when you get a minute... I am sure LOTS of us would like to learn more about how ultra-cap (F) capacity translates into Watt-hrs for getting a handle on possible braking regen.Yes and yes. Don't have time to go into it now.
Hi Dan,I am sure LOTS of us would like to learn more about how ultra-cap (F) capacity translates into Watt-hrs for getting a handle on possible braking regen.
Hi Dan,Then sizing the ultra-cap system to twice that amount to allow for working voltage range and losses would give an aproximate cost to evaluate
To get above 20% extended range from regen, you'd need a very efficient system and be making like 10 stops per mile, every mile. Your expectations may be inflated. But you can define a drive cycle and do an energy spreadsheet analysis and see if it is in the ballpark.when considering the regen would probably extend range 20-30% for typical urban conditions; as compared to adding 20-30% more standard lead batteries for the same range.
Yes and yes. Don't have time to go into it now.
What would the total cost be for a lithium battery system capable of the 160 kW required to stop the bus in 7 seconds for a couple million cycles?Considering their largest capacitor they make of that model (165 farads at 48v) is 213,000 joules roughly, or 0.059kwh, why didn't they just use lithium ion batteries?
Bus has been running for 4 years. This was a capacitor up-grade. It is a parallel hybrid, energy recovery/launch assist. It increases fuel economy about 25% on stop intensive routes. The ultracapacitors will last the life of the vehicle whereas any battery available will not. Total life cycle cost is better with capacitors than batteries.I assume one of those caps was in the $1000 range a piece... for a mere 0.05kwh, they'd be hard pressed to have the bus functioning by the time lithium dies, let alone make the added durability of caps worth it.
Am I missing something on the cost effectiveness table here?
low voltage high amperage cylindrical cells would work fine as they could be charged at a 10-15C rating in bursts for a lot of short cycles.What would the total cost be for a lithium battery system capable of the 160 kW required to stop the bus in 7 seconds for a couple million cycles?
You're correct it will last the life of the vehicle, no doubt about it. The question is if 2 lithium cell replacements is cheaper than 1 set of those, my guess is yes since you're upgrading after 4 short years.Bus has been running for 4 years. This was a capacitor up-grade. It is a parallel hybrid, energy recovery/launch assist. It increases fuel economy about 25% on stop intensive routes. The ultracapacitors will last the life of the vehicle whereas any battery available will not. Total life cycle cost is better with capacitors than batteries.
I don't disagree with the choice per se, I'm just curious on the cost effectiveness or if the government should have been going with different engineering standards. Ultracaps are well and good but the weight addition, cost addition likely will be more damaging to overall performance per dollar than batteries or dropping the hybrid design completely. Granted I lack the political "prowess" to do much else besides cost benefit schema, clearly there is other motivations out there.Yes, energy density for batteries is much higher than ultracapacitors. But that is not the only factor when choosing the energy storage system. This application required little energy and lots of power, high efficiency and durability. Ultracaps made sense.
Hi Technologic,How much amperage for a 30mph stop are you REALLY dumping into these caps? I can't imagine it's over 1500A.
The BMS for such a system would have to be custom I'd imagine, but in reality that voltage/amperage would be a simple thing to find in a fast charging lithium component...It is fused at 300 amps. 680 volts max.
I looked into batteries for this application. Still am. Basically anything that is actually available, with the required support (BMS), cost more than a single set of UCs. And the up-grade was to the best UC available because the original UC (sourced from Russia 5 yrs ago) was not an option for continued development and commercialization.
If you can add a component (or system in this case) to an existing vehicle which can recover cost in the life of the vehicle and reduce fuel consumption and emissions, what's wrong with that?
ok, I am trying to work my way thru this...KE = (1/2)*M*v^2. Use units of kilograms (kg) for mass (M) and meters/second (m/s) for velocity (v) and the KE units are Joules (J). Surprise!
I think it probably has a lot to do with charge/discharge rate. The "deceleration event" would typically happen over the course of maybe 5 to 10 seconds, and the acceleration event is similarly short. While the total energy may seem small from an EV perspective, the Power is massive, because the time is very short.Considering their largest capacitor they make of that model (165 farads at 48v) is 213,000 joules roughly, or 0.059kwh, why didn't they just use lithium ion batteries?
I assume this system cost 15k-20k in caps. Whereas the 0.84 KWH in this pack would cost roughly $200 in lithium form.
Maybe I'm missing something here on energy densities/price, but usually ultracaps are freaking expensive
Yeah, I guess. Still haven't found my calculator, so trust your math. Now the 230kJ was just the kinetic energy. So you'd subtract losses from that and really need only like maybe 160 or 170kJ of usable energy storage. And the current profile for a complete decel will resemble a triangle. So, the maximum current will probably be on the order for 400 amps. Just kinda guessing. But it looks like you got the right idea going there.229837 Joules available from a single typical stop, since Joule = W*s, and an average stop is maybe 10 seconds of braking, that means it would come in at about 23000 watts for 10 seconds. WOW. so at 96 volts, thats a max of about 240 amps. Obviously more than (any kind) batteries can absorb...
This all gets into the system design. You have to keep the maximum capacitor voltage where the manufacturer has set it. And you have to keep max voltage below the limit of your motor controller. So, you either live with half voltage when the caps are discharged, or look at some type of voltage controller between the caps and the rest of the propulsion system. Such a device is often called a buck-boost DC/DC converter. Not something you can buy off the shelf. And would be on the order of power and size of the motor controller. Maybe you can steal one from a Prius. Or just design the system around a 2 to 1 voltage swing.so the next step, to figure number of caps required requires knowing the voltage. My EV happens to be a 96v system, so I am assuming I could build a bank of ultracaps in series or parallel to provide a matching 'low voltage' of 96 v, and a max of double that, right?
my question is which voltage to use in looking at the ultra cap specs to match this all up. and then, if the 'charged' ultracaps are at 2*96 volts, how would I bleed energy back out to my system without frying controller and motor