Most designers forget Murphy's law. For instance, the original design has a live power 12 volt dc into the voltage regulator. Contact points can stick and draw the battery down but I have seen a generator short out causing the contacts to weld together and the wiring to burn.
From what I've read on this site over the years, the dreaded ammeter fire seems to be the most talked about. Properly done, an ammeter is as safe as any other gauge in the dash, but there must be plenty of them out there that are not. I've never had an issue with an ammeter, but I'm very careful to properly size wiring and make sure the connections are well done. And I always try to use an old "made in the USA" ammeter. On those vehicles that have a low-amperage capacity ammeter too small for upgraded charging systems, I run a secondary external shunt. The ammeter no longer reads correctly, but the needle deflection is all I am really concerned about anyway.
One thing I try to remember but sometimes forget is disconnect power source (Battery) when working on electrical. Pretty easy way to see sparks fly.
Please don't take this the wrong way, but I don't understand this at all. Maybe it is "House" vs "Automotive" electricity but I've never seen a "DANGER High Amperage" warning sign. If Volts don't move how come there are DANGER HIGH VOLTAGE signs? Bob
House = alternating current i.e. back and forth along the wire. Car = direct current i.e. flows just one way down the wire. Yes an over simplification, their similar but different. An alternator makes alternating current until it's rectified (converted) by the diodes in the alternator case to direct current. Sorry about adding to the confusion. -Dave
Those signs warn of the possible potential of "high voltages" actually jumping to a ground, without even touching anything, but getting too close. ... like the high voltage in a car coil can jump/arc to a ground, through the air if close enough, and poor insulation.
Car electricity will grab your attention too. Once accidently touched the back of the alternator with a metal watch band while setting the timing on a slant six. The watch landed about six feet away with a hole burned through the band and I got a neat little scar on my wrist. I've learned a bit since age 15 and take all that silly stuff off before getting under the hood now. -Dave
Years ago a neurologist came into the shop and stated that contact with a car battery and your wedding ring with cause the ring finger to fall off. Ring has been on for 38 years and shows no easy signs of coming off. Bob
Gold is an excellent conductor of electricity. I have shorted a wrench across battery posts to a wedding band and almost lost that finger. Instantly, It almost fried the finger to the bone.
12v in contact with your skin won't hurt you. 12v shorted out by a piece of metal which is in contact with your skin, will give you a nasty burn. Be careful. Please excuse the spelling. I posted this with my phone.
Electricity is electricity, doesn't matter where it is, it all works the same. Now, voltage and current can be different, but the underlying properties are all the same. Using the water analogy, voltage is 'pressure'. As an example, let's say you have a dirty, grease-encrusted rolling frame in you driveway and you want to clean it off but all you can use is water. So, you drag your garden hose out there and turn it on. No nozzle on the hose, just the open end; how much stuff do you think you'll knock off? Now connect that same hose to a pressure washer. You still have the same volume of water (or if it were electricity, current or 'Amps'), but at vastly increased pressure. No problem cleaning that chassis now, and you have enough pressure to seriously injure somebody if applied directly to their body parts. You've raised the pressure (voltage), now that same volume (amperage) can do work. As to why you see 'High Voltage' signs, that has to do with the human body's 'natural' resistance. This can vary widely; both from person to person, but also due to environmental conditions. Generally speaking, anything under 25 volts will just make you uncomfortable at most; most people won't be able to even feel it. 25 to 50 volts, some people will feel this, some won't, if you do feel it it will be very unpleasant. Above 50 volts, any shock can kill but the higher the voltage, the more likely it will be fatal. Above 300 volts, encounters can easily be fatal or cause permanent physical damage. As to 'High Voltage' signs, these usually identify voltages above 600 volts, usually in the kilovolt + range. Once you get into the kilovolt arena, if you're lucky it will kill you; survivors are almost always terribly burned. In the 50 years I've been around the trade, I can only recall one guy who survived a multi-kilovolt shock incident, and he lost both arms at the shoulders besides being terribly disfigured.... And the amount of harmful current is small; up to about 90 milliamps (or only .09 amp), it can be bad but not fatal. 100 to 200 Ma (.1 to .2 amps), it's nearly always fatal due to heart damage. Above .2 amp, heart damage usually doesn't occur (but will required restarting the heart) but tissue burning does. But for any current to get 'into' your body, you must have enough voltage to overcome your body's resistance. You could walk up to a 10 volt bar with 10,000 amps running through it and touch it with no harm. Touch a 10,000 volt wire with 1 amp in it, and it will blow your arm off and kill you dead....
^^^^^^^^^^^^^^^^ I'll reread that a few times and try to understand it. Just last month I was power washing some steps and the high pressure line blew a hole in the center of it. If that high pressure water was electricity all the drenched shrubs would be on fire, correct? Bob
If a solder joint fails that wire/connector is over 450 degrees. Automotive has another element that commercial or residential seldom has, vibration. In some instances even wire movement. No solder related fails in my experience, well not yet at least. I'll give it another 45 years...
There seem to be solder failures on printed circuit boards in modern cars. The wires are all crimped.... Please excuse the spelling. I posted this with my phone.
Hey, I got the matching scar on me wrist, only difference was I was 60 when I got mine, not 15! Barley got against the back of the alternator, literally welded the links of the watchband together. Didn't take long to figure out welding watch band links together is NOT a good idea while your wearing it.
