# Winter Lead-Acid Tips?



## rbgrn (Jul 24, 2007)

I'd like to put together an article for dealing with Lead Acid packs in the winter. Do you guys have any suggestions?


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## stormcrow (May 28, 2008)

I am bumping this because I am interested in it too.

I had read somewhere (dont remember where, sorry) of someone suggesting throwing some of those hand warmers you use for hunting in your battery boxes. It seems like a novel idea, although you would need a lot of hand warmers to survive the whole winter.
Other than that, the only thing I can think of is insulating the heck out of your batteries. But hopefully someone else can come up with something better than that.


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## madderscience (Jun 28, 2008)

Lead acid batteries lose useable capacity as the temperature drops. Typically they are rated at about 80 degrees farenheit, and at freezing (32 degrees farenheit) the usable capacity can be substantially less than what you could get at the higher temperatures.

here is one example temperature vs. capacity graph.

http://www.pacificpowerbatteries.com/aboutbatts/deep%20cycle%20battery%20faq/dcfaq4.html

Other than the loss of capacity, cool temperatures will not hurt the batteries so long as they are kept charged and do not freeze (which requires downright arctic cold)

So applying this to driving in the winter: 

If you can, insulate your batteries with a layer of hard foam board on the bottom, all sides and the top. This is fairly easy and cheap to do with a new build but can be a pain to retrofit to an existing car. (note a hint of regret here). The insulation alone will keep the batteries warmer while charging and driving and will allow you to add battery heaters too if needed, which can run while the car is charging to keep your temperature up. 

If you do not have insulated batteries, at least do something to keep the wind off of them. Add a thin layer of plastic sheet or something to prevent direct wind chill from affecting the batteries.

And bear in mind the reduced range that comes with cold, and with the use of more accessories (wipers, heater, lights, etc) and with increased rolling resistance from colder oil in the drivetrain and driving through rain, snow, and otherwise non-ideal weather.

So factoring all of this in, a car that can cruise 50 miles under ideal conditions at 80 degrees on a nice summer day might only manage 30 or 40 miles on a cold, dark, windy, rainy day on the same route once you factor all the extra loads and reduced battery capacity in.


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## Jimdear2 (Oct 12, 2008)

Howdy,

I had suggested this idea elsewhere in a discussion about heaters.

It would probabley be a pain to retro fit but maybe someone just starting might want to try.

Here is my dollar two ninty five idea.

First decide if you want to keep hot water heating. Not necessary but, helpful.

Design the battery box(s) with some form of hot water heating, use tubes or water to air heat exchangers. Insulate the box. Lots of different ways. DIY your way through to the solution.

I would design the a water reservoir into/around/under the main battery box the one with the largest mass.

Get one or more of those Zerostart block heaters, you mount it to the water reservoir and heat the batteries and water reservoir While ON THE GRID charging your batteries. That Is a huge thermal mass, once it is warmed up it will stay warm for a long time. Use a pump to move the water around to other boxes to equalize temperatures.

I wont take this further except to say tie this into the water heating system for instant heat.

There are lots of problems to solve, queastions to answer, math and formulas to work. In other words lots of fun for the DIY person.

Have fun building it, I had fun thinking of it.

Jim


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## TexasCotton (Sep 18, 2008)

I used to sell drum heaters and you might try that.


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## rfengineers (Jun 2, 2008)

rbgrn said:


> I'd like to put together an article for dealing with Lead Acid packs in the winter. Do you guys have any suggestions?


Move to Florida?

But seriously, At a minimum I would suggest preheating the battery boxes while you are plugged in, and insulate, insulate, insulate.


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## Coley (Jul 26, 2007)

Mine aren't insulated at all and the way I work it is to charge them in the evening, for about an hour, in case I need to do a short run.

Then, in the morning a timer turns on the charger for a of couple hours. This warms them up enough to reduce the power loss quite a bit.

As you start to drive, stay under 100 amps for the first mile or so and that will warm them some more, plus the transaxle lube will warm a bit. Then just drive on.....

