How to read an amp gauge

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jonnyrose

jonnyrose

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So I've just finished the wiring in my 1968 dodge dart,and wired up the amp gauge,when you turn your car on but not start it should the gauge move to the the charge side of neutral?
 
Guage should go to left side of center with engine off and a load like head lights on

With engine running, needle should be centered or to the right of center With no load.


If yours is reverse, just switch the wires on the ammeter
 
jonnyrose said:
So I've just finished the wiring in my 1968 dodge dart,and wired up the amp gauge,when you turn your car on but not start it should the gauge move to the the charge side of neutral?
Click to expand...
Should move slightly to the discharge side, as you're drawing power from the system. You may have it wired backwards? Try turning on the headlights without starting the engine. What way does it move then?
 
jonnyrose said:
So I've just finished the wiring in my 1968 dodge dart,and wired up the amp gauge,when you turn your car on but not start it should the gauge move to the the charge side of neutral?
Click to expand...
No, just a guess but you may have a wire set reversed.
There will be a small current drain with the ignition on and the motor not running so the needle should move slightly to the discharge side
 
That's what I was thinking,I've got the battery wire on the side closets to the speedo,and alternator black wire closes to the oil
Gauge
 
RED is stamped into the circuit board. Its pretty much impossible to see when installing so I've always flagged black with a lil piece of electric tape ( since the 1 time I made the same mistake anyway ).
 
from assy drawing
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upload_2020-3-29_9-17-12.png


Ammeter measures current flowing in or out of the battery.
Current flowing to the starter solenoid and starter does not go through the meter.
The meter on a '68 shows 40 amps to 40 amps.
A slight discharge at start is expected. This would be 2-5 amps flowing to the starter relay and ignition coil.
At fast idle, immediately after start the ammeter might show as much as 20 - 30 amps charging. It would only show that much if the battery is a little lower than normal.
In less than a minute, the current should drop toward zero as the battery charges. Quickly at first and then more slowly.
At slow idle with a stock alternator you may see the battery discharge slightly when lights and accessories are on. Accessories being things like wipers, and heater fan. It will then charge as soon as the rpms come up while driving.

If a charge continues for a long time, it could be an indication of high voltage causing overcharging. While the meter is showing that charging check the voltage. If its the normal range, everything is fine and the battery just needed a long slow charge.
 
Yep they were backwards,all good now,and yes it goes to almost the c after starting and then goes to just above center when idling ,thanks for explaining how to read it, I have fusible links on either side under the hood,just in case something goes sideways,but it's cool having it function
 
Mattax said:
View attachment 1715496139
At fast idle, immediately after start the ammeter might show as much as 20 - 30 amps charging. It would only show that much if the battery is a little lower than normal.
In less than a minute, the current should drop toward zero as the battery charges.
Click to expand...

Actually this depends on several things..........

How large is the alternator (output)
How discharged the battery is, IE it may have been sitting for a couple/ few weeks
Whether you had to crank the "eck" out of it to start, and so on

I used to have an SW 100A ammeter in my beat up Landcruiser, SB Mopar, and the big frame 120A alternator. That thing would BURY the ammeter for a few seconds on a cold start up, and PEG it after using the "wench."

But you are right about one thing.......After starting, it should show some charge, and if headlights, heater, etc are on, you should have "enough alternator" to keep the needle to right of center above idle, and "eventually" the needle should drop down and run at center
 
I wrote it that way 'cause if the OP or as you say, anyone else, sees the ammeter peg out near 40 amps, its best they assume something big has gone wrong.
Better safe than sorry.

jonnyrose said:
Yep they were backwards,all good now,and yes it goes to almost the c after starting and then goes to just above center when idling ,thanks for explaining how to read it, I have fusible links on either side under the hood,just in case something goes sideways,but it's cool having it function
Click to expand...

Glad that was it.

If the charging increases with engine speed, then it would be worth making some additional checks.
One is to make sure the voltage is not increasing with rpm to the point its above 15.0 V .
Another is make sure the voltage is not dropping below 12.8 or 13.0 V at idle with no accessories or lights on.

Final observation. In most systems just one fusible link is used. It should be between the battery and the firewall connector.
A second link is sometimes needed, but there ought to be a good reason for it. Otherwise its unneeded resistance to flow. Both itself and the extra connections.
 
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