oltmanndIf I'm a commuter agency, or even short haul intercity, I'd be all about trying to get hybrid locomotive that could keep me at 2 mph/sec or better all the way up to track speed. (And then get a good hunk of the energy back on braking! - with batteries continuing to charge during the station stop.)
RPS in Fullerton has been saying they can provide that for a number of years.
In my opinion you'd use some combination of on-board KERS and supercapacitor banks for fast regenerative-braking storage in the absence of 'punctuated catenary' or smart third rail. This would then be used for controlled-rate charge and discharge of the actual chemical traction battery between its 20 and 80% or whatever is optimal for its battery chemistry by now -- even with the somewhat cockamamie RPS plan to rebuild cells from BEV batteries en masse to get the necessary capacity, you'd start having trouble if you tried slamming that acceleration and deceleration rate repeatedly across the battery alone with typical peninsula-size loads.
timz oltmannd If I'm a commuter agency, or even short haul intercity, I'd be all about trying to get hybrid locomotive that could keep me at 2 mph/sec or better all the way up to track speed. (And then get a good hunk of the energy back on braking! - with batteries continuing to charge during the station stop.) How possible do you suppose it is?
oltmannd If I'm a commuter agency, or even short haul intercity, I'd be all about trying to get hybrid locomotive that could keep me at 2 mph/sec or better all the way up to track speed. (And then get a good hunk of the energy back on braking! - with batteries continuing to charge during the station stop.)
How possible do you suppose it is?
I think the correct question is how practical it is, as it appears to be possible with existing technology. My recollection is that LFP batteries are good for repeated 5C charge/discharge rates and with specific energy of say 140w-hrs per tonne, a 10 tonne (11 short ton) battery would be good for 7 MW. Coupled with perhaps 3 MW from the prime mover, 10 MW would be good for 50,000 lbf tractive effort at 100 mph, 62,500 lbf at 80 mph and 100,000 lbf at 50 mph. The fastest charging would be during initial deceleration - the question is if the prime mover can make up for the difference between accelerating energy and regenerated braking energy.
I've been wondering about hybrid passenger locomotives since reading about EMD's F69 (12 cyl 710 with AC traction motors) back in the 1990's.
Erik_MagMy recollection is that LFP batteries are good for repeated 5C charge/discharge rates and with specific energy of say 140w-hrs per tonne, a 10 tonne (11 short ton) battery would be good for 7 MW.
Until it's near fully charged would be the short and snappy answer. There's a tradeoff between specific power and specific energy, hybrid cars, trucks, commuter locomotives would require high specific power.
Note that the 7MW charge rate would be for less than a minute, with charge rate decreasing as the train slows down. The key question is how many of these rapid charging cycles could be handled by the battery without degrading the battery? My impression is that number varies with with depth of discharge per cycle. I've lso seen many repports on modifications to Li-ion batteries to allow large numbers of high rate cycles.
Erik_MagThere's a tradeoff between specific power and specific energy
Exactly.
LFP (lithium iron phosphate) batteries have a higher specific power (watts/kg or watts/lb) than Li-ion batteries. Li-ion batteries have a higher specific energy (w-hrs/kg or watt-hrs/lb) than LFP batteries by about a factor of two. Batteries for a hybrid commuter locomotive would be designed for high specific power (long with a high cycle count), while batteries for a pure battery-electric locomotive would be designed for high specific energy.
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