ToothDoc

The other day, the car was sitting outside for 10 hours in 5-10 degrees F. The car turned over, but not the usual way. It was a little slower... But still worked. I charged up the batteries after 1 1/2 weeks and about .9 amps went in. Next charge will be 1 month of daily driving.

jkeifer3

Hello. Did you solder the cells together or have them welded? Also, what material did you use to strap them together? Looking forward to seeing what the long-term viability of the pack is.

ToothDoc

The cells were soldered - you have to take care not to cover the vent holes on the negative terminals. They're A123 cells from ebay and I have 20 of them. 5 packs for 4 cells in series so at 2.3 amps each, that's a total of 11.5 amp hours at 13.2 volts. Because of the reduced power at startup at 10 degrees F, I'm starting to think a 7 pound pack might be a more appropriate replacement for cold weather startups (that would be a 23 amp hour capacity). I've just done the ghetto thing for now - just taped the batteries together and onto the bottom battery cover in the car. I'll occasionally post up the progress.

ToothDoc

cold weather updates... No problem except one night I left it outside for the whole night and the temp got to 0 degrees F. I had to try to turn on the engine about 5 times or so before it kicked on. Unlike lead acids that get weaker and weaker, the Li Ions start weak but keep on cranking it and the batteries start to get warmer and warmer and then gets more and more powerful. So, it works down to single digits easily, but negative and 0 degrees outdoors all night is a little tough. So, after 2 weeks of use, I decided to charge up the battery and it was still 95% full. It appears that the car's alternator is keeping the battery charged so now I feel safe to say that the one mishap probably was a result of me leaving something on all night which drained the battery completely.

RedfoxXx

Just FYI if you charge a lithium battery too much, they can get very hot and even explode. (Like the dell laptop batteries a few years back) Li batteries should be charged with some kind of control system. A voltage controlled current source is ideal, however some companies even use a temperature sensor to monitor the Li battery in a unit to warn if they get to hot. You could try to cheat this by selecting the peak voltage of a battery cell right at what the alt. can produce (14.5V+-?) so that it only trickle charges. But I would be careful about charging them with a uncontroled voltage source such as your alternator!

Also the heat from your engine bay is only going to degrade the life of your battery back, I bet it will not last for a year, LI battereis only las for 2-3 years from the manufacture under normal temps.

ToothDoc

RedfoxXx, I measured the peak voltage of the voltage regulator and alternator and it will never charge the LiIons to 100%. It'll stop around 90-95% full charge which is what I have noticed. We'll see how long it lasts. I'll be the guinea pig for this one.

RedfoxXx

The only thing standing between you and a car fire is a substrate about the thickness of your hair, and I think your insurance company is gonna laugh at you when they see what you did.

also Li batteries are only good for 2-3 years after they leave the factory. so lets say you got cheap ebay batteries and they sat on a shelf for 6 months before they got to you were talking 18 months of life under normal conditions. The heat from your engine bay is going to accelerate their deterioration! also if you completely drain those suckers you are DONE because they can not be %100 cycled.

I think its cool for a day at the track but for around town I would take the 10 year military design life of the PC 680 any day of the week + less of a chance of a car fire.

ToothDoc

Perhaps you are correct. I've had a Lithium Polymer fire in the past - several of them actually. These are LiFePO4 with vents so the fire possibility is much lower/non existent. I also did drain it almost 100% on accident that one time and have charged them back to full capacity. I'll just have to see how long they last in my car - I'll keep on reporting my findings.

MicaISF

i am with you on this.
LiFePO4 batts are very different from Li polymer batts. i don't know where that 2-3 year battery life come from. At least with my laptops and electronic equipments, i have never had a lithium polymer battery that lasted fewer than 3-5 years when i finally replace my equipments. i would agree that overcharging could be a bad thing; A charge regulator would be a good idea.

BYW, there is nothing wrong with ebay batteries as long as the source is reliable. just because they are less expensive on ebay does not make them inferior.

Jaker

Hi there,

Is this battery still functioning correctly for you? Also, what gauge of wire did you use for the run from the individual packs (each pack of 4 cells) to the connection to the car's battery terminals?

Thanks.

daedalus

iTrader: (2)

very cool idea and project...

but I have to ask - why not just get a braille?

http://www.braillebattery.com/

MicaISF

A lithium iron phosphate batt is much lighter and carry more charge than a dry lead acid batt with the same weight.

Jaker

The LiPo batteries on the Braille site are pretty light, but nothing like this battery. Also, did you look at the prices for the Braille batteries? The cheapest ones are around $1,800.

ToothDoc

So far so good. I haven't charged since last time and I haven't had any difficulty starting - but it hasn't been below 0 degrees F. The charge stays at 1 notch above the center on the voltmeter in the dash which seems to be consistent with a 95% charge. I'm keeping it in until it no longer works.

The wires are 12 guage and there is 5 of them in parallel. The initial startup seems to crank up to 500 amps (based on my ammeter) on a cold startup, but since it is such a short time, the wires do not get warm or anything.

For those DIYs, I'd definitely recommend so far. A123 LiIons (LiFePO4), 4 in series and 5 in parallel. During soldering, make sure the negative terminals are not completely covered up so the vent holes stay open.

No indication of overcharging. The voltage regulator on the alternator simply doesn't give high enough voltage to charge the battery to 100%. The only possibly issue is that if you leave it for a long long time w/o turning it on once in a while, the car's electronics might use up the 12 amp hour capacity and when it's below 0 degrees F, it has a hard time starting.

BUT, when it's cold, keep on cranking... Unlike lead acids, the continuous cranking gets the batteries warmer which actually reduces internal resistance and eventually turns over. That was when it was negative something all night and the car was outside all night.

timeToy

iTrader: (11)

Braille also make nice Ion Lithium Car batteries


The lighter Dry Lead Acid start at $150 up to $299; Yes Ion Lithium ones start at $995 up to $2000 (for a 12V battery)