Can the alternator run the car by itself?

[P.S.]

Several weeks ago, was on a nice 40 mile trip in the A when it was getting close to sunset. Had just pulled a real long hill and pulled over at the next opening to let traffic go by. After 6 or 7 cars went by, nobody coming, pulled out and was going again. Turned on the lights and was driving merrily away for a few minutes, then suddenly, the car just lost all it's "go" and went BANG!. Luckily, there was a wide spot to pull over (not many on this narrow, 2-lane winding road), so pulled off. Troubleshooting revealed that the 30 amp fuse installed on the typical starter-mount bracket was open. Installed a new fuse, and made it the rest of the way without incident.

Troubleshooting for a couple days afterwards revealed no wiring trouble or anything amiss. Besides having a 6 volt pos gnd alternator, the car has full halogens front and back. The lights draw around 22 amps total, then add the ignition system current draw, and you're getting even closer to that fuse's breaking point. The fuse was several years old, decided it just gave up out of age and stress.

Anyway, that isn't the purpose of this post. Here is the actual question-

When the fuse blew, the car was running at 45-50 MPH and the alternator was putting out enough amperage that the ammeter was still showing "charge". So, when the fuse blew, the only thing it did was disconnect the battery from the electrical system. The alternator was still putting out enough that it should have kept the car running, correct? Or, do these automotive alternators stop putting out current if they detect no battery?

I really don't know much about cars, I'm an electrical guy. So to me, this is really confusing. Can any of you car guys shed some light on this please?? Shouldn't the alternator be able to run the car without a battery?

[Sparky]

Yes, the alternator can run the car even if the battery is dead. However, if your fuse setup is like mine, if it blows it cuts off current getting to the ignition system so the engine will stop.

[P.S.]

Yes, but the ignition system is on the alternator side of the fuse. The fuse is in series between the battery and the rest of the car. The fuse blowing does not disconnect the alternator from the ignition system or the lights. That's what has me puzzled.

[Tom Wesenberg]

If the battery is dead the alternator may or may not have enough magnetism left to self excite.

[Sparky]

Originally Posted by P.S.

Yes, but the ignition system is on the alternator side of the fuse. The fuse is in series between the battery and the rest of the car. The fuse blowing does not disconnect the alternator from the ignition system or the lights. That's what has me puzzled.

Hmm, you're right. Maybe it's what Tom says above.

[Bill Goddard]

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P.S. and Tom W. Could it be that the total current draw wasn't leaving enough to charge the battery and it went too low to excite the alternator. Also - I think the bang was from the fuel dumped into the muffler that ignited. A member in my club blew a muffler seam when his stater mounted fuse bracket fell apart and shorted out intermitantly. I have some serious doubts about the starter mounted fuse idea because of these problems. When it blows it can cause real damage. Why not fuse the circuits individualy? Bill G

[Tom Wesenberg]

Bill,
I can't imagine that you were using more current than the alternator can produce.
If I was to install a fuse I think I'd just put one on the lights/horn terminal at the cutout. I don't like the idea of a fuse blowing while I'm in an intersection and causing me to loose spark.

[Willie Krash]

The alternator if one wire will use residual magnetism in the rotor pole pieces to turn the alternator on regardless of battery. I don't believe a 10si one wire alternator has secondary regulation. Without seeing a battery the alt will go high and more so the faster it spins. As some point the coil will shut down from the high voltage and as the car slows the voltage will drop and the coil will fire.....all that unburnt gas...Pow.
Check your brake light. May be blown. That's my take.
BTW the residual magnetism is very weak and this why after sitting all winter the alt may be slow to turn on. As the alt speed increase more lines of force are induced into the stator. Once the voltage rises the VR clamps down and basically goes into a regulated feedback loop.
What you saw on the amp gauge were the loads, not the battery.

[Tom Wesenberg]

Originally Posted by Willie Krash

The alternator if one wire will use residual magnetism in the rotor pole pieces to turn the alternator on regardless of battery. I don't believe a 10si one wire alternator has secondary regulation. Without seeing a battery the alt will go high and more so the faster it spins. As some point the coil will shut down from the high voltage and as the car slows the voltage will drop and the coil will fire.....all that unburnt gas...Pow.
Check your brake light. May be blown. That's my take.
BTW the residual magnetism is very weak and this why after sitting all winter the alt may be slow to turn on. As the alt speed increase more lines of force are induced into the stator. Once the voltage rises the VR clamps down and basically goes into a regulated feedback loop.
What you saw on the amp gauge were the loads, not the battery.

But on the Model A the amp guage is NOT placed between the alternator (generator) and load, and only shows what goes into the battery or out of the battery.

[P.S.]

Thanks for all the input, guys!

Yes, the POW! was from unburned fuel/air in the hot muffler. That's a given. If you're driving your A at 45-50 MPH and just shut the key off with your foot still on the accelerator, it will go POW! Luckily, the muffler seems to be intact. Have been driving it for weeks now after this happened, and it still sounds the same as it always did.

Bill, Yes agreed. I do have a cool little fuse block, and the plan for the winter project is to install that and fuse things separately. And, for this very same reason!

Tom/Willie, No, I wasn't using more than the alternator could produce. It was carrying the electrical load AND charging the battery at the time. The ammeter was showing "charge" because the load did not exceed the output available, and there was plenty of current headroom to also provide charge for the battery.

Willie, This car doesn't sit, it gets driven at least once a week.

Anyway, this problem will be gone forever once the new fuse block is in and the wiring modified (again) so everything has its own fuse. However, the curiosity remains- Why couldn't an alternator run the car even with no battery in parallel to it? Hmmm....

Looks like some experimentation is in order.

Thanks again!

[Tom Wesenberg]

When starting from a dead stop, the alternator NEEDS a small electrical feed to excite the fields and start charging. With the fuse blown no electricity is available for feeding. On newer cars the idiot light is the feed to excite the alternator. On one wire 6 volt alternators there is a small feedback and that is what drains the battery when it sets for long periods without being used. The residual magnetism in an alternator won't generate enough electricity to get past the diodes and feed back into the circuit.

The residual magnetism in a Model A generator will generate 1/2 volt, and this is fed back to the field windings to increase the magnetic strength and increase the output.......and the cycle continues uncontrolled until it reaches it's limit by design, which can be up to about 40 volts. That's why it's important to have a battery in the circuit at all times, or have an EVR in the generator to limit the output.

[sturgis 39]

I miss my Model "A". I put it away about a week ago. We have about four inches of snow on the ground after a day of rain. I would go south for the winter but the dog likes the snow and cold weather.

I have two fuses on the Model"A". One is a circuit breaker actually and the other is on the starter. I have a power house generator. The circuit breaker is on the light circuit.

[Willie Krash]

Thanks Tom you are right, now I have doubts as my fuse popped out of it's holder and I had the same symptoms and now am doubting that my amp gauge was showing positive as I really didn't know the fuse was gone until the the car stopped running.
Too add to this interesting discussion re: residual magnetism I do not believe that an alternator (one wire) will work without it. OTOH I would suspect that a one wire alt would not go high if it's open circuit. In the case you cite of an alternator with an exciter we see the difference. The current in the filament will pass voltage needed to turn on the alternator at low RPM. LEDs used on early VW's are problematic, it takes some speed to get them excited and I would suggest RM as a component, but once they are turned on they typically stay on even at very low idle.
Thanks again. I do enjoy the discussion.

[gweilbaker]

Tom,

If his car was already