12v lead acid battery heater

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ripple4

Well-known member
Joined
Sep 18, 2018
Messages
110
Location
Toledo, Ohio
With the polar vortex just happening and these negative-F cold blasts being a regular thing for 10’s of millions of people I wanted to share my thoughts on a 120v heater for the 12v lead acid battery. Lead batteries perform at their peak at around 77F both in expected life and also ability to provide current. So when the temps drop into single digits the battery is only going to provide 50% or less of what it’s rated at on the sticker. While the leaf does not have a ICE starter motor to power, the car does seem to be very sensitive to a low voltage situation of the 12v battery, and a battery heater cannot hurt there.

To try out this idea I cobbled up some items I had laying around to illustrate one way to do this, the heating plate approach, the picture shows a 150w 120v 4”x5” silicone pad and just about the cheapest temperature controller rigged up to heat the 12v lead battery to 77F/25C. $30 or so will buy a nicer temperature controller with better cable management. The second and probably better way to do this is the battery blanket approach, i bought a zero start 280-0055 battery blankets for the long term. This blanket is lower power, only 50w, but its also insulated, so it will keep the heat in better. Being 28” long it should completely cover the perimeter of the group 51 battery size.


https://ibb.co/LpXgRdB


Here is some reading on cold temperature performance of lead acid batteries:
https://apps.dtic.mil/dtic/tr/fulltext/u2/a239115.pdf\
 
As I started reading I was going to suggest a battery blanket. If the car will be used daily, an unheated insulating blanket (and possible a trickle charger for the coldest nights) should suffice.
 
IssacZachary said:
Thanks! This would be awesome to do in connection with a LiFePO4 12V battery. Those die young do to the cold. Probably the reason they aren't used.

The other reason (aside from cost) is that lithium batteries require a BMS (unlike lead acid batteries, which just tie the cells together with what is essentially a bus) for long life, and the BMS not only adds more cost - it also adds the risk of failure and damage to or destruction of the cells.
 
LeftieBiker said:
IssacZachary said:
Thanks! This would be awesome to do in connection with a LiFePO4 12V battery. Those die young do to the cold. Probably the reason they aren't used.

The other reason (aside from cost) is that lithium batteries require a BMS (unlike lead acid batteries, which just tie the cells together with what is essentially a bus) for long life, and the BMS not only adds more cost - it also adds the risk of failure and damage to or destruction of the cells.

Yes. Unbalancing can be problem with anything with lithium cells in series.

For the record, lead acid are not connected in parallel on a bus. They have the same series configuration that lithium batteries do. The difference is that they can tolerate being overcharged, whereas lithium cannot. So you can keep the cells balanced in a lead acid battery just by keeping it charged up to 100%.

Which brings up another problem with lithium. Lead acid batteries do best at 100% charge. Lithium batteries of any sort usually like being left charged at around 50%.

There are 12V lithium ion polymer batteries for sale designed for automotive purposes. I'm not sure how well the hold up or if they have balancing circuits. But what I do know is that they usually they don't have very low temperature ratings in their specs, except the ones made by Winston (formerly Thunder Sky).
 
For the record, lead acid are not connected in parallel on a bus. They have the same series configuration that lithium batteries do.

I didn't write "in parallel." My Vectrix runs at 143 volts, with the (Leaf) cells tied together with buses. I believe that automotive lithium batteries just use what would normally be a higher series voltage configuration, but undercharged to 13 or so volts to keep the cell SOC below 100%. I'm not certain of that, though.
 
Series is series. It doesn't matter if you use bus bars, wires or tabs. It's not going to affect how the battery balances or not.

Normal lithium ion cells, like the chemistries used in the Leaf, Tesla, cell phones, hover boards, etc., can't be used for automotive purposes because their voltage can't be multiplied into 10 to 14V with 12.8V being nominal. 3.6V or 3.7V times 3 is too low, and times 4 is too high.

