Quote:
Originally Posted by dcb
batteries don't like high load
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The graph is depicting the Peukert Effect.
This can be misleading / confusing to some people.
The battery discharged at 3C does not loose significant amounts of mWh compared to the same battery discharged at 2C... or 1C.
The batteries do not actually hold less energy when you discharge them faster ... Chemical reactions in batteries take time ... the faster you try to pull energy out of a given battery the faster you will seem to initially discharge it ... but if you give the chemical reactions time to catch up ( rest ) you get what some of the old time EVers call .. 'growing amps' ... The chemical energy didn't just appear from no where ... it was there before ... you were just electrically drawling off energy faster than the chemical reaction could keep up.
I will agree however ... that this effect is a dis-advantage of Batteries .. and by proxy BEVs , compared to gaseous and liquid fuels which do not reduce in power output until the tank is next to empty... but while a loss of power toward the end of a batteries capacity is a negative for BEVs ... it is also a separate issue from MPGe.
Quote:
Originally Posted by dcb
batteries do not necessarily charge efficiently "The coulometric charging efficiency of nickel metal hydride batteries is typically 66%,
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This is a often quoted piece of mis-interpreted information.
Even if we ignore other batteries have different cycle efficiencies for charging and discharging.
This 66% number is more accurately the cycle efficiency of some of the common NiMH charge termination methods ... which is not the same as the cycle efficiency of the NiMH battery itself.
Typical NiMH charging systems over charge the battery ... which throws away energy ... kind of like trying to poor a 1 gallon jug of water into a shot glass ... sure you can keep pouring ... but you won't ever fit 1 gallon into that little shot glass ... and the 66% efficiency number is using that kind of testing methods.
If you don't believe me ... feel free to run the test properly for yourself.
NiMH is actually over ~90% cycle efficient... exact number will vary some with specific conditions.
Proper testing includes:
#1> Accurately determine the storage size of a single NiMH cell.
From a full charge, how many mAh will it discharge?
#2> To prevent overcharging ... only put in what you know it can hold.
If your AA NiMH puts out ~2,000 mAh on discharge ... put in ~95% of that ~2,000 mAh during charging... or ~1,900 mAh.
#3> Measure the mAh given during discharge
#4> Repeat the above a minimum of ~3 times.
Every time I have done this ... I have ended up with ~90% cycle efficiency numbers.
Remember for this type of test you are counting the mWh going into and out of the battery ... the efficiency of the charger , and the dis-charger are separate issues , and should be isolated form your battery testing data.
Quote:
Originally Posted by dcb
So even suggesting that an EV is %90 efficient from the wall is coocoo.
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Like most things ... it depends on the specifics.
Temperature ... specific parts ... driving methods , and context ... etc.
But yes over 90% efficiency is achievable today with modern technology you can buy today for a BEV ... If you want I can give you some specific components that will result in over 90% BEV efficiency.
In practice we don't use the best components and people drive in wasteful methods ... so the % will be lower ... just like it will be lower for both the BEV and the ICE... neither one operates all the time at their peak efficiency.
Quote:
Originally Posted by dcb
I also don't think %15 is a fair number for ICE, it takes the driver and any recent advancements out of the equation. It is entirely possible to operate a car near it's peak efficiency, folks here do it all the time. Even if you look at a reasonably idiot proof efficiency car, the prius, it is rated at %37
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The Prius is a very efficienct gasoline ICE ... but it is not possible to operate the vehicle on a yearly bases in the tiny ~39% efficiency window.
After the engine is warmed up ... in it's tiny sweet spot of RPM and torque ... when all the factors align perfectly ... then it gets a maximum of ~39% efficiency... see attached graph bellow ... the ~39% efficiency point is only in the 195 g / kwh part of the graph ... and only after the ICE is warmed up.
Sorry ... but 15% to 20% energy efficiency ... is about what the average ICE averages out throughout the year , for operating energy efficiency ... winter being the worst season.
Quote:
Originally Posted by dcb
I'm not convinced yet the BEV's dominate in efficiency full cycle.
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Full cycle ... ALL methods of using fossil fuels are horribly energy inefficient forms of using solar energy.
In terms of energy efficiency Full Cycle Renewable energy sources for either ICEs or BEVs are greatly more energy efficient than any fossil fuel option.
In terms of Full Cycle energy efficiency RE-BEV is more energy efficient than RE-ICE... ICE efficiency kills it ... plus Photovoltaic cells ( as bad as they are ) are more energy efficient than photosynthesis.
Quote:
Originally Posted by dcb
range and initial cost and availability make liquid fuels attractive for transportation.
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100% agree.
Quote:
Originally Posted by dcb
Also, the rolling resistance/weight thing. The problem with extra weight is not just extra rolling resistance, but also you only get a small fraction of your acceleration energy back in electric regenerative braking.
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Far more than the 0% of friction brakes.
When you add up the energy kwh spent ... you do not have to travel very far distances ... before rolling resistance losses in kwh dominate massively over the kwh used for accelerating.
Additionally ... F = MA ... to increase the energy needed for the same acceleration you would have to increase the weight by the same % ... a ~50% increase in energy for accelerating would require ~50% more total vehicle weight ... it is a linear relationship ... just as rolling resistance is linear with weight as well.
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Quote:
Originally Posted by RobertSmalls
The good news is, for the first time ever, we have EPA efficiency data on a PHEV in electric drive, and when running on fossil fuel.
That is to say, 13.6 KWh = 1 gal, in terms of how far it will drive a Volt.
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Excellent point.
In a vehicle with the same aerodynamics ... the same weight ... etc.
The Volt shows at the vehicle level ... a ~2.6x energy advantage to the BEV mode ... as a gallon of Gasoline actually has ~36 kwh.
Which is similar to the other studies already posted.
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Quote:
Originally Posted by JasonG
Well tell ya what,
when you build an EV that can pull a 16,000lb trailer at 55 MPH for 350 miles I'll conceed that electric is on equal terms.
Heck, if you can find one that can do either I might
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You left it too open ... and too easy... prepare to go back on your claim ... or conceed.
Even with old tech ... using lead acid batteries , etc ... a 1,500 HP BEV Locomotive that runs for 12 hours per charge ... can pull much more than a 16,000 lbs trailer ... a modern version using modern components like Lithium batteries ... would easily be able to run for 4x a long as this Lead Sled.
Here's a picture of the Lead Acid one in Altoona Pa ... they built to test the platform of a BEV Locomotive without a diesel generator.
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Quote:
Originally Posted by roflwaffle
I don't think anyone is saying that either one is on equal terms. An engine can't beat a motor for reliability or efficiency and a motor can't beat an engine for refueling times or energy storage. Each one has it's advantages and disadvantages.
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100% agree.
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Quote:
Originally Posted by dcb
but that is an arbitrary point in the system, ignoring all the conversion losses to that point (which are many), from the days when all there was was gasoline basically, and puts the alternatives at an unfair disadvantage.
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I agree ... it is an arbitrary point in the system ... just like picking the fossil fuel and ignoring the energy efficiency losses from solar energy to produce that fossil fuel it in the first place is also an arbitrary point in the system.
But it is the arbitrary point in the system that our current MPG system is based on... it is the currently widely accepted standard.
We are not likely to change our entire MPG system the public uses, by including the losses up-stream... the public expects 1 gallon pumped to = 1 gallon ... to go 30 miles when they drive 30 miles ... etc... is that an arbitrary point in the full energy cycle ? ... of course ... but that is the way the public does it at this time ... that is the current standardized method.... as flawed as it may be.