Battery heating for EV efficiency

[Christ]

Ben -

Solar heat. Park your car in the sun (like you want to in the winter, anyway) and make sure there is access for your batteries to either directly benefit from that heat, or at least get the residual heat from the passenger compartment.

[NiHaoMike]

Wouldn't the batteries degrade faster if they're too warm? I remember that unused batteries should preferably be refrigerated (but not frozen). Really low temperatures probably aren't too good for them either, though.

What about add a reversing valve to the A/C so it also works as a heater and add a control circuit so it can cool down to 90F or heat up to 40F as needed whenever the charger is plugged in? And maybe also heat or cool as needed on command by remote control.

[bennelson]

Originally Posted by vpoppv

does the amount of charge time change at all during the winter?

Good question! I am not sure. I just plug in at night and it's charged in the morning.

Voltage tends to be lower with cold batteries. Voltage is the main thing that effects speed, so yes, you may have a lower speed in the winter, and maybe poorer acceleration as well.

Also, if your voltage is lower, you need more amperage to do the same work, so you pull more amps!

[orange4boy]

Good thread Bennelson.

Wouldn't the batteries degrade faster if they're too warm? I remember that unused batteries should preferably be refrigerated (but not frozen).

You are thinking of alkaline primary batteries. Keeping batteries cool will keep them charged longer but they should be warmed up prior to use. Some batteries are more heat sensitive than others but any blanket warmer will probably not get floodies hot enough to damage them especially in the winter.

Even though battery capacity at high temperatures is higher, battery life is shortened. Battery capacity is reduced by 50% at -22 degrees F - but battery LIFE increases by about 60%. Battery life is reduced at higher temperatures - for every 15 degrees F over 77, battery life is cut in half. This holds true for ANY type of Lead-Acid battery, whether sealed, gelled, AGM, industrial or whatever. This is actually not as bad as it seems, as the battery will tend to average out the good and bad times.

From: Deep Cycle Battery FAQ

Heat is a killer of VRLA. Many stationary batteries are kept in shelters with no air conditioning. Every 8°C (15°F) rise in temperature cuts the battery life in half. A VRLA battery, which would last for 10 years at 25°C (77°F), will only be good for 5 years if operated at 33°C (95°F). Once damaged by heat, no remedy exists to improve capacity.

From Battery University

This is the lead acid battery in the Prius which has a short life. I don't know why they went with a VRLA. I would be interested in seeing if it gets overheated in it's compartment.

Capacity VS temp...

[dwtaylorpdx]

In real life I do data center modifications and other fun,

The big wet and gel battery UPS systems need to be at 68 degrees to get full pull on the batteries we actually control the environment better for the UPS than the computers..

On a megawatt ups a couple degrees makes a huge difference on run time, its better to be just a little hot than cold..

Dave

PS: They cell adhesive heat packs for batteries. But you need to allow for letting them shed heat as well. I think a box with a thermostat and a small muffin fan would do the trick.

[Rokeby]

Originally Posted by orange4boy

...This is the lead acid battery in the Prius which has a short life. I don't know why they went with a VRLA. I would be interested in seeing if it gets overheated in it's compartment.

Capacity VS temp...

The following is for non-Prius drivers...

The only lead acid battery in the Prius is the little, 12V, motor cycle-sized
one that is the source for power for all electronic systems but the HV battery
and the electrically assisted friction brakes. The HV battery provides power
for the HSD (Hybris Synergy Drive, the heart of the Beast) and...

Via a DC to DC converter, keeps the 12V battery fully charged when the car
is in the "Ready" mode, that is ready to drive or actually being driven.

The 12V battery lives below the floor pieces in the hatch back area, at the
rear of the car, on the passenger side. It pretty much sees the same
ambient temps as the passenger cabin and the HV battery, which is right
behind/below the rear seat. In high temps such as after a hot-soak in a
uncovered parking lot in high summer, it endures those temps somewhat
longer than the HV battery. The HV battery is cooled by air drawn from the
passenger cabin and exhausted from the car behind one of the rear fenders.
The 12V battery is not so directly cooled, or heated in winter for that matter.

Typically, the 12V battery has a service life of 4 years. (However in both
very hot and cold conditions, say Arizona and Alaska, its life can be reduced
by half. Especially if it was not fully charged when it was delivered to the
original buyer... or is ever discharged due a light left on overnight, etc.) It's
most important function is to boot the computers when the car is started --
something like 7 computers and 14 ECUs (Electronic control units, very
simple, single function "computers").

If the 12V battery is dead, ain't no way the car can start, even though you've
got the HV battery sitting there just a few feet away.

The 12V battery does not have to provide starting amps. Once the various
computers are booted, the HV battery comes on line, provides both HV and
12V power, and MG1, (Motor Generator 1) is used as a starter for the ICE.

So, that's the 101 level course on the Prius' 12V battery.

[bennelson]

I got a chance to work on my improved battery warmer.

Basically, it's just a tray of hardboard with spacer strips of plywood over the top of it. The heat tape runs between the spacer strips, and a layer of aluminum goes over the top of the whole thing.

Plug it in and the heat tape warms up the aluminum, which spreads out the heat to the batteries sitting on top of it.

I'll let you know more when I actually get it in my battery box!

[bennelson]

Here's the video!

http://www.youtube.com/watch?v=Y_L1OhD2K0k

[bennelson]

I also tossed this up onto INSTRUCTABLES as just the video.

EV Battery Warmer Part 1

[Daox]

Looks pretty good Ben.