huh ... my 58 with a 63 amp alternator hasn't fried the ammeter, or even pegged it, and I've run the battery down good using the starter to move the truck across an intersection when it ran outta gas, then had to crank it long enough to get fuel flowing again .... maybe you guys are talking about the older AD gauges - or the wimpy gauge Stuart cites on the Austin
I've always converted my old trucks to alternators and never shunted the ammeter - no problems
Bill
Thanks for that,
here's a picture of the non-wimpy stock Chevrolet 40A ammeter pegged on my '50 3100, it was like this when bought the truck, the PO obviously didn't think that an ammeter shunt was necessary when he fitted a 68A alternator.
Any device which shunts the ammeter with a low resistance will stop it pegging, but the lower the resistance you use for the shunt, the less the needle will move. If you use a short length of large diameter copper wire, the needle may not move at all, so not really worth having the ammeter in circuit IMO.
I used a shunt with known resistors rather than a length of wire/piece of sheet metal because it allows you to accurately calculate the FSD (Full scale Deflection) of the ammeter, I used 3 100W 1 ohm resisors in parallel which gave an FSD of 70A on my truck; and yes, the ammeter needle goes right the way over when I start the truck after leaving it for a few weeks.
