Voltage Measurements - health 2018 F150

[meep]

So, just on a whim I installed a digital voltmeter in the F150. I study in it, sometimes running accessories, engine off. It’s got a larger battery and small solar panel on the camper shell, and a 600 Watt inverter I use mostly to recharge hand tools from when needed. Especially when running the inverter for extended periods, I’ve been wary of battery charge.

I picked up a couple of different voltmeters from amazon. Not all of them were accurate, but this one measured within 0.05 volts of my Klein meter in the garage: https://www.amazon.com/dp/B07RFCG475?ref_=cm_sw_r_cp_ud_dp_HW47QS94T7C8EPSBZ8AP. It’s shallow enough that with the tabs bent in the back, it installed more easily than it should in the headliner (mine is an XL and doesn’t have any kind of console up there). I ran the wire down the passenger A-pillar and tapped the 12V accessory outlet in the dash.

Cold start: 14.8, tapering down after 15-20 seconds to 13.5.
2 minutes after cold start, it likes to cruise at 12.5-12.4 volts. Upon braking, it will jump to 14.7-8. As soon as we are sitting, down to 12.5. Rolling again, 12.5, maybe 12.4. Will jump to 14.7-8 if the foot is lifted off the throttle. I was running the A/C during all this.

Lights on - 13.5V rock solid no matter what.

It’s a pretty aggresive strategy, I’ll give it that…

-m

 

[LazyDog]

This new charging systems are a lot different when compared to the older systems.

 

[Randol]

This new charging systems are a lot different when compared to the older systems.

Yes they are, tied into the BCM and under software control. Some compensate for the age of the battery and must be reset when a new battery is installed. My 2020 Mini Cooper S is one of them.

 

[eljefino]

Do you hear the HVAC fan rev up and down when the voltage changes?

 

[meep]

Do you hear the HVAC fan rev up and down when the voltage changes?

I watched it today with the AC on. At lower selected fan speeds, the voltage continues the dance between 12.5 and 14.7. I cant hear a difference however it feels like it breathes a bit more on decel, so maybe it does. At higher fan speeds, the voltage is lifted to 13.5 and doesn’t change.

for kicks and grins I turned on the rear defrost grid. That does not get a priority.

I’ll bet a high speed command sent to the radiator fan triggers a 13.5. And maybe a connected trailer.

 

[tom slick]

Get Forscan and you can really monitor stuff

 

[eljefino]

I bet your HVAC fan is PWM modulated, perhaps with an RPM feedback control. "Turbo" fan mode may also trigger higher alternator voltage. The EPA used to test cars on "the loop" with the HVAC off, maybe they still do.

 

[meep]

I bet your HVAC fan is PWM modulated, perhaps with an RPM feedback control. "Turbo" fan mode may also trigger higher alternator voltage. The EPA used to test cars on "the loop" with the HVAC off, maybe they still do.

Agree - it’s a 7 step soft knob, and it ramps up and down gently during a/s/s. The other thing which could mask it is the vehicle voltage changes are also ramped and not immediate, enough to mask it.

also, it’s warmer today, and once the truck was good and hot, cruise voltage was dipping down to 12.3, with 14.5 max, so it’s got temp in the algorithm as well. At 12.3 standard cruise voltage on warm days, I’m rather surprised we don’t see these things eating batteries faster. That’s not a healthy voltage to me… but maybe they cram enough amps in during deceleration to have gotten the math right.