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Open Roads Forum  >  Tech Issues

 > Cold Ambient Temps = Higher Alternator Voltage?

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otrfun

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Posted: 02/14/21 08:00pm Link  |  Quote  |  Print  |  Notify Moderator

Our '16 Ram 3500 Cummins (220a alternator) typically charges around 14.3 - 14.4v about 95% of the time. On occasion charge voltage will drop to 13.9v on a long trip when the batteries get topped-off really well.

This morning temps were almost zero (F) when I started our truck. Alternator voltage ramped up to 14.7v momentarily then immediately down to 12.1v (battery sag voltage after one engine start) about 4 or 5 times before it finally came on steady at 14.6v (it seemed like the voltage was exceeding some kind of threshold and was purposely being turned off, then on again for another try). In any case, it remained at 14.6v during our entire 6 hour drive on the freeway. Typically it will gradually drop (14.4v to 13.9v) as the batteries work towards a full charge. However, no voltage drop whatsoever on this trip.

After a bit of snooping online, it seems some manufacturers boost charging voltage when there's very cold ambient temps. Any chance this may be occurring with our truck?

RLS7201

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Posted: 02/14/21 09:11pm Link  |  Quote  |  Print  |  Notify Moderator

If your alternator has a solid state built in regulator, what you are seeing is designed in and normal.

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Posted: 02/14/21 09:25pm Link  |  Quote  |  Print  |  Notify Moderator

Before this thread gets run away with.. slightly higher voltage in cold is normal and the voltage sags you were seeing where the grid heaters cycling.
Your truck is fine.

scottykrug

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Posted: 02/14/21 09:34pm Link  |  Quote  |  Print  |  Notify Moderator

^this. Ours does it too.

* This post was edited 02/14/21 10:41pm by scottykrug *


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time2roll

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Posted: 02/14/21 09:44pm Link  |  Quote  |  Print  |  Notify Moderator

I would assume all is normal by oem design. This is why they dumb down the gauges in some to just show normal.


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pianotuna

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Posted: 02/14/21 10:47pm Link  |  Quote  |  Print  |  Notify Moderator

Temperature compensation is something I desire in any charging device I use.


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Posted: 02/15/21 07:55am Link  |  Quote  |  Print  |  Notify Moderator

What are you using to measure the voltage ? The gauges on you dash are not very accurate.

Constantly >14.0V is actually not "normal" ! After running for 5-10 minutes, the voltage should be <14.0V

Make sure all battery cable connection are clean and tight. Constant high charging voltage could also mean your battery is on its last legs.

CA Traveler

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Posted: 02/15/21 08:17am Link  |  Quote  |  Print  |  Notify Moderator

My experience with a external accurate voltmeter is that alternators/regulators are rather poor at adjusting the charging voltage due to temperature. Perhaps related to how/if temperature is detected.

Both my RV charger and solar charger with external probes attached to the battery terminal adjust the bulk/absorb charging at expected.


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Posted: 02/15/21 08:39am Link  |  Quote  |  Print  |  Notify Moderator

The Dodge Cummins engine has Grid Heaters in the intake for cold weather starting. This will cause the voltage to drop after starting in cold weather. The heater will cycle on and off until the intake manifold reaches 60 degrees or you go over about 7 MPH. I think that's what you are seeing.


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mbopp

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Posted: 02/15/21 08:47am Link  |  Quote  |  Print  |  Notify Moderator

Yes, higher voltage is a design feature. At one time I had a graph showing temperature vs voltage for a charging system. Now the alternators are controlled by the engine computer.


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