[nolife]

He is talking about when things with coils are turned off, like relays and solenoids etc.. Inductors generate current of the opposite polarity when they are turned off, most larger things already have a diode across the coil to absorb this. I don't know where the +25v figure came from because the voltage an inductor gives off can not be higher than the voltage that charged it up (+12v). The real problem is the reverse polity of the current, not the voltage it is at. This "problem" is not going to be any different with or without a battery in the car. The battery is too far away electrically to be effective at filtering this out.

Another note since I jumped back in this...

A voltage regulator regulates a positive lead +12v higher than the ground lead. Without a battery, that ground would now be like a "floating ground". Meaning the ground could drift to +5 volts and the positive would now be +17 volts. It may fluctuate rapidly as well through leakage in the alternator. When measured across the chassis and a positive line, you would still read +12v and everything would work. Problem may be if decide to hook a battery back up during that time. You could probably swap a battery out while the car is running 19 out of 20 times without a problem.

[trueblue01]

Personal experience from my "formative" years. If you start your 1979 f-150 with a charged battery, then remove said battery to put in a "dead" battery so you can fast charge it because you own neither a charger or jumper cables, before the dead battery can be put in, 5 minutes tops, your truck will shut off. When you reinstall the good battery and try to start your truck, it won't. You now get to spend the day identifying all of the fusible links in the wiring harness that did their jobs and stopped you from destroying the entire electrical harness. True story.

[1slo5.0]

Originally Posted by ryans88gt sounds like a really dumb idea. Go get a $15 battery charger at Wal-Mart. If you can't afford that in order to be safe, then sell your car and buy a honda.

+1

Originally Posted by mdvaldosta Don't try to charge a dead battery with an alternator, puts alot of stress on it (the alternator). Alts aren't meant to to charge, only maintain.

and +1

[1slo5.0]

Originally Posted by HACKGT350 it doesnt put any stress on the alt. it will put out the same volts and amps if it was charged already its just bad for the battery

Alternators are not designed to charge, they are designed to maintain a charge.

[nolife]

Originally Posted by trueblue01 Personal experience from my "formative" years.

Okay, based on the statistics I pulled out of my ass, the next 19 times you do it, you'll be fine

[neverfastenough1]

I swear, whenever nolife and fogged get involved in threads, I feel stupid. Half the time I am like what the heck did he say? Makes me wish I went to college. Not an insult by any means. I would have to say I wouldn't do that with a computer controlled car either. Done it with carbed cars, but probably wasn't the smartest thing to do then either, but didn't hurt anything.

[fogged306]

Originally Posted by nolife He is talking about when things with coils are turned off, like relays and solenoids etc.. Inductors generate current of the opposite polarity when they are turned off, most larger things already have a diode across the coil to absorb this. I don't know where the +25v figure came from because the voltage an inductor gives off can not be higher than the voltage that charged it up (+12v). The real problem is the reverse polity of the current, not the voltage it is at. This "problem" is not going to be any different with or without a battery in the car. The battery is too far away electrically to be effective at filtering this out. Another note since I jumped back in this... A voltage regulator regulates a positive lead +12v higher than the ground lead. Without a battery, that ground would now be like a "floating ground". Meaning the ground could drift to +5 volts and the positive would now be +17 volts. It may fluctuate rapidly as well through leakage in the alternator. When measured across the chassis and a positive line, you would still read +12v and everything would work. Problem may be if decide to hook a battery back up during that time. You could probably swap a battery out while the car is running 19 out of 20 times without a problem.

Where did you find that the ground would be a floating ground w/o a battery? I am just not seeing how that would be possible, considering the rectifier provides the pos and neg with or without a battery. From what I understand, A floating ground doesn't fluctuate in voltage, rather provide a ground within a specific circuit that is seperate from the common ground, basically to isolate the specific circuit. Honestly, I'm somewhat rusty at the technical stuff, so if you have a link to that I'd love to read up on it, I could be wrong about that but, thats what I remember.

... and neverfastenough, Thanks for the compliment, but I'm no wiz at this stuff really, just a 2 yr degree... long time ago. You should see the forum I'm on about ecomodding, there are electrical engineers on that site that make me look silly every time I open my mouth... or should I say, use my keyboard.

[neverfastenough1]

Originally Posted by fogged306 ... and neverfastenough, You should see the forum I'm on about ecomodding

Enough already, I admitted I am dumb, you don't have to through stuff like "ecomodding" at me. j/k, I know all about that stuff. Well at least how to spell it and that I never freaking (almost cursed, but refrained) heard of it before. Glad I wasn't the only one that thought that ground theory was wrong.

[nolife]

I was thinking more along the lines of a ground loop http://en.wikipedia.org/wiki/Ground_loop_(electricity). Without a battery, what is the reference of "zero" volts? Since there is nothing to ensure the negative of the battery (which is disconnected) at the same reference as the negative side of the alternator (or chassis ground), it can drift. The internal regulator simply adjusts to make a 12v difference between the two sides. If your "ground" was really at +10 volts through leakage, your positive would now be at +22v. The resulting output of the alternator would still be +12v as it is designed to do. I'm not going to try it (based on the story above with the F150) but I think you could test this. Run your car with negative battery terminal disconnected. See if there is ever a voltage difference or a changing voltage between the chassis ground and the negative terminal. There are many different type of regulators though. My experience with AC/DC generators is with 3 phase ungrounded systems many moons ago so my thinking may be wrong.

[nolife]

Originally Posted by neverfastenough1 I swear, whenever nolife and fogged get involved in threads, I feel stupid. Half the time I am like what the heck did he say? Makes me wish I went to college. Not an insult by any means. I would have to say I wouldn't do that with a computer controlled car either. Done it with carbed cars, but probably wasn't the smartest thing to do then either, but didn't hurt anything.

With cars, sometimes theory and ideas are great but that is absolutely no match for what everyone else has in actual real world experience.

[fogged306]

Ok now I see what you're getting at. Actually a simple point really, and quite possibly a valid one. That would explain what happened in the F-150. The rectifiers wouldn't have any effect on how high the voltage could go, it would just give a DC voltage. The only thing that I can think of is that the actual voltage regulator circuit itself operates at 12vDC. I don't know if the reference to ground went up to, say 10v, if that regualtor would still function or not, and if not, I believe that they go into open loop as default which would bring the voltage back down into the normal operating range with a 0v ground +/- a small tolerance, I'm sure, before it closed again. Good point though, I actually may try to test that out at work when I get some time.

[neverfastenough1]

Originally Posted by nolife With cars, sometimes theory and ideas are great but that is absolutely no match for what everyone else has in actual real world experience.

Agreed