Fluctuating Battery Levels

[FusionHybrid2013]

I am wondering if this happens to anyone else?

 

I turn my car off and the battery meter shows 10% - 25% full

 

I turn my car on the next day and it shows 25% - 50% full

 

This happens consistently, although to varying degrees. It usually only goes up by about 1/8 of the meter, but this morning it went up by at least 1/4. The perceived extra charge along with perfect weather allowed me to get a personal best 58mpg on my 36 mile trip into work this morning. The extra charge is like getting a birthday present everyday. I am sure that the magical battery charging fairy isn't visiting my car while it is parked, so does anyone have an explanation?

[corncobs]

Same thing here; last night I got home when in EV+ the ICE had to come on for a little bit so finally home the SOC was probably below 30%. This morning it looked like almost 50% and I was able able to creep away using EV only.

 

Maybe there is a little fairy flying by each night to give the battery some love. ;-) Hopefully that doesn't sound too dirty.

[neod192]

Are you sure you don't have an Energi? LOL

[acdii]

vosmosis

[corncobs]

vosmosis

Well that's what I call minimalistic; looks like that's an acdii creation not even google return useful results. ;-)

[murphy]

Well that's what I call minimalistic; looks like that's an acdii creation not even google return useful results. ;-)

Probably is but I decode it as voltage osmosis.

[acdii]

Probably is but I decode it as voltage osmosis.

WINNER WINNER CHICKEN DINNER!!!!

[VonoreTn]

What is your average, for the round trip to work? 58 is impressive, but maybe it's downhill slightly with the wind behind you. If you get that kind of mileage consistently, maybe it's time for me to upgrade. ;-)

Edited May 30, 2013 by VonoreTn

[FusionHybrid2013]

Here are some pics of what I'm talking about:

 

Before - Taken @ 6pm EST on 5/30/13 as I'm turning my car off when I arrive at my house

After - Taken @ 7am EST on 5/31/13 as I'm turning my car on to go to work

Combined = After and Before guages next to each other (After is bigger)

 

This difference seems a little less than what I'm used to seeing, but pretty close. It looks like maybe a 1/10 increase rather than the 1/8 that I generally estimate. It looks like at least one other person has seen this, so its not just me. Any ideas on why it happens?

[acdii]

I have seen this on battery packs. When they cool down and rest, their capacity/volts increase. Seen it happen with NiMh, and LiPo.

[Guardian_Bob]

I have seen this on battery packs. When they cool down and rest, their capacity/volts increase. Seen it happen with NiMh, and LiPo.

 

Two things, as the heat increases, so does the resistance over the wires: https://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity#Temperature_dependence

 

In addition, LiPo batteries must be kept below a particular temperature or they will fail. The computer may be estimating that cost in (battery drain) when you turn your car off, but not when you first start it up.

[acdii]

LiPo and Lion are different, I thought the Ford uses Lion. I have seen what happens when a LiPo gets over used, not a pretty sight, and one I NEVER want to see happen in a car. Especially when you consider my kids are sitting right in front of the battery pack! Lion packs are far less likely to do what a LiPo does, and it would take a massive failure on the Hybrid system for that to occur.

[Guardian_Bob]

LiPo and Lion are different, I thought the Ford uses Lion. I have seen what happens when a LiPo gets over used, not a pretty sight, and one I NEVER want to see happen in a car. Especially when you consider my kids are sitting right in front of the battery pack! Lion packs are far less likely to do what a LiPo does, and it would take a massive failure on the Hybrid system for that to occur.

 

You're right, I misremembered the technology.

 

Still, heat changes the measurement. Using Ohms law I=V/R or V=IR. Since R increases, I decreases. But because R is assumed to be resistance at normal operating temperature, the computer estimate may be off, especially when starting a cold engine. Now you can use thermistors and correct for such deviations or you can wait for the engine to heat up. The former requires more hardware and software, so Ford likely went with the latter.

[acdii]

 

You're right, I misremembered the technology.

 

Still, heat changes the measurement. Using Ohms law I=V/R or V=IR. Since R increases, I decreases. But because R is assumed to be resistance at normal operating temperature, the computer estimate may be off, especially when starting a cold engine. Now you can use thermistors and correct for such deviations or you can wait for the engine to heat up. The former requires more hardware and software, so Ford likely went with the latter.

Thats what I was thinking. I dont know if that gauge reads volts or capacity. Difference between NiMh and Lithium is the voltage drop is constant on Lithium, where NiMh the voltage drops only under load. When I check voltage on my RC stuff, I can tell state of charge based on the voltage on the LiPo/Lion, but on the NiMh I have to put a load on it to read SOC.

 

If it read Volts, then the fluctuation makes sense since at rest the voltage will rise in these packs, I see it all the time with my plane packs. After a flight I check voltage, and before I put it on the charger I let them cool down, and I can see a voltage rise when I place it on the charger before I start the cycle.

[FusionHybrid2013]

 

Two things, as the heat increases, so does the resistance over the wires: https://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity#Temperature_dependence

 

In addition, LiPo batteries must be kept below a particular temperature or they will fail. The computer may be estimating that cost in (battery drain) when you turn your car off, but not when you first start it up.

 

Since I won't even attempt to understand that wiki, I'm going to run with my interpretation being that there is a magical battery charging fairy that visits my car every night...

 

Or that heat is the cause of the fluctuation. Thanks for the explanation.

[Guardian_Bob]

 

Since I won't even attempt to understand that wiki, I'm going to run with my interpretation being that there is a magical battery charging fairy that visits my car every night...

 

Or that heat is the cause of the fluctuation. Thanks for the explanation.

 

Well the key is, the charge isn't fluctuating, only the measurement. Think of it like using boiling water to measure temperature. At sea level it boils at 212. Well if you go to the top of Mount Everest and boil water, you might assume that means the water is 212, when in fact is is only 167. (Granted at the top of Mount Everest, you don't really care, you just want something warm.)

 

The air pressure (as a function of elevation) is a hidden variable in your temperature measurement, it can be accounted for, but only by using other devices to determine your altitude and some math.

 

In much the same way your battery level measurement depends on the hidden variable of temperature.

 

Or in other words, it isn't a fairy who's adding extra charge. It is a gremlin who's messing with your measurement.

[GrySql]

 

I'm going to run with my interpretation being that there is a magical battery charging fairy that visits my car every night...

First it was the tooth fairy when my teeth fell out as a kid and I found out later that was, mmm, a fairy tale.

Next, Santa Claus was outted.

Now, the battery fairy is spotted and debunked.

This is depressing.

 

Especially now, at my age my teeth are falling out again and I could use the money....