I have been testing Lithium Poly cells for several weeks now and want to share what I have found.

Hi Red,

I'm left-handed. Any chance we can see the graph with time on the x-axis?

I looked at it for a while and didn't understand the significance of the various cells. Can you please explain further?

Regards.

This is how I read it.

Look at the KoKam 2000 (2AH) plot.

At a constant 15A draw, it provides 7.5 min of operation.

mah/15000ma = 7.5min/60

x = 1875mah

1875/2000 = 94% capacity

I can do better than that . . . I can send you the Excel spread sheets and you can make the graphs any way you want.

Besides this is about flying time - so it should be on the vertical axis - if it was for cars I would have put it on the horizontal axis and done it in furlongs/fortnight.

Red,

It must be all my years in the communicaions industry that has me yearning for time (or frequency 1/t) on the x-axis and amplitude on the y-axis.

Yes, I can re-chart it "my way" like a Big Mac.

Thanks.

Excel data coming to you back channel.

Red

Let's see what this looks like "my way".

I see what hoppy is pointing out. You can pick a current draw and determine the runtime using the various cell types.

The Kokam 1500HD cell looks like it has the highest dynamic range overall...but I am not comfortable with this type of data.

Is there any data for the Kokam 1200HC cell we can add to this?

Use log on the vertical axis to spread that data out a little bit.
hoppy

Hi Red & Greg
I am new to Li-Poly batteries and would like to know if you have information on the Kokam 640HD and the 1200HC.
I am using these batteries at 5C and having capacity problems. I am getting approx 350ma from the 640HDs and 500ma from the 1200HCs. What am I doing wrong?

Will

Always appreciated Red. Good info, and perfect timing (for me anyway ). Thanks!

Hi Will,

I have seen these low mAh readings on chargers like the new Triton and believe that they are not accurate.

It could also be the loss of capacity at the 5C rate which may be up to 50%.

Another possibility is that you are not charging or discharging them sufficiently.

The real sanity check is a flight test. We did this using a 3-cell pack of Kokam 1200HC cells. The flight duration was indeed doubled from our 10-cell, 600AE pack but the charger showed a low capacity when re-charged.

What cut off voltage are you using. I just looked at the data on the 1500s (have not tested 640 or 1200) and at 5C to 2.7 volts we are getting an average of 97% of 0.2C capacity. Same for recent batch of 700 mAh cells. On the 340 mAh cells at 6C we saw 98% of the 0.2C capacity. 10 cells in each test batch. All charging done with Kokam Lipo 402.

New line of batterys test and all. And price !!!
http://www.rcgroups.com/forums/showt...hreadid=149319