The ones used in automotive batteries are a lithium polymer battery. Lithium polymer batteries are solid electrolyte batteries that usually have higher C rates but lower over all energy densities. They also have a nominal voltage of around 3.2V, which is much better since multiply 4 and you get 12.8V, just about the same as lead acid. The typical chemistry is normally refered to as lithium iron phosphate (LiFePO4).

12V Lead acid batteries are 2V cells tied into 6 in series.
 
I'd like to learn more about this subject, and it may well be the case that the posts i see on this forum with the always be trickle/float charging comments may still be valid for normal temperatures. but there seems to be a warning against charging a lead acid battery that is very cold. I am taking about temperatures colder than 0F, the comments i have found on Canadian, Alaskan car forums and trucking websites, as well as the battery university website indicate its best practice to warm up the lead acid battery before charging. The reasons being given is that at these cold temperatures the electrolyte can freeze, but short of that it will get a thicker viscosity, like toothpaste they say, and also higher electrical resistance. While microprocessor float charger might prevent it, there is the risk that the changing causes hydrogen production in a way not seen at normal temperatures, and will also trap the gas making an explosion much more likely, or best case the charging will be ineffective.
 
An update about the battery blanket, the zero start 280-0055. I ordered mine in from some guy in Canada on ebay. I tested it, compared to the pad heater. with the pad heater the battery the battery increased in temperature about 20F above ambient in 90 minutes burning 150w. the blanket heater heats the battery 25F above ambient in 60 minutes burning 45watts, so the blanket is definitely the way to go. I used two 36" heavy duty zip ties to hold it onto the battery. I have read reviews that these should not be taken on and off, just install it and leave it there forever as the flexing may damage the heating wires inside.


https://ibb.co/Htbkd4x
 
How many AH /HR does it consume, roughly? I assume it cycles on and off after reaching the set temp. I know a guy who has to walk 5 blocks evening and morning, so he can plug in a trickle charger. Small car with small aluminum engine.
 
The zero start 2800055 that I have here is 120v A/C and 50w, so that's like .4amps. I don't think its thermostatically controlled, so it just heats until the battery reaches equilibrium temperature, 50W in = 50w out. I have a mechanical timer that turns on 90 minutes before i leave in the morning, but it could be pluged in all night too, 10 hours would cost $.07 at my power rate, 90 minutes is a single penny. maybe other brands and models have different power/control mechanisms, or one could be added like that cold temperature power cube sold in home improvment stores. I see this for only mornings/days that are in the single digits and negative F temps. Above 30F, the battery should not have a temperature related loss of power.
 
ripple4 said:
I'd like to learn more about this subject, and it may well be the case that the posts i see on this forum with the always be trickle/float charging comments may still be valid for normal temperatures. but there seems to be a warning against charging a lead acid battery that is very cold.

To the best of my knowledge, the warning against charging cold batteries is because a very discharged, very cold battery could have become frozen solid; and fast-charging it (especially trying to jump-start it) may cause it to explode.

I doubt that attempting to trickle-charge a frozen battery at 20 watts would be enough to cause an explosion (though a frozen battery would fail to charge). Regardless, if you know that the battery is not frozen, then I don't think you need to worry about damage from trickle-charging.

The act of trickle-charging a battery also creates some heat. So my method to heat the battery up has always been to hook-up a trickle charger on very cold nights. I use a BatteryMinder Jr. these days: while the battery is charging, it is warming-up; and once charged, when the charger is doing its "desulfation" thing, that should add a bit of heat also.

Insulating the battery would also minimize heat losses, so would be valuable with, or without a heat source.
 
The battery warmers I have used about 50w also do have a high temp cut out, but when it's cold enough to plug them in it will never get that warm. For the heck of it I did try it in summer at 85 and it did cycle on and off, but below freezing I don't think it would ever get that warm.

I also would use a trickle charger, it adds a few watts of heat and keeps the battery topped off, two benefits in one. Granted it won't warm as much as a warmer, but the Leaf doesn't need to crank an engine over to "start".
 
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