BYD BBox

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Re: BYD BBox

Postby offgridQLD » Mon Mar 06, 2017 7:40 am

You wont see lifep04 cells in a commercial EV because the energy density of lifep04 is much lower than other lithium chemistry that have 3.6v nominal pr cell and charge to 4.2v vs 3.2v nom and max charge to 3.6v of lifepo4.

Lifep04 is also much harder to monitor SOC as voltage doesn't reflect SOC in a realistically measurable way. Though the lithium chemistry used in EV voltage can be used as it's a much more liner drop in voltage as the SOC decreases.

You wont see lifep04 in a modern mobile phone, tablet or laptop. Lifep04 has some nice features (predominantly safety) and perhaps flat voltage (if that's an advantage for a particular application) along with cycle life.

I think lifepo4 is a good match for stationary storage applications. Though when battery factory's are already producing billions of cells in one chemistry (the most popular chemistry for EV's, laptops and so on then naturally you will end up with that chemistry in the Stationary storage offerings. Even if it isn't the most ideal chemistry of choice.
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Re: BYD BBox

Postby Gordon-Loomberah » Mon Mar 06, 2017 10:41 am

offgridQLD wrote:Lifep04 is also much harder to monitor SOC as voltage doesn't reflect SOC in a realistically measurable way.


Just add a calibrated shunt to accurately monitor current in and out of the battery, and monitoring becomes easy as. Monitoring only voltage in any battery chemistry for SOC is meaningless unless it is always done under zero charging-zero load conditions, after a wait for the voltage to settle.
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Re: BYD BBox

Postby offgridQLD » Mon Mar 06, 2017 11:29 am

Yes sorry I shouldn't have said just measuring SOC but more so measure SOC discrepancy between cells in the meat of the capacity curve.

So It's a lot easier to measure SOC discrepancy as a voltage discrepancy due to the linear and much sharper voltage drop over the cells capacity range.

There is no way in hell your going to be able to balance a lifepo4 cell in that flat section of the capacity scope measuring equipment isn't that good. Any equipment that mentions it can balance lifep04 without taking the cells down to the lower or upper knee is unrealistic.

Though as i see with my electric car even if your only cycling the cells many times from 40% soc - 80% soc the cells still remain balanced and are being actively balanced over this soc scope. As the BMS can take (measurable) voltage references between cells and act on them. By then time there was a (measurable) voltage discrepancy in a lifep04 cells in the flat voltage section of SOC they would be very large unbalance in SOC.

This link shows a graph with a few different lithium chemistry you can see the lifep04 is very different.
https://e2e.ti.com/blogs_/b/fullycharged/archive/2013/09/13/giving-more-life-to-lifepo4-batteries
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Re: BYD BBox

Postby australsolarier » Mon Mar 06, 2017 5:24 pm

https://www.youtube.com/watch?v=pCDuM_apIg8

here some interesting things about batteries
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Re: BYD BBox

Postby juk » Thu Sep 21, 2017 11:55 pm

tom rickard wrote:In my research on expanding my power generation, I came across the BYD B-Box, currently available for $1500 for a 2.5kwh unit, expandable to 10kwh (4 units in parallel).

These are LiFePO4 cells, and I was talking to the supplier of my LiFeTech cells who informed me that these type of LiFePO4 cells are rubbish, and not even close in quality to the cells he supplies (of course he has a vested interest)

It begs the question though, are all LiFePO4 cells created equal? If not, what exactly makes a cell a good one? Obviously I don't mind paying double for a cell that will last 3 times as long, but will it?

In any case, I think the BYD looks a more appealing option than the LGResu, simply because of the lower volatility chemistry. It is plug and play compatible with SMA / Victron inverters (and others).

Does anyone have any info on either the BYD, or what exactly I should be looking for in a LiFePO4 cell?


The lifetech guys have been over promising for about ten years now. Some might say it's misleading.
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Re: BYD BBox

Postby australsolarier » Fri Sep 22, 2017 7:18 am

if anybody here is still worried about all of the above, price and longevity,
i think that tesla wall 2 might be a good bargain. i think it is still the cheapest and can be used for off grid application. they can be ganged up. they give you a ten year warranty. and they come with an excellent software. (and tesla probably won't disappear in 2 years)
you basically screw it to the wall and forget about it, if you are inclined that way.

lg resu can be hooked with the selectronic with slight modification.
i have my gbs lifepo4 cells close to 2 years now. one year in full use. though they have some erratic behavior over 3.4V, they keep reasonably balanced and no weak cell discovered yet. i have thrown 150A at them and drawn 200A (a trial to see how much the selectronic does before it turns itself off, 9kw for several minutes, did not turn off)
i would go for the batrium bms though. might still go for it.
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