LiPO and cold winter temp

The Canadian tire 12V resistor wire heating products are on sale until Thursday night. Appears the 53" X 39" blanket has LOTS of the silicone wire, $19.49 (29.99). Thanks for the product numbers Lifepo4ever .

I opened the 12V heated blanket , its rated at 66W , a big drain even for a separate pack . There is 73 feet of resistor wire , 1/16" dia., 12 silver strands , no markings .There are 3 temp sensors rated at 70C , so 4 pcs. of wire in series . There is no other current limiting device. Resistance of the 73" series circuit , measured at soldered ends is 2 ohm ( pad tested at 9 ohm ), The LED & resistor in a parallel circuit was removed for both readings.

I tested this for 20 minutes and it eats AH's quik. The wire can be held firmly , not hot , just very warm, quite suitable heat . The copper plugin feed is twice the dia. in metal but was hotter than the resistor wire...WTF ? Is this the same resister wire Liveforphysics spoke on ? Will a shorter lenght use less watts ?

this heat seat is to big 66watt!!! , if you plan use like me in a small enclosure you only need 10 watt , i reduce the current and voltage with a dc /dc from lyen and now my box is
about 20 degre celsius and the outside temperature tonigth was -10 here ,iwas a little bit busy yesterday but tommorow will do a video of the final setting
also the battery it self build up some heat inside the isolated lunch bag

Due to the laws of energy, you guys do realize the "lost watts" from cold batteries can not go anywhere but to heat the batteries, right? =P So running any sort of heater outside the batteries from the batteries themselves is ... well ... I can't for the life of me figure any use for that. Nothing is a better heater than heating the inside of the cells, IMHO.

As far as I have read, it is mostly cold weather charging not discharging that reduces cycle life. So no use in having a separate (cheaper smaller) pack for heating the main pack either.

Now if you had that heater run pre-charging (connecting charger would first connect the heater, and the charger would not start until pack temp is enough) and have an insulated box, so that the heater would keep heating the pack if charger plug is in everytime it drops below an another set temperature ...

I don't think anybody wants to use a cold battery's energy to warm it up . There are 2 working solutions in the thread using battery energy to keep itself and / or another battery warm . If it takes 2 batteries to function in a cold climate , so what...its a solution to a 5 month range & cold cycle wear problem . There is also a need to heat outside over night , but switching to an AC power source . So far no one is using / reporting the chemical heating pacs...they should arrive by mail around spring thaw.

The 66 watts for 73 feet of wire is useless...what can be done with other lenghts and voltage ? Will a higher voltage use less current for X amount of BTU's ? Is there technology thats more efficient than resistor heat ? ( affordable )

There are so many variables for each persons needs : range / TIME / temperature . There is no single solution...excluding a generator . Some of us don't understand that electric bikes is a warm climate thing .

I've always use tiis website as MY REFERENCE for battery informations.

I personally tested in my lab by myself more than half what they explain.

There is an interesting explanation on this page about battery use in high and low temperatures:

http://batteryuniversity.com/learn/article/discharging_at_high_and_low_temperatures

The dry solid polymer battery has found a niche market as backup power in warm climates. The battery is kept at the operating temperature with built-in heating elements that is fed by the utility grid during normal operation. On a power outage, the battery would need to provide its own power to maintain the temperature. Although said to be long lasting, price is an obstacle.

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While -20°C (-4°F) is threshold at which the nickel-metal-hydride, sealed lead-acid and lithium-ion battery cease to function, the nickel-cadmium can go down to -40°C (-40°F). At that frigid temperature, the nickel-cadmium is limited to a discharge rate of 0.2C (5 hour rate). There are new types of Li?ion batteries that are said to operate down to -40°C.

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I guess that about the -40, they are talking about the LiFePo4...

Lithium-ion works within the discharge temperature limits of -20°C to 60°C (-4°F to 140°F). The performance is temperature based, meaning that the rate capability at or below -20°C is reduced due to the increased impedance of the electrolyte. Discharging at low temperatures does not harm the battery. Lithium-ion may be used down to -30°C (-22°F) with acceptable results. Larger packs will be necessary to compensate for the reduced capacity at these temperatures.

