[Greenflight]

Hey folks, I was looking through ebay and I found a few lots of relatively small (laptop size and smaller) lithium ion cells. Some of these were going really cheap, too. Some are scratch-and-dent, some are just plain cheap.

Figuring 14V and 4 A/h per battery, you could get a 140V, 200 A/h pack with 10 series packs of 50 parallel batteries in each pack, for a grand total of 500 laptop-size batteries (of course, you could go even further and figure 4 cells per battery, for a total of 2000 cells). Not too awful bad.

At 600A peak current, that works out to about 12A per battery. Should be easily manageable for a battery in that size range.

Now, knowing that some manufacturers are already building lithium packs made up of thousands of small lithium cells, is there any reason it couldn't be done with these cheapies off of ebay?

No cracks about soldering irons getting worn out, please.

 

[ev3k]

Correct management of charging parameters might be a challenge without some type of monitoring/control circuitry for each battery in the series/parallel array...

Steve

 

[Greenflight]

Yeah, you'd probably need to have a balancer on each parallel stack, but electronics are cheap...

I'm just wondering if it would be economical in terms of size and weight?

Just on a side note, I figured out that it would probably take about 8000 cell phone batteries...

 

[Craig]

...so I suppose you haven't heard about those hundreds of laptop batteries bursting into flames? If you do buy laptop batteries from ebay, make sure they're not the ones that are supposed to have been recalled

 

[Greenflight]

Yeah, that would probably make the news... Come to think of it, lithium polymer batteries would probably be a better idea than lithium ion. More stable.

 

[Craig]

or very expensive "safe" batteries (like the valence saphion, or lithium iron phosphate). those won't explode if they're overcharged, unlike lithium polymer