Teardown: High-voltage Li-ion BMS

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a4x4kiwi
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Teardown: High-voltage Li-ion BMS

Post by a4x4kiwi » Wed, 08 Aug 2012, 14:26

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PlanB
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Teardown: High-voltage Li-ion BMS

Post by PlanB » Wed, 08 Aug 2012, 23:52

40 mile range from a 16kwh pack is 250Wh/km. All the sums I've looked at on this site over the years suggests 160Wh/km should be more like it?

And speaking of batteries has anyone been following this saga?
Assuming you got lucky like Sutho & ended up with some decent 7S3Ps they just scrape in at 102Wh/kg. The commercial pouch packs out of China at x4 the price are even worse at around 62Wh/kg. Why wouldn't you just go with Thunderskys et al which manage 100Wh/kg comfortably, seem a lot more robust with plenty of celltop type BMSs to choose from & you can secret them all over the place like Weber & Coulomb?
Last edited by PlanB on Wed, 08 Aug 2012, 14:00, edited 1 time in total.

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Johny
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Teardown: High-voltage Li-ion BMS

Post by Johny » Thu, 09 Aug 2012, 15:56

PlanB wrote: 40 mile range from a 16kwh pack is 250Wh/km. All the sums I've looked at on this site over the years suggests 160Wh/km should be more like it?
Yes but it's dragging around a complete ICE and extra generators and such - exhaust, petrol tank etc.

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Teardown: High-voltage Li-ion BMS

Post by jonescg » Thu, 09 Aug 2012, 17:28

A123 cells, ignoring packaging, should give about 130 Wh/kg. Still pretty lame compared to EiG cells, which deliver 175 Wh/kg and an impressive 370 Wh/litre.

Thundersags are good for their Wh/dollar, but not for their weight or volume. And if you can be bothered spotwelding a whole stack of Panasonic cells together you can get something close to 250 Wh/kg and close to 450 Wh/litre. Too bad the power density is too low to be of much use for EVs, but with enough of them in parallel you should do OK.
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Richo
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Teardown: High-voltage Li-ion BMS

Post by Richo » Thu, 09 Aug 2012, 20:52

That artical was terrible.
Why would anyone care that Chevy are using an Automotive grade opto.
Seriously c'mon.
Or perhaps the use of a CAN bus for thier BMS.
Really - who would have thought.

And so many board for a BMS.
Some of those don't look like they are even for the BMS.
The one in the middle with 2 caps and a slot looks more like a power driver.

Give the engineers an open signed cheque book as see what happens.
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No wonder it took so long!
So the short answer is NO but the long answer is YES.
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Teardown: High-voltage Li-ion BMS

Post by woody » Fri, 10 Aug 2012, 11:44

Johny wrote:
PlanB wrote: 40 mile range from a 16kwh pack is 250Wh/km. All the sums I've looked at on this site over the years suggests 160Wh/km should be more like it?
Yes but it's dragging around a complete ICE and extra generators and such - exhaust, petrol tank etc.

They're only using 60%DoD, I.E. 10kWh / 40 miles = 10kWh / 62km = 160Wh/km :-)
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Richo
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Teardown: High-voltage Li-ion BMS

Post by Richo » Fri, 10 Aug 2012, 20:48

60% DOD is probably to extend the cycle life of the poor Lipos.
I guess they didn't have access to LiFePO4 technology to profit from.

Edit: forgot the iron...
Last edited by Richo on Fri, 10 Aug 2012, 10:50, edited 1 time in total.
So the short answer is NO but the long answer is YES.
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Teardown: High-voltage Li-ion BMS

Post by Simon » Mon, 13 Aug 2012, 05:02

When I first heard about the limited access to the full pack capacity I thought GM must be real concerned about battery longevity! However it does make sense for any plugin hybrid to keep the DOD low because you are going to have some drivers using the maximum available range daily (or twice daily) and wear out a pack sooner than a pure EV that has a lower DOD for the same distance.
The Volt allows greater Depth of discharge to take place as the pack ages.

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