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High Voltage Amps Up the Automobile

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Re: Greater potential shocks
ChasChas   3/21/2012 11:23:53 AM

This is getting wild. I understood the capaciter style battery fell out of favor because of the potential of dangerous discharge. This brings us right back.

Ken E.
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High voltage and high amps; why both?
Ken E.   3/22/2012 1:00:26 PM
Where is all this power going?  For example, there was mention of a device rated 900v/500a continously, nearly half a megawatt, roughly 600HP!  Really?  This flies in the face of efficiency, the usual reason for being of electric vehicles. 

I'd have imagined the higher voltage is employed to reduce amps, copper, and weight, but there's little mention of that here, in fact the emphasis is on high voltage and amperage.

I'd love to see cars go to a 24v primary battery, cutting existing amperages and wire sizing in half.  This is considered an inherently safe voltage to handle with your bare hands.  (Not that you should.)

Finally, even these higher voltages have been used for a century or more routinely in industry, I'd expect protection schemes there will crossover, with modifications for compactness and lightness.  I've been working with them my entire adult life, and I'm close to retirement.

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Re: Insulation too
Ratsky   3/26/2012 3:48:22 PM
For years now, the operating temperature requirements for electronics in the engine compartment has been the "old" MIL-spec range of -40 to +125 C!  Vehicles are expected to start and run from a (very!) cold start near the poles, and also to operate fine with engine compartment temps way above boiling water.  Typical IC engines are designed with optimal running block temp around 110C.  Before jumping into the automotive industry some years ago, I had done a lot of extreme hi-rel electronics design (both MIL and CO-grade telecom and 911 call centers), and the auto requirements made that look easy!

Re the "wattage" comments: just because a relay is rated for X volts and Y amps does NOT imply a capability of controlling an XY-watt load!  Switching devices have multiple ratings (especially with inductive loads like big motors): carrying capacity and interrupting capacity are only two of the parameters, and both may have separate limits for V, A, and VA.

I also remember that at least 20 years ago, the UNANIMOUS agreement in the auto industry was that the "ancient" (e.g. late 1950s) 12VDC (incidentally, it's really 13.8VDC nominal) would soon be replaced by "24V" or maybe even 40V batteries and alternators, for multiple reasons including reducing the weight of all that copper whose usage was going up rapidly as electronics took over more and more of the subsystems of the vehicle!  I guess nobody remembered their basic physics (if they ever learned it); INERTIA applies to many areas, even the marketplace!

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Re: Insulation too
Ratsky   3/26/2012 3:52:06 PM
Oh, I forgot an important point: anither compelling reason for the very high current rating is for FAST CHARGING reasons (so-called "Level 3" or 30-minutes for a full recharge), not so much for running the motor(s), even for a racing vehicle!

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Re: History and safety
dhenz   7/4/2012 2:46:58 AM
electric cars has certainly changed the electrical system of vehicles. the old 12v model has bigger range and Im looking forward to see low cost alternators and batteries and I believe it wouldn't be impossible.

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