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Old 11-26-2007, 12:58 PM   #224 (permalink)
MetroMPG
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Join Date: Nov 2007
Location: 1000 Islands, Ontario, Canada
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Blackfly - '98 Geo Metro
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Last 3: 70.09 mpg (US)

MPGiata - '90 Mazda Miata
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Fancy Metro - '14 Mitsubishi Mirage top spec
90 day: 58.72 mpg (US)

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SW makes another good observation and then furthers my education some more...

Quote:
Originally Posted by MetroMPG
The forklift controller limit is in the neighbourhood of 400A, but it also has a bypass, which will feed full battery current to the motor under certain (logic) conditions.
Quote:
Originally Posted by SW
That must be analogous to a tourque-converter lockup clutch. It does make a lot of sense. At those high amperages, the semiconductors are just ohmic switches dissipating a lot of loss because of their even slight resistances. If the duty cycle of the PWM gets close enough to 100%, it might as well use a relay (metal) instead of silicon.

EDIT: that should mean that the system should be more efficient at the equivalent of WOT.

BTW, silicon resistance goes down with temperature. That's why there have to be preset thermal or current limits or they will fuse together (read self-destruct). When you do overload a power transistor, you will be able to see glowing silicon a split second after it pops the lid off the device's case and a split second before it clouds the view with smoke. Don't ask me how I know this.
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