ripple4
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12v lead acid battery heater

Tue Feb 05, 2019 9:33 am

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.

Image
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\
Last edited by ripple4 on Tue Feb 05, 2019 12:29 pm, edited 1 time in total.

LeftieBiker
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Re: 12v lead acid battery heater

Tue Feb 05, 2019 11:35 am

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.
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IssacZachary
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Re: 12v lead acid battery heater

Tue Feb 05, 2019 6:20 pm

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.
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LeftieBiker
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Re: 12v lead acid battery heater

Tue Feb 05, 2019 6:31 pm

IssacZachary wrote: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.
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IssacZachary
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Re: 12v lead acid battery heater

Tue Feb 05, 2019 8:25 pm

LeftieBiker wrote:
IssacZachary wrote: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).
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LeftieBiker
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Re: 12v lead acid battery heater

Tue Feb 05, 2019 8:28 pm

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.
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IssacZachary
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Re: 12v lead acid battery heater

Wed Feb 06, 2019 4:27 am

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.
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LeftieBiker
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Re: 12v lead acid battery heater

Wed Feb 06, 2019 4:55 am

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.


Clearly whatever I will write will be wrong, even if not written so, so I'll drop that.
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ripple4
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Re: 12v lead acid battery heater

Wed Feb 06, 2019 7:12 am

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.

ripple4
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Re: 12v lead acid battery heater

Wed Feb 27, 2019 6:38 pm

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.

Image
https://ibb.co/Htbkd4x
Last edited by ripple4 on Thu Feb 28, 2019 5:43 pm, edited 1 time in total.

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