Ammeter gage

[Gr8tewhite05]

New alternator installed 9/21 and battery "health" checked 9/22. Around the beginning of November the gage , at start up,would go to discharge and stay there for about a 1/2 mile, then kick over to the charge side. BTW, 2005 2500 with 195,000 miles, original owner. I know my memory isn't what it used to be but I'd swear this thing went to charge after start up and then back down to the middle mark when charged.Should I be looking at or testing something in particular? Thanks!

 

[petersonj]

The gauge you are referring to is not an ammeter gauge - it is a voltmeter gauge. I am guessing it looks similar to the photo below. The voltage reading should normally be within the area marked in black. The short tick in the center usually represents 14 volts. Your gauge may or may not have numbers associated.

There are two things that make this gauge operate differently than how voltage gauges operated over 20 years ago. One is the temperature sensor under the driver side battery, the other is the post-cycle operation of the grid heaters.

The battery temperature sensor: Battery temperature is one of the inputs to help determine upper limit voltage set by the voltage regulator. A 100° day may set a maximum of 13.5 volts (your gauge would read a bit to the left of center). A 30° day may set a maximum voltage of 14.8 (your gauge would read a bit to the right of center.

The post-cycling of grid heaters: As ambient temperatures drop, the length of time the grid heaters remain on prior to starting the engine increases. Then, after the engine is started, post-cycling of the grid heaters begins. The grid heaters will continue to cycle until certain parameters are met as the engine warms, or if a specific road speed is reached (usually somewhere above 20 mph).

As you can imagine, the current draw on the batteries is very large considering the initial grid heater operation, the operation of the starter motor, and finally the grid heater post-cycling operation. During grid heater post-cycling, the batteries and the alternator work together to supply the amperage required. So, on a cold day it would be normal to see the voltmeter reading quite a bit to the left of center until the post-cycling of the grid heaters is complete.

If you are seeing this operation as described above, then the charging system is probably fine. If the gauge movement to the left of center is much greater than described, then you could have a charging system problem or batteries that are reaching the end of their life.

- John

 

[Gr8tewhite05]

The gauge you are referring to is not an ammeter gauge - it is a voltmeter gauge. I am guessing it looks similar to the photo below. The voltage reading should normally be within the area marked in black. The short tick in the center usually represents 14 volts. Your gauge may or may not have numbers associated.

View attachment 136071

There are two things that make this gauge operate differently than how voltage gauges operated over 20 years ago. One is the temperature sensor under the driver side battery, the other is the post-cycle operation of the grid heaters.

The battery temperature sensor: Battery temperature is one of the inputs to help determine upper limit voltage set by the voltage regulator. A 100° day may set a maximum of 13.5 volts (your gauge would read a bit to the left of center). A 30° day may set a maximum voltage of 14.8 (your gauge would read a bit to the right of center.

The post-cycling of grid heaters: As ambient temperatures drop, the length of time the grid heaters remain on prior to starting the engine increases. Then, after the engine is started, post-cycling of the grid heaters begins. The grid heaters will continue to cycle until certain parameters are met as the engine warms, or if a specific road speed is reached (usually somewhere above 20 mph).

As you can imagine, the current draw on the batteries is very large considering the initial grid heater operation, the operation of the starter motor, and finally the grid heater post-cycling operation. During grid heater post-cycling, the batteries and the alternator work together to supply the amperage required. So, on a cold day it would be normal to see the voltmeter reading quite a bit to the left of center until the post-cycling of the grid heaters is complete.

If you are seeing this operation as described above, then the charging system is probably fine. If the gauge movement to the left of center is much greater than described, then you could have a charging system problem or batteries that are reaching the end of their life.

- John

Thanks John. I just replaced the battery temperature sensor and will check the batteries again. Not sure where I got ammeter.

 

[petersonj]

Not sure where I got ammeter.

Probably because ampere gauges were used from the beginning when batteries with charging systems were installed on vehicles. The ampere gauge continued to be used for decades. Sometime in the early 90's (I think) the changeover to using voltmeters happened.

- John

 

[Ozymandias]

Where did you buy the Alternator?

 

[Gr8tewhite05]

Where did you buy the Alternator?

The original quit on a trip while we were in Richfield, Utah. KMR Diesel handled the swap.

 

[Ozymandias]

The original quit on a trip while we were in Richfield, Utah. KMR Diesel handled the swap.

I ask because the rebuilt ones have a very bad track record.

I suggest also to check the main grounds and the cross-over cable for any corrosion.
The ECM checks voltage from the drivers side battery but the Alternator charges to the passenger side one.

 

[Gr8tewhite05]

Thanks, I appreciate the feedback. Will check those tomorrow.