[IamIan]

Originally Posted by P-hack

here is a modern tdi:


1. motors are not always at peak efficiency.
A. generally not efficient at slow speed, starting at about 0% efficient at very low rpm.

Finally... he sees the light


The Pusher ICE starts at 0% efficiency ... just as you write here ... while the same minimum is not the case for the generator.

The generators fuel to electrical conversion efficiency is independent of vehicle speed ... be it x% at 0 MPH ... or the same x% at 50 MPH ... or the same x% at 100 MPH... same is NOT true for the ICE pusher via transmission to the wheels ... just as you write here ... The ICE starts at 0%.

Originally Posted by P-hack

B. efficiency is still largely load dependent. Peaking around 90-95%

ie = Depends on the situation
He's seen the light.

Originally Posted by P-hack

2. Controllers are not %100 efficient, say %90 (large heat sinks)

Why are you using antiquated low efficiency controllers?

How about without even using (state of the art) ... but still several years old ~99.2% link

Originally Posted by P-hack

3. The generator has losses going from mechanical to electrical, like %80 efficient.

Why are you intentionally stacking the deck by using antiquated low efficiency motor to go with the antiquated low efficiency controller?

How about without even using (state of the art) ... but still several years old ... ~98% efficient Link

Originally Posted by P-hack

These are just swags, but let me total them up for this example so we have at least a starting point. Lets say demand is optimal.

.95 * .90 * .80 * .95 = 0.65 efficient in steady state mode with optimum load.

Your math is wrong.

The 95% was for load ... or Transmission efficiency ... not ICE efficiency... ie there should only be one .95 in the above equation.

The posted BSFC has a peak efficiency of 196 g/kwh which is about ~39% efficient from fuel to drive shaft.

Correcting that but still using your antiquated low efficiency devices you get:
.39 ICE(Fuel to Mechanical) * .8 Motor (Mechanical to Electrical) * .9 (Controller) * .8 Motor (Electrical to Mechanical) *.95 Transmission = ~21% Efficient.. still better than the ICE start at 0% you pointed out above.

Using better devices ... that are still several years old ... and no where near as good as State of the Art ... we get:

.39 * .98 * .992 * .98 * .95 = ~35% efficient ... with still using the 95% efficient transmission ... a direct drive BEV would get a peak of ~37% Efficient from that same ICE.

What do you know ... results depend on situation.

Originally Posted by P-hack

compared to a tdi that is %95 efficient (assuming some effort in driveline optimization) at driving the wheels under optimum conditions.

It's NEVER 95% efficient ... the BSFC peaks at ~39%.
.39 * .95 = ~37% peak

like I wrote before ~37% peak is a higher peak than the generators ~35% peak... we'll ignore for the moment the ~37% direct drive BEV peak.

Originally Posted by P-hack

But if the tdi direct drive has to "compete" with the generator, the "at the wheels" bsfc for the tdi is like 206 gm/kwh. Whereas the same efficient engine running a generator is like 301 gm/kwh.

Remembering that the Generator can get it's ~35% efficient at ANY vehicle speed ... but the same is not equally true for the Pusher ... with the finite limits of it's transmission.

At any vehicle speed the Generator can still get the ~35% efficiency.

But the finite transmission on the pusher means it can't do the same ... it's efficiency will vary with the torque and RPM of the wheel ... down to a minimum of 0% Efficiency as you posted at the top.

Even if we gave the ICE Pusher a bit of help by avoiding those 0% points ... and instead just looked at it's worst BSFC points ... which on that BSFC is ~270g/kwh which would be ~28%
.28*.95 = ~26% efficiency.

Which is what I wrote before ... the ICE Pusher will have a lower minimum efficiency under various vehicle travel conditions.

Originally Posted by P-hack

So lets play the load the battery for peak bsfc game now, but first note that pretty much any operating condition above 3 bar will be to the advantage of the direct drive in this graph already.

Nope ... not until it gets past ~35% ... which is about ~220g/kwh ... which this posted BSFC has areas worse than that as high as 15 bar at low RPM ... and doesn't even start to get above that until around ~7 bar at any RPM.

Originally Posted by P-hack

5. lithium batteries are 80%-90% in charge/discharge efficient under optimal conditions.

Incorrect.
under optimal conditions they are above 95%... round trip.
See page 21
pdf Link

Originally Posted by P-hack

6. Say you have a %90 efficient charger and bms, which is also dependent on state of charge and current.

See above ~99.2% efficient controller that includes regen to charge the batteries.

And there are some people who don't use a BMS ... but even if you did ... it consumes only tiny tiny tiny % of the total net power and energy... not even 0.1%.

Originally Posted by P-hack

So aside from the fact that you can't ever touch most of the bsfc graph with a generator in front of this tdi driving the wheels, you are looking at a generator efficiency of
.65 * .90 *.90 = 53% efficient when loading the generator for bsfc (assuming all the electrical are in a fairly optimal operating range). That is a wheel bsfc of 369, below the very bottom line on the bsfc chart.

See above for corrections ... of other situations.

Originally Posted by P-hack

Now you may take issue with the specific numbers here, but the point is clear, there are a lot of losses in the series proposal.

There can be ... that is one situation... that you are focused on... with numbers you pulled from thin air ( no references ).

What you seem to keep trying to avoid ... is that there are other situations that can result in smaller hits to the generator ... and larger hits to the ICE Pusher.

Depending on the situation ... see above ... with references ... the pusher can be bellow 27% efficient when vehicle speed and travel conditions force force the ICE into less efficient points on the BSFC ... due to finite limits of the transmission ... while the generator could sustain above 35% at any vehicle speed and travel conditions ... because it is not connected to the road... and wheel RPM and torque don't effect the generator ... but do effect the ICE pusher.

Originally Posted by P-hack

I have heard speculation about higher peak BSFC with rpm targeting but I have never seen any actual data, nor do I know that a cvt wouldn't still be more efficient than an "electronic torque converter" in maintaining target rpm.

See above.

As for the cvt ... same things apply ... it has it's limits ... and can not keep the ICE at peak efficiency under any wheel RPM and torque.

Under some situations the cvt will do better ... and in other situations the cvt will do worse than a manual transmission.

Originally Posted by P-hack

Sending all your ICE power through a generator to drive your EV wheels certainly seems like an inefficient solution all around, and requires %54 more engine in steady state for the same power at the wheels in this example.

See above.

- - - - - - - -

A bit of an extreme example ... but might be a useful thought exercise:

Think about why freight trains and cargo ships ... have pretty much all stopped using mechanical transmissions ... and instead pretty much all use ... a combustion generator to provide electrical power to an electrical motor that actually moves the train wheels or the ship propeller ... is it a giant conspiracy? ... do they love to waste energy and fuel on less efficient options? ... I don't think it is either of those ... I think in their different situation the pros and cons clearly leaned against the mechanical transmission and very much in favor of the generator / electrical combination instead.

Originally Posted by P-hack

Need to see someones work backing up their belief that series is more efficient, regardless of the starting bsfc. Otherwise it is just a religion.

See above... for some example situations ... do NOT try to make this a black and white always A or always B ... as I have been pointing out over and over again ... that is NOT how it works ... who wins ... depends on the situation.