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Now we have answers! :wink:

So the use of heating element IS usefull :wink:

Doc

A science based study thats easily understood : Journal of Power Sources : "Cydling degradation of an automotive Lifepo4 lithium-ion battery" . Address of a free source : http://mtrl1.mne.psu.edu/Document/Zhang_JPS_11.pdf

The study is recent and had funding from gererous motors . Its a prismatic high capacity cell . 600 1C cycles at temps of -10C to +50C . The elevated temps are as important to battery heating as the low temp facts . Equally important to the facts within this study is the reference , another 39 papers . ( there appears to be a misprint of 6000 cycles in one reference , I think #20 or #22...maybe not...find that paper )

These facts are about a chemistry made by a specific manufacturer , they do not apply to the competitors version of this chemistry or other types of cells.

Use web based sites like Battery University for keywords , do a google advanced search , limit search to domain ".edu" , results in facts not opinions or manufacturer / vendor spin . ( beware the exceptions )

There are other papers on results of tweaking various chemistries of battery types . This is very useful for sorting out genuine suppliers , there has to be published reports behind any major manufacturing , demand the facts .

I'm just learning topics too .

So I'm thinking that if your bike has to be outside to freeze for many hours an AC battery blanket/warmer is a good idea,then maybe if you can easily stuff some cheap chemical warmers in around the pack it should keep the battery warm for the duration of any trip in cold weather. Yes some of us do have to ride in cold weather,and a frozen battery is useless.
I made a trip in -10 C a week or 2 ago and after about 1/2 hour the batteries ran low very quickly.

Doctorbass said:

...
Now we have answers! :wink:
So the use of heating element IS usefull :wink:

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YES ! Thanks for information.
But that siteis not recommend charge cold batteries (below 0°C).

Lithium- ion offers good charging performance at cold and hot temperatures. The acceptable charge range is 0° to 45°C (32°F to 113°F). It is recommended, however, to reduce the charge rate to less than 1C at temperatures of 5°C to 0°C (41°F to 32°F).

It is important to know that consumer grade lithium-ion batteries cannot be charged below 0°C (32°F). Although the packs appear to be charging normally at freezing temperatures, the cell impedance goes up and the acceptance of the ions on the anode is drastically reduced.

What is most troubling is the plating of metallic lithium that occurs on the anode. The higher the charge rate, the more pronounced the plating will be. A prolonged charge at cold temperatures will eventually compromise the safety of the pack. The plating is permanent and no amount of cycling can reverse this effect. Unknown to the user, such a battery will become more vulnerable to failure if subjected to impact, crush or high rate charging. Venting with flame could be the result.

Quality chargers reduce the charge current at cold temperatures and avert a charge altogether below 0°C (32°F). When charging a cold battery, allow the pack to warm up before putting it into the charger. Discharging a lithium-ion battery at cold temperature does not cause any harm. The lower performance will only be noticeable while the pack is dwelling in the cold state.

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One thing Im trying to figure out is if the electrolyte causes high impedence in the battery then the battery should heat up. After 1 or 2 Ah it should be at a temperature where it can peform normally. I keep my battery in one of these bags. http://www.axiomgear.com/products/gear/bags/trunk/robson-lx/ Even when I dont do a full do a full discharge they are slightly warm to the touch and if the bag can keep in the heat the battery generates then this should be a non issue. I would just worry about sluggish performance when you first ride. And under estimate capacity by 10-20% due to energy being lost due heating within the pack itself. We cant measure that through our CA because the losses happen before the shunt.

The study is recent and had funding from gererous motors . Its a prismatic high capacity cell . 600 1C cycles at temps of -10C to +50C . The elevated temps are as important to battery heating as the low temp facts . Equally important to the facts within this study is the reference , another 39 papers . ( there appears to be a misprint of 6000 cycles in one reference , I think #20 or #22...maybe not...find that paper )

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If I read the study correctly, the repetitive cycling was all done at 50 deg C at 3C. Only the temperature during "characterization", which occurs only every 300 cycles, varies. The only thing I can conclude is that if I drove to work for a year ( or 300 days) at 50 deg G (don't know how I would manage that) and then one day it was suddenly -10 deg C, I would expect the capacity to increase, although the average voltage would decrease. Then, after driving around at 50 deg C for another year, and it was suddenly -10 deg C, I'd see a big change in the capacity over when it was new or after the first year.

