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Discussion Starter #1
There is quite a bit of concern and discussion about operating a Lithium powered Ranger EV in cold temperatures. This thread is being started in the expectation that we can gather our collective experiences and knowledge in one spot so others can benefit. Please keep your posts to this thread focused on Lithium battery packs for the Ranger EV.
 

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With Lifepo4 pulling high current at or about 0c can cause long term capacity reduction. Its supposed to be caused by copper being plated into the carbon matrix, into which the ions / charge move through the cells. So the trick is to limit this condition, ie get them warm before you use them.

They also take less charge when at or about 0c so when you charge, again do it when the pack is warm, ie just finished using it.

So ultimately its about keeping the pack warm ie above 0c by a few degrees, when charging, and before you use it.

When starting off in the cold conditions, use the vehicle at as low a load / performance as possible give the pack some time to warm through having power flowing through it. Threat the pack gently, long life is somewhat dependant on you treating it kindly.
 

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With Lifepo4 pulling high current at or about 0c can cause long term capacity reduction. Its supposed to be caused by copper being plated into the carbon matrix, into which the ions / charge move through the cells. So the trick is to limit this condition, ie get them warm before you use them.
I have not heard that one before. Do you have a reference on the chemistry behind it? Is it LiPo, or LiFePO4, or pretty much any lithium chemistry?

I ran my pack for a bit at -26C. The pack started out fully charged, and was not happy about moving the Ranger at all. I got the 'jitters' ... where it surges a bit as you press harder on the throttle ... at under 3 mph.

As I used some energy and the pack warmed up a bit, the 'jitters' happened at higher speed.

After I got it into the heated garage and left it over night, the pack was still at 54V. So not FULL but over 80%. It took a bit of a charge, but not too long.

They also take less charge when at or about 0c so when you charge, again do it when the pack is warm, ie just finished using it.
What Jack over at EVTV explains is that, during charging below 0C, the lithium metal plates out of the electrolyte. So charging is doing permanent damage at that point, since the lithium is no longer available to exchange electrons. I went through his footnotes for the published papers and could only see the summaries without paying. But it seemed to check out.

This is sort of consistent with my buddy's Mitsubishi Outlander hybrid. It has NO regen braking until the battery warms up. And youtube ... as much as you can trust youtube information ... has many stories of no regen on Teslas when they are cold.

So ultimately its about keeping the pack warm ie above 0c by a few degrees, when charging, and before you use it.
My charger (DeltaQ) won't charge at all unless the pack is at 10C or higher. I think that's a bit paranoid, but I guess they don't know where the temperature sensor will be installed, or how accurate the sensor is.

I have not checked if regenerative braking works below 0C. The SEVCON knows what temperature it is ... I think ...
 

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This is from a email from Voltronixs


As far as charging lithium ion cells, in your case, they are enforced by the BMS to not permit charge below freezing temperatures because of the reduced diffusion rate of the anode, which could cause thermal runaway if current demand increases while the internal resistances of each cell also increases. The safest operating temperature range while charging is around 41˚F-113˚F. Anywhere below 64˚F and the BMS according to your profile settings will start reducing the Charge Current limit by 14 amps every degree Celsius drop or 1.8˚F.
 

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Discussion Starter #5 (Edited)
Cold WX OPNS

In my Ranger VLi when operating in temperatures below 50 F (10 C) I apply power carefully and avoid high amperage draws. The Lithium as well as PbA packs are chemical reactions and are sensitive to temperature. I think it is important to remember that there can be Technically Identifiable issues that do not really translate into Practically Experienced problems. Is the service cycle life of the pack reduced by using it in temperatures below 50F? Technically yes. By how much? Practically, I expect that I will not detect it.

"When starting off in the cold conditions, use the vehicle at as low a load / performance as possible give the pack some time to warm through having power flowing through it. Threat the pack gently, long life is somewhat dependant on you treating it kindly." Grumpyb-------------Totally agree.... JackA
 

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This is from a email from Voltronixs


As far as charging lithium ion cells, in your case, they are enforced by the BMS to not permit charge below freezing temperatures because of the reduced diffusion rate of the anode, which could cause thermal runaway if current demand increases while the internal resistances of each cell also increases. The safest operating temperature range while charging is around 41˚F-113˚F. Anywhere below 64˚F and the BMS according to your profile settings will start reducing the Charge Current limit by 14 amps every degree Celsius drop or 1.8˚F.
Thanks for the source.

Voltronixs uses LiFePO4 cells, right?
 

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This is a pic
 

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Discussion Starter #8
Winter Over Li

LiFePO4? Yes

Interesting specification is self discharge at "normal operating temperature" I think a Ranger EV Li can be safely stored over the four months of winter cold without being recharged. If 100% SOC at start after 160 days the pack would be at about 82% so deduct some for cold weather and I believe winter over is possible without harm.
 

