Charging Battery with Alternator - Warning

[Mattax]

We've discussed this here more than a few times. Usually about how easy it can be to cook the battery or overloading the charge wiring. Here's another reason. "Any attempt to charge a low battery by the alternator will result in stator windings burning out"

ebay item # 222689173585 This is an old reman by The Remanufactured Motor parts company. Box says 1973.
p/n is RO 291167 but haven't found a cross ref yet to 'rating' or Chrysler number.

 

[67Dart273]

Yup, a failing in general design WHICH CONTINUES WITH AT LEAST SOME VEHICLES CURRENTLY

 

[Dana67Dart]

So if you leave your lights on in a parking lot and comeback to find a dead battery you are supposed to use someone else's alternator to recharge your battery and cook theirs?????

 

[Mattax]

So if you leave your lights on in a parking lot and comeback to find a dead battery you are supposed to use someone else's alternator to recharge your battery and cook theirs?????

Yes, well kind of.

My guess, based on the location of the tag and the first sentance is they were most concerned with someone who had really run the battery way down.
A few hours in the parking lot is bad, cause its too low to turn over the engine, but maybe not as the worst cases.
Not that I would have ever done such a thing.

OK. So I did, and we had no charger even back at our base and that was a good 20 minute drive away. After getting the jump start, I had to baby the throttle to keep the charge rate down. I coasted where ever possible in neutral, kept in in 3rd and lowest rpms as possible. It would take hardly any effort for the charge rate to go over 20 amps. Turning the lights on helped keep some load off the charge circuit as long as I could keep the rpms down. But it also meant more load on the stator. So I wasn't helping the alternator by doing that. However the battery and the charge wires were my big concern, and for good reason.

It may be entirely coincidental that a year later that alternator gave out. It happens that today I was checking through my stack of alternators to see what was wrong with them. I assumed the one mentioned above had a bad diode. It turns out one of the stator leads showed an open winding. Hmmm.

Maybe just a cheap rewinding or replacement stator but maybe not the whole story.

That's how I stumbled across that e-bay ad. I was looking for photos of 37 to 60 amp squarebacks. The parts book shows 65 amp units had a different housing and I wanted to verify which one mine is if I could.

 

[67Dart273]

............Battery charger.......... The idea is heat and duty cycle. If you can "get a jump" and get going and a short trip home, you are likely OK, but I would not run it for hours to charge it up

When I bought my 70 V code, I didn't know that. The owner, a friend, had bought a new VeeDub camper van, and the dealer in Sacramento insisted on holding the Roadrunner for collateral. Some parking lot jock ran it clear down dead and left it that way ---left the 4X flashers on. FOR A MONTH. I flew up to get it, on a side note, my baggage on a PSA flight from San Diego to Sac was a small overnight bag, and a spare tire tied up in cardboard!! LOL

When we first jumped and started it up, the battery was so dead that the alternator would not "self excite." We had to let it run for a few minutes before it would "pick up" and charge.

Nevertheless, I jumped in and drove it hours and hours south.........to NAS Miramar. It was all downhill from there LOL

Before I owned it, when it was new. He and I had been to Lions, where he'd trophied in pure stock

Me about 71--73. I was an ET in the Navy at Miramar, ETR-2, I fixed GCA RADAR and TACAN. The reason there are no longer "dust trails" on the sides is that some young chick had a-holed the car down in National City, and "limelight and all" told the cop "I just didn't see him!!!" The girls were window shopping, I was stopped for a light in traffic

This poor old faded photo from a 35mm slide is either 73 or 74. By this time I had swapped a 340 into it, and THAT was a lot of fun!! You might notice it has "funny lookin" turn signals up above the bumper in the grille. That's because I had aircraft landing lights in the bumper. I got a ticket for them earlier in CA, had them mounted in the high beams Got caught in an infamous CA roadside emissions trap

Incidently, you hear some of us on here talking about damaged ammeters and bulkhead connectors. Both the original owner and I were amateur radio ops then as now (George still has his ORIGINAL callsign!!) and that car "ate" the bulkhead connector back then. I drilled it out and ran larger gauge wireing through there. Obviously before Al Gore invented the internet!!!

 

[Tooljunkie]

Alternators arent battery chargers.
Running lights on a dead battery just increases the load.
Fans of accessories off. And drive it like you always do.
But get it on charge as soon as possible.
A trickle charge is always better than a fast charge.

 

[Mattax]

I agree TJ, but there was no choice. Even with the lights on occasionally and rpms down the whole trip, the battery was super hot in 25 minutes or so and took hours to cool. Next morning it was cool and would take additional charging. It would have been much much much better to have had a charger running at 2 amps or less.

