Car battery -- charging questions

[KenJackson]

I spent 6 years in the US Navy, as an electrical operator, and to my recollection, I NEVER disconnected the generators, from the grid.
This just sounds counterintuitive to me.

Me to. But I must share my vaguely related experience.

In the late 70's I was driving a long way through the night when I noticed my car lights were getting dim. Out of curiosity, I pulled over and measured the voltage across my battery. Zero volts! I didn't think that was possible, especially since the engine was still running. So I pulled one terminal off the battery. The engine sped up. The dead, defective battery had become a load on the alternator.

I drove the remaining hundred miles at night with the battery disconnected. When I came to a stop light or stop sign I would turn the lights off before I came to a stop. (I was already rigged for reduced electrical, so nothing else was on.) Then when I started moving again, I would wait until I had a little speed before turning the lights back on. When the lights came on the car immediately stalled, but momentum kept the car moving so it jumped itself. Ugh Boom and off I went. What an educational experience!

 

[jim hardy]

When the lights came on the car immediately stalled, but momentum kept the car moving so it jumped itself. Ugh Boom and off I went. What an educational experience!

Sounds more like behavior of a DC generator than an alternator. ...

Was that in the days before alternators, perhaps an early 1960's vehicle ?

 

[KenJackson]

Sounds more like behavior of a DC generator than an alternator. ...

Was that in the days before alternators, perhaps an early 1960's vehicle ?

No. It was a '74 Dodge (Mitsubishi) Colt.
But it would have been the same for either alternator or DC generator. It either case, turning on the lights added a huge load that caused the voltage to instantaneously drop enough to prevent the ignition system from generating spark for a few until it recovered.

OK, maybe saying "it jumped itself" was a little dramatic, but the car did loose all torque for a couple seconds and came back with a lurch.

 

[jim hardy]

No. It was a '74 Dodge (Mitsubishi) Colt.
But it would have been the same for either alternator or DC generator. It either case, turning on the lights added a huge load that caused the voltage to instantaneously drop enough to prevent the ignition system from generating spark for a few until it recovered.

OK, maybe saying "it jumped itself" was a little dramatic, but the car did loose all torque for a couple seconds and came back with a lurch.

Got it. Electronic ignition likely has a minimum voltage at which it'll still go.
Had voltage made it all the way to zero the alternator should not have re-bootstrapped. But from just a few volts it will..
Incandescent lamps when first switched on draw ~10X full current , though only briefly while the filament warms, and that could swamp a 30 amp alternator as you observed.

I was thinking of a total voltage collapse. An old fashioned generator would then disconnect itself and re-boostrap up on residual magnetism.
If you have a car with old fashioned brush generator, mechanical fuel pump, and manual not automatic transmission,
you can take the battery completely out and start it with a push or a roll down a hill.

 

[johnnyrev]

Wow--an automotive thread! I've been waiting for one of these! Most of my exp is in the automotive/heavy equip field.

Still reading through, will get back...

I'd want a 150 amp alternator to leave me 57 for charging the battery

I need a 150 amp alternator to charge up the juice I burned through in my life lol

[EDIT/RETURN] OK, I'm back. This one was fun! "Old" Jim, you reminded me of some of the things I did, like re-soldering the commutator on my car to go on a date, using a paper bag to set the distance between the coil and the flywheel on the lawnmowers I used to fix up and re-sell during tough times. Burning EVERY load on my car when the generator on my old MG was overcharging... Good times. I still tell the joke British beer is warm because Lucas built the fridge...

 

[Guineafowl]

Wow--an automotive thread! I've been waiting for one of these! Most of my exp is in the automotive/heavy equip field.

Still reading through, will get back...
I need a 150 amp alternator to charge up the juice I burned through in my life lol

[EDIT/RETURN] OK, I'm back. This one was fun! "Old" Jim, you reminded me of some of the things I did, like re-soldering the commutator on my car to go on a date, using a paper bag to set the distance between the coil and the flywheel on the lawnmowers I used to fix up and re-sell during tough times. Burning EVERY load on my car when the generator on my old MG was overcharging... Good times. I still tell the joke British beer is warm because Lucas built the fridge...

Careful now! British ale enthusiast and brewer here. It's served at cellar temperature, 12-14 degC, so it's cool but not so cold you can't taste the complex flavours.

 

[Tom.G]

Wow--an automotive thread!

And filing the ignition points with a nail file (destroys the nail file) and setting the gap with a matchbook cover. Double thickness of matchbook cover for setting the plug gap.

 

[johnnyrev]

Emery bits bad for electrical, Tom.G but it is a lawn mower after all lol. And just joking, Guineafowl. But seriously, "cellar" means different temps to different regions. When I was a kid we had to take measures to prevent permafrost from jacking the whole house out of the ground.

A good meter reading on an active charging system should be between 13.8 and 14.2 volts. Too much more and it will boil the water out of the electrolyte. The in-dash volt meter or ammeter isn't accurate enough. You may expect to lose about .1V or so per connection in the main cables on a good-running vehicle that has been in operation, which accounts for some of the variance. It really affects you in extreme heat or cold.

On an o-scope an alternator will produce a nice "bubbly" waved DC signal that doesn't interfere too badly with other electronics on the particular vehicle it is installed on. Now the field ground is usually controlled by the car's computer, not by an external or even an internal regulator as much anymore.

The alternator can cause issues when one of the diodes burns out, because it introduces a new frequency into the vehicle's electrical system. Looks like an oddly shaped square wave. This will mix with the engine control system frequency and any specific sensor frequencies, like crank sensor, cam sensor, speedo sensor, etc, causing all kinds of hard to diagnose problems. This new frequency will vary with engine speed, which is often why the problems are more noticeable at idle and mid-range vehicle speeds.

Anybody familiar with dial tones (hams, etc) know that all the dial tones on a standard phone key pad are made with just two audio tones. Imagine what mixing a new frequency in with the other inputs to your car's computer would do when one or two of your diodes goes out. Next add a spark plug wire that fires intermittently, that Alpine stereo the kid wired in by running speaker wire from the inside of the car to where he wrapped bare wire around the battery terminal, the alignment tech running the diesel tank dry on his test run and the customer coming back shouting "You changed my oil and now my radio won't work," and, well, welcome to my world.

//several edits and redactions, I just wrote too much stuff//