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Old 07-31-2010, 07:49 PM   #34 (permalink)
Rokeby
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I've watched the videos and my first comment is they desperately need
to find an editor. The videos could easily be cut in half and increase
their content ratio by 100%. Maybe Count DaMonay can help.

I'm not competent to comment on the purely electrical elements and
calculations, especially when carried out to 4 decimal places.

That said, I think there was some experimental design errors or
misunderstandings in the original 356e tests that has lead to this
brouhaha.

As I understand it, three conditions were tested with the 356e:

C1 - Brake pedal regen only
Brake pedal - deceleration by regen and friction brakes
No pedals - freewheeling ( I'm not saying "glide" as it has Prius-specific
meaning and includes a small power draw on the HV battery.)
Accelerator - acceleration only.

C2 - Max regen
Brake pedal - deceleration by "aggressive" regen and friction brakes
No Pedals - constant "aggressive" deceleration by regen
Accelererator - acceleration only

C3 - No regen
Brake pedal - deceleration by friction braking only
No pedals - freewheeling
Accelerator - acceleration only

The perceived problem came up when the figures suggested that the
car used less power over the 47.6 mi. course for the second condition
over the first, and the third case - no regen whatsoever - over the
second.
Overall conclusion: regen in an EV offers no energy savings/efficiencies.

In C1 there is freewheeling and some regen via the brakes.
In C2 there is no freewheeling and a lot of regen.
In C3 there is a lot of freewheeling and no regen.

My observation is that C2 is not about regen at all. It is about
essentially constant deceleration at all times except when the
accelerator is depressed. It would be like driving with a dragging brake
shoe. You would have to accelerate -- that is use power -- to maintain
speed when you would otherwise be freewheeling.

To me, this is not a surprising experimental result.
It would also be less efficient to drive around dragging a 200 lb. anvil behind.

I do not yet understand why C3 -- no regen -- looks more efficient than
C1 -- some regen. I suspect that, as is noted later in the series, it has to do
the nature of the road course driven, having to do with stops/starts,
topography, and ratio of city vs. country, regen "friendly" vs. "unfriendly"
driving.

There may be two additional things that would confound accurate energy use
and efficiency analysis between C1 and C2. I am at/beyond the limits of my
EV/battery understanding here.

Both the test runs for C1 and C2 were made on the same day.

1. Someone said long ago that to properly warm up a Prius for a FE/MPG,
trial, the car needs to be driven for 20 miles or so before the event. In this
way you get, for lack of a better term, a "whole car" warmup, including all
rotating equipment; transmission, rear axle, wheel bearings, pump bearings,
etc.

There is no mention of the 356e being warmed up prior to C1, this could
mean that the the 356e would have been less efficient on the C1 run
compared to the C2 run.

2. The internal temps of the drive batteries during the runs could have
fuzzed-up the data. I believe that the C1 and C2 test runs were done on
a warmish, 90 degF day. It is well known for the Prius anyway that when the
HV battery gets up over 100 degF, it suffers from both reduced capacity and
reduced ability to receive a charge and deliver power.

I don't know how effective the 356e's drive battery cooling system was/is.
Without taking temps before/during/after each run there is the possibility that
temps were not equal for both runs.

Which run this would favor would depend which run was at the hottest part of
the day.
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