This has worked well down to -10 F degrees, with lead acids.

Don't know how the GELs will work with this method.....


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## evcars (Mar 15, 2008)

Winter driving question:
My car's range dropped from 40 miles at 80% full during the summer to just recently 15 miles at 60%. I have the 8 volt energizer batteries and am wondering if its the cooler weather or bad batteries causing the drop? After going 15 miles today, the batteries were all about 8.15-8.24 volts.


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## madderscience (Jun 28, 2008)

I don't know exactly what the temperature differential is between when you got 40 miles and when you got 15, but if the difference is 80 degrees to 32 degrees farenheit:

DOD miles temp
80% 40 80F
60% 15 32F
80% 20 32F (extrapolating here based on your 60% dod number)
80% 32 32F (expected range based on the math and chart)

so you are seeing 1/2 the performance at the cooler temperatures.

If you look at the battery capacity vs. temperature chart I put up in a previous post on this thread, it looks like you lose about 20% of useful capacity at the cooler temperature, so based on that and your 40 miles during the summer I would expect a range of about 32 miles. Note that this assumes all other conditions are the same.

So where is that 12 miles going? (difference between 32 and 20) Are you running a heater? those can knock 10% or so off your range depending on wattage. Driving in the rain or snow will adversely affect your rolling resistance. Driving into a strong headwind will increase your aerodynamic drag losses substantially. Running lights, wiper, defroster fan, etc puts more load on things too. Finally, since it is cooler the air pressure in your tires may have dropped a couple PSI. Check that out and bring them back to the highest safe pressure you can. Assuming they aren't already, insulate the batteries if possible. If that is not possible, at least ensure they are protected from direct road spray and wind chill. 

It is of course that you are developing a weak battery. Make sure to check electrolyte levels and balance them regularly of course. If you can, monitor battery voltages under load and see if any one of them is sagging substantially more than the others under the same conditions. That is the best way to spot a weak cell. A voltmeter and extra long test leads would probably facilitate that.
Good luck.


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## rbgrn (Jul 24, 2007)

Thanks for the replies, guys!

I'm trying to get a list of 5 or more tips assembled so that I can put together an article on winterizing your EV. 

Keep em coming!


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## HighTech (Nov 12, 2008)

I am a Nascar fan so that is the first place I went to look this up since I am also interested in keping my car fit in the cold weather here in Colorado.
Nascar wasn't much help other than saying keep your car in a garage or covered that I am assuming with a tarp to help keep some cold out.
http://www.nascar.com/2007/auto/cct/11/27/car.care.battery/index.html

I thought about using something like a block heater if the darn thing won't boil the battery since I don't know how hot they get.
It would damage it if it was too hot.

The other thing I can think of is a heated garage, woodstove idea.
makes it pain in winter to keep it going though and needs lots of firewood.

What about those cap batteries that were mentioned? If I remember right, caps don't lose charge during any temperature change.
Anyone looked into this?


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## madderscience (Jun 28, 2008)

For battery heating, A fellow in seattle has had good success using soil warming cables for plants and greenhouses:

http://www.wrapon.com/products/gqswc.html

The big ones provide about 150 watts of heat, the same as if you had a large incandescent bulb providing heat. The cable can be snaked around underneath the batteries to spread out the heat evenly. The cables have an adjustable thermostat.

Obviously for this to be effective the battery enclosure needs to be fully insulated (top, sides, and bottom) to trap the heat. 2" rigid builder's styrofoam works great and adds virtually no weight but in tight spaces the extra volume used could be a problem.


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## stormcrow (May 28, 2008)

One thought I had for insulation is some stuff called Reflectix. It is basically a sheet of bubble wrap surrounded by two sheets of tin foil. It's flexible, is only 1/4" thick, and is ridiculously good at reflecting heat. The only thing you might have to be careful of is putting down a barrier between the Reflectix and your battery. I'm not sure if this stuff will carry a current, but better to be safe than sorry. You can find it for sure at a Menards or possibly at other hardware stores. Seriously, this stuff is great.


