Ted Lowe's S-10 EV

[ted.lowe]

Check out my bright yellow S-10 EV here:

http://tedlowe.fveaa.org

[ted.lowe]

On my drive home from Chicago after shooting the 190 North TV segment last Tuesday, my EV developed the following symptoms:

• Controller seemed very hot (ambient conditions were very hot and humid too)
• Couldn't draw much current out of battery pack
• Pack voltage seemed high enough (had only driven 22 miles and had 2 hours charge at 110V at CCGT)
• Very sluggish performance (due to low current availability)
• A quick visual inspection of all the battery connections didn't show any loose, corroding or melting.

After i got home, i charged for about 5 hours at 220v and let the controller cool down. Unfortunately, the problem persisted.  i drove another 8 miles (slowly) to Jean's house to borrow her car and drop off my cat because i was leaving on my vacation early the next morning.  i didn't plug-in while i was gone on vacation since i had a full charge (minus 8 slow miles).  When i got home 5 days later, the battery pack was very very drained and the EV would barely move (controller mildly squeaked & pulsated).

All of this "data" lead me to believe (incorrectly), that my controller got too hot, went into thermal-limiting mode (self-preservation) but still was damaged.  i was guessing that some of the output MOSFETS blew up (giving me only some of the current i should have).  The drained battery pack after returning from vacation was a mystery to me, since the controller was off (via key-controlled contactor) and shouldn't have been drawing current.  So i went to sleep with all this data swirling in my head and planned to take a fresh look in the morning with more tools and test equipment in hand.

i can't believe what i found the next morning!  i'll post the 'problem' and how it explains the symptoms above, in my next post.  In the meantime, feel free to reply with your detective ideas/guesstimates to see how close you come to the answer.

[ted.lowe]

Ok, here is the what i found!  See the gallery below to see pictures and more info.

It was a BAD BAD BAD battery that melt down internally!!!  It still had 3 volts across it so the 'apparent pack voltage' was still relatively high.  But it couldn't pass any current (thus the 'out of juice' sluggish performance).  It didn't look bad from the outside, so i missed the problem on my initial inspection.   Also, ASSuME-ing that the problem was due to a thermally limiting controller caused me to give less attention to the battery pack. 

Morals of the story: 1) Buy/build a battery pack monitoring system (to monitor total voltage and the voltage, temperature (and maybe even the water level) of each battery; 2) Keep the batteries cleaner since i may have noticed the problem sooner; 3) make a more thorough inspection before driving anymore (despite how 'hurried' i am or how hot out it is); and 4) don't ASSuME!

Has anyone every seen/heard of such an issue ?

http://www.fveaa.org/members/tedlowe/internal-battery-meltdown

[larry.backes]

Interesting.  Any thoughts as to why it melted down?  Do you think it was bad from the factory?  Also, you had said the pack didn't hold a charge during vacation, do you think the melt down cause a dead short to the battery box?

Larry

[todd.dore]

Ted -

One couldn't have scripted a better battery melt-down in a Hollywood movie!  I've never seen anything quite like the bottom of your battery - total chaos!

I will have a BMS, but not something that monitors temperature (for now).  I've purchased a PackTrakr with 2 additional modules, so it can monitor 18 batteries.  The display will show the voltage for each of the 18 batts, plus the pack in total.  It will also monitor the real-time amps used (battery amps) and the resulting power (kWh).  As such, it will also serve as an e-meter by calculating the SOC.  I think a future upgrade will be able to have a temp. input, although I would need temp. sensors on the batteries to read this.

Good moral of the story - monitor the batteries as best you can!

For PbA, what happened to you is a nusaince.  For Li-ion (depending on the battery chemistry), it could be lethal - once a Li-ion battery goes into thermal shutdown, then you have a chemical fire which you cannot put out, and will spread to the other batteries.

-Todd

[ted.lowe]

Great Todd, let us all know how the PackTraker works for you.  Perhaps you can give a talk/demo at a future meeting once you're familiar with it. 

i thought about buying such an item, but i really have my (EE) heart set on designing/implementing a similar homebrew device.

You're right about the power of LiIon bats in a thermal runaway situation...  the fire/explosion would make a lb of C4 look mild :-)

[ted.lowe]

Good questions Larry.  i'm not sure whether i'll EVer know the exact cause.  Probably not a factory issue since it had 8k miles on it already (would think it would have already failed by now if defective).

The melted battery and the mess it made in the battery box definitely create a MAJOR ground short as evidenced by these observations: 1) Got a pretty major shock when touching the chassis and one of the battery terminals, 2) As you said, the battery pack was (VERY) dead after 5 days of sitting, and 3) my NG3 charger shutdown just after starting (completely confused by the voltage/current relationship it was measuring).

Interesting.  Any thoughts as to why it melted down?  Do you think it was bad from the factory?  Also, you had said the pack didn't hold a charge during vacation, do you think the melt down cause a dead short to the battery box?

Larry