LiFePo4 - reduced cold weather performance?

I have a duct tape 36v/10Ahr battery that I use on a daily basis.
I'm not using a Watts Up, as I don't have anywhere to mount it on my trike, so not sure what the pack is actually doing.
However, I do have a throttle that has 3 LED's. In recent days, I have noticed that the green light goes out fairly quickly under moderate load, but I noticed this morning, that the amber LED, also went out fairly quickly, maybe within a k or two. I usually find that the amber light stays on until I get home on the return trip.
Apart from thinking that the pack is somehow dying (God forbid! It is LiFePo4 after all), I'm suspecting that it might be temperature related, as it was around freezing (0 C)this morning on the ride to work.
Anyone got any info that LiFePo4 performance is affected by lower temperatures?
I know SLA suffers badly at low temps, so maybe all battery chems suffer to some extent?

I live in Montana, US and I have yet to meet a battery of any kind that would choose to live here with me and be happy about it. :lol:

Check the voltage on each cell, and make sure one of them didn't drop out, decreasing voltage, and thus triggering the amber-light...

-JD

Its 85 degrees F in Fairhope AL and batteries never lose potency due to the cold here! Sorry! Of course our motors melt, but thats another story!
otherDoc

With LITHAGRA, I never sagga...

Ok, I kept an eye on my LED's for the ride home, bearing in mind that I don't charge at work. The temp was fairly mild at 15 C. The amber LED stayed on for pretty much the whole trip home, just starting to fade out about 1/2 k from home.
This shows me that the performance is indeed lower at reduced temps.
On the ride to work this morning, it was about 5 C, and I noticed the same sort of thing, but not as bad as yesterday. The amber light faded out on me during the ride to work.
Another factor that may be an issue, is that my bike lives in the garage, and is charged there, so is essentially the same temp as ambient temp.
It may not be taking a full charge at the lower temperatures.
I did recall reading somewhere that LiFePo4 can take up to 10% more charge at warmer temps, just can't remember what that temp was!
My deduction?
LiFePo4 performance is reduced at lower temps, but probably nowhere as bad as SLA. I did a fairly intensive internet search, but couldn't locate any data to support this, other than the reference to a higher capacity at warmer temps. I guess the opposite is then true, a reduced capacity or performance at reduced temps.
Guess it would be nice to be able to quantify this, but I'm not in the position to do the testing required.

I have lipo4 and sla battery packs. Once there is ice on the ground i will stop riding my ebike for the winter. Should i store my batteries indoor or outdoor. Sometimes it gets to -30C here.

Can i let my sla freeze and not have to top them up once a month?

I know on some of the LiCo cells I work with, storage is ok from -40 to +55C. It does get dangerous at that temperature because risk of freezing the electrolyte means risk of a short. Im not sure its the same for LiFePo4 but you could probobly get away with it. If you can I would just bring them in and put the slas on a trickle charger when its really really cold.

I know squat about cold, but I'd be inclined to store em indoors. I'd do something to cycle the lifepo4 too, pretty frequently, or remove the bms during the storage. A few stored packs have had a cell group dragged down by the bms somehow.

I kept limn batteries out over last winter...I was riding with them last year. I put them on charge after every use, and they seemed to be fine all winter, exposed to -40 rarely, -30 frequently.

I also left 48v sla's out all winter connected to a charger constantly, and noticed no degradation in the summer.

having lived and worked in Yellow Knife i can lend some personal experience. located at 62N latitude you are guaranteed that from November to March you will have -30C weather most of the time. at -40C SLA are pretty much useless. stored at those temperatures the batteries will loose almost all of the capacity in a short period of time. left outside a car battery will be dead in as little as a month. everyone up there has some way of heating the battery overnight. either thermal blankets or heating pads. many people actually block off the radiator inlets and add some tarps or something to the undercarriage to enclose the engingine compartment as much as possible to prevent the motor from freezing even while it is running. the top of the motor may be hot but the oil pan will stay quite cold.

when you have less than an hour of daylight during the winter flashlights and batteries become important. no matter what kind of battery you have performace really goes down once you go bellow freezing. at -20C expect about half the run time that you would at room temperature. below -20 the performance drops dramatically. at -30 or -40 chemistry doesn't really matter. the battery life is so short you don't count on it. you keep your phone, radio and flashliught batteries warm by wearing them under your coat.

storage recommendations from Isidor Buchman of Cadex Electtronics:
" * Keep batteries in a cool and dry storage area. Refrigeration is recommended but freezers should be avoided. When refrigerated, the battery should be placed in a plastic bag to protect against condensation
* Do not fully charge lithium and nickel-based batteries before storage. Keep them partially charged and apply a full charge before use. Store lithium-ion at about 40% state-of-charge (3.75-3.80V/cell open terminal). Lead-acid batteries must be stored fully charged.
* Do not store lithium-ion fully depleted. If empty, charge for about 30 minutes before storage. Self-discharge on a depleted battery may cause the protection circuit to trip, preventing a recharge.
* Do not stockpile lithium-ion batteries; avoid buying dated stock, even if offered at a reduced price. Observe the manufacturing date, if available.
* Never leave a nickel-based battery sitting on a charger for more than a few days. Prolonged trickle charge causes crystalline formation (memory).
* Always store a lead acid battery in full-charge condition. Observe the open terminal voltage and recharge the battery every 6 months or as recommended by the manufacturer. "

rick

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The BMS issue is real, because the BMS has some control circuitry there is some parasitic loss which, under normal conditions dosn't matter but after a month or two you may have deeply discharged cells. Just check on them every couple of weeks.

i second that. the BMS means that lithium batteries will have more self discharge than any other chemistry. put them on a 7 day timer hooked up to the charger if your not using them.

