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replacement batteries slightly larger capacity ?

Posted: Mon Jun 19, 2017 7:18 am
by BiggieJohn
I recently had my 2012 battery replaced under warranty.
Notice the Ahr is 66.14. at full charge, 395V * 66.14Ahr = 26kw

hmmmm
Screenshot_20170615-045122.png

Re: replacement batteries slightly larger capacity ?

Posted: Mon Jun 19, 2017 9:21 am
by rmay635703
No one ever said how big your replacement could be ;)

That said 2013+ batteries are slightly bigger to start compared to 2011

Re: replacement batteries slightly larger capacity ?

Posted: Mon Jun 19, 2017 9:31 am
by alozzy
Maybe because not all the kWh are useable because the BMS prevents the cells from dropping below a certain voltage.

Re: replacement batteries slightly larger capacity ?

Posted: Mon Jun 19, 2017 9:56 am
by BiggieJohn
alozzy wrote:Maybe because not all the kWh are useable because the BMS prevents the cells from dropping below a certain voltage.

The old 24Kw battery had 22.5Kw usable.
I guess I need to do a full range test one of these days and make sure I have LeafSpy running the whole time to see how much gets used.

Re: replacement batteries slightly larger capacity ?

Posted: Mon Jun 19, 2017 10:07 am
by Oils4AsphaultOnly
alozzy wrote:Maybe because not all the kWh are useable because the BMS prevents the cells from dropping below a certain voltage.
Even accounting for that, that's a pretty big buffer isn't it?

My 30kwh battery at full charge shows 394.91V and 78.96 AHr for 31.18 KWh. While usable capacity is 28 KWh, giving me a ~10% buffer. OP's buffer, assuming the same 22kwh usable capacity would be almost 20%!

Any suggestions on how to determine if OP has a bigger buffer or more usable capacity?

Re: replacement batteries slightly larger capacity ?

Posted: Mon Jun 19, 2017 1:44 pm
by RegGuheert
BiggieJohn wrote:Notice the Ahr is 66.14. at full charge, 395V * 66.14Ahr = 26kw
The voltage of the battery drops during discharge. As a result, you need to multiply the Ah capacity by the *average* discharge voltage in order to get at kWh. I think the average discharge voltage is around 375V, so that gives about 24.8kWh.

Re: replacement batteries slightly larger capacity ?

Posted: Mon Jun 19, 2017 2:24 pm
by Stanton
BiggieJohn wrote:I recently had my 2012 battery replaced under warranty.
Notice the Ahr is 66.14. at full charge, 395V * 66.14Ahr = 26kw
This is common for "replacement" battery packs in "old" Leafs (like mine).
If you search the threads, you'll notice that the 66.14 number seems to be some sort of default max the BMS reads...until the actual capacity falls below that number and it starts dropping just like any other battery pack.
So yes, there does seem to be a bit of a buffer at the top of the lizard packs.

Re: replacement batteries slightly larger capacity ?

Posted: Tue Jun 20, 2017 12:25 am
by cwerdna
BiggieJohn wrote:
alozzy wrote:Maybe because not all the kWh are useable because the BMS prevents the cells from dropping below a certain voltage.

The old 24Kw battery had 22.5Kw usable.
I guess I need to do a full range test one of these days and make sure I have LeafSpy running the whole time to see how much gets used.
Battery capacity is measured in kWh, not "Kw".

kW and kWh are very different metrics. It's the same as confusing gallons with horsepower. Think of kW = horsepower, kWh = gallons.

If one charges at 1 kW (or 1000 watts) for 6 hours, 6 kWh came out of the wall. If it's at 6 kW for 1 hour, it's also 6 kWh. If it's 1 watt for 6000 hours, it's also 6 kWh.

One pays for electricity at home in cents per kWh. There are a few utilities w/residential plans where they not only bill per kWh but also have demand charges, but that's rare and complicates calculations. (Demand charges aren't unusual on many commercial plans.)

(BTW, 1 hp = ~0.746 kW. And, many .gov sites say 1 gallon of gasoline=33.7 kWh.)