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Battery Voltage vs. Temp.

3K views 16 replies 7 participants last post by  S Keith 
#1 ·
Kind of a theoretical question, but I did some searching and couldn't find any answer. Does anyone have a reference book or other data which might show loaded battery voltage vs. temperature? I think we all know that a cold battery doesn't deliver as high a terminal voltage, but I have not seen a curve or graph.
Thanks.
 
#2 · (Edited by Moderator)
Cold battery conditioning

jime,

I am wondering the same thing. I have been reconditioning my pack for the first time per prolong guidelines and it is about 0 C outside. My original pack voltage when I bought the car two weeks ago was 151.15. On first charge it settled to 170.1V. On second charge it settled to 171.6V. its resting now from its third charge. All of these at about 0 C. Remove spaces to follow link.

There is a helpful paper here also https://www.google.com/url?sa=t&rct...AOXXxXi5ALrajtdCQ&sig2=wMWNuyMVaGff5ka09LowkA
 
#3 ·
I cannot speak to the chart Jim is asking about, but I can say 40 deg F is minimum temp for grid charging/reconditioning.

A heated garage, a means of providing heat to the car cabin (for pack fan to pull through pack), or pack removal to a warm area is needed for winter time grid work.

I guess that goes in hand with Jims' comment of a cold pack not delivering as well, it also doesn't receive as well.
 
#6 ·
Good question, and since I'm no electrical expert (I just follow their sound advice) I must defer to those with the know-how.

Jime can probably give some detail, along with Peter, or S Keith.

My info reference is from Jeff at HybridAutomotive.

I've always tried to have a pack temp around 70 deg F for grid charging (using an obdiic&c to see temp).
 
#7 ·
Anything above freezing +1 or 2 degrees is fine for charging, it just takes longer or is perhaps slightly less efficient at the low end.

For power delivery and max IMA oompfh the cells need to be above 20C and preferably about 35-40C. The Insight will not allow maximum motor current with the battery temp below 20C.
 
#8 · (Edited)
I think I'm a little more skeptical than others on the effectiveness of grid charging at cool to cold temps, though I don't have any proof. I think there's a very good chance that a pack at only say 32-40 degrees F can have real trouble charging at only a ~350mA rate. Personally, I wouldn't expect a good full charge from a grid charger if the pack started at temperatures that cold. I'd drive the car first and use the pack, to warm it up, then I'd grid charge it.

Here's some of what the Panasonic NiMH manual has to say about charging and temperature:
"1. Charging, 1.1 Charging temperature
Charge batteries within an ambient temperature range of 0°C to 40°C [32F-104F]. Ambient temperature during charging affects charging efficiency. As charging efficiency is best within a temperature range of 10°C to 30°C [50F-86F], whenever possible place the charger (battery pack) in a location within this temperature range. At temperatures below 0°C the gas absorption reaction is not adequate, causing gas pressure inside the battery to rise, which can activate the safety vent and lead to leakage of alkaline gas and deterioration in battery performance. Charging efficiency drops at temperatures above 40°C. This can disrupt full charging and lead to deterioration in performance and battery leakage.
"

Note that the usual low rate of charge is 0.1C, or 650mA, yet grid chargers are usually only 350mA. Also, we're usually dealing with older, tired-er cells - so 350mA at 32F, trying to charge tired cells, seems like a recipe for not-so-good charging...
 
#9 ·
I think I'm a little more skeptical than others on the effectiveness of grid charging at cool to cold temps, though I don't have any proof. I think there's a very good chance that a pack at only say 32-40 degrees F can have real trouble charging at only a ~350mA rate. Personally, I wouldn't expect a good full charge from a grid charger if the pack started at temperatures that cold. I'd drive the car first and use the pack, to warm it up, then I'd grid charge it.

