[Dougnutz]

Hi all. It's been a while since I did the floodie to lithium conversion on my truck and all has been going well. But lately I've been seeing numbers from my CA that make me think something is wrong with it.

The short version is that I put the lithium in during mild weather for my area 40-50 degrees. Then proceeded through the winter. I noticed a dramatic drop in performance when the temp drops below 30 but frankly it's still just fine for my uses. Now that the weather is steadily above 80 I have noticed significant improvement in performance and apparently range, according to my CA.

The same trip that takes 27 ah in 40 degree weather takes 18 ah in 80 degree weather. Can this be correct? Am I really seeing this large of an increase in range or is my CA lying to me?

[Ziggythewiz]

I think the CA has some sort of temp calibration that makes a significant difference. Also, what kind of wH/m do your readings translate to?

[dougingraham]

You need to compare the watt hours instead of the amp hours. When it is cold the battery voltage is lower so you use more amps to compensate. The Rolling Resistance is higher when it is cold because the wheel bearing grease and transmission/differential lube is more viscous. I could imagine a 20% difference but would expect 15%. Anyway compare the watt hours next time. The difference will be less in the energy comparison but for the purposes of range comparison amps works.

Probably some of this is real and some is instrumentation.

[Dougnutz]

I don't think the vehicle is taking less energy to make the same trip. Unfortunately I won't be able to compare watt hours until it turns cold again. But I don't expect notable change. The Rolling Resistance may be slightly higher but I think that will prove negligible.

The explanation that seems to make the most sense to me is that voltage is remaining notably higher in warmer weather resulting in significantly less ah consumed to do the same work. What is surprising me is how much of a difference there is.

Does anyone else notice a significant range difference between batteries at 40 degrees and 80?

[dtbaker]

Originally Posted by Dougnutz

...I've been seeing numbers from my CA that make me think something is wrong with it.

the CA has no temp compensation, and goes off 'zero' significantly with temp change, especially under low-amp charge or even floating while just sitting. You can re-zero the amp reading at seasonal temp, check voltage, and/or zero the 'trip' kWhr, put a kill-a-watt meter on your wall and check the kWhr you put in compared to what the CA says.

[DIYguy]

The CA does output Watt-Hours . . . and amp hours and watt-hours/mile, and miles(or kms) and volts and amps and peak amps at low volts and and a lol

[EVfun]

I've haven't noticed a change in range because I don't push my range enough take notice (and don't count amp hours except when testing.) What I notice is a noticeable drop in internal resistance. Now that they are warm I can nail them for 7C (420 amps) and not drop below 2.7 vpc. In the winter when the pack is cold I drop slightly below 2.7 vpc at 5C (300 amps) until I drive a bit.

My pack is never blow freezing, the car sits in an attached garage and western WA doesn't have very harsh winters. Still, the internal resistance goes up almost 50%, from around 1.4 milliohms now to about 2 milliohms. Not bad for little 60 amp hour Thunder Sky LiFeYPO4 cells.

[MN Driver]

Originally Posted by EVfun

I've haven't noticed a change in range because I don't push my range enough take notice (and don't count amp hours except when testing.) What I notice is a noticeable drop in internal resistance. Now that they are warm I can nail them for 7C (420 amps) and not drop below 2.7 vpc. In the winter when the pack is cold I drop slightly below 2.7 vpc at 5C (300 amps) until I drive a bit.

My pack is never blow freezing, the car sits in an attached garage and western WA doesn't have very harsh winters. Still, the internal resistance goes up almost 50%, from around 1.4 milliohms now to about 2 milliohms. Not bad for little 60 amp hour Thunder Sky LiFeYPO4 cells.

That's really good data, I know you've posted info like this before but I don't know what temperature you are at for that level of sag. I'm asking because I'm looking to use 60Ah cells and 2.7v at 5C is more than acceptable for my car(with more cells), we have a much colder climate here in Minnesota but all I really need is to get near the level of performance you have and I'd be more than set. I don't think I'll need to add much heat at all to get the performance I need but was wondering if aiming for a 32 degree pack temp on the coldest winter night would be fine, and if your data is at, say 40 degrees, I'd think I'd be all set.

[GizmoEV]

Originally Posted by MN Driver

That's really good data, I know you've posted info like this before but I don't know what temperature you are at for that level of sag. I'm asking because I'm looking to use 60Ah cells and 2.7v at 5C is more than acceptable for my car(with more cells), we have a much colder climate here in Minnesota but all I really need is to get near the level of performance you have and I'd be more than set. I don't think I'll need to add much heat at all to get the performance I need but was wondering if aiming for a 32 degree pack temp on the coldest winter night would be fine, and if your data is at, say 40 degrees, I'd think I'd be all set.

With my 200Ah TS pack at 0°C a draw of ~250A will easily pull the cell voltages below 2.93V (that is what my BMS was set at). This is with a fully charged pack. FWIW, a short drive down and back up my hill, ~3 miles, was enough to raise the temperature of my pack above 0°C so I could charge it. The current at these temps was ~1C for most of the hill climb.

[GizmoEV]

Doug,

I find that I have to correct the CA's calibration periodically. It appears to be temperature dependent but not always. That is one reason I don't leave mine on all the time. It goes off with the key but I have an override switch so I can turn it on without anything significant on in the car. I recalibrate it at that point. That could be part of the reason you see the results you are seeing.

I usually charge my car through a Kill-A-Watt meter and record my energy usage per mile. This naturally includes charger inefficiencies along with battery inefficiencies. I've attached a graph of the last 2.5 years. I installed and started using my batteries in the first part of January 2010. The dark blue squares are the individual miles/kWh I got. That first winter wasn't too cold. I only wish I could correlate the results with pack temperature but I don't have that data.

Note that a while after January 2011 I quit charging so often so the last part of the graph is "condensed" compared to the first part. You can see the fewer number of charges done with the DOD below 10%.

In any case, I'd expect you to have similar results to mine.