So I am not sure this study is useful for the question of repetitive cold weather performance. Did not check any of the references.

For one data point, I ride my bike in pretty much every day, with highs in the summer around 90 deg F (32 deg C) and lows in winter as low at 14 deg F (-10 deg C, that was this morning actually). I have a battery with about twice the capacity I require for the ride and charge it at around 0.3C in my unheated but enclosed and connected garage (temps never get below 40 F as far as I know. Pipes do not freeze. The furnace is in this garage so it stays warmish even in the coldest weather). I park my bike outside after riding to work and the temps can be sub-"freezing" all day but usually aren't. Some days when it is bitter cold (like today) I park it inside. I have had two cells fail in a year, but have no idea if it is related to the temps. Personally, I don't think so but don't know. The freezing point of water is of no unusual significance here as far as I can tell except as a reference point. There is no significant water in a LiFePO4 battery and if there is some residual water, it is likley full of ions and would not freeze until considerably below freezing.

If anyone finds a paper in which a battery is continuously discharged at low temps but charged at more moderate temps, let me know. That is the study I want to see.

What I read in li-ion peer reviewed literature is batts are damaged with cold & hot temperatures . The above paper lists some facts from the sources . Ref. 22 states 70% capacity fade at 55C after 100 C/DC cycles . My intent is about heating / insulating your battery . 55C = 131F . Reusable heat pads get to 130F , add the heat of discharge & you MAY do damage . If a pad is against a cell I would expect "may" changes to "will" . Other cells MAY be fine depending on number of pads , the insulation effect , type , & R value .

12V heating with car type seat heater RESISTOR WIRE parts & the cutout = 70C temperature risk .

Padded lunch bags are very poor at preventing conduction loss ( but the cats ass for at least one battery ) . 2" of small cell foam + above heat is a serious problem . My earlier 2" ref. in this thread was considering PASSIVE insulation for several hours outdoors starting with a indoor temp batt .

A thin quality radiant barrier is also a concern depending on...and on..and on...

ANY heating method needs careful testing .

Cold temp results for 600 charge (?) / discharge cycling : 25.8 % CAPACITY FADE at -10C . POWER FADE is 61.6 % at 0.0C ; 77.2 % at-10C .

..."primary MECHANISM of capacity fade is loss of CYCLABLE LITHIUM"... This is not reversible, its damaged cathodes .

Also in this paper's 39 reference's is chemistry studies to counter-act the irreversible damage .

There is no water in a lifepo4 cell...its dry electrolyte .

This is an off topic OPINION : I find comedy in the science based papers : the success of lifepo4 electrolyte is an ACCIDENT...the particles clumped into 100 nm size during manufacture of the desired engineered particles of 40 nm...it became the standard . "The devil is in the details" .

I'm just adding my request for more info, if anybody has it.

I noticed that my (old/free) 9aH SLA that give me 10mi or so in warm weather (I consider 20F+ warm), only gave me 3.5 or so at -10F (had to stop at a store and warm them up in the lobby).

I put a current shunt on the pack and measured 40A (the programed limit on my stock 9FET with a 9C 9X7), and with the battery between 40 and 50F.

I then charged it and left it outside at -20F for 3 hours.

It still delivered just over 20A. 2C for SLA batteries that an infrared surface temp meter showed at -17F. Not bad considering that they 'cease to function' at -4F, aye?

Will NiCd or one of the Lithium batteries do as well, or better?

Do the nanotech batteries do better than other Lithium at low temps. (I would expect they do, but haven't seen any info.) Wish I could afford to buy some and experiment before spring, but that would have to be low on my budget.

This is a question I've been trying to figure out since I first decided to build an e-bike, and the most common answer is that no battery will work in the cold, when presumably, they just don't want to talk about cold temperatures.

