# 40-50% increase in range with warm weather??



## Ziggythewiz (May 16, 2010)

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?


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## dougingraham (Jul 26, 2011)

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.


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## Dougnutz (Aug 22, 2011)

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?


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## dtbaker (Jan 5, 2008)

Dougnutz said:


> ...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.


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## DIYguy (Sep 18, 2008)

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


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## EVfun (Mar 14, 2010)

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.


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## MN Driver (Sep 29, 2009)

EVfun said:


> 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.


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## GizmoEV (Nov 28, 2009)

MN Driver said:


> 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.


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## GizmoEV (Nov 28, 2009)

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.


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## EVfun (Mar 14, 2010)

MN Driver said:


> 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.


It is really hard to say, but it is above 40F. Pack interior temperature right now is 82, inside the garage is 86, and outside is 74 (with 70% humidity, not very western WA), and the overnight low was 60. 

I'm going to do some historical weather checking to figure out what my January was like before shooting off a number...

It looks like winter around here could have been well described as being 42 for a high and 29 for a low. The garage only rarely gets below freezing inside as I blow a little attic heat into it in the winter (but the garage isn't insulated, so it doesn't stick around.) I have to guess that the pack temperature gets down to between 45 and 50. It is really hard to say as I drive less but the garage runs further above outside temperature in the winter.


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## Dougnutz (Aug 22, 2011)

@evfun Thanks for that info. I live in the western wa area too so your numbers are particularly relevant to me. 

@everyone. I have noticed that the CA tends to change calibration, I haven't noticed why but it doesn't seem to have a big impact on the reading. I may be wrong so I will be watching that closely. I do leave it on all the time so that may attribute somewhat but I think the main difference is that the voltage is staying so much higher. 

I live in a particularly hilly area and in the winter with cold batteries the voltage drop is very noticeable, this obviously requires more amps to do similar work. I'm starting to think that is what I have really noticed. Since I have been looking at Ah as a "fuel gauge". I'll start paying attention to the WH to see if there is a noticeable difference


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