No Bob and that's probably why the water analogy doesn't work so well for you. The water isn't like electricity ( moving electrons) at all, you can't spray electricity out the end of a wire all over everything. Unlike water, electricity needs a path to move and to move along a clear path without obstructions will keep it safe. That one of its laws that electricity follows. This is why a blown fuse will stop the flow, it breaks that path. However voltage and amps are very similar to pressure and volume. You can physically see pressure and what varying it up and down will do. You can physically see volume and what varying it up and down will do. That is Unlike voltage and amps that can't be seen, only measured with a meter. You can only see the effects of too much amperage by assessing damage after the fact. Generally it's a blown fuse if the person followed his part of the deal.
Crimp connections are great if they're done right and the wire is properly strain relieved. Any crimp connection I do under the hood gets a piece of shrink sleeve over the barrel for added protection.
I always install a total kill switch as close to the battery as possible. That way I can sleep at night!
If they are done right And If the wire is properly strain relieved. The first "if" requires the very intimate knowledge of what exactly "right" means for crimped connections. The second "if" requires the same type of knowledge for exactly what "properly" is to strain relief. I'll also add that not all crimp connectors are created equal, there's some real junk out there, No matter what you do or what precautions you take or how right or properly crimp connections are done - with junk connectors all you have is junk in the end.
Watch what kind of fuses you're buying - I know it's tough to find quality stuff now but most of the Chinese fuses are nowhere near what they are marked as. If you need a relay that's on all the time, look into a continuous duty type - I got the ones I used for the fuel and water pumps on my avatar altered at Surplus Center - I think they're called B-2 or something like that. On the crimp connection issue, buy a real ratchet style crimper - not a pair of pliers made out of 10 ga. When I built my plane I found that even though they are expensive, aircraft circuit breakers are the only way to go - they may pop out and cut off some circuit, but it gives you time to resolve the issue and reset easily once the fix is done. Also, for real critical stuff, the teflon insulated aircraft wire with the silver plated strands is the best stuff out there, but it is expensive. Then again, it's hard to pull over to the side of the road at 10,000 ft.
As newly married guy not used to wearing a wedding band I touched the ring to the battery cable at the starter on a 55 V8 once. Don't, I say don't stick that burning finger in your mouth. Worked for a guy in a shop a few years back. He and I didn't see eye to eye on the rubber boot on the back,of an alternator. I wore him out for not making them available for me to use. Well he was wrenching on the alternator bracket and hit the bare stud of the alternator with a wrench. The 10 ga. Wire from alt. To starter smoked in an instant. I wore him out again but this time I had all the boots I wanted the next day. Cost us a day rewire on the engine harness.
When I was 17 I owned a 56 Olds 98 convertible. It had power everything and the bundle of wires going to and from the fuse panel was over an inch thick. It shorted one day and burned up all the under hood wiring. Turned out to be the feed wire for the fuse panel rubbed on the sharp edges of the firewall hole...no grommet! Couldn't see it 'till I pulled the engine to put in a cherry-pie 50 ford when I tired of fixing wiring and buying regulators and generators for the olds... Now, I'm very careful about clamping wiring and always using a NEW rubber grommet in each hole.
Kinda what Jim said - around the headers and such - we zip or tie things/wires down close - but in the heat -sorry - of the moment we hit the gas and shift some gears - the motor moves maybe and pulls loose our tight secured wires - got to leave a little slack for those hard shifts - now my story... shortly after a rebuild of my trucks 390 motor - and driving it around some - I pull up to the buddies at their shop - guess it dieseled enough - to start a carb fire - the carb was pretty fresh I thought - I quickly started looking for a rag towel or something while one of the guys called the fire dept - had it out as the fire dept got there but they still dosed it with the foam stuff....some much for the good looking engine.....still have the truck and she still purrrrrs to this day....just not as pretty.....
ALL the classics I look after have a KNOB SWITCH between the neg. side of the battery and the ground strap. At $5, TOO CHEAP not to use!!! Combined with a cable lock on the hood, I have a po'boy anti-theft, my ride can't be hot-wired. TOO EASY to cut the power during electrical tasks or troubleshooting... OR the first sign of smoke on the road. Old wiring or new, it just doesn't get any easier or cheaper than that to PROTECT your ride!!!
I always install a cut off switch that is accessable from the drivers seat and cut off when the car is not in use. Also install volt gauge not amp gauge. Been lucky and not had any issues over the past 20 years.
The last electrical fire I had was caused by a failed AMP Meter.my guess is that the '65 amp alternator coupled with the amp draw of all the components in use put too much strain on the 30 amp meter. I cured the problem when I rewired and replaced the amp meter with a voltmeter.
I think about electrical stuff when I'm depressed, it really helps since nothing makes me feel more depressed than trying to understand electricity and its use in the automobile. All the other problems seam a lot better now, plus the '12 T is running after a 17 year nap, Hershey is next week, life is good. Think I'll knock some dents out of a fender or sand something. Bob
Interesting how some folks don't have any trouble understanding electricity and it's use in cars...but most folks do. Maybe it's because I grew up in a family of engineers, or something? We always were playing with electric and electronic stuff, since I can remember. The neat thing about electricity is that it seems to always follow the "laws". It looks like it's doing strange and mysterious stuff, but that's just because we don't think about things from the point of view of electricity. If we could, it would all make sense.
When I'm driving my hot rod, an electrical fire is the furthest thing from my mind; much more pressing concerns: like all the idiot drivers we are blessed with now-a-days.
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