Li Ion – VS – LiFePO4 ?

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Robert
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Li Ion – VS – LiFePO4 ?

Hi guys,
I am looking forward to construct sort of an electric scooter that, hopefully, I could later manufacture and sell in small series.

Right now I am thinking about the kind of batteries should I use, Li Ion or LiFePO4.

If I heard it right, Li Ion ones are more-or-less unsafe and can easily explode if overcharged, also the pack cannot be simply soldered together, as there should be a separate wire going out from every battery to the charger, so that it could control and balance all that bats. in the pack, right? Also, while not sure that its true, I was told that Li Ions cannot be soldered in Parallel, only in series, therefore you cannot increase the Amps, is that so?

As for the price, I found them at about $2.9 + shipping for 3.7v , 2200mAh. That way a pack of about 36v, 8800mAh would need about 40 units and would cost roughly 120$.

The price for the LiFePO4, I believe, could be somewhere similar, with a higher safety. Do you know whether they need a separate controller for each unit? Can they be wired in parallel, etc. ?

Thanks!

LinkOfHyrule
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Re: Li Ion – VS – LiFePO4 ?

Yeah, Li-ions are a little...touchy. Nothing bad should happen if you take care of them.

The wire going from each cell to the charger thing you're talking about is called balancing. This is done with LiFePO4, too. I don't know anything about the discharge curve of li-ions, so I don't know if you can put them in parallel or not. If you can't put them directly in parallel, then you can at least put multiple packs in parallel somehow. Kind of a PITA to do, though.

Even without a BMS (battery management system; takes care of balancing and such), that's a really, REALLY good price for lithiums. Only about $0.40/whr! Granted li-ion doesn't last as long as LiFePO4, but that's almost cheaper than what I paid for my lead-acids. O_o Where did you find those? I may be interested...

LiFePO4s are definitely more expensive than those. The cheapest you can get them is from PingPing on eBay, for about $0.70/whr. Those particular ones don't take kindly to high discharge rates, too. They are safer than li-ion, but not as energy dense. The cells can be wired in parallel without any problems.

The author of this post isn't responsible for any injury, disability or dismemberment, death, financial loss, illness, addiction, hereditary disease, or any other undesirable consequence or general misfortune resulting from use of the "information" contai

Robert
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Re: Li Ion – VS – LiFePO4 ?

Thanks for the advice!
They're in China, you can find them here
http://ffxny.en.alibaba.com/product/200097771/202755632/_18650_Li_ion_Battery.html

R

andrew
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Re: Li Ion – VS – LiFePO4 ?

I think there's too much safety risk using a large Li-ion pack commercially in an EV. Not only safety, but risk of property damage. If there's a fire, there could be a huge settlement in a property damage lawsuit. With a large number of cells, and a complicated BMS, what will happen when the BMS fails? What if the charger fails, and severely overcharges the batteries? The nice thing about LiFePo4, is that they are not going to start on fire or explode.

Ideally LiFePo4 need a BMS which monitors the voltage of each cell for cutoff, and balances the cells. An option is to charge each cell with an isolated power source at a constant current/voltage (much like lead-acid). There's talk on the endless-sphere forums of doing that with DC-DC converters:
a DC-DC to charge li-ion... GREAT!!

[url=/forum-topic/motorcycles-and-large-scooters/587-my-kz750-electric-motorcycle-project]KZ750 Motorcycle Conversion[/url]
[url=/forum-topic/motorcycles-and-large-scooters/588-fixing-my-chinese-scooter]900 watt scooter[/url]
Pic from http://www.electri

Robert
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Re: Li Ion – VS – LiFePO4 ?

Oh, just got an answer from them.

LiFePo4 battery ,3.2 V, 3000 mAh
FOB Tianjin USD 4.2 /pcs

I guess this price sounds good, what do you think?

chas_stevenson
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Re: Li Ion – VS – LiFePO4 ?

If by 4.2 you mean Four dollars Twenty cents ($4.20) then yes that is a good price. The best I have seen is around $10.00 a cell. If you can get them at that price I'll take 120 cells, maybe that might bring the price down a little more if ordered in larger quantities. 120 cells @ $4.20 = $504.00. I paid $560.00 for the 60 cells I have so to me that would be a deal.

Grandpa Chas S.

andrew
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Re: Li Ion – VS – LiFePO4 ?

That sounds like an amazing deal. Can you get any specs on the cells?

[url=/forum-topic/motorcycles-and-large-scooters/587-my-kz750-electric-motorcycle-project]KZ750 Motorcycle Conversion[/url]
[url=/forum-topic/motorcycles-and-large-scooters/588-fixing-my-chinese-scooter]900 watt scooter[/url]
Pic from http://www.electri

wanders
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Re: Li Ion – VS – LiFePO4 ?

LiFePo4 battery ,3.2 V, 3000 mAh
FOB Tianjin USD 4.2 /pcs

I guess this price sounds good, what do you think?

If that is a 3 Ah cell at $4.20/unit in smallish quantities, then yup, that is a very good price, if the product is legit and has good specs. I would be interested in a KW-hour or two of these units. It would be great to get samples before buying in quantity to test. DoctorBass over at ES is doing that right now on some larger format Headway cells.

I personally would rather have somewhat larger cells (e.g. 38120 format with ~10 Ah or thereabouts), but with LiFePo4's, I would go with a good deal per watt-hour rather than to get my exact cell format.

Willie

HCT
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$4.20 at what quantity? , what about impedance figure ?

The price of 4.20 pcs I believed is based on this " Minimum Order: 3000 Piece/Pieces " copied directly from their site , this work out to be about $0.50 W/H very good price .
Would love to know the internal impedance of those cells

HEAT & LOSS & INEFFICIENCY RELATED DIRECTLY to IMPEDANCE

andrew
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Re: $4.20 at what quantity? , what about impedance figure ?

Robert, can you get some more specs? What is the cell size for the LifePo4? Can you get some samples for testing?

I've been running some numbers for a range extender pack for my motorcycle, and I'm very interested in any LiFePo4 that could work. I may be interested in getting 1-2 hundred.

[url=/forum-topic/motorcycles-and-large-scooters/587-my-kz750-electric-motorcycle-project]KZ750 Motorcycle Conversion[/url]
[url=/forum-topic/motorcycles-and-large-scooters/588-fixing-my-chinese-scooter]900 watt scooter[/url]
Pic from http://www.electri

Robert
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Re: $4.20 at what quantity? , what about impedance figure ?

Hi Andrew,
I have ordered some samples from them that I will hopefully get in about a week. I will test them and post all the specs. / photos, sizes, etc.

Yes, $4.20 is the price for the minimal order of 3000 units. If the specs will be good, I will order that amount for my product and then see how we could share the rest.

R

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