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Old 08-20-2011, 10:23 AM   #5004 (permalink)
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Originally Posted by Greg Fordyce View Post
Hi Jim, looking at your tractor I suddenly had a thought about your Headway cells. I am going to assume you are using the 16ah 40160. I found some specs for them on the web.

Thanks for taking the time to do the research.

We are using the 38120 8 ah cells

Originally Posted by Greg Fordyce View Post
So you have 3 cells in parallel for 48ah which at 10C is 480 amps. At 500 amps you are already over the max discharge current. Also when you parallel cells you can't be certain that all cells will share the current equally so you need to derate the max discharge current by some value (I am not sure by how much though).
The 38120 cells with their 25 C rating, will give an overall output of 600 amps from the 50S/30P configuration for (by our actual testing) up to 1 minute. We also did our best to match the parallel sets for internal resistance

Originally Posted by Greg Fordyce View Post
Another thing to notice is that cycle life is stated for 2000 cycles at 1C. I will be interested to see how the headways hold up to that abuse. But maybe since you are using them for racing (ie, only intermittently) and not daily driving they will be fine. I was talking to someone recently who had tried running Thunderskys at around 5C and was getting cell failures in as little as 200 miles. Please let us know how your cells hold up to the abuse.
We took the derating of the cycle life into consdideration when we chose to go with lithium. We figured on only 10% of the rated life would be 200 cycles. Since we generally only run 10 to 15 pulls per year we should get a few years of use from the pack.

Due to other initial problems, we haven't run the pack enough to get any real feel for life or performance yet.

Originally Posted by Greg Fordyce View Post
The only other Headway pack I know of being used in a car is Damien's aka Jack Bauer. This is also a relatively small pack at 48S4P if I remember correctly. How's your pack doing in your bmw Jack? It will be interesting to see how well these small packs hold up in daily use.

We've been watching Damian's results, so far he seems pleased with the performance.

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