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LiFePO4? Yes

Interesting specification is self discharge at "normal operating temperature" I think a Ranger EV Li can be safely stored over the four months of winter cold without being recharged. If 100% SOC at start after 160 days the pack would be at about 82% so deduct some for cold weather and I believe winter over is possible without harm.
I am seeing no loss of capacity over a year with a 4-cell pack. I didn't really intend for the test, but I didn't happen to use that pack.

Background

Jack over at EVTV has some LiFePO4 cells that were purchased and just stored in his shop for several years. He checks them once in a while and reports the voltage. It fluctuates a bit, but I think that has more to do with temperature than state of charge. IE - no loss of charge.

He has sold a couple of these old batteries, when someone kills one in a pack and needs to replace it. These old cells that were never in service do appear to have lost some capacity, but not really lost any charge.

I can confirm that used/surplus cells that I cycled to determine capacity, matched the capacity to put into 12V packs, and then charged to about 3.2V ... measure about the same when checked each month in my heated garage.

I know that voltage is not a great way to estimate 50% soc but it's also about 70 a-h on a 140 a-h cell. Which started out life as a 160 or a 180 a-h cell in 2013 or 2014.

So I guess I'm going to ask if there are parasitic loads on the ranger that may use the energy from the pack. I am not aware of a chemical method for the LiFePO4 batteries to lose charge while not supplying a load. Lead acid cells have a well documented self-discharge chemical path. So am I just poorly informed?
 

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Discussion Starter #10
Lithium Self Discharge

My Ranger EV Voltronix Li has a BMS that is always powered so there is consumption of power. According to "Battery University" LiFePO4 and all the Lithium chemistries exhibit self discharge. The rate of self discharge is correlated with pack temperature.
 

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I have Thundersky cells that have been standing for 8+ years and they have shown very little change in cell voltage. That includes getting down to around 0c in the storage. In any vehicle that has a BMS you will see some degradation, the BMS will slowly take the pack down, some with larger balancing resistors can take a lot out of a pack in an attempt to maintain the balance.

With many chargers (I think the Delta q on a lithium algorithm will do the same) they shut down after so many hours of being initiated. That means that leaving the vehicle plugged in does not prevent it going flat over time. This also means the 12v will go flat with BMS load etc. On some of my customers vehicles I have included a simple 12v powered programmable charger, that turns the mains off for 15 mins (just after midnight on a sunday) this then re starts the charger. This has been shortened on one car using Lifepo4 and with a very active BMS to add wednesday night as well.That saved the council who owned it from having irate staff who didnt look after the car from leaving it for a week and finding the 12v flat and the pack reduced in range. Its still in daily use 4 years later and is still mostly OK (One low capacity cell in an inconvenient location)
 

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My Ranger EV Voltronix Li has a BMS that is always powered so there is consumption of power. ----------------------
Is the green LED on with the key off?

Mine powers on and off with the key:
P8150004c.JPG
 

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My Ranger EV Voltronix Li has a BMS that is always powered so there is consumption of power. According to "Battery University" LiFePO4 and all the Lithium chemistries exhibit self discharge. The rate of self discharge is correlated with pack temperature.
I am surprised to see a 5% self-discharge in the first 24 hours. The battery voltage ends up higher than rated when you remove it from the charger. I recall the voltage drop during that time being described as the lithium ions migrating from the surface to within the cathode. I don't remember the source. I'll assume that it was EVTV.

I found a paper describing the self-discharge
https://iopscience.iop.org/article/10.1088/0957-4484/24/42/424009/meta

But unlike other scientific papers, it does not appear to describe the chemical source of the self-discharge.

I have seen a voltage drop that is consistent with self-discharge on LiMnO ... with some LiNiO .. however leaf cells are listed. The pack voltage drops with time .. not quite as quickly as Battery University lists. Perhaps the BMS doing the monitoring is responsible for some of that voltage drop.

I'm still looking for a chemical explanation for the self-discharge. The quest continues ...
 

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My experience does not suggest that Lifepo4 cells self discharge to any real extent over time. If stored with no BMS. If there is any internal shorts , yes they will self discharge over time. But then they are not perfect cells. If there is a BMS attached, yes they will go down in voltage, but thats not self discharge.

On the cold front. I have been testing a 30ah Li ion cell for two weeks in my freezer. And its showing no voltage drop at all. I had hoped they would show a real loss, enabling me to explore simple ways of destroying poor condition cells. I may try a big discharge on this cell to see how it reacts. I have others that have not been frozen, so can do a back to back test. It would be interesting to see how they worked in temps below what I can achieve in a domestic freezer.
 

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My experience does not suggest that Lifepo4 cells self discharge to any real extent over time. If stored with no BMS. If there is any internal shorts , yes they will self discharge over time. But then they are not perfect cells. If there is a BMS attached, yes they will go down in voltage, but thats not self discharge.

