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Amp to Volt meter question

14K views 18 replies 8 participants last post by  55 Tony 
#1 ·
When you change over do you just splice the alt wire to the battery
wire? Then wire in the volt meter?
 
#8 ·
Personally, I would not mess with an ammeter anymore....All that current flowing under the dash is just a fire waiting to happen...Totally, old school and unnecessary, IMHO.
 
#14 ·
Tony, there are basically 2 types of ammeter gauges.

One kind has no shunt, you run the full charging current through the meter. This is no a good situation, as you need longer wires and they have to be big ones. And if the ammeter is mounted in a panel below the dash like was common way back when, then you also have two "hot" posts that could short to something unintentionally. The other deal on this is those ammeters won't be up to the output of modern alternators. They were designed for 25-35A generators.

The second kind has a separate shunt (resistor) - with this type very little amperage is run through the gauge, so the wires to the gauge can be small.

A few OEM ammeters from the 60s use a shunt. Stewart Warner used to sell (may still) ammeters with shunts calibrated to the gauge.

But here's the important part. You can tell everything you need to know about charging output with a voltmeter. OEMs have used voltmeters almost exclusively since the mid 70s for indicating alternator output.
 
#15 ·
Rick, I know how ammeters work. Some had a shunt inside, some had a fairly heavy gauge wire around a core and no shunt, and yes the external shunt ones were few but the most safe. The ammeter is actually reading the voltage drop across the shunt. As far as the voltmeter doing everything the ammeter did is not always true. It is still very possible for there to be a drain on the battery when the voltmeter shows 14 volts. Especially on a 3 wire when people run the small red wire to the wrong place (anywhere besides the battery) or a one wire also depending on how it's wired and in both cases where the voltmeter is wired to. Throw in all the relays people are using that are wired to the battery and have there own fuse and the odds of a false reading go up much higher if they jumpered the red sense wire on the alternator. I wouldn't call myself an expert but I did have a few years of electronics training plus 38 years of on the job training and I learned a little bit about the basics.
 
#16 ·
Do you already have the ammeter in place? If so, and you want to switch to a voltmeter(it is a better indicator, for MOST normal operating cases), you can tie the ammeter wires together(do a reliable job) and tape or shrink wrap. If you add a third wire into this, you can use this junction as the voltmeter pickup point.
 
#17 ·
Chalfont, PA



Hey jwscab, I used to go through Chalfont a lot many years ago. Did they ever finish the 202 bypass? What a hassle it was to go from Lansdale to Doyelstown during rush hour! Are the bowling lanes and the ice cream stand still there? At one time they were owned by a former major league baseball player but I forget his name. Played for the Oakland A's which I don't think exist anymore.
 
#18 ·
Yes, the bypass is completed. About 2 yrs now and it's really helpful. The only downside is that the speed limit is 40 and it's more like a 50mph road.

The ice cream shop and bowling alley are gone, they demo'd them about a yr ago, but I guess were vacant for some time. Not completely sure, I've only been in Chalfont for 4 yrs.
 
#19 ·
Wow, you are lucky you only had to wait 2 years, they stopped the bypass construction I think in the early 1970's. I know in 1979 anyway that there were dead ends and no construction going on.
I'll stop the Off Topic stuff now, just brought back memories and I was curious what it's like now.
 
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