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## ElectriCar (Jun 15, 2008)

Not sure how this would work but heat tape for preventing pipes from freezing will generate some heat. It's rated in watts per foot and likely available at Grainger, McMaster Carr?, and hardware stores & plumbing supply stores. They don't get "hot" but they will get warm and in an insulated box should do the job.

They operate on 120V power from your home but will operate on your pack voltage if it's not too high. 144V probably would be ok. The thing about running it on your pack is the cable has to be rated for the voltage. Look at the cable and it should be written on it.


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## ElectriCar (Jun 15, 2008)

stormcrow said:


> One thought I had for insulation is some stuff called Reflectix. It is basically a sheet of bubble wrap surrounded by two sheets of tin foil. It's flexible, is only 1/4" thick, and is ridiculously good at reflecting heat. The only thing you might have to be careful of is putting down a barrier between the Reflectix and your battery. I'm not sure if this stuff will carry a current, but better to be safe than sorry. You can find it for sure at a Menards or possibly at other hardware stores. Seriously, this stuff is great.


Radiant barrier is made from a 99+% pure aluminum foil so yes, it will conduct followed by meltdown/flames possibly!

I lined the floor and back of the cab in my truck when we replaced the carpet! I was going to do the doors but they already have a foam blanket and I suspect the thickness would present an alignment problem.

Don't get it at Lowes or HD as they're very expensive. Try http://innovativeinsulation.com I've used it for several years and these folks are NOT expensive!


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## aldaeron (Jan 29, 2009)

If you take a lead acid, charge it to full capacity in a heated garage (let's say at 80F) then drive outside. 

1) Will an insulated set of batteries stay warm by being used to power the car?

2) If I park all day and let the car cool down, I know the capacity will be reduced - what changes? The voltage? Or AH capacity?

3) If I park all day and let the batteries cool to 32F, I know I will lose ~25% of capacity. If I reheat the batteries right before I leave back to 80F using some sort of DIY heating system, will I get that 25% back? Or is it lost forever?

4) If the power in #3 is lost forever, it would seem like a good idea to use a little bit of power to keep the insulated batteries warm all day so they wouldn't lose capacity (only on days you know you will be using the car again later in the day or if it is on wall power). Has anyone tried this?

Thanks!


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## madderscience (Jun 28, 2008)

aldaeron said:


> If you take a lead acid, charge it to full capacity in a heated garage (let's say at 80F) then drive outside.
> 
> 1) Will an insulated set of batteries stay warm by being used to power the car?
> 
> ...


1) Yes. both charging and discharging will generate some heat in the batteries. If your battery pack is insulated that heat will persist. 

2) Primarily usable AH capacity. voltage may drop slightly. You should still be able to use voltage to calculate effective SOC at the current temperature.

3) Cold does not actually discharge the battery, it just makes the chemical reactions go slower, which effectively reduces the capacity of the battery. This means if you reheat the battery via some external means your usable energy capacity should recover.

4) To the best of my knowledge most battery heating setups work by heating the batteries via some sort of thermal wire/pad while parked and plugged in. A well insulated pack should stay warm enough to work well for the 8 hours or so it sits at work, and once you come home the charging plus heating will warm things up again. For what it is worth, even in my uninsulated packs, my car was still melting snow above its batteries 12 hours after a charge finished when we had some snow a few weeks ago. There is significant thermal mass there!)

A couple of other things:

Cold by itself does not actually hurt lead acid batteries provided they are kept to a safe SOC for the temperature and it isn't so extreme as to freeze them. Actually their shelf life, etc. will be longer as the chemical reactions (sulfation and plate corrosion) that destroy LA over time will be slowed down too. Don't heat your batteries past 80 degrees F or you will shorten their lifespans for the same reason cooling them extends it. sulfation, plate corrosion, etc will speed up. Also too much heat can warp the plates.


