LiFePO4 batteries with 30C discharge rating???

[Little-Acorn]

Most LiFePO4 batteries I've seen for e-bike applications, usually have discharge rates around 1C. So, a 20Ah battery can put out 20 Amps continuously for one hour, before being exhausted. If you try to discharge it at, say, a 2C rate (40 Amps), it will do it. But instead of lasting 30 minutes as you would expect, it goes exhausted sooner than that, in maybe 15 or 20 minutes.

Hobby City (a mail-order hobby shop in China) has long had lithium-polymer batteries with the high discharge rates typical of that technology. But now they have started selling a few LiFePO4 batteries, which they advertise as having similarly high discharge rates. One set of LiFePO4 batteries are advertised as having a 30C discharge rate! And that's a "continuous" rate, its max rate is 40C. If true, this means that a 4.5Ah battery can discharge at 135 Amps. Only lasts two minutes, but that lets you get the entire burst of energy stored in the battery - it won't die before putting out its entire 4.5Ah at its rated voltage.

Examples:

6-cell LiFePO4 4.5Ah battery, 30C(!) continuous rate, $69.99:
http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=10311&Product_Name=Turnigy_4500mAh_6S2P_30C_LiFePo4_Pack

3-cell LiFePO4 4.5Ah battery, 30C(!) rate, $39.51:
http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=10310&Product_Name=Turnigy_4500mAh_3S2P_30C_LiFePo4_Pack

2-cell LiFePO4 4.5Ah battery, 30C(!) rate, $25.56:
http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=10309&Product_Name=Turnigy_4500mAh_2S2P_30C_LiFePo4_Pack

Of course, no e-bike needs 135 Amps at 36 or 48 volts or whatever. That would fry any known motor, and/or twist the axle right out of the fork even with a torque arm or two installed.

But the good news is, a relatively small battery (like 48V at 4.5Ah) can be used, and will easily kick out the 20 or 30 amps the motor needs to climb hills, accelerate rapidly, etc. without the battery voltage sagging or falling off prematurely.

My guess is, a 48V 1000W motor doesn't always run at 1000W (approx. 20 Amps). When speeding up or climbing a hill, it might use the entire 1000W. But for most cruising on relatively flat ground, some riders will back off on the throttle and cruise at maybe 15 or 20 MPH, and only draw maybe 10A from their battery during that time.

Until now, someone with a 48V 1000W motor, has to buy a 48V 20Ah battery (up to $1,000 for a good one like a Ping battery) to get full performance (20 Amps at 48V) under all common conditions. One benefit is long range, since the battery is so big. But that price tag hurts.

Now, he can buy two of these 6-cell 30C 4.5Ah batteries and two 2-cell batteries, and use them in series to produce 48V Total cost is less than $200 (plus shipping), and the bike will perform just as well as with the big battery... until the battery runs out, which obviously it will do in 1/4 the time.

Has anyone tried any of these high-discharge-rate 30C LiFePO4 batteries? Are their advertised claims, true?

 

[geetarboy]

Hey L-Acorn, I'm looking at another battery system myself and just checked these out. The 12 cell pack is shown @ 19.8 volts? Which I guess is like a standard 16 volt set-up - so 3 would give you a 48 volt system? You'd still need some kind of BMS system. It seems like an equal trade-off "high power short range vs. moderate power long range"- myself, I need more range and power, and it seems like pingbattery has a good reputation from what I read. But you're right - the $ and the wght. but, beats SLA. I think we all want more power with less weight, I wish the technology would move faster and the price would drop.Hope you find the best one to suit your needs.

 

[tostino]

Of course, no e-bike needs 135 Amps at 36 or 48 volts or whatever. That would fry any known motor, and/or twist the axle right out of the fork even with a torque arm or two installed.

I would like to respectfully disagree with that lol. With my battery pack made out of konion and emoli cells, I can peak at over 400a if I had a controller and motor big enough.

My current limit is 120a at 51v nominal. My 9c motor is fine with that, and so is my 4110 modded 12 fet infinion. My drops are not in bad shape, and neither is my axle. The single torque arm is holding it tightly. If I could start my battery pack construction all over again, i'd go with closer to 100v rather than my 51v nominal, and keep the same high amp limit. The more power the better for me.

 

[dogman dan]

Heh, heh, of course any motor can do 135 amps at 48v. Its when you ask for how long, that the debate begins :wink:

They sound like nice cells. I'd like to see em in 10 ah, 36 and 48v blocks with 100 amp bms. Then you could stack em paralell as needed for the range you intend to ride. Anything less than 10 ah is useless to me personally. The nearest shopping to my house is 12 ah away round trip. Work is 15 ah away one way. 48 volts is plenty for me, but a 50 amp controller would be nice. I'd still cruise at 15 amps or so, but for the hills, amps would be good.

Edit, actually looking at the links now, two 6s packs and one 2s pack would cost under 200, and add a cheap ebay bms for a 48v 4.5 ah pack. Could be a nice way to pop some amps to a lightweight trail riding E-MTB. You don't need big AH to blast on a bmx track. Still kinda pricy compared to other deals out there, but the packs could tuck into spots on the bike that headways wouldn't fit so good.

Also good for making a boost pack. 4 6s packs would get ya up that big hill.

 

[amberwolf]

Of course, no e-bike needs 135 Amps at 36 or 48 volts or whatever. That would fry any known motor, and/or twist the axle right out of the fork even with a torque arm or two installed.

I'd also disagree the second sentence. My non-hub motor setup could draw more than that (and has) without destruction or damage, starting up in higher gears from a dead stop with a load of cargo on it. It's probably not *good* for it, but it has not hurt it.

(this does not count the recent failure of chain derail that caused a 150+amp current draw after everything jammed up, and blew the controller due to the very fast large current spike and at the time insufficient heat dissipation capability).

I don't necessarily disagree with the *first* sentence, in that they probably don't *need* that much current for any length of time for most applications. But the ability to have it when it *is* needed would be nice.

 

[tostino]

Well by that thinking, no car needs more than 40 horse power . It is sure nice to have it when you need it though! I am in Florida, and probably have the lowest need for low end power because there are no hills. So rather than have a bike that can climb a wall, i'm using my power for high speeds .