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Discussion Starter #1
http://hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=14616

Each pack:
22.2V & 5AH, 45C continuous = 225A, 90C Burst = 450A, 842g, 90$.

15 Series & 10 Parallel packs from above:
333V & 50AH = 16.65kwh, 2250A cont., 4500A burst, 278lbs, 13,500$

I did a quick search to find more info on the cycle life, but all i could find were the canned sales pitch of lasting two times longer than previous li-po cells. So if we say 500cycles was the cycle life before, 1000cycles now is pretty good. Charging almost once a day would mean almost 3 years of cycle life...especially when kept at, or around, the continuous discharge level.

A lightweight, aerodynamic, conversion that uses about 200wh/mile could drive ~83 miles until 100%DoD...The pack would also allow be able to supply a Warp11HV motor with 500hp from 0-4500rpm...
 

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I can give some details of the standard 20C packs cycle life, I recently ran 200 cycles at 100% discharge and 6C, with a 2C recharge. Cutoff voltages 4.2 down to 3.3. Around 80% capacity at end of test.

In another test, 5C discharge, 1C charge, and 4.15v-3.5v cutoffs, 200 cycles left 86%.

Cycling down to just 3.8v per cell, 200 cycles left 93% of full capcity.

Worth pointing out that not many make 5AH from new, you can count on 4.7-4.8AH. Cycle life calculations were made from the actual capacity when first tested, not advertised capacity.

On 1000 packs checked and tested on delivery, 7% had a defective cell and had to be returned.

I must get in a couple of Nano packs and see if they really are double the cycle life..
 

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If I used those I'd stop at nominal 3.7v and charge to 4.1v, maybe even 4v. What is interesting about these is the endless-sphere guys pull acceleration loads with their e-bikes and they don't sag below 3.8v most of the time until they are close to being discharged.

Running these without a system that will cut the power if they go over or under a safe voltage is foolish. Might be optional with LiFePO4, but not with these LiPo cells.

Some of the guys on ES who keep their charge/discharge cutoffs conservative have been getting over 1000 cycles and still running them. It seems the cycle life is tough to pinpoint due to different types of usage. I've brought these up before, typically always get shot down for it due to the safety factor of having them in a car, just be sure to make sure they don't go over or under voltage and stay in a safe temperature range and don't charge at or below freezing.
 

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Discussion Starter #5
So there IS a fire/explosion danger with these cells. However if used on a dragster or competitive racecar of some kind, I don't see the difference between the danger of these cells and nitromethane, racefuel, nitrous, etc.

Glad it was mentioned that LV/HV limits and temperature control are important when using these more sensitive cells.

Extracting the cells and creating your own custom packs looks to be neccesary.

The minimal voltage sag is huge...the higher voltage would allow the Warp11HV to spin to a higher rpm...With Headway cells Crodriver's Warp11HV had 378kw (500hp) @ 4500rpm (340V *i think* sagged down to 270V & 1400A)...with these cells it might be possible to push the motor rpm range out a bit more, maybe 5000rpm+?
 

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"Glad it was mentioned that LV/HV limits and temperature control are important when using these more sensitive cells."

IMHO, This is important with any lithium cell. There are a few instances of A123's popping like popcorn with pictures on this forum that demonstrate the point.
 

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I fly RC-helicopters and I own a couple of 20C, nano-tech 35C and 45C batteries.

3.6V is generally the lowest you go with these if you want longevity. I would be very interested in seeing what higher C charge or discharge would do to longevity, since in RC 200 cycles is considered pretty good.

As far as I know, I am still a noob so I have not worn any packs out yet, old packs mostly loose "punch" ie. they fail to hold voltage or give enough amps. But with lower discharge rates this should be much less of a problem.
 

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So there IS a fire/explosion danger with these cells. However if used on a dragster or competitive racecar of some kind, I don't see the difference between the danger of these cells and nitromethane, racefuel, nitrous, etc.
Oh, yes indeed. There are numerous examples of guys burning entire houses down with these chemistries. There are also a lot of users of them so I think statistically its not that bad, especially if you take some care. Most danger seems to lie in charging (incorrectly) or puncturing, with over-discharge next.
 

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Here's what I don't understand: 45C is >200A and those puny wires don't look like they'd like passing that much current for very long! They should be able to supply 200A for about a minute without over-discharging the cell. What will happen to the wires in that time? :confused:
 

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Hi Frank

I was wondering the same so I did some sums

Assuming 200 mm long - 3 mm diameter copper
at 200 amps = 20 watts (0.1 volts)
at 20 watts the wire is heating at 4C / sec

After a minute the copper is at 240C + ambient (30C?) - 270C - the insulation is smoking!

If the wire is 4mm diameter then it will generate 11 watts, the temperature will rise at 1.2C/sec to 76C + ambient - 106C
Probably not even smoking

Sounds marginal - but it could work!
 

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Thanks lads. I was contemplating how to put some of these in parallel but you'd have to be pretty careful (and clever I expect.)
 
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