 

[Bodyperson]

Leave the jump vehicle hooked up as long as you can.

 

[Tooljunkie]

Have had to do it myself,but i dont make a habit of it.

Had a crew that would work with the truck radio playing,and run it dead constantly.
It was equipped with an isolator and a second battery for a winch.
So they would use it to boost.
Smoked alternator and burned up several isolators. Finally the cause came out in a discussion,put an end to misssd diagnosis and comebacks.

 

[James Camp]

Maybe i am missing something here, but what is the purpose of a voltage regulator, i thought once the battery was at full charge, and by driving 5 to 10 minutes the regulator steps down how fast the charge is according to the number of things like lights and wipers, if your alternator continued to charge at the same rate any time you started your car, if the regulator don't drop the voltage to the battery, it wouldn't matter if you had a weak battery or not,your battery would explode

 

[Mattax]

Maybe i am missing something here, but what is the purpose of a voltage regulator, i thought once the battery was at full charge, and by driving 5 to 10 minutes the regulator steps down how fast the charge is according to the number of things like lights and wipers, if your alternator continued to charge at the same rate any time you started your car, if the regulator don't drop the voltage to the battery, it wouldn't matter if you had a weak battery or not,your battery would explode

I'll give this a shot.
The regulator
tries to maintain the system at approximately 14 Volts.
it controls power going into the alternator's rotor. It's spinning electro-magnet. More current into the electromagnetic, the stronger the magnetic field.

The battery
draws current when recharging just like devices such as a lights or electric motors.
The voltage across the light or battery determines how much current it will draw.
For example, headlights at 14 volts will draw around 10 amps. If they are supplied power at 17 Volts, they might draw over 15 amps (in which case the circuit breaker will trip or the lights will burn out quick).
A battery is different because its draw varies with its charge state.
example 1:
A battery that has just started a car may initially draw 10 to 20 amps when supplied at 14 volts.
After a minute or so, it will draw 5 amps at the same 14 volts.
Within 5 minutes, it will be drawing less than an amp.
Continually subject to 14 Volts, eventually a wet cell car battery reaches an equilibrium where the chemical reaction essentially stops. It has a surface charge of around 13.2 volts, but really only has stored energy at 12.8 Volts. Lots of stored energy. Enough to turn the starter motor and then some.

example 2:
A battery that is fully discharged will draw more than 20 amps when supplied at 14 Volts.
The current must be limited if we don't want it drawing 40 amps.
Reducing the voltage is how its usually done.
Some chargers do this automatically, or we can do this manually by setting the charger to a lower rate.

When there is no charger available, we can take advantage of the limits of the alternator design to reduce current to the battery.
An alternator's capacity to produce power goes up with rpm.
If the alternator speed can be kept down, many alternators simply can not supply 40 plus amps at 14 Volts when the engine speed is under 1000 rpm.

 

[Tooljunkie]

It regulates voltage. Generally speaking, 14.2 to 14.6 volts. Thats all it does.
Low voltage battery discharges,high voltage and it damages battery and electrical systems. The alternator matches the demand.

 

[Mattax]

This is a moderately discharged battery hooked up to charger.

(1) Charger attached and dialed to bring voltage across battery to 14.2 Volts. Current draw was around 35 amps.

(2) As current did not drop after a couple of minutes, I manually turned the charger down to get 13.3 volts, 8-10 amps

(3)45 minutes later voltage has come up to 14.4 V, yet the charge rate is down to 5 amps.

When that battery charger was new it had a temperature probe to place in a battery cell. It would have automatically reduced the power if the acid started to get too warm.

 

[Mattax]

TJ makes some good points.
Power comes from either the battery or the alternator; whichever has the higher voltage.
The amount of power supplied equals the demand.

 

[Dave NEO]

they rarely get that dead to cause problems for charging system after you get jumped and started - if you are old enough, you know you've done it and seen it a thousand times with no probs..

 

[Dave NEO]

............Battery charger.......... The idea is heat and duty cycle. If you can "get a jump" and get going and a short trip home, you are likely OK, but I would not run it for hours to charge it up

When I bought my 70 V code, I didn't know that. The owner, a friend, had bought a new VeeDub camper van, and the dealer in Sacramento insisted on holding the Roadrunner for collateral. Some parking lot jock ran it clear down dead and left it that way ---left the 4X flashers on. FOR A MONTH. I flew up to get it, on a side note, my baggage on a PSA flight from San Diego to Sac was a small overnight bag, and a spare tire tied up in cardboard!! LOL

When we first jumped and started it up, the battery was so dead that the alternator would not "self excite." We had to let it run for a few minutes before it would "pick up" and charge.