On the cold front. I have been testing a 30ah Li ion cell for two weeks in my freezer. And its showing no voltage drop at all. I had hoped they would show a real loss, enabling me to explore simple ways of destroying poor condition cells. I may try a big discharge on this cell to see how it reacts. I have others that have not been frozen, so can do a back to back test. It would be interesting to see how they worked in temps below what I can achieve in a domestic freezer.
I have some data for you - just empirical since I don't have a scientific approach written up.

The packs were charged up (2 x 51 A-h pouch cell packs, 1 x leaf cells * 7 cans) to 55.6V on Monday evening. This was not a full charge ... it stopped there when the charger overheated and ramped down it's charge rate to 1.5 amps. I moved the 2011 Ranger I call Ranger #4 outside and parked it. I did get the 12V split onto a separate battery, and added the winch, light bar etc. So there is no longer a load on the 48V pack from the DC converter as the DC converter is no longer connected.

Tuesday, temperature was as high as -26C during the day. But it was -30C (about 15 below zero F) when I took the Ranger for a spin. High speed, 2wd, likely a couple of tires low since it felt like at least 2 tires were flat ... or out of round? Ran up and down the driveway (550 feet each way, plus turn around, say 1200 feet total ... 1/5 of a mile?). Empirically High speed was nowhere near as fast as it normally is. No trouble codes on the controller. I don't have the pack voltage showing on the dash as yet, so I can't tell how low it dipped. But I'm assuming that the reason that pedal-to-the-metal was not very fast is due to sag on the pack voltage scaling back max speed on the SEVCON.

I will take Ranger #4 out for a spin each night and compare empirical results, noting the temperature when it goes out. I can connect a portable meter to the pack and get a starting pack voltage and a running-at-max-speed pack voltage for the rest of the week. I have a clamp-on meter that can measure the DC current ... but I don't think I can get the meter somewhere that it will be visible while I'm driving. I'll see if it works when setting it to Peak and then looking at it after the drive.
 

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I have some data for you - just empirical since I don't have a scientific approach written up.
My new wiring for the 12V accessory battery is having issues. No data for the past few days. While troubleshooting .. in the -25C cold (maybe 13 below 0 F) ... I touched something with my meter and blew a fuse ...

I can't get the Polaris into the garage to troubleshoot further. Working on it this evening. I'd like to figure it out, fix it, and get some cold weather testing in. It's supposed to be -25C to -30C all week.:ekk:
 

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I can't get the Polaris into the garage to troubleshoot further. Working on it this evening. I'd like to figure it out, fix it, and get some cold weather testing in. It's supposed to be -25C to -30C all week.:ekk:
I didn't get the 12V issue tracked down. But I ran the Polaris last night wired direct into the switched power posts under the hood. -31C and it runs. Not fast, but it runs. My Fluke meter registered 63V on the battery ... so I think there is an issue with the meter reading weird in the cold. So .. not that I am confident about it .. but the Fluke showed the pack voltage dipping below 40V. The Sevcon controller was definitely limiting current based on the input voltage dipping. High speed was a bit faster than walking speed, with the throttle to the floor.

No amp reading either, since I have not re-routed the pack through a shunt resistor.

I'm not using the DC converter, 48 - 12V. But the rest of the Ranger works at -31C. It's supposed to be -35C later this week. I'm interested if there is a point where the batteries refuse to put out any power at all.
 

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Interesting. Can you compare your meter with another meter?

-30°C would be -22°F here. It rarely gets below -12°C = 10.4°F here.

I don't think I have used my EV when it is in the 20s here.
I think I have a couple of no-name meters I can compare to. It likely won't happen tonight ... maybe tomorrow.

It's supposed to be colder tomorrow anyway :(
 

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I think I have a couple of no-name meters I can compare to. It likely won't happen tonight ... maybe tomorrow.

It's supposed to be colder tomorrow anyway :(
It was only -33C last night. Not enough difference.

It was -38C this morning, so I took 5 minutes, brought out a small battery for 12V (the fuse problem is still not solved) and ran the Ranger #4. At -38C the battery was barely able to generate enough torque, in low, to move over 4 inches of snow where it's parked and onto the driveway. I ran it a few hundred feet forward and reverse and put it back into it's parking spot.

I didn't check the pack voltage this morning. I'll do that after work with a different meter than last time.

BUT:
- The SEVCON works fine at -38C. There is NO REGEN at all. I believe that the SEVCON has an internal temperature sensor, since there is no BMS attached.
- the throttle works fine at -38C
- the brakes ... sort of work ... they engage fine but they don't release quite right. I guess that's a fairly typical hydraulic type issue.
- the CV boots flex, I'm not sure if I cracked the boots in this cold weather ... I'll check next time I have it in the heated garage. They test may cost me a set of boots, or perhaps just a shortened life?
- the motor works fine at -38C.

Next up is to check the pack voltage and detail how bad the sag is. It would be nice to know what current the pack is capable of putting out.

After that is putting anderson connectors on the batteries so that I can disconnect the cold battery packs that are permanently mounted and attach a temporary warm pack from my garage to test out cold weather performance
 
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