DaveAK

03 December 2010, 1143

First off a question. What kind of maximum current draw are you guys seeing from your batteries? (From a typical street bike perspective, not from a 1/4 miler!)

I've been looking at all the offerings that various chip manufactures have and it seems like Coulomb counting is the way to go. From what I can gather they achieve this by sampling the current at a given period and basically summing as they go. Well, I can do that easily enough, right? I can think of several ways to do it with varying degrees of accuracy.

So, next question. Let's say that I have 8 10Ah LiFePO4 cells in series at a manufacturers suggested charge level of 3.65V, with a LVC of 2.7V. This gives me a 8x3.65x10=292Wh pack at full charge. When my cells have depleted to 2.7V, has my Ah also been lowered? And if so by how much? If I say that the battery is now empty can I consider my Ah as zero, (or thereabouts)? (8x2.7x0=0Wh). Voltage drops by 25% from a full charge to what's considered empty but you get more than 500Wh out of a 2kWh pack, don't you?

When I start counting Coulombs I'll start with the assumption that my 10Ah pack is 36000C and I'll count the Coulombs until I hit LVC, so I'm sure I can figure out the answer to my questions above, but it would be nice to know that I'm heading in the right directions, and not missing something crucial. :)

I've been looking at all the offerings that various chip manufactures have and it seems like Coulomb counting is the way to go. From what I can gather they achieve this by sampling the current at a given period and basically summing as they go. Well, I can do that easily enough, right? I can think of several ways to do it with varying degrees of accuracy.

So, next question. Let's say that I have 8 10Ah LiFePO4 cells in series at a manufacturers suggested charge level of 3.65V, with a LVC of 2.7V. This gives me a 8x3.65x10=292Wh pack at full charge. When my cells have depleted to 2.7V, has my Ah also been lowered? And if so by how much? If I say that the battery is now empty can I consider my Ah as zero, (or thereabouts)? (8x2.7x0=0Wh). Voltage drops by 25% from a full charge to what's considered empty but you get more than 500Wh out of a 2kWh pack, don't you?

When I start counting Coulombs I'll start with the assumption that my 10Ah pack is 36000C and I'll count the Coulombs until I hit LVC, so I'm sure I can figure out the answer to my questions above, but it would be nice to know that I'm heading in the right directions, and not missing something crucial. :)