jbm@eos.UUCP (Jeffrey Mulligan) (03/15/88)
From article <560001@hpcljws.HP.COM>, by jws@hpcljws.HP.COM (John Stafford): > I wouldn't quite claim it is safe to work at automobile voltage (12V) > levels. The second factor, current, comes into play here; cars may only > be 12 volts, but there are (especially when starting) quite a few amps > around. > Kids: don't try this at home! Someone posted something on rec.autos about the following stunt: they rigged up an "alarm" which consisted of a wire from the ignition coil to an electrode in the seat cushion. This was a practical joke, and the funny part was that, after starting the car and getting an initial kick in the pants, every time the victim touched the key to turn the motor off or the door handle to try and escape, he got a shock. My question is: are there any hazards from the type of shocks encountered in auto ignition systems. I have gotten painful little zings just from having my arm touch a spark plug wire while reaching over for something else.
phd@SPEECH1.CS.CMU.EDU (Paul Dietz) (03/16/88)
From article <560001@hpcljws.HP.COM>, by jws@hpcljws.HP.COM (John Stafford): > I wouldn't quite claim it is safe to work at automobile voltage (12V) > levels. The second factor, current, comes into play here; cars may only > be 12 volts, but there are (especially when starting) quite a few amps > around. I seem to remember that if I started my old bug in a particular way, it would always give me a bit of a shock. I also seem to remember reproducing this on other bugs of the same era (1970). Unfortunately, I don't remember what the conditions were. Maybe you had to hold the metal horn bar while turning the key? Anybody got more info? Paul H. Dietz ____ ____ Dept. of Electrical and Computer Engineering / oo \ <_<\\\ Carnegie Mellon University /| \/ |\ \\ \\ -------------------------------------------- | | ( ) | | | ||\\ "If God had meant for penguins to fly, -->--<-- / / |\\\ / he would have given them wings." _________^__^_________/ / / \\\\-
gvcormack@watdragon.waterloo.edu (Gordon V. Cormack) (03/17/88)
In article <334@eos.UUCP>, jbm@eos.UUCP (Jeffrey Mulligan) writes: > From article <560001@hpcljws.HP.COM>, by jws@hpcljws.HP.COM (John Stafford): > > I wouldn't quite claim it is safe to work at automobile voltage (12V) > > levels. The second factor, current, comes into play here; cars may only > > be 12 volts, but there are (especially when starting) quite a few amps > > around. Give me a break! 12 volts is absolutely safe. Reminds me of when people kept fiddling with my science fair project (a long time ago), so I put up a large sign: DANGER 50,000 OHMS! Believe it or not, this kept them away. > My question is: are there any hazards from the type of shocks > encountered in auto ignition systems. I have gotten painful > little zings just from having my arm touch a spark plug wire > while reaching over for something else. Actually this is (fairly) safe. There are lots of volts, (50KV) and there is plenty of current, but it is radio frequency AC, and so travels along your skin, not through your organs. You may be startled into a heart attack or something, though! Don't try touching High Voltage DC, like in the back of TV sets -- that will kill you instantly. -- Gordon V. Cormack CS Dept, University of Waterloo, Canada N2L 3G1 gvcormack@waterloo { .CSNET or .CDN or .EDU } gvcormack@water { UUCP or BITNET }
prager@Data-IO.COM (David Prager) (03/19/88)
>startled into a heart attack or something, though! Don't try touching >High Voltage DC, like in the back of TV sets -- that will kill you >instantly. Instant Death. Think about it. Wanna bet? ------------------------------------------------------------------- David Prager (w)206-881-6444 (h)206-485-4397 FutureNet Corp 10524 Willows Rd. NE Redmond, WA. ...uw-beaver!entropy!dataio!prager 98073-9746 or whatever works.
