Posts by Stevie

Bah!

VinceH is indulging in the oldest (and lamest) game on the internet (I've never done what you've done but I'm here to tell you that you did it wrong).

Or ... have I just fallen for the cunning VinceHbot trap?

Re: hmmm.... or a broach.

Or perhaps he needs to make a hexagonal hole in a bar of steel ...

Real engineers knonwhat a broach is.

Re: Speed of light = your [sic] hitting it

Yes, this works in Star Trek, but In the "real world" there are other factors at work to prevent an uncooperative target being nailed quite so easily with a steroid-grown flashlight.

One is accurately ranging and bearing on a fast moving target with a weapon that needs to be trained on the target for an appreciable time.

Another HFL* mitigating factor is something called "path length", a property of real lasers that makes long distance killing with a beam of coherent light more problematical than vaporizing something fifty feet away in a lab. I'll let you research this yourself Peter2 rather than explain it myself.

And although the laser beam is propogating at lightspeed, the altazimuthal gymbal that points it at things will be reacting at a much lower rate of speed.

* Huge Frikkin Laser

Re: Frikkin lasers

[laser beatis smoke and mirrors]

Interesting. But then, hitting a stationary target always works, even for Sergeant York and Copperhead.

When the target is moving, and moving fast, it's usually a very different and much sadder tale.

It was, when push came to shove, the final nail in the allready well-nailed coffin of the SDI project back when no-one at the MoD remembers. That also proposed huge frikkin' lasers (among a raft of other barely workable-in-the-lab ideas).

Re: own EV happens to have the exact same problem 4 Steve K

One of the problems you have in a charged LiPo is the stored energy in the cell which complicates handling a fizzing or popped cell even if not currently burning.

Better hope your protection electronics are in good shape if you ever try charging a fully discharged LiPo battery.

This battery design is riddled with the most gotchas of any so far commercially available. When delivered in a "lightweight" configuration we are basically talking a fire waiting to happen.

Aside: My dad used to teach industrial electronics at college level. He came home one night to report that a discharged Duracell Alkaline AA battery (then a fairly recent innovation) had been sitting on his lab eye-level shelf when it spontaneously exploded. His students changed their trousers, then theorised an internal short, but thereafter he had them swap out the batteries on the instruments before they discharged beyond a certain point. Student eyeballs were two a penny it was true, but a decent multimeter was hard to replace.

Re: own EV happens to have the exact same problem 4 Steven Raith

You mean having the batteries well inside the crumple zones, in the area of the car specifically designed to avoid having to absorb the impact from an accident, because it also happens to be where the occupants are?

No, I mean what I actually wrote, explicitly. The Tesla's batteries are in the floorpan which is anything but "inside the crumple zone". Two Tesla fires that I can remember came about because of the road contacting the floorpan at speed. No crumpling was involved, but there was plenty of burning.

The crazy idea you seem to feel is worse than sticking sheets of lithium under the seats is the way other manufacturers are doing the trick. The reason the Tesla isn't is so that the car has some luggage space, a problem with those other vehicle designs. Tesla is also enabling people to drive much faster than people do in those other designs.

Which is why they need that proximity-triggered "Yeehaa!" klaxon.

Re: Sulphuric acid is bad on your skin

Well not for nuthin' but my years in the lab at Climategate University, (East Anglia) proved time and again that even the concentrated form of Sulphuric Acid gave me plenty of time to get to the tap to wash it off, and I had terrible eczema at the time which made my skin super-sensitive*. Absent a nearby water supply I suppose you'd be in trouble eventually. Eyes are a whole different class of problem, as is ingestion of course.

I stand by what I said about the relative safety of lead acid batteries, the automotive iteration being engineered and over-engineered to be robust under a welter of adverse conditions that would have a Lithium battery "venting with flame" (actual language from manufacturer's fact sheet). About the only thing you can do to endanger your life while handling one is to short the terminals, then not notice.

Internal shorts are rare with a car-type lead acid battery because under the heavy load a starter motor puts on one the plates actually try and move to touch each other, and so are separated by non-conductive baffles. I used to have a see-through Lucas battery of the type, and it was an education to use and charge it, I can tell you.

* I did get a nasty skin burn off concentrated "nitrating mixture" when the bottle spat at me once in that same lab, but they don't put that stuff in batteries, thank Tesla.

Re: standard operating procedures

I believe that it's not the voltage of the battery that is the primary concern, but the energy density of the cells that compose it and the failure modes of those cells.

A lead acid battery has a relatively low energy density under most conditions when compared to a lithium battery, and a very sturdy housing (but can still weld a spanner across its terminals if you are a clown when handling them and may explode as the electrolyte boils when that happens) but the Lithium batteries used in EVs have an extraordinarily high energy density which is barely contained by the housing.

When a lead acid battery fails it may include a fire. When a lithium battery fails it almost always includes a fierce fire comparable in visuals to an Estes solid fuel rocket motor.

Lithium batteries also have many more failure modes that are potentially fire-causing than a lead acid accumulator (though I just had a lead/acid gel battery that when connected to a UPS - which turned out to be faulty - got so hot I sustained a serious burn while disconnecting it).over-discharge, over-charge and physical damage will all cause fires (in the case of over-discharge, when the charger is next connected if it doesn't include the necessary circuitry).

A lead acid battery will typically survive such conditions without catching fire, though it may not work ever again if you boil off the electrolyte or punch a hole in it (all been done in my sight by the way). Lead acid gel batteries have different issues but again rarely catch fire (though I've seen one burst).

Re: own EV happens to have the exact same problem

Well, not if the batteries are not arrayed across the floor pan. if they are in the trunk/boot or under he hood/bonnet there is a reasonable expectation that the batteries will be better protected in a crash (probably wishful thinking on my part) and will stay in place while the rescue team is working. The Tesla's innovative layout poses some special concerns.

But your point about a lithium battery is a lithium battery is well taken.