[frodus]

Originally Posted by bmentink

I am looking at the curves for the 16Ah cells, they must be a lot better perhaps .. will check when I get home ..

Doubtful that it's the 10C curve, but if you have it, can you post it?

I need to get my hands on one. I can only go to 160A, so 10C is about all I can do with my discharging setup, but it's continuous and fairly accurate.

[bmentink]

Still looking for the 10C curve, I have it somewhere ..

In the meantime I will post the 5A charge/discharge curve which shows the internal resistance of Headway cells ... much lower than there datasheet, which just says <8mohm. I have attached both the datasheet and the curves for your perusal ..

[frodus]

Is that curve from headway? How are they testing the IR? Not sure how, but it looks like they're using only one current and watching voltage and doing V/I, but it doesn't work out, so I'm stumped. That curve is at 0.35C.

I just can't believe that at 10C the rise is less than 20degrees, I've done enough testing to know that even an A123 cell rises more than that, with a lower IR. I've tested a 16Ah cell, and less amps, and it rose more than 20 degrees.

I'll wait for the 10C curve.

[bmentink]

Originally Posted by frodus

Is that curve from headway? How are they testing the IR? Not sure how, but it looks like they're using only one current and watching voltage and doing V/I, but it doesn't work out, so I'm stumped. That curve is at 0.35C.

I just can't believe that at 10C the rise is less than 20degrees, I've done enough testing to know that even an A123 cell rises more than that, with a lower IR. I've tested a 16Ah cell, and less amps, and it rose more than 20 degrees.

I'll wait for the 10C curve.

Yes, that curve is from Headway. I have also attached more curves for both the 15Ah cell and the 16Ah cell .. however, the temperature rise is only indicated on the 15Ah cell, no actual curve.

I have asked Lorainne(Headway) to re-send the temperature curves as I have misplaced them.

[Duncan]

Hi bmentink,

Any more thoughts on your group buy?
I have decided to ask for 150 - if you go ahead

[bmentink]

Originally Posted by Duncan

Hi bmentink,

Any more thoughts on your group buy?
I have decided to ask for 150 - if you go ahead

Hi Duncan,

Just trying to get together some other folk ... will let you know ..

[karlos]

Originally Posted by bmentink

Hi Duncan,

Just trying to get together some other folk ... will let you know ..

Did you get my PM? It's a bit earlier than I wanted but I could be serious about joining the group buy at that price.

[bmentink]

Originally Posted by karlos

Did you get my PM? It's a bit earlier than I wanted but I could be serious about joining the group buy at that price.

Hi Karlos,

No, did not get your PM, actually it is a bit early for me as well, but will note you as an interested party as well. Where are you located? and how many cells?

[frodus]

Originally Posted by bmentink

Yes, that curve is from Headway. I have also attached more curves for both the 15Ah cell and the 16Ah cell .. however, the temperature rise is only indicated on the 15Ah cell, no actual curve.

I have asked Lorainne(Headway) to re-send the temperature curves as I have misplaced them.

Exactly! Even though it's a 15Ah cell, (the 16Ah cell won't be much different. Same chemistry, same cell style) Those documents show a 50C (29c to 79C) rise on a 15Ah cell at 10C (150A)..... and that is way over the actual spec of 60 degrees C, by almost 20degreesC.

That is way too hot. Put them in a pack, and you compound the issue. Even if you cool them, the temperature inside the cell will be hot.

Then look at the voltage drop. 10C voltage drop is going to be right at 2.6V. You notice that the curve increases a little right? That's because of heat. the 2.6V valley is what you should go by, because you should only be doing bursts anyway, so you'll spend more time at the very initial part of the voltage curve.

I still say build a larger pack, so your "continuous" is closer to 5C or lower.

[karlos]

Originally Posted by bmentink

Hi Karlos,

No, did not get your PM, actually it is a bit early for me as well, but will note you as an interested party as well. Where are you located? and how many cells?

I'm up the other end of the country, Whangarei and at this time need 560 16amp cells. I'll PM my email address.