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TR6 TR6 Question..ammeter
- Thread starter prb51
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Jedi Knight
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No, I believe they were only rated at 30 amps
TR3driver
Great Pumpkin - R.I.P
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FWIW, it's not difficult to add a shunt on the back of the stock TR3 ammeter, to increase it's full scale reading. I did exactly that, many years ago when I converted to a 60 amp Ford alternator.
You'll need to experiment a bit to get the right shunt value. I originally used steel "handy" wire for my shunt, and added strands across the ammeter terminals until the reading for the headlights was roughly 1/2 what it was before. That worked well for a long time, but when I redid the dash, I replaced it with a length of 16 AWG copper. ISTR I started with about 1 foot, and gradually shortened it to about 5" or so, to get the desired ratio.
BTW, stock TR3 generator only rated for 19 amps. Early TR6 alternator was almost twice that, at 36 amps. In theory it could drive the ammeter slightly beyond full scale, but that won't hurt anything. They aren't exactly precision instruments /bcforum/images/%%GRAEMLIN_URL%%/smile.gif
You'll need to experiment a bit to get the right shunt value. I originally used steel "handy" wire for my shunt, and added strands across the ammeter terminals until the reading for the headlights was roughly 1/2 what it was before. That worked well for a long time, but when I redid the dash, I replaced it with a length of 16 AWG copper. ISTR I started with about 1 foot, and gradually shortened it to about 5" or so, to get the desired ratio.
BTW, stock TR3 generator only rated for 19 amps. Early TR6 alternator was almost twice that, at 36 amps. In theory it could drive the ammeter slightly beyond full scale, but that won't hurt anything. They aren't exactly precision instruments /bcforum/images/%%GRAEMLIN_URL%%/smile.gif
OP
prb51
Luke Skywalker
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Randall,
For some reason I thought the TR6 gauge would be about 60 amps, oh well.
Ok, exactly how do I shunt the original gauge? From your quick description it sounds like you shunted across the pos/neg on the gauge and experimented with wire length/thickness to get an approx. 1/2 value.
Help...
For some reason I thought the TR6 gauge would be about 60 amps, oh well.
Ok, exactly how do I shunt the original gauge? From your quick description it sounds like you shunted across the pos/neg on the gauge and experimented with wire length/thickness to get an approx. 1/2 value.
Help...
TR3driver
Great Pumpkin - R.I.P
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prb51 said:
That's it exactly. Inside the ammeter is just a small coil of heavy copper wire; what you are doing is trying to match the resistance of that coil so that 1/2 the current flows through your shunt, and 1/2 through the ammeter.
Way back when, I tried measuring the ammeter resistance and came up with 1.2 milliohms, which would be 3.5" of 16AWG copper. However in practice the shunt needed to be higher than that, perhaps because of contact resistance at the ammeter terminals. Since I had the early ammeter with the clamp-type terminals, it was easy to start long and keep trimming until I got it close enough to suit me. I took it loose from the panel and let it hang on the wires while I picked the shunt.
(Really, it doesn't need to be all that accurate. You're only interested in about 5 different readings anyway : no charge, charge a little, charge a lot, discharge a little, discharge a lot.)