Testing began in California at the start of this year from Stockton to Barstow and ended in April as far as I know. The terrain consists of flat running through the agricultural valley from Stockton to Bakersfield, the steep mountain grade over Tehachapi Pass to Mojave and flat desert running to Barstow. I'm guessing they purposely chose the cooler part of the year to test. Both the valley and the desert average 90s and higher in the summer.
It's their performance at very low and very high ambient temperatures I'm really curious about. Lithium batteries lose capacity as they get colder. So a battery that has 100% capacity at a temp of 75°F, will go down to only 25%-30% capacity once you get close to 32°F and lower. At the higher temps, you have to worry about overheating. Not only will it shorten the overall lifespan of the battery, but it could also make them explode.
This locomotive almost certainly has battery cooling fans to keep the temps down in warm climates. I wonder if they have heating elements to keep battery temps up in colder climates so their capacity doesn't go down.
I own a Goal Zero Yeti 3000 solar generator with a 3,075 Watt-Hour Lithium-ion NMC battery. It has safety monitoring and cooling fans. It doesn't allow charging if the battery hits 32°F on the low end and 113°F on the high end. It also stops me being able to draw power from the battery at temps -4°F and 149°F respectively.
In the solar generator world (excluding deep cycle lead-acid based systems) there are two main lithium battery types.... Lithium NMC (Nickel-Manganese-Cobalt Oxide).... and LiFePO4 or LFP battery (Lithium Iron Phosphate).
NMC's main advantages over LFP are a higher power density and typically cheaper upfront cost than an LFP battery of the same watt-hour capacity. So an LFP battery of the same exact physical size as an NMC battery, will pack less watt-hours of battery capacity.
NMC's main disadvantages are that it's batteries are more prone to exploding if the battery ever overheats (NMC Thermal runaway 210°C (410°F). High charge promotes thermal runaway. .... Vs..... LFP Thermal runaway 270°C (518°F) Very safe battery even if fully charged) ... or is punctured by a hard object. LFP batteries are far less susceptible in both of those attributes.
While my Goal Zero's NMC battery is rated for 500 cycles to reach 80% of it's original capacity, an LFP can get 3-5 times that amount of cycles. That also depends on battery temps and what your charge/discharge range is. Also.... LFP has a little bit longer charge shelf life. Tesla is slowly moving to LFP batteries. Goal Zero currently doesn't offer a LFP battery option or upgrade. I'm not even for sure if my current charge controller is compatible with an LFP battery even if they were to offer such an option in the future.
The chart from battery university in the link below shows keeping a battery charge/discharge range of 65%-75% capacity gives your battery the longest overall lifespan.... with a 45%-75% being the 2nd best range..... 25%-75% being the 3rd best ..... and progressively worse as the chart shows for other ranges.
https://batteryuniversity.com/_img/cont ... s-web2.jpgI keep mine in the 65%-75% range the majority of the time, but I will go as low as 45% if I need to draw from it for an extended time. I've had it over 3 years and it's still going strong.
Posted: Fri Apr 30, 2021 12:35 pm