BYD BBox

Getting into the nuts and bolts of wind and solar power components, installation and performance issues, ask technical questions, answers and tips

Re: BYD BBox

Postby offgridQLD » Mon Mar 06, 2017 8:40 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.
Offgrid 2008, Selectronic PS1 6kw/48v inverter, x 2 Midnite solar classic 150 MPPT, 3960w NE PV 24 x 165w BP panels, 4200w NW PV 21 x 200w DAQO PV, 16x400ah lithium.
offgridQLD
Solar Crusader
Solar Crusader
 
Posts: 2073
Joined: Thu Jan 26, 2012 12:50 pm

Re: BYD BBox

Postby Gordon-Loomberah » Mon Mar 06, 2017 11:41 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.
http://gunagulla.com Loomberah weather and astronomy including live solar radiation intensity and UV + Gunagulla aquaponics, organic eggs and cherries
User avatar
Gordon-Loomberah
Community Moderator
 
Posts: 5360
Joined: Thu Sep 24, 2009 10:41 pm
Location: Loomberah NSW Australia

Re: BYD BBox

Postby offgridQLD » Mon Mar 06, 2017 12:29 pm

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
Offgrid 2008, Selectronic PS1 6kw/48v inverter, x 2 Midnite solar classic 150 MPPT, 3960w NE PV 24 x 165w BP panels, 4200w NW PV 21 x 200w DAQO PV, 16x400ah lithium.
offgridQLD
Solar Crusader
Solar Crusader
 
Posts: 2073
Joined: Thu Jan 26, 2012 12:50 pm

Re: BYD BBox

Postby australsolarier » Mon Mar 06, 2017 6:24 pm

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

here some interesting things about batteries
australsolarier
Solar Crusader
Solar Crusader
 
Posts: 285
Joined: Sun Mar 28, 2010 10:27 am

Previous

Return to Components, Installation And Performance

Who is online

Users browsing this forum: Google [Bot] and 2 guests

new solar power specials