Yesterday I learned the hard way that a Lifepo4 battery can NEVER sit in the cold for any reason. NEVER NEVER NEVER.

I rode to work yesterday and plugged in the battery charger to a parking garage outlet. The garage was cold but it though it was ok to plug in and charge. WRONG.

The battery did not charge. I thought it did.

So I started to bike home thinking everything was ok. About half way there the BMS cut out and the battery went completely dead. The cold temperature lowered the voltage and the BMS shut down to prevent damage. And it happened in Garfield Park in Chicago of all places. One of the most dangerous neighboorhoods in the US. I was going nuts biking hard to get out of that area. I was lucky i didnt get shot or robbed.

I finally got home ok and charged the battery inside the house. 5 hours later I took the battery out in the cold and rode for 12 miles and the battery was perfectly normal.

Write that down taj......

Time to put a heater in your battery box and plug that in with your charger.

Just has to be enough to keep the battery at room temperature within the box. If you get one of those little electric heating pads with the electronic thermostat on it, and put that in there, with the thermostat on lowest setting it'll probably work for this purpose. Just keep in mind the ones I've used have 15-20F hysteresis before they turn on or shut off, so don't set it high enough to get the pack hot!

Can you give us a link with one of these heating pads?

Sorry, I get mine from thrift stores for use on my aching bones, since its' not generally cold enough here in Phoenix to need them for batteries. So I don't know where you might order them from. But any thermostat controlled wall-AC powered heater pad would work. Even those for reptile cage under-tank heaters and such. Just as long as you don't get one powerful enough to overheat anything--you just want to keep it around room temperature.

I was considering the hand warmer route to keep the trunk warm.

As long as your using the battery while riding the voltage will not lower enough to be shut off.

This is my first winter riding in the cold. lessons learned

http://images.google.ca/images?hl=en&source=hp&q=wine%20heat%20belt&um=1&ie=UTF-8&sa=N&tab=wi

I make my own wine, been eyeballing those heat belts, water resistant and just warm enough if the pack was wrapped up in a vinyl pouch or similar insulating bag along with the heat belt

How about a simple oil pan pad heater for a car? Here is one that is just glued onto the oil pan, it's nice and flat and would never get hot enough to hurt anything.
I'm going to get one when I move back to Montana or when I might be charging with out being able to warm the batteries first. I can't imagine that this little 50Watt would over-heat anything, and if it's at the bottom of your battery pack, should heat the whole thing fine.



http://www.warehouseautoparts.com/Specialty_Line/Kat/kats_24025_silicone_hot_pad.htm

You may want to check on that first.

My stick on pan heater would get the oil bubbling!!!


Juiced

That pad would burst the second I hit a Chicago pot hole. ..

There is no need to use a heating pad or anything while riding. I just biked 11 miles and it 26 degress outside. The battery worked fine because it was WARM before I put it on the bike. ad started riding.

Pet store. Reptile heating pad. Expensive, but it will gently toast without overcooking since that would kill a snake. Tiny one will do. Small enough to carry.

Another option would be a regular heating pad from the drugstore. Like people use to warm a sore back. They have thermostats so you can set the heat.


BTW. it's 62F out right now. First day this year I worked in a short sleeve t shirt. Ha ha ha ha ha!

LI-ghtcycle said:

How about a simple oil pan pad heater for a car? Here is one that is just glued onto the oil pan, it's nice and flat and would never get hot enough to hurt anything.
I'm going to get one when I move back to Montana or when I might be charging with out being able to warm the batteries first. I can't imagine that this little 50Watt would over-heat anything, and if it's at the bottom of your battery pack, should heat the whole thing fine.

http://www.warehouseautoparts.com/Specialty_Line/Kat/kats_24025_silicone_hot_pad.htm

Click to expand...

I think this could be a good cheap solution. There must be oil pan heaters that are limited to a certain temp. How heavy is one of those little guys?

BTW you could stick on the top of the battery as well as the bottom. Doesn't matter which side you stick on, remember this is conduction heat transfer, not convection. wiki the suckers

lester12483 said:

That pad would burst the second I hit a Chicago pot hole. ..

There is no need to use a heating pad or anything while riding. I just biked 11 miles and it 26 degress outside. The battery worked fine because it was WARM before I put it on the bike. ad started riding.

Click to expand...

What do you mean burst? I think all that in there is a heating element. (Oil pan heater, not Oil heater)

I thought the issue here was to use it while charging, not while riding. And warming up batteries before a ride.