Nevertheless, I jumped in and drove it hours and hours south.........to NAS Miramar. It was all downhill from there LOL

Before I owned it, when it was new. He and I had been to Lions, where he'd trophied in pure stock

View attachment 1715265732

Me about 71--73. I was an ET in the Navy at Miramar, ETR-2, I fixed GCA RADAR and TACAN. The reason there are no longer "dust trails" on the sides is that some young chick had a-holed the car down in National City, and "limelight and all" told the cop "I just didn't see him!!!" The girls were window shopping, I was stopped for a light in traffic

View attachment 1715265733

This poor old faded photo from a 35mm slide is either 73 or 74. By this time I had swapped a 340 into it, and THAT was a lot of fun!! You might notice it has "funny lookin" turn signals up above the bumper in the grille. That's because I had aircraft landing lights in the bumper. I got a ticket for them earlier in CA, had them mounted in the high beams Got caught in an infamous CA roadside emissions trap

View attachment 1715265734

Incidently, you hear some of us on here talking about damaged ammeters and bulkhead connectors. Both the original owner and I were amateur radio ops then as now (George still has his ORIGINAL callsign!!) and that car "ate" the bulkhead connector back then. I drilled it out and ran larger gauge wireing through there. Obviously before Al Gore invented the internet!!!

now was that because you ran a pretty good kicker behind that CB ----c'mon...tell the truth... lol. (yes I still have my call sign and skipshootin' pirate radio license!)

 

[Ricks70Duster340]

now was that because you ran a pretty good kicker behind that CB ----c'mon...tell the truth... lol. (yes I still have my call sign and skipshootin' pirate radio license!)

I had my ham license back in the 70's but had CB friends too. They used to call the amp a "footwarmer"! I had a small 2M rig in my car but never enjoyed it like I did my full system at home! Preferred CW anyway...

 

[Dave999]

you can make ths issue worse by adding in a 90 amp alternator and not updateing the wireing
flat battery and that beefy alternator not good...

same problem with the ammeter it gets hot the insulation on the studs where they pass through the gauge case melts and fireworks follow 36 amp 60 amp or a big modern one... if the battery is too flat

 

[Mattax]

It's really about controlling the charge rate, which is a function of battery size and charge state. Because none of these older systems regulate current to the battery.

The warning, and the point of this thread, is that something will get damaged. The only thing that varies is what will get damaged more.
If the alternator is running at or close to its maximum capacity for extended period of time, it will get damaged.
If the battery is drawing over 25 amps for extendentd period of time, connectors will get damaged. The ammeter connectors just being two of the several that will likely be damaged depending on the model.
If its wintertime in upper Michigan, the battery is probably frozen...and recharging a frozen battery will not end well.
If its in the middle of summer and a 'sealed' battery, a high charging rate could also do bad things to the battery.

When these cars got heavy duty 60 and 65 amp alternators, they also got matching heavy duty, higher capacity batteries.
I do not know the entire reasoning, but clearly in part the higher capacity battery uses up a smaller percentage of its stored power for any given operation.

 

[Dave999]

and the reason they all didn't get 65 amp alternator and HD battery will have been cost couple $ on every car made adds up to a whole lot

 

[Mattax]

True, but also a lot of unecessary weight.
It takes about 3 amps to keep a car running with points ignition.
Driving with the headlights on and wipers running was still well within the capacity of a standard alternator.

 

[Mattax]

It seems in retrospect that loads began to get underestimated as electric items got added and changed. A big one was the change in headlamps around '73, also having the parking lights on with the headlights, and then the addition of side markers. For emissions controls the run circuit sometimes got electric choke assist, idle stop solenoid, etc. All that little stuff added up.

That said, the current needs of a mid 70s A-body will be similar to those I measured on my '85 Grand Wagoneer. This is alternator output measured with a clamp meter.
Its pretty similar in terms of electrical equipment and lighting. Only notable difference is the self-energizing 12SI alternator.

That would still be within the capacity of a '34 amp' Chrysler alternator while driving down the road, or high idle.
But it could not do all those things and recharge the battery at slow idle.

Also, 27 amps through a single 1/4" wide blade connector - that's probably pushing the limits of what those connectors should be used for.
This is the advantage of splitting the alternator output wires before the bulkhead (1975-76 standard), or using spade (1963, 65) or ring terminals as on some of the optional heavy duty wiring.