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Old 12-12-2007, 08:45 PM   #498 (permalink)
MetroMPG
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Join Date: Nov 2007
Location: 1000 Islands, Ontario, Canada
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Blackfly - '98 Geo Metro
Team Metro
Last 3: 70.09 mpg (US)

MPGiata - '90 Mazda Miata
Last 3: 51.27 mpg (US)

Winter beater Metro - '00 Chevrolet Metro
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OK, did my first batch of MPGe calculations, and stuck it in the car's gas log.

Man - what an oinker! Now, this is calculated at the plug, not at the battery pack, but still - that's the way the EPA does it.

50 km / 31 miles total, 6 charge cycles, using 16.7 kWh total according to ye olde kill-a-watt.

Conversions: 3412 BTU/kWh; 114,500 BTU/gal (US).

One thing I noticed is there's a correlation between distance driven and MPGe. The shorter the distance driven before recharging, the higher the energy consumption.

It's somewhat of a weird concept, but it makes sense. Charging is most efficient when the batteries are empty - they'll gulp down the amps as fast as you can feed 'em (within reason), and SOC will rise rapidly in response. But as the batteries approach "full", the charging efficiency seems to drop. The batteries bubble and burp and heat up (relatively). It takes more and more to push them that last 10-20% to "full".

Also, the charger has a 3 hour timer for its "finish cycle". So if I unplugged the car fresh from the charger, drove it down the driveway and back, and plugged it in immediately, it would take 3+ hours to give me the "fully charged" light again.

Also also, if I leave the charger plugged in after the "fully charged" light comes on, it keeps trickling the pack, lowering the MPGe calc of the previous drive cycle.

Also also also, the pack loses charge just sitting idle. If I drive it over the course of a couple or 3 days before recharging, I'll get lower MPGe than if I drive the exact same route fresh off the charger.

So complicated!

Anyway - it's good to have a baseline. Time to start figuring out how to hyperwatt this puppy.
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