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## ElectriCar (Jun 15, 2008)

I've thought of using pipe heaters or heat tape. It is available at home stores and is basically a cable that generates a small amount of heat to keep pipes from freezing. Not going to get hot but if plugged in and inside a battery compartment it should keep them from getting cold. 

I've thought of connecting it to the wiring for the charger so when the truck is connected it will be energized. They have a heat sensor to shut them down at some temperature though I don't know what that is but they won't allow it to get HOT.


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## tj4fa (May 25, 2008)

Radiant electric flooring under the batteries.

[URL]http://images.google.com/imgres?imgurl=http://ecx.images-amazon.com/images/I/41YKA8DDTVL._SL500_AA280_.jpg&imgrefurl=http://www.amazon.com/ThermoSoft-Electric-Radiant-Heating-System-TT5-120/dp/B000G6XF0U&usg=__rjqc27Q2ccTrtK24P5XmYeeq0QE=&h=280&w=280&sz=14&hl=en&start=12&um=1&tbnid=PKwEgj4CyRDOPM:&tbnh=114&tbnw=114&prev=/images%3Fq%3Dradiant%2Belectric%2Bfloor%2Bheating%26um%3D1%26hl%3Den%26rlz%3D1T4DKUS_enUS293US293%26sa%3DN[/URL]


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## Frank (Dec 6, 2008)

The other thing that happens (I think) is that the internal resistance goes up, hence higher sag, hence lower power. The solutions are the same: heat the batteries or drive slower.


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## Cimpso (Nov 10, 2008)

Frank, 
The reason that lead acid batteries loose their capacity in the cold is that the chemical reactions that produce energy are slowed down due to the lower temperatures, that combined with fluids (tranny fluid, deferential oil etc) are colder and start to turn into molasses in the cooler temps. 
http://www.popularmechanics.com/automotive/how_to/4301503.html

Tj4fa, 
I'm not sure how much heat is required to keep the batteries warm, but at 120v and .75A you only have 90Watts (120x0.75= 90). Radiant flooring with low powers such as this are only meant to warm the tiles/ flooring enough to keep your feet from feeling cold; and thus your self. Buuuuut over the time charging on-grid combined with the heat generated from the batteries charging, it may be adequate. 

Stormcrow, 
The "Reflectix" product is only designed to reflect radiant heat, and as member Electricar mentioned, it is 99%+ pure aluminum, which happens to be a good conductor of heat. Placed in direct contact with your batteries it will act as a heat sink and negate any effects gained by it's radiant qualities.

Hope this info helps!


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## Cimpso (Nov 10, 2008)

Whoops!
Didn't realize that Madderscience got the battery info up before me! (My bad!) Spot on!


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## ElectriCar (Jun 15, 2008)

Unreal. I just went to Waycross, Ga to my FIL's where he is closing his business and retiring. I walk in and look down on his desk in front of me and there's a brand new section of heat tape there. I picked it up and he told me to take it if I wanted it. 

Just what I've been talking about. It says it's rated at 104 watts and is I probably 10-15' long. I'm tie wrapping it to my rear pack cables tomorrow and will try it tomorrow night! It's supposed to get to 40 tomorrow night so it's not real cold but Monday night it's back down to 30.

I don't know about y'all but my truck is pitiful after sitting out all night when it's in the 25-30 range. When warm and charged up, it rocks!


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## Frank (Dec 6, 2008)

Thanks Cimpso: the point I was trying to make (not well I guess!) was that in addition to losing apparent capacity due to battery slowdown, higher internal resistance also manifests itself as larger sag, therefore less power is available for a given current flow from the batteries. If someone tries to drive at warm-weather performance levels they will tax the batteries even more because you need to hammer them harder to get the same output. Sag can increase by 50% from hot summer temps. to cold winter temps. and power will decrease accordingly. I guess the winter tip would be to slow down!


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## Cimpso (Nov 10, 2008)

Indeed Frank, 
The winter tip to just slow down is just gold, for it applies to Ev's as well as to common sense driving regular ICE vehicles!



"Shhhhhhh. My Common Sense Is Tingling" -Dead Pool


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