suggested hooking it up to the main 3-phase supply where it comes in to the grey box by the front door of the clean room, and has given some pointers for how to connect it in, but I could do with some advice on circuit design/component selection, as this is a bit beyond my normal scope of RC and motors.
The plan is to put a current transformer (of the correct 150/5 ratio) on each phase of the supply, rectify the output of each transformer then combine them (I believe Joe mentioned using some kind of summing amplifier?) and put the resulting current through the ammeter. I imagine the circuit will look something like this (apologies for my slightly jank circuit diagram):
The selection of parts is my main sticking point, I think the current transformers are pretty easy, these should do the trick: 150/5 Current transformer I’d then probably included a 5A fuse on the output of each individual transformer, to protect them from too much current.
Next is the rectifying, which I know very little about. Would a simple bridge rectifier work (eg cheap and cheerful bridge rectifier) or would I need something fancier to get results in this use case?
Lastly would be adding together the signals, is there something stopping me from putting the outputs of the rectifiers in parallel? If so, what would the alternative be? After combining I’ve stuck a 6A fuse to protect the ammeter from excessive current (if somehow the 3 transformers are all output more than 2A at once then the total will be too high for the ammeter)
Any advice/suggestions would be much appreciated!
Ed