Car battery -- charging questions

[OmCheeto]

When the generator quits you're relying on the battery of course.
...
Tinkering is good. Some of us learn our basics that way.

Nowadays cars are utterly dependent on alternator to go beyond a very few miles.

1.12 miles, to be precise, if you owned a 1994 Chrysler LeBaron convertible, with a V6. (I love Google Earth!)

1. Left parking spot at work. Drove 0.16 miles, heard some unfamiliar noises, along with some flashy dash board lights. Pulled over, turned off the car, and saw something rolling down the hill. Picked it up, and could not identify it. Popped the hood, and noted that the serpentine belt was a bit loose, as in, lying in a heap. Decided that the thingy that had fallen off was the some kind of spring loaded tension device. Determined that there was no way to maintain tension on the serpentine belt, even though I had a roll of duct tape in the car.
2. Started car, and drove 0.55 miles to the nearest convenience store, as I needed supplies, as this was going to be a LONG day. Turned off engine, got some bottled water, and the engine would not start. Being that I was somewhat of an expert in battery temperament, I let it sit for 15 minutes. The car then started right up.
3. Drove the car 0.41 miles back to my parking spot. Turned off the car. Just for kicks, I tried starting it. Barely a click.
4. Came back the next day, with all manner of alternative energy supplies. Successfully made the 11 mile trip home safely, and fixed that darned problem.

If yours quits, shut off everything especially air conditioner, roll down windows and limp home.

old jim

Old cars(and boats) make for some fun adventure stories.

ps. Good thing that whole story started on a Friday afternoon, and the sun was out all day Saturday.

 

[jim hardy]

...

Successfully made the 11 mile trip home safely, and fixed that darned problem.

11 miles ? Didn't overheat ? Probably that was the 3.0Liter engine? Its water pump is driven by timing belt not serpentine .

Old cars(and boats) make for some fun adventure stories.

I'll second that. It's what we learn by those (mis)adventures that so enriches our life.

 

[OmCheeto]

...

11 miles ? Didn't overheat ? Probably that was the 3.0Liter engine? Its water pump is driven by timing belt not serpentine .

Yes. I was most fortunate.
But don't get me started on "let's put the thing that goes out the most, in the most inaccessible spot. That'll get Om and Old Jim to buy new cars..."
I chucked my 2nd to last car, just because it's water pump was inside the stinkin' engine.
Just checked my new(ish) '09 vehicle. (Yes, I eventually gave up, on my '80s & '90s POS*s...)
The water pump is external.

I'll second that. It's what we learn by those (mis)adventures that so enriches our life.

As they say, what doesn't kill you...

* POS:

 

[Guineafowl]

Sorry to (slightly) hijack this thread, but does anyone have a comment about jump starting modern cars? I've had advice that ECUs and other units that talk over the CANBUS can be fatally damaged by jump starting. I was advised to 'be careful', but without an explanation of exactly how. Apparently the acceptor car's alternator can produce a voltage surge once started that feeds into the donor car's electronics and buggers them.

I would have thought that A) The acceptor car's alternator would be regulated not to do this, and B) The batteries linked in parallel would buffer any surges effectively.

 

[jim hardy]

I would have thought that A) The acceptor car's alternator would be regulated not to do this, and B) The batteries linked in parallel would buffer any surges effectively.

There are two dangers that i know of

one was mentioned earlier in the thread,
when the strong donor battery is connected to the weak acceptor battery only a small current should flow - enough to raise the weak battery to 12.6 volts.
The trouble is, if the cables get hooked backward the strong battery does its best to reverse the polarity of the acceptor electrical system
which applies -12 where +12 belongs
In datasheets for automotive IC's you'll see "reverse polarity protection" mentioned. Manufacturers learned about reverse jumpstarts the hard way.
And about under-the-hood temperatures.

The other is , since garages get a lot of calls in dead of winter when the starter is asked to crank an engine with oil that's thick as molasses,
it used to be common to hook two batteries in series and jump-start with 24 volts which makes the starter really go.
Hence the 40 volt input voltage tolerance on that automotive IC above.
Hint - don't have any lights on when receiving a 24V jumpstart.

But I think the practice is very rare anymore.

 

[donpacino]

Sorry to (slightly) hijack this thread, but does anyone have a comment about jump starting modern cars? I've had advice that ECUs and other units that talk over the CANBUS can be fatally damaged by jump starting. I was advised to 'be careful', but without an explanation of exactly how. Apparently the acceptor car's alternator can produce a voltage surge once started that feeds into the donor car's electronics and buggers them.

If they designed the electronics correctly, the canbus should be galvanicly isolated (ideally optically) from the power bus. This means that no voltage surge should damage other devices on the communication buses. This doesn't necessarily protect the device seeing the voltage surge Like jim said it is common for automotive parts to be rated for 40V or more. They will also have surge ratings, and should be designed to handle jump starting the battery.

 

[OmCheeto]

...
Hint - don't have any lights on when receiving a 24V jumpstart.
...

Since the OP's question has been answered, and we now are apparently going off on car electrical tangents, I thought I should share one more story, as it involves "headlights" as a voltmeter, and crappy battery connections.

About 25 years ago, my friend called me, and asked me for some help.
At the time, he lived about 30 miles away, but at the moment, was only 1/2 mile from my house.
So I drove over, and he said that there was something wrong with his car, which at the time was a 1965 Dodge Dart. (He now drives a freakin' Ferrari 308. I hate him.)
Anyways, he said his girlfriend had just left, and he had replaced the starter in his car 3 TIMES, but the car still wouldn't start.
Which somewhat reminded me of 10 years earlier, when I replaced my carburetor 3 times in one day, only to have the clerk give me the stink eye when I asked for a fourth, as all of his carburetors were defective. But that's another story.
So anyways, I had my friend turn on his headlights.
They were quite bright, so I knew the battery was charged.
Then with the lights on, I asked him to start the car.
The lights went out.
I told him to stop, turn off his lights, and give me his lug wrench.
He was somewhat perplexed, as changing his tire didn't seem to be the right option for fixing a "starter" problem.
Anyways, I rapped the top of both of his battery connectors, and said "try now".
The car started.

For the next 5 years, he sent all of his girlfriends to my house, as I was apparently some type of automotive electrical genius.

 

[Tom.G]

RE Post #64

but does anyone have a comment about jump starting modern cars?

RE Post #48

Even the electronic voltage regulation is slow in response to a 'Load Dump' event. Don't ever, ever, ever disconnect the battery while the alternator is running.

I haven't investigated these approaches in detail but they seem to fit the requirements.
1) Once the disabled car is running, shut off the engine of the rescue car before disconnecting the jumper cables.
That way you don't risk a 'Load Dump' event from the rescue car alternator.

2) An even safer approach would be shut off both engines before disconnecting the jumper cables. Obviously this would have to be after the disabled battery had gained enough charge to operate the starter.

P.S. A few months ago a neighbor didn't do something 'right' when jumping a girlfriends car. His repair bill was just over US$3000.

 

[arydberg]

I believe Ford has a 130 amp alternator in some of their vehicles.

Sometimes these are for Police cars.

 

[Guineafowl]

Sometimes these are for Police cars.

Our Land Rover has a 150 A one as standard. Probably to cope with the extra load of the PTC element in the heater matrix, and the beefier battery in a diesel car.

 

[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//