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I really liked the EV1.
It's a great car. A real step up from the previous electric
vehicles; an electric pickup in the late 1980s and more recently
a converted Toyota Paseo. Here's a thumbnail picture of both the EV1 and the Paseo
charging together in my driveway. Click on the small picture
to get a bigger version.
The EV1 is faster (0 to 60 in 7.6 seconds according
to Popular Mechanics) and has a longer range (50 to 90 miles
per charge for the original lead acid version). It looks good
and has all the amenities; CD player, air conditioning, and
much more.
At one point we had 2 EV1s. That was before the recall. After
that we reverted back to a single EV1, one iof the 1999 models
with NiMH batteries. The range was much farther but the acceleration
was not as good as the 1997 lead acid version. The newer gen
II model handles better though. Almost like a sports car.
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Range and what's with these gauges?
One of the biggest problem right now with EVs is
the limited range. Batteries are just not good enough yet. As a
result its very important to have enough feedback from the car to
be able to change your driving habits to get the most out of the
battery pack. To do this you need a good "fuel" gauge and some idea
of how much fuel you are using. The fuel in this case is the amount
of the battery capacity available. The EV1 has a pretty good state
of charge (SOC) gauge that gives a fairly accurate reading of how
many amp hours are left in the pack. Unfortunately its very coarse
with only 11 bars to indicate the SOC. The indicator for power use
uses the same set of bars and is set up as almost a log scale of
the power being used. There is also a range estimate that makes
a guess at the remaining range based on past history.
After driving the car once or twice it was pretty
obvious some improvement or enhancements could be made to the range
and SOC gauges. It was rather surprising to see the range increase
as I drove instead of decreasing and when the pack got low the miles
slipped away a lot faster than when the pack was full. I've also
noticed that the SOC seems to be based strictly on the amp hour
capacity of the battery. Unfortunately lead acid batteries have
this annoying problem of sagging as loads are applied. This means
the voltage drops the more amps are pulled from the pack. This effect
is even greater when the SOC is low. To hold the same power level
more amps must be drawn from the pack when its at a low SOC than
when its at a high SOC. This effect can become very significant.
At 100 amps there is about a 10% difference, at 200 amps its up
to 14%, and at 300 amps it's nearly 20%. So the deficiencies with
the current gauges are:
- Range gauge is based on too much history
- SOC gauge is not power compensated (and not
linear with actual SOC)
Better gauges
Before explaining the solution to the gauge deficiencies
let me provide some background. On the electric Paseo
I had an E-Meter
that had a serial port on the back of it. I wrote some software for
the PalmPilot (Palm Computing Platform) and collected voltage and amperage reading
once a second from the car. After much analysis and experimenting
the PalmPilot software was good enough to use as the SOC gauge for
the car. From this experience I learned a lot about lead acid batteries,
particularly gell cells (Optima yellow tops) like the ones in the EV1.
Now that I have an EV1 to drive I couldn't pass
up the chance to collect data from it. It turns out there is a diagnostics
port under the dash on the drivers side that produces a steady stream
of data. Unfortunately there are no documents on the port. Even
the service manuals don't cover it. After some help from others
and lots of feedback experiments the codes are at least partially
broken. The PalmPilot software has been updated and is collecting
data from the EV1. It now provides alternative
views or gauges of the battery pack status with a more fine grain
and more accurate SOC gauge and several range indicators based on
several power use cases. The PalmPilot software I wrote is available
for download
and more information
is also available. I've also put together some notes on how to hook
up to the port and how to parse the data stream. The data collected
can be graphed using a
simple Java program which can be downloaded as well.
Driving tips
After driving EVs for a few years and watching
the gauges you learn how to drive to get the most range from the
batteries. The EV1 is like any other EV in many ways but there are
some interesting differences. I've assembled a number of
driving tips based on my experience so far.
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