On 5/5/2011 12:02 PM, Stephen Trapani wrote:
I think Larry once explained why the amps get cut in half, but I forgot.
I have an amp meter installed in line between the alternator and the
battery switch. Last weekend I had a borrowed Fluke clamp meter. When I
put the clamp on the line coming out of the alternator it read exactly
half of what the in line amp meter was reading. Why is that?

Stephen


There are two kinds of clamp on ammeters - the ones good for AC only,
and the ones that work for AC and DC.
The AC only kind are cheaper, but they expect to find single phase
alternating current.

As several folks already mentioned, the usual Auto alternater uses an
internal three phase full wave rectifier stack, which uses six
rectifiers typically. Because adjacent phases overlap, the AC current
component is rather less than half the peak current amplitude.Cheap AC
clamp on meters read low in this situation.

This story is all well and good, but you mentioned Fluke specifically,
and I don't think they actually make the cheaper AC only clampons - but
I could be wrong.

Brian W