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dhenz
User Rank
Iron
Re: History and safety
dhenz   7/4/2012 2:46:58 AM
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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.

Ratsky
User Rank
Platinum
Re: Insulation too
Ratsky   3/26/2012 3:52:06 PM
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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!

Ratsky
User Rank
Platinum
Re: Insulation too
Ratsky   3/26/2012 3:48:22 PM
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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!

Ken E.
User Rank
Gold
High voltage and high amps; why both?
Ken E.   3/22/2012 1:00:26 PM
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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.

ChasChas
User Rank
Platinum
Re: Greater potential shocks
ChasChas   3/21/2012 11:23:53 AM
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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.

D. Sherman
User Rank
Silver
History and safety
D. Sherman   3/21/2012 11:17:26 AM
NO RATINGS
I realize the article is about the shift to higher voltages in automotive electrical systems, but the "history" portion at the top of the article makes no sense at all, particularly this line: "When the battery alone wasn't powerful enough, engineers augmented it with an alternator and a fan belt."

There was never an automobile that included a battery but provided no means to charge it. Some very early ones had a magneto for the spark, a hand crank for starting, and carbide lamps for headlights, but as soon as the magneto was replaced with a coil-and-points ignition system, a generator was needed to charge the battery. In fact, some early vehicles had generator-driven electric lights before they had an electric starter or a battery.

Also, if one is writing a brief history of automotive voltages, it should be mentioned that all military vehicles since about 1950, and some heavy civilian vehicles throughout that time period, have used 24 volt systems for exactly the same reason higher voltages are being used today -- to reduce the amount of copper needed to carry high power levels.

As far as the safety issues go, I think the only way we're going to get anywhere without prohibitive expense and inconvenience is if we accept that the standard of comparison be "no more dangerous than a tank of gasoline" rather than "can't possibly be hazardous under any circumstances".

Pete Ostapchuk
User Rank
Iron
Re: BMW's Percussion disconnect for Z3
Pete Ostapchuk   3/21/2012 10:45:33 AM
NO RATINGS
Trawickim had some interesting observations. The safety feature that disconnects the battery reminds me of the fuel pump shutoff switches on some cars. Even the 12 Volt batteries should have some means of disconnecting. I'm reminded of a car fire that was extingushed only to reignite because of a short in the wiring. The fire extinguishers ran out before the battery did and the car was a total loss. Some industrial machhines have an emergency stop button that kills all the power. If you adjust the nuts and bolts on your battery connectors, you can push them down onto the battery post with a twisting motion and they will lock into place. You can also pull them back off in case of an emergency. If you have side posts, oh well.      Pete O. 

rdthybrid
User Rank
Iron
HV
rdthybrid   3/21/2012 9:45:14 AM
NO RATINGS
In developing hybrid construction equipment, inverters are now using 800 VDC capacitors and the bus takes several minutes to reduce to a voltage that isn't deadly.  So, future accidents are highly likely.  However, you can't force a new technology without hazards especially when consumers need the new product to perform to the exact same specification as the traditional product.

Charles Murray
User Rank
Blogger
Re: BMW's Percussion disconnect for Z3
Charles Murray   3/20/2012 7:44:28 PM
NO RATINGS
Interesting...thanks for the heads-up, trawickim.

Rob Spiegel
User Rank
Blogger
Re: BMW's Percussion disconnect for Z3
Rob Spiegel   3/20/2012 1:26:42 PM
NO RATINGS
What a smart idea from BMW. I would imagine that feature is helpful to emergency personnel who have to wrangle accident victims out of cars. 

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