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Nuts & Volts
04 March 2011, 1035
8Ah Lipo at a good price. Maybe by the summer they'll have come cheaper ones and some in the US warehouse! exciting stuff

Here are the specs and links


Spec.
Capacity: 8000mAh
Voltage: 6S1P / 6 Cell / 22.2v
Discharge: 30C Constant / 40C Burst
Weight: 1256g (including wire, plug & case)
Dimensions: 172x69x52mm
Balance Plug: JST-XH
Discharge plug: 5.5mm Bullet-connector (without housing)

Price:
6S = $88.18
5S = $73.49
4S = $58.80

Link to new product page
http://www.hobbyking.com/hobbyking/store/HobbyKing_New_RC_Products.asp?orderBy=recently

Coninsan
04 March 2011, 1100
Damn, using those I could have a 30C 96Ah pack within the same space as my 60Ah TS pack :p

Tony Coiro
04 March 2011, 1112
So, I was talking to a friend of mine about li-po and he brought up an interesting point. Does it bother anyone else that they claim 40C "burst" as opposed to "peak"? :D

Harold in CR
04 March 2011, 1140
links lead to "Page doesn't exist anymore" ???

If y'all go to HK site, and look at the batteries, and scroll down, sometimes there is a "Swarm" button.

If 6people apply to that link, listing AN Email address, then, the item can be ordered at a cheaper price, yet. Several sales of this type have gone well over on the ES Site.

Nuts & Volts
04 March 2011, 1234
links lead to "Page doesn't exist anymore" ???

If y'all go to HK site, and look at the batteries, and scroll down, sometimes there is a "Swarm" button.

If 6people apply to that link, listing AN Email address, then, the item can be ordered at a cheaper price, yet. Several sales of this type have gone well over on the ES Site.

Sorry I copied the info from ES and didnt fix the links (fixed it now). Also I used the Swarm sale last week to buy some 6s 5ah 20C packs for my ebike. Swarm price on the 6s 8ah is $81.39


Tony i believe that is probably a very accurate way to lable LiPo :)

DaveAK
04 March 2011, 1328
If you put 5 of these packs in parallel to get 40Ah does 30C constant discharge give you 1200 amps continuous? I get really confused with parallel/series amps/volts and what the overall effect is of combining cells.

Harold in CR
04 March 2011, 1359
A link to page 7 of a thread, explaining how this all works.

http://endless-sphere.com/forums/viewtopic.php?f=10&t=24154&start=90

DRZ400
04 March 2011, 1414
Whats the cycle life like though? With my RC lipos I don't get more then 70-80 cycles befroe I notice a lose in power.

DaveAK
04 March 2011, 1429
A link to page 7 of a thread, explaining how this all works.

http://endless-sphere.com/forums/viewtopic.php?f=10&t=24154&start=90
OK, thanks. So in reality, if you've got a 400 amp controller, a large 40Ah pack of LiPo's doesn't need to be built from 30C cells, but more like 10C. And that would be 10C peak, depending on your expected continuous draw.

Just thinking out loud. :)

Nuts & Volts
04 March 2011, 1434
Dave, you are correct in your math. 1200A cont and 1600A peak :)

DRZ the cycle life will be less than a TS, CALB, or GBS cell.
But you can build a pack that is
half the weight
half the volume
on a smaller motorcycle which may be lighter
with more power

This all means you can make a small kWh pack that costs less goes farther on less.

This makes up for the cycle life for me :) I am spec'ing my next build for 800 cycles at 80% DOD. At 80 miles per charge that is 64,000 miles. I think ill wanna upgrade to something new before then :)


Things that will help to increase LiPo cycle life is charging and discharging to set limits (voltages), and with a warm to hot pack.
Keeping the discharge to a responsible level helps too

This are technically challenging so they may not be for everyone.

Nuts & Volts
04 March 2011, 1436
OK, thanks. So in reality, if you've got a 400 amp controller, a large 40Ah pack of LiPo's doesn't need to be built from 30C cells, but more like 10C. And that would be 10C peak, depending on your expected continuous draw.

Just thinking out loud. :)

Thing to think about is that at say 100A discharge rate a 30C 5ah cell will provide more energy than a 10C 5ah cell because the 30C will have a lower internal resistance. Less energy is lost as heat in the cell itself.

DaveAK
04 March 2011, 1447
Thing to think about is that at say 100A discharge rate a 30C 5ah cell will provide more energy than a 10C 5ah cell because the 30C will have a lower internal resistance. Less energy is lost as heat in the cell itself.
Thanks, I hadn't appreciated that fact, but how significant a difference? I'm working on the basis of maybe 10C being cheaper/easier to obtain than 30C, (although things are changing all the time), but a lower C may not be as economic in the long run as a higher C. Ultimately I'm thinking of balancing the complete package of motor/controller/batteries such that no one item is particularly over or under spec'ed compared to the rest.

Nuts & Volts
04 March 2011, 1456
Thanks, I hadn't appreciated that fact, but how significant a difference? I'm working on the basis of maybe 10C being cheaper/easier to obtain than 30C, (although things are changing all the time), but a lower C may not be as economic in the long run as a higher C. Ultimately I'm thinking of balancing the complete package of motor/controller/batteries such that no one item is particularly over or under spec'ed compared to the rest.

