99.999% of people, even after they have what DC electricity is, explained to them, will only know of or encounter two sorts.
1.5 VDC primary cells like AA, C, D etc.
12 VDC secondary lead acid batteries in their car.
So, DC is “safe”, hark back to edison and tesla/westinghouse etc.
In my trade as a marine engineer 30 years ago working on stuff that was old then, I would *often* come across huge banks of traction cells (big slabs of battery shaped like a slim pack of business cards) each one being 2 VDC, made up into big parallel and series connected banks that often ran to about 110 VDC.
It was instantly fatal to fuck with it, metal spectacles, metal watch straps, metal rings, and of course spanners and other tools, would result in horrific injuries and sometimes death, and then there was the voltage and current itself, with DC you get two seemingly random choices, depending on *which* muscle groups spasm and lock up when the power hits them, you either get thrown clear and suffer torn muscles and ligaments, or you get clamped on and the torn muscles and ligaments and all the rest of you start to cook, literally.
In later years in IT I’d see similarly huge DC battery banks in telephone switch exchanges, but the voltage was much lower, usually 48 VDC, still enough to very badly injure you, and possibly kill you… so not *as* dangerous as 110 VDC, but not “safe” by any means.
Bus bars would be slabs of solid copper bar, 2″ x 1″ and up, and it was common to space the +ve and -ve bus bars by enough distance that you couldn’t put one hand on one and one hand on the other by accident, so +ve down on side of a battery bank and the -ve down the other side 10 feet away or more.
Live superheated steam and heavy rotating machinery were other things that were treated with similar levels of respect, fuck with it and die, make a mistake and die, lose focus or attention and die, and if you don’t die and do live, you injuries might be so severe and painful you wish you did.
Now, in 2017, we are getting EV’s on the road with three times these DC voltages, and similar current delivery capacities, and if 110 VDC is possibly fatal, 350 VDC is fucking lethal.
It’s all very well to say “it’s contained” and that “safety precautions” have been made, but the people making these choices and decisions and designing this shit didn’t grow up working with 110 VDC and the injuries and fatalities it created… I did, I personally knew first hand;
- one guy, we’ll call him Fred, his metal frame spectacles fell off, shorted the terminals on a big 110 VDC bank being charged by a 2 cylinder Gardner diesel and DC genny, tops of the batteries blew off taking all his face and both eyeballs and both ears and much of his neck and throat, he lived, with some hearing in one ear.
- another guy, we’ll call him Tom, stainless steel rolex watch strap completed the circuit between a cable he was handling and an improperly shorted battery cage frame, his hand came off, though the stump was mainly cauterised.
- two other guys, call them Dick and Harry, both had a hand clamp on and the power went through their bodies, killing and cooking them at the same time.
Three of these four incidents happened within 100 feet of me, people who weren’t there attempt to be grisly as say they assume it is the smell that stays with you.. it isn’t, it’s the taste, that shit gets in the air and you breathe it in and taste it.
All batteries are basically chemical storage mediums, it’s chemistry at work inside the battery, and you can pull an isolator all you want, that chemistry is still there, wanting to work… just gimme a fucking circuit bitch, any circuit will do.
So yeah, I’m sure Tesla et al can design an EV that doesn’t cook the unwary when then a rear light cluster is changed out, but what of firefighters and recovery guys and anyone else involved with an accident damaged vehicle?
As someone who worked recovery for a while, I can tell you one of the first things you did with a mangled wreck was check the engine compartment, if you saw diesel injectors, you relaxed, if you saw spark plugs, you started to get cautious, if you saw LPG plumbing, you started to get very very cautious.
As someone who worked in motorway recovery, and who was also a time served marine engineer, I can tell you now, if I was still in recovery, my policy would be I’m not touching your fucking wrecked EV, not with anything less than a grab claw on the end of a HIAB anyway.
I had occasion to look inside the guts of an EV late last week, it only just occurred to me today, those big beefy DC power cables weren’t armoured, not properly… in the boats the SWA cable was itself run in thick wall steel pipe duct. and it was already tucked away behind an outer steel hull and some inner steel bulkheads… in a telephone exchange the busbars were contained within a very robust reinforced concrete building with some brick exterior cladding…
In an EV it’s all behind biscuit tin gauge metal and monocoque pressed construction.
If there is one thing I know in life it is that “projected” and “real” are never the same thing, those euro ncap crash tests and videos can look as impressive as fuck, then in real life you get to a job and it don’t make no odds if the car was no stars or five stars for crash protection, 40+ tons of lorry and cargo just went through it like it was tissue paper.
The only way you can make 100 series connected 3.4 VDC cells safe is by making 25 separate banks of 4 in series with physical breakers in between, so that all the breakers open simultaneously with the airbag, and in a way that they can’t be closed or shorted .
Won’t be happening before the fatalities start to mount.
Don’t take my word for it, go talk to someone with hands on experience of working with high voltage and current DC systems… they’ll all say the same thing, for any voltage or current combination, DC is more scary than AC, and when you add in secondary cell high voltage DC, it’s really not something to trifle with or under-estimate.