I can also tell you that if you move them, the wire insulation on an ebikes.ca controller will break in the cold (as will most out of China). I need to change out all my wires, especially when I mount them on the FS frame.

Thanks to Doc for the info gleaned so far.
Bob

Thanks for the PMs with links and advice. I'm still left with about the same thing, from the MFGs, MIT, and Caltech. ALL lithium is 'usable' to -30c. Nothing to indicate how much current I can pull at -29, or what happens if I use them at -31. I would expect a curve, not a ledge.
It really doesn't make sense that I can pull 90C from a 45/90 nanotech lipo at -29 with no problem, but it won't deliver 1C and -31, in which case the infinite voltage drop will ruin them.
I really expect the nanotechs are the way to go for cold, but would like to see some data, preferably test data. I also have a hard time believing that all the lithium technologies have the same -30c ledge.
I assume the colleges are just quoting the MFGs. I would like to see some real world testing. I agree with PDF about the above testing, as well as noting that it doesn't test at cold temps.

The idea of putting them in an insulated enclosure and using heaters which draw power from them is not appealing, but might be the way I end up going.

As to my tests with the sla, I chose the smallest batteries I had because I expected the greatest droop from them (duh). (they were drooping to the 40v low voltage limit) Also, it doesn't cost as much to ruin free batteries.
The main point I was trying to make was that I was amazed at how much they DID put out. I assume I did them farther damage. (If you don't use a battery heater, you have to replace your car battery every winter here!)

Would love more data before I buy batteries for next summers ebike build. Otherwise, I will probably post info next winter (have to wait for summer to make the money to buy batteries to test.)

Thanks to all,
Bob

I have only just made my pack and it is the most exposed cell structure possible until I make my cover (they are mounted on my toptube). As my luck would have it we suddenly had loads of snow and -1 to +1 degree temps for weeks. This is what I noticed.

12s lifepo4 headway runing 40a infineon controller with new mac motor.

warm weather 3.1v a cell on the flats 2.9v a cell on the monster hills

In the cold 2.9v for the first half mile on flats (i deliberately didnt pedal to see if they heated) and 2.7v on the hills.

Once the pack stopped feeling cold to the touch after a few short blasts (not warm at all but not painfully metal cold) they started behaving almost the same as the normal weather voltages. I think some good insulation and enclosure might be the only thing you need around the freezing point.

My cellpro powerlab charger also auto limits to 500mah trickle in the cold but after 1 hour like this it will allow faster rates. I seem to remember the Internal resistance rates starting at something silly like 25mohm and dropping back to 5-6mohm after a short charge period.

My ten ah pack starts acting empty almost after 7-8 ahs drawn in the cold but more like 8.5-9 in the warm.

I will make my pvc cover for them shortly or just stop going outside for a while brrrr poor batteries

"Pad Heaters" $5-$6 per pair


Batteries vs Cold - heat pad test results, in "series" etc.

I have a large battery in my e-moped made of four hundred 18650 cells. The dimension is roughly 17'' wide by 11'' deep by 7'' high. I can't plug in at work and this winter, after the moped sat at -10 degrees Celsius for 5 hours, the top speed was way down and so was the torque.

Which solar panel would I need to power a battery warmer like this one? http://www.canadiantire.ca/AST/brow...13118P/Temro+50W+Battery+Warmer.jsp?locale=en

Thanks
Ray

using adaptto mini-E, so and bringing pack/display/controller inside to bulk balance charge isn't an option, so i'm going to test this Temro Battery Warmer (same as Canadian tire one?) out to keep the pack warm overnight...


let's see if we can keep the garage standing till spring...

This was a great read on temprature and batteries. I left my ebike outside this past winter and it was cold out, it must've been -15C or more! I remember the chill well now, yeah -20C and the wind had a bite to it. Lithium Ion is what I used. I just gotta have it setup so I can take the battery with me inside. Should be easy enough to accomplish. Otherwise an enclosed box, transformer wire, say 10-15W with a thermister setup. Then plug in to wall outlet.

2-3 5v pads and a cheap controller. Insulate with foam. My buddy copied the plan and commute in below zero, with ZERO sag.