You would need to know the difference in Ri (internal resistance) between the cells. This you can measure by calculating the voltage drop at a particular current draw. I have been looking around is found that current lipo are about 2 to 5 mOhm Ri. The nano tech cells are like 1mOhm apparantely.

Anyways from there you pick a current 100A lets say and you. Calculate P=I^2 * R. This is power loss so use the ratio of P 10C and P 30C to determine the percentage difference in energy lost. Additionally the 10C cell will thus heat up quicker which increase resistances and it losses more energy. Not that much more in practice

DaveAK
04 March 2011, 1519
Purely going on safety would it be reasonable to say that you'll be "stressing" the 30C less. Less heat and less chance of ruining your pack, (and maybe your life)?

podolefsky
04 March 2011, 1520
OK, so I calculate the power loss due to internal resistance to be 10W for 1mOhm and 50W for 5mOhm @ 100A. Now compare that to the total power drawn with, say, 100A @ 72V, which is 7200W. The 5mOhm battery loses about 0.7%, the 1mOhm loses 0.14%.

So we're talking less than 1% for all Li batteries. Need to consider whether the cost is worth saving another ~0.5%.

podolefsky
04 March 2011, 1534
'Cause I'm a math junkie, I just used the Elmoto spreadsheet to estimate range for my bike, and then every thing the same except 1/2 the chassis and battery weight. I went from 80 mi to 88 mi of city driving. So 10% increase in range, assuming 1/2 is realistic.

But that doesn't account for the reduction in total kWh. If I go from a 4.6 kWh pack on my bike to a 3 kWh pack on the lighter bike, I go from 80 mi range to 59 mi. So the weight savings doesn't make up for the energy loss - but lighter bikes might be nice for other reasons - their easier to handle, and if you have a small bike like a 250 it might be the only thing that fits in the chassis.

(Oh, and I know 80 mi range isn't realistic, I'm just using it for comparison)

DaveAK
04 March 2011, 1546
Weight seems to have very little bearing on the numbers I'm getting. If I go from a 460lb bike to 230lb my range goes from 48.65 @ 50mph to 53 and top speed stays the same. But if I keep the bike at 460lbs and pack in an extra 25% kwH I get 60.82 miles.

Packing in more kwH seems to be more important than cutting weight, although of course it all helps in the end.

Nuts & Volts
04 March 2011, 1558
'Cause I'm a math junkie, I just used the Elmoto spreadsheet to estimate range for my bike, and then every thing the same except 1/2 the chassis and battery weight. I went from 80 mi to 88 mi of city driving. So 10% increase in range, assuming 1/2 is realistic.

But that doesn't account for the reduction in total kWh. If I go from a 4.6 kWh pack on my bike to a 3 kWh pack on the lighter bike, I go from 80 mi range to 59 mi. So the weight savings doesn't make up for the energy loss - but lighter bikes might be nice for other reasons - their easier to handle, and if you have a small bike like a 250 it might be the only thing that fits in the chassis.

(Oh, and I know 80 mi range isn't realistic, I'm just using it for comparison)

Touche! Thanks for crunching the numbers. So my thoughts are overestimating some things. Main reason I am going LiPo is because I can fit a larger kWh pack into a smaller motorcycle than i have now. I also want to go higher voltage as well which eliminates prismatic cells.

So main El Motor advantages of LiPo is cost, acceleration, and handling. Minor range improvement.
Disadvantage pack building and construction. Additionally the LiPo quality control is a little lower (been good to me thou, 32/32 turnigy cells have come in working fine).


And Dave it is not high current thats makes LiPo angry. It is mainly overdischarging to too low of a voltage (going into thermal runaway) or overcharging to too high of a voltage (going into thermal runaway).

Coninsan
04 March 2011, 1610
And Dave it is not high current thats makes LiPo angry. It is mainly overdischarging to too low of a voltage (going into thermal runaway) or overcharging to too high of a voltage (going into thermal runaway).

I can back that claim up. In all test I've seen where LiPo cells have gone bananas have been at overcharger or over discharge, then a typical failure would be induced in the form of stricking the cell or heating it up additionally to the point where the thermal reation within gets out of proportions. Wanting to test this reation on a propperly balanced pack I got.. a fizzle - a hiz and a bit of smoke, no flames or explosion. The only difference between LiPo and LiFePO4 in regards to safety is that if LiPo goes of in a worst case sceneario, it will release cases with a higher temperature than LiFePO4.
A little understanding for LiPo from my side..

Just my five cents, please continue, I'll be lurking in the shadows in the meanwhile :p

DaveAK
04 March 2011, 1627
And Dave it is not high current thats makes LiPo angry. It is mainly overdischarging to too low of a voltage (going into thermal runaway) or overcharging to too high of a voltage (going into thermal runaway).
Thanks! That's good to know. I'll store that little nugget of information away for future reference.

Nuts & Volts
04 March 2011, 1631
Well put Coninsan. With the same BMS, a LiPo battery simple fails worse than other Lithium, not more often.

Really LiPo just demands more respect :)