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50Amp - Any Li-Po can support? - 1/11/2004 4:50 AM   
greenbridge


 

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Status: offline 		Hi,

Any Li-Po can support 50Amp with 1P only? What about 80Amp? I mean constant current, peak could be double.

Thanks in advance.

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RE: 50Amp - Any Li-Po can support? - 1/12/2004 6:19 PM   
Matt Kirsch



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Status: offline 		No single LiPoly can handle that much current, but it is okay to parallel multiple LiPoly packs together. Pick your poison; any LiPoly will work if you gang enough of them together

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RE: 50Amp - Any Li-Po can support? - 1/12/2004 9:35 PM   
finchero


 

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Status: offline 		2s irate lithium polymer at 2600mahx2=52amps continuous(10c)

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RE: 50Amp - Any Li-Po can support? - 1/12/2004 10:40 PM   
Greg Covey



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Status: offline 		Typically, you parallel the Lithium Polymer cells until you get the desired current delivery plus some level of overkill.

As the new cells keep emerging, we need less and less of them in parallel.

There is a new cell about to emerge that will deliver a 1P current delivery above 40amps. This will change the way most medium and higher powered planes fly just like the Kokam 340SCH cell did at its 20C delivery rate.

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RE: 50Amp - Any Li-Po can support? - 1/13/2004 10:13 AM   
greenbridge


 

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Status: offline 		The problem is that the parallel simply double or triple the battery weight once you got enough voltage. This is why I am looking for 1P LiPo which can support 50A or more. My F5B is running much more beyond 50A, actually close to 80A. I've been using Ni-Cd for enough time, I would like to be benefit from the new Li-Po cells. Kokam 340 can be discharged at 20C which is good, but it is only 6.8A due to the small capacity. To get 50A, I need to have more than 7p. Whatever the weight of the cell is, I won't be able to get significant advantage comparing to Ni-Cd if I am forced to have constant multiplier of 7. Of course charging will be another serious issue.

I can't wait to see the 1p 40A battery Greg mentioned. What will be the capacity, size, weight and price?

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RE: 50Amp - Any Li-Po can support? - 1/13/2004 4:55 PM   
Matt Kirsch



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Status: offline 		You may not save much in the way of weight, but duration will be very much improved.

With F5B, you can look at the "short burst" C ratings of cells. Motor runs are on the order of 2 seconds, correct? A short burst in LiPoly terms is 10 seconds. This will allow you to use fewer parallel packs, and save weight.

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RE: 50Amp - Any Li-Po can support? - 1/13/2004 8:04 PM   
Greg Covey



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Status: offline 		greenbridge,

Looking at my attached density chart, you will see a 4x jump in energy stored with Lithium cells over energy stored in NiCd cells. This is why LiPo cells are sometimes refered to as "quad" cells and NiMH cells as "Twi" cells (or twice cells).

Reguardless of the number of paralleled cells, you will see a huge advantage with Lithium cells over NiCd cells when it comes to stored energy. As for other issues like safety, cost, and charging, these are more debatable.

The new cell that I mentioned before will be a capacity of 2100mAh (2.1AH). The rest of the information will be revealed soon enough.

Regards.

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RE: 50Amp - Any Li-Po can support? - 1/14/2004 10:17 AM   
greenbridge


 

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Status: offline 		Hi Greg,

You are right. So far the F5B motor run time is less than 20 seconds in most of cases.

Do you know what would be the general rule of calculating "short burst"C from normal discharge C in case the manufacturer didn't publish the data?

Many thanks in advance.

Greenbridge

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RE: 50Amp - Any Li-Po can support? - 1/14/2004 10:34 AM   
GordonFreeman



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Status: offline 		Greg, enough teasing already, please spill the beans about these new 40 amp dealies. I was thinking about getting a 2S2P Tanic 3000 mAh to suit my needs, but...

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RE: 50Amp - Any Li-Po can support? - 1/14/2004 11:34 PM   
Matt Kirsch



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quote:

ORIGINAL: greenbridge
Do you know what would be the general rule of calculating "short burst"C from normal discharge C in case the manufacturer didn't publish the data?


Unfortunately, there's no hard-and-fast rule, or even a rough rule of thumb here, let alone a mathematical formula. There are many diffferent people with many different philosophies designing LiPolys, so you can't be guaranteed that all designs will have the same (proportional) operating properties...

The simple fact of the matter is, if the manufacturer doesn't publish the data, and won't divulge it, then you shouldn't buy their product. That short burst data is VERY important when it comes to sizing LiPoly packs in weight- and performance-critical setups. You can't always, and don't always need to, build a pack that can handle a full-throttle run for the entire duration of the pack.

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RE: 50Amp - Any Li-Po can support? - 1/15/2004 4:07 AM   
greenbridge


 

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Status: offline 		Matt,

Thank you very much.

I've found some manufacturers have 7C LiPo batteries at about 1800mAH. This means 1p can go up to 12.6A. I am checking the short burst rate with them.

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RE: 50Amp - Any Li-Po can support? - 1/15/2004 8:33 PM   
Greg Covey



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Status: offline 		Gordon,

I appologize if I came off as "teasing". My intent was to reveal a new product without getting in trouble -- a tricky venture. My guess is that a few more days will finish the wait.

greenbridge,

I typically use a factor of 1.5 on my Lithium cells for short term bursts. I feel that this is conservative, and, so far, hasn't caused me any problems.

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RE: 50Amp - Any Li-Po can support? - 1/22/2004 4:26 PM   
greenbridge


 

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Status: offline 		Hi All,

I found one battery vendor claimed their cells can meet 10C pulse rate. One of the model has 5000mAH capacity with the size of 6.5mm x 49mm x 135mm. This means it can support 50Amp short burst discharge with 1P only.

I will contact the vendor soon to find out more about this cell. Really attractive!

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