I'm thinking of getting one of these - http://www.ebay.co.uk/itm/181034239452?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649 The red and black wires are obvious, and I'm guessing the yellow wire goes to the smaller connection on the alternator ? How on earth does it measure the alternator's output in Amps - I'm baffled
Keep looking at this one in the fond hope it will make sense. ) Whilst I can see parallel pick up for voltage which then gives a good indication as to whether or not the Alternator is balancing the load, quite what the Ammeter side is supposed to be indicating I don't know as its range is so low as to be virtualy useless, unless what is being shown is not an Alternator but a Dynamo with an external field connection then knowing the Field current would be another way of gauging the absorbed power ie load on the machine. But that would be reliant on the operator being aware of expected values...maybe thats why it has a stepped shunt?
You would have to mount that one, in the engine bay in series with the B+ wire from the alternator to check it is charging the battery. Apart from the crummy wiring diagram, some of the other meters on that eBay shop are more interesting. Some of them have remote shunts and still read to 0.1volt , so a multicore low current low voltage cable could be routed from the shunt and voltage pickup in the engine bay to the dashboard. But what I dont see are any that do +/- 50A current, the sort of thing that shows +ve current charging from the alternator or -ve current discharge when the engine is stopped.
I see, so the "alternator" in the diagram is actually a motor being tested for current used. A confusing diagram!!! I'll stick with my present system then, where the long since removed Alternator - starter - battery thick cable has been replaced. The charging is now via now via a thick cable directly from the alternator to the battery. There's a shunt midway and from each side a thin wire to the dashboard ammeter ( each thin wire being fused at the shunt end).
Re the chinese pic: you'll see the motor doesn't have a -ve supply - it goes through the "ammeter". The only issue you'd have is that the shunt'll have to be quite hefty. I wouldn't say the fuses need to be there. You can understand now why ammeters went out of fashion (unless you're an MG driver with string-backed gloves and a wife with a headscarf). When alternators came in, monitoring the charging voltage alone was sufficient to show everything was working properly, and much easier to implement (and cheaper).