al@cs.strath.ac.uk (Alan Lorimer) (03/21/88)
In article <5773@watdragon.waterloo.edu>, gvcormack@watdragon.waterloo.edu (Gordon V. Cormack) writes: > In article <334@eos.UUCP>, jbm@eos.UUCP (Jeffrey Mulligan) writes: > > From article <560001@hpcljws.HP.COM>, by jws@hpcljws.HP.COM (John Stafford): > > > I wouldn't quite claim it is safe to work at automobile voltage (12V) > > > levels. The second factor, current, comes into play here; cars may only > > > be 12 volts, but there are (especially when starting) quite a few amps > > > around. > > Give me a break! 12 volts is absolutely safe. Reminds me of when > people kept fiddling with my science fair project (a long time ago), > so I put up a large sign: > The 12V supply in a car is quite capable of delivering currents of the order of several hundred Amps. Ok, so what can happen? Well I heard of an accident happening to someone a few years ago, whereby the bracelet of his watch became welded accross the starter motor terminals. The current in the bracelet cause it to heat up (it became red hot in fact) leading to severe burns. When I heard this I thought that this must be a pretty unlikely type of accident, and that it would be a lot of trouble to arrange such a situation. Until it happend to me too..... I would agree that 12V is safe from the dangers of electric shock, but please be aware of the dangers of low impedance sources, and take care to remove any jewelry before starting work. -- UUCP: ...!seismo!mcvax!ukc!strath-cs!al DARPA: al%cs.strath.ac.uk@ucl-cs JANET: al@uk.ac.strath.cs
ralph@ecrcvax.UUCP (Ralph Hill) (03/23/88)
In article <888@stracs.cs.strath.ac.uk>, al@cs.strath.ac.uk (Alan Lorimer) writes: > The 12V supply in a car is quite capable of delivering currents of the > order of several hundred Amps. Ok, so what can happen? Well I heard > of an accident happening to someone a few years ago, whereby the > bracelet of his watch became welded accross the starter motor > terminals. > ...burns, etc.. > > I would agree that 12V is safe from the dangers of electric shock, > but please be aware of the dangers of low impedance sources, and take > care to remove any jewelry before starting work. > > UUCP: ...!seismo!mcvax!ukc!strath-cs!al DARPA: al%cs.strath.ac.uk@ucl-cs > JANET: al@uk.ac.strath.cs Watch the long tools too! You can easily damage tools or parts of the engine. The way to do this is to bring one end of the tool in contact with some part of the engine, and the other to the + terminal of the battery, or the heavy wire going to the starting motor (as was the case for the watch above). The way you avoid it, is to disconnect the - terminal of the battery. Having learned, I now disconnect the - terminal, and put an insulating cover over the terminal, before beginning any non-trivial under-hood work. My lesson: I managed to stretch a long feeler gauge from the + terminal to the cam shaft while setting the valve lash. Fortunately the cam shaft was a much better conductor than the feeler gauge, and there was good contact between the feeler gauge and the cam shaft and the cam shaft to its bearings, ... (i.e., no hot spots). The cam shaft, cam follower and bearings all lived. The feeler gauge made and exciting N-amp fuse! I consider my self very lucky. I spent a long time checking for bits of feeler gauge welded to the cam face, and had bad dreams of welding bits of tools to all sorts of things. The feeler gauge was borrowed. Fortunately the owner was glad to learn the lesson without risking his engine and thought it was a feeler gauge well spent. ralph hill P.S. the third party repair manual for my current car begins most under-hood repair sequences with "disconnect the battery negative terminal"
wtm@neoucom.UUCP (20 Bill Mayhew) (03/25/88)
Back when I was a hippie communist radical (are you listening NSA?) in undergrad school, I owed a very disreputable purple 1969 Chevy G-10 van. The van had a very large metal button in the center of the steering wheel for sounding the horn. The metal button was attached to the horn relay's coil, and pressing the button completed the circuit to ground. The fun was that if you were touching anything metal (or had on leather soled shoes), you got your brains shocked out when you let go of the button. The trick was that the metal button delivered a nasty inductive kick from the relay coil when the circuit was broken by releasing the button. It was a very graphic illustration of why supressor diodes are placed across relay coils. It was also a good illusration of poor design. It would have been relatively easy to design the button so that it was not electrically hot. I'd imagine that something similar was happening with the Volkswagen key switch. Probably an inductive jolt from the starter solenoid as the key was released. Anybody that has worked on a car knows that