Hot Lifepo4 after ride

[brainfarth]

I put 30 miles on my lifepo4 48v 20ah yesterday and when I checked my pack, it was pretty hot.. I let em cool down for about 2 hours before putting a charge on em. I'm just wondering if that's normal. I've never put that many hard miles on them before(big steep hills). And on a side note, I attempted to video the adventure and after the trip I noticed the camera lens fogged up inside the waterproof case(Sony as20). Gonna have to heat it up a little before closing it next time. Big bummer since it was a beautiful day.

 

[USAEBIKECO]

Yes, lifepo4 batteries will be hot after a long ride. The battery discharging is the reason. It is normal but make sure to have some way of cooling the battery. I air cool mine by leaving a small opening on the canvas bag.

 

[Ykick]

I've found IR temperature guns to be very useful tool on eBikes. Battery cells, BMS (bleed balance resistors), controllers, motors, brakes, tires - merely point and shoot to see if anything's close or exceeding sensible temperatures. If you cook, it's also very handy in the kitchen, LOL....

 

[MadRhino]

Lifepo does heat, but normally safe.
There are some rides, when I monitor my RC lipos temp by the smell. :wink:

 

[dogman dan]

I'm sure I could run some headways till nice and hot, if I wanted to.

What's going on, is the internal resistance of a battery increases as it discharges. Near the end of your very long ride, the resistance is higher and the battery will warm itself more as you run. Running slow that last bit of the battery before it's empty is good practice.

This is true of all brands, all chemistries. The difference is the degree to which it's noticeable. ANY battery that got really hot discharging was run too hard for itself, IMO. You may be fine during 90% of the run, but if the battery got more than warm, got really hot, then you should slow down more near the end of the ride. Perfectly normal to have a battery get noticeably warmer than body temp, 100-110F, that's no big deal. But if you see shrink wrap shriveling up, feel it's very hot to touch, or hot enough to smell the heat shrink getting soft, BACK OFF. You can make it hotter if you have enough insulation around the battery, like a padded bag in summer. Great in winter, but maybe you need to vent the bag in summer.

If it gets pretty warm immediately, then you have a problem, it could be a bad cell cooking off, or just a very over worked battery. Too much motor and controller for that battery. Too small a battery will work it too hard with a big motor and controller.

 

[dnmun]

dogman is right. when the pack has reached a low SOC then it is harder for the lifepo4 matrix to provide the free lithium ions into the electrolyte that are needed to transport the current through the cell. same is true for lipo.

so fewer carriers means the resistance goes up and so the cell heats up rapidly at the end of the charge.

this is when most of the puffing occurs from gas formation at the electrolyte/electrode interface imo.

your hills are steeper than anybody else also so the current is much larger when you are going up the last hill to your place up there on top.