Here's some of what the Panasonic NiMH manual has to say about charging and temperature:
"1. Charging, 1.1 Charging temperature
Charge batteries within an ambient temperature range of 0°C to 40°C [32F-104F]. Ambient temperature during charging affects charging efficiency. As charging efficiency is best within a temperature range of 10°C to 30°C [50F-86F], whenever possible place the charger (battery pack) in a location within this temperature range. At temperatures below 0°C the gas absorption reaction is not adequate, causing gas pressure inside the battery to rise, which can activate the safety vent and lead to leakage of alkaline gas and deterioration in battery performance. Charging efficiency drops at temperatures above 40°C. This can disrupt full charging and lead to deterioration in performance and battery leakage.
"

Note that the usual low rate of charge is 0.1C, or 650mA, yet grid chargers are usually only 350mA. Also, we're usually dealing with older, tired-er cells - so 350mA at 32F, trying to charge tired cells, seems like a recipe for not-so-good charging...
I agree in part - one may need to factor in a few extra hours of grid charging to compensate for the low temp charge inefficiencies.

I've witnessed 130°F pack temps at 32°F ambient after 9 hours of 350mA grid charging w/o cooling. I elected NOT to splice into the fan due to the low temps. Clearly, I should have.

Once a cell has elevated above ambient temps, ambient temps aren't relevant. Cell temps are. Charging, even at low currents, produces heat.

Charging Batteries at High and Low Temperatures ? Battery University

Indicates 0.1C charge between -18°C and 0°C. 0.3C between 0°C and 10°C. At all times, 350mA is below those recommendations.

Aggressive cooling during low ambient temperature charging may slow charging, but once the CELL TEMP is 10°C or higher, ambient temp is irrelevant and charging should proceed normally. I do not have additional low temperature data, but I believe that if a 350mA charge can raise cell temp to 130°F in 9 hours w/o cooling, it can raise it to 50°F in a reasonable time even with cooling.

Charging without cooling for a couple hours or operating the car as you suggested should eliminate any issues with low ambient temperature grid charging. Even better would be force charging with the car to peak SoC.
 
#10 ·
^Generally sounds reasonable to me. The only thing I wonder about is how it's possible to reach 130 F temps charging at 32 F at only 350mA. That seems like an indication of a cell NOT charging, but rather, just converting the current to heat...

I don't know if there's a difference between a dysfunctional cell not charging and converting all current to heat, versus a fully charged cell converting excess charge current to heat. But even charging a fully charged cell at 350mA - at ambient temps, let alone 32F - I've never seen one heat-up even close to 130F. The highest in-car charging temp I've ever seen is about 124F (no fan even)...

I could see a dysfunctional cell or cells in a pack not charging properly and converting the current to heat, heating up to 130F. But I can't see a functional cell, charging properly, doing so...
 
#11 ·
^Generally sounds reasonable to me. The only thing I wonder about is how it's possible to reach 130 F temps charging at 32 F at only 350mA. That seems like an indication of a cell NOT charging, but rather, just converting the current to heat...

I don't know if there's a difference between a dysfunctional cell not charging and converting all current to heat, versus a fully charged cell converting excess charge current to heat. But even charging a fully charged cell at 350mA - at ambient temps, let alone 32F - I've never seen one heat-up even close to 130F. The highest in-car charging temp I've ever seen is about 124F (no fan even)...

I could see a dysfunctional cell or cells in a pack not charging properly and converting the current to heat, heating up to 130F. But I can't see a functional cell, charging properly, doing so...
This was a healthy Prius pack undergoing a restorative charge/discharge cycle after 140K, and 7 AZ summers. Temp readings were as reported by the battery ECU using the 3 thermistors at the pack middle and both ends. The configuration and orientation of the prius pack/modules are pretty much a worst-case situation for heat accumulation without forced air flow. they are packed in tight and allow for almost no natural convection. By comparison, the Insight sticks are separated by miles with a much larger and free flowing volume in which convection can occur (by comparison - still not a good idea to charge any installed pack without cooling).