a starter solenoid is capable of sizable v=L di/dt. Also, up to 200-300 volts can appear across the primary side of the ignition coil, as the coil functions as a ringing choke resonant circuit when the points open up. That is why the "condenser" is across the points. The condenser's primary responsibility in not to limit RF emission, as you'd first guess. Of course, CDI electronic ignition changes the picture a bit. There is a good description of igniton systems in a 1939 book on IC engines by Walter Lichty. I also used to own a 1956 Caddie that had a Wonder Bar delco radio. The output used a pair of 12V6 beam power pentodes. They had a plate voltage of about 350 volts that was derived by a mechanical vibrator driven power supply. In a sense, it was a component audio system. The AM tuner was separate from the power amp / power supply. The amp also had an extra <unused> audio input. It was a very good AM receiver, which I still have stashed somewhere in my basement. As a matter of fact the delco radio saw some duty in the purple van. (Sufficiently old-farted?) --Bill
john@anasaz.UUCP (John Moore) (04/04/88)
In article <888@stracs.cs.strath.ac.uk> al@cs.strath.ac.uk (Alan Lorimer) writes: %In article <5773@watdragon.waterloo.edu>, gvcormack@watdragon.waterloo.edu (Gordon V. Cormack) writes: %> In article <334@eos.UUCP>, jbm@eos.UUCP (Jeffrey Mulligan) writes: %> > From article <560001@hpcljws.HP.COM>, by jws@hpcljws.HP.COM (John Stafford): %> > > I wouldn't quite claim it is safe to work at automobile voltage (12V) %> Give me a break! 12 volts is absolutely safe. Reminds me of when %> %I would agree that 12V is safe from the dangers of electric shock, Can you spell "Inductive Kickback"? This is generated when current through an inductor is interrupted. That's how ignition works, for example, and it generates thousands of volts from the twelve volt supply. Starter motors can also generate high voltage, with enough stored energy to KILL YOU! 12V automobile systems are not completely safe from electric shock!!! Take care. %UUCP: ...!seismo!mcvax!ukc!strath-cs!al DARPA: al%cs.strath.ac.uk@ucl-cs % JANET: al@uk.ac.strath.cs -- John Moore (NJ7E) hao!noao!mcdsun!nud!anasaz!john (602) 870-3330 (day or evening) The opinions expressed here are obviously not mine, so they must be someone else's.
krc@cs.purdue.EDU (Kenny Crudup) (04/07/88)
In article <827@anasaz.UUCP>, john@anasaz.UUCP (John Moore) writes: > Can you spell "Inductive Kickback"? > Starter motors can also generate high voltage, with enough > stored energy to KILL YOU! 12V automobile systems are not completely > safe from electric shock!!! Take care. > John Moore (NJ7E) Yeah, but it seems to me that when the key is released from the 'start' position to the 'on' or 'run' position, that the starter solenoid releases the winding from the rest of the auto electrical circuit. At least I hope so, considering the amount of computerization in modern cars. -- Kenny "_R_o_b_o_B_r_o_t_h_e_r" Crudup krc@arthur.cs.purdue.edu Purdue University CS Dept. W. Lafayette, IN 47907 inews: Error code 257: .signature +1 317 494 7842 joke too stupid: Not included
wtm@neoucom.UUCP (Bill Mayhew) (04/09/88)
The inductive kick delivered by the starter solenoid is likely to be worst when the solenoid disengages. This is due to the effect of V=L dI/dt. The dI/dt is a pretty big number as I tends to go from something like 10 amps for a starter solenoid to zero in a couple of microseconds. The result is that V = some big negative number (like 250 volts, for instance). If one's hand is on the keyswitch, which just happens to have the lock barrel be hot (some do), you just might get a friendly jolt! Maybe that is why VW keys are platic-coated around the top, huh?? As I said previously, the metal horn button on my Chevy G10 van used to shock the bajeezus out of me due to the kick from the horn realy, and the realy coil was less than an amp! (The horn itself was about 15 amps). Modern fancy radios and ECM (thats Electronic Control Module, not Electronic Counter Measures!!) electronics in cars are very heavily bypassed with protective diodes and multisection pi filters on the vcc inputs. I currently have a 1983 AMC Alliance that has a Bendix TBI fuel injection system (the CA models have Bosch multiport EFI). Just about everything in the car is equipped with supressor diodes. I was pertty impressed that they were pretty careful about EMI/EMC design. $5 question: why is the Alliance turnsignal indicator so ridiculous? It is a one lamp design like the VW bug, but unlike the Bug, AMC used a USA 4-wire turnsignal design -- which means they had to use two diodes to combine L and R into a single lamp! Seems like it would have been easier for them to just use two bulbs and be done with it. A lamp must be cheaper than a diode, even these days. --Bill