The Stovebolt Site Forums The Shop Area The Electrical Bay Amp Meter Question

Should the amp meter be midway between D and C when the key is in the off position? When I am driving the indicator needle is generally to the left of center. with the motor off it moves to dead center. All the other gauges drop to the left when the key is off. The gauge is the stock guage in my 57 Chevy 3100. The truck has a new alternator on a 350 sbc.

Thanks, Mike

yes, that's the way of it, and my '57 would run just left of center when charged and running .... watch what happens when the engine first fires, as it replaces the juice used by starting - also turn on the lights when the engine is off and see what happens .... remember this is 50's tech, amps flowing, not volts in the batt

Bill

I am a bit confused about what you guys are calling left. Is it left looking at the ammeter? If so, I would say that is discharge side. Moving to what I call left would mean that the alternator is dead and as red58 said, an ammeter shows amps flowing and a vehicle will discharge while running when the alternator is putting out nothing. If I have my left backwards, red's statement is correct.

So it's supposed to be in the middle? I thought mine had something keeping it from going to "C."

yes left is the discharge side [always with a vehicle left/right are from the drivers position], but dead center is key off only, commonly when running and everything is fine the gauge will/can show slightly toward the discharge side, even tho there's no real discharge happening [other than the coil] - if the gen/alt is dead, it'll show a LOT to the left, maybe all the way - notice these gauges are so high tech they have NO numbers on them, but they aren't just "C" or "D" and you don't want it to ever show steadily to the right, the battery will get fried .... the circuit is controlled by the regulator, and there will be times when the battery is charged enough for the regulator to cut the generator out of the circuit

yes JD, center is off/normal, a definite movement left = discharge [D], often just momentary until regulator cuts the generator in - movement to the right = charge [C], and should steadily move back to center as the generator brings the battery back up, faster after a 'small' draw, slower after a major draw, like extended cranking

Bill

Could the amp meter be connected the wrong way round? does it move towards "C" when the lights are turned on when the motor isn't running? If so, just reverse the connections at the back of the amp meter.

Stuart.

what's backwards? nobobdy's said anything here to indicate backwards operation .... my first response above suggested watching how the gauge operates under different current flow situations - being slightly toward either side under normal operating conditions tells you nothing about what's really happening except that's what's normal for that gauge, they're very much an "on/off" deal, showing what the regulator is doing

the ammeter is like your VOM ammeter, a small movement indicates a small amperage, and when the engine is running and drawing no more than the ignition uses, there's no need for a fully charged battery to be getting charged, that's why there's a regulator involved, it determines when the generator needs to be kicked in and how much

Bill

mserges said that the amp meter needle moves to the left when the motor's running; discharge is to the left on the amp meter in my truck. That's why I suggested turning on the lights with the motor turned off, if the amp meter is connected the wrong way round the needle will kick over to the charge side.

Stuart.

he didn't say it "moved to the left", he said it's "generally to the left of center" and related that to the needle position with the key off - "center" is relative on these things

I suggested watching the gauge under different conditions to show that "kicking over" is different than being, say, a needle width or 2 off center all the time, which can be the normal indication of a no charge situation with the key on, motor running or not

Bill

Bill,
You're correct, he didn't type the words "moved to the left" so I am guilty of paraphrasing mserges post; but the meaning I take from the original statement is that the amp meter indicates discharge when the motor is running because the needle is left of centre.

So there is a possibility that either the charge circuit is dead and that the battery hasn't gone flat yet, or the amp meter connections are reversed. Or maybe that the amp meter needle is just insensitive to current running through the meter.

Turning on the lights with the motor not running should indicate whether the amp meter is reversed,or whether the meter is insensitive.

Stuart.

I misread, I thought that Stuart Giles said that his did that, sorry, I will delete my post.

well, the assumption you made Stuart is that any reading of the needle to the left is a bad thing, and means something's wrong ... considering the low-tech nature of gauges from the 50's, it doesn't even have to mean there's actually a discharge happening, but yes, the lights will indicate the gauge is reading right [key on or off], so I'd say the normal condition of the system is about as much discharge as required by the coil, which is a miniscule draw on the battery, which will be topped up once it drops below a certain point and the regulator shunts some generator output to it

driving a 58 [with alternator] daily that reads:
- dead center when the key is off,
- about 1/3 from center to the left ["discharge"] when cranking,
- a slight bit to the right ["charge"] for a second or 2 immediately after starting,
- about 1 needle width to the left of center when driving regardless if any electrical on or off,
- about 3 needle widths toward the left at idle with lights or heater on ....
I read what he said as a gauge operating exactly correct and suggested some things to confirm that

my 57 with a generator acted just the same, never at dead center except with the key off

there's a reason that they went to volt gauges, amp gauges don't tell you much about the state of the system unless you know how the system works and are familiar with the vehicle

Bill