Quote:
Originally Posted by Ecky
If the goal is weight savings, I don't think a lithium is going to achieve it in cold climates.
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Yeah purely weight savings I don't think you will gain much. And personally, I think spending $200 on a battery system to save a couple pounds would never pay off. Cool factor yes. But I'm not here to tell you that! I'm a nerd too and wanna do cool stuff with my internet friends as well. haha
But I have no doubt 18650 cells could start a starter motor in cold conditions. The correct way to me to do this would be to rig up your battery on a test bench, throw it in the freezer, and see if it will crank the car when cold. If it can't start the motor you can clamp it, interpolate up, and then redesign you battery to get your ccas.
Then rig it up again in the freezer, (you can even take a freezer you don't care about and throw on an aftermarket switch and turn it into a fridge and hit whatever temp your heart desires) and throw on your battery heater and see what it takes to hit 65F. A lot of these systems designed to keep a value like this will bounce back and forth effortely and keep target like magic. We did something similar with a self driving robot, and were afraid since the wheels weren't squared correctly it would pull in a direction. Nope. It compensated the whole time like magic and you couldn't tell it wasn't perfect. Its just SOCs process thing so much better than humans.
Final point, Its just what sort of daisy chain of parallel and series will get you the correct cca, reserve capacity, and voltage.
I'd say the main benefit would be is if you buy panasonic/lg/sony etc.. legit cells and stay between 40-70% discharge the rated cycle life is something on the relm of 40,000 cycles.
Rated capacity on deep cycle lead acid batteries (not starter batteries rated for 20% dod.) is 400-500 cycles at 80% dod, and only 1500 cycles at 50% dod.
Reference: depth of discharge (dod): rated safe discharge from 100 to x %.
cold cranking amp (cca or ccas): when battery chemistry slows and resistance increases internally, this is the amps the cell will output when cold at whatever temp.
But saying all of this I have experience designing these things for indoor facilities, not the outdoors. I haven't even seen below 28F here in AR this year. I think it was 58F today.
Oh, also the lithium cells are something on the order of 5-6x more power dense. For our autonomous robot project we had we built a pack of 18650 batteries that weighed 0.7 pounds, and everyone else had some config of lead acid batteries weighing 12 pounds. Extreme case, but it was hilarious to see our cargo capacity vs vehicle weight compared to everyone elses.