I spliced into the blower fan and drove the temps way down. At the end of the charge with ambient at 40°F, the pack was sitting in the 60's. Subsequent 1.6A bulb discharges demonstrated the pack took the expected amount of charge (about 3 hours to discharge to 200V nominal). Low current deep discharge brought the pack back from the brink. Prior to the recondition cycle, the in-car available capacity was only 625mAh out of 2600mAh max. After a single cycle to 1.1V/cell, it was 1600mAh. It's been almost exactly a year since with no issues or subsequent battery maintenance.
 
#13 · (Edited)
Come on man... you're reaching... I might buy it once you've established your "12V" sticks aren't just dead. How do the two "spare" cells measure? How do they react to charging?

If those have been under the hood and operating at lower temps (<50°F), you may have found the reason NiMH shouldn't be used as a 12V - the car does not regulate 12V charging based on NiMH chemistry. It's been shoving > 0.1C into the "12V" and the battery is damaged.

EDIT: Assuming these are Reaktors, auto charge does not behave like a grid charger and is an invalid comparison. Auto charge changes the current based on voltage response. Every time it crosses a cell voltage threshold, it's going to stumble on a deeply discharged battery and can stall. A valid comparison would have been to use manual charge set to 0.4A. You would have seen your voltage continue to climb and charge just like your 6.5A charge (except slower) and a grid charger. You weren't seeing one cell waking up, you were seeing 10 cells showing 0.13V and the charger thinking it was only charging a single cell. Honestly, had you walked away and come back in an hour, you likely would have seen it charging at 0.4A at close to nominal.

The phenomenon you describe is 100% attributable to the equipment and does not support the theory.

The real question here is why was your "12V" completely flat?
 
#15 · (Edited)
Canadian car, ecu revision '506' bcm.mcm '305'

Just some data points from -10F -23C located in a Koppen Dfb boreal climate zone. [Ab.Ca] It's cold.
Bvo lately is exceptionally high operating in the cold ambient conditions, 182V Bvo, the Maximum possible was observed closely after startup. Nice to have all the bars lit on the dash, but .. The small 'f' ima fan indication is shown on the obdiicc gauge as self heating is attempted. SoC is concomitantly maxed out at 82% - absolute max level noted with forced charging -but not much depth behind SoC for use in reality though. Bam varies ~4-8A. With driving off soon and a pulse or two of ima use, the Bvo will fall slightly, but holding 178-179V is common and back up towards 182V is common at that temp. The ima battery is in self warming mode iirc.
Initially in am, after pm run and left parked in elements, Bte is found around -16C in morning, 'warm' still from last night's ~2-3C, ].
..fwiw: I'm not using Mima but for very sort blips and the battery doesn't want to put out very much on its own for assist until around -9c iirc.
Then the Bvo drops to around 168V; SoC is about 67% and with more use, and Bte rises , often no higher than 10C.
In spite of the apparently higher SoC and Bvo, I still avoid using assist or heavy regen via Mima and anyways, conditions don't warrant lots of torque.
The IMA behaves like this each year and then settles down after the first cold snap. A P1449/1447 code will usually be thrown with first exuberant driving with warmer temperatures in the springtime.
In the cold, if I had a choice I would want a lithium-titanate battery, although if I nurse my NiMH along, it may be alright in the cold for a while, albeit not as usable.
My Canadian ecu got a cold weather revision: "506"
https://docs.google.com/spreadsheets/d/1hSpAMLn7JwvbvxWcM8rR-8z_UvA3UkyuJV6ZSo0Npaw/edit?usp=sharing
Code:
CAN 2000 MT 
BCM#1K100-PHM-305	
MCM#1K000-PHM-305	Software rev:1C 02 76 00 00	
[B]ECM 37820-PHM-506[/B] 	Software rev:6C 01 11 00 00* 	
2008	K66 Recall: *new ECM per DC [diagnostic code] Recall. [Tech Service]Bulletin V.5-07 [V.#??TSB]
________________
On subject of lead batteries, they do seem better for temperature range than lithium. This is one of the reason I'm interested in the Li-titanate type lithium batteries on account of their cold temperature ranges and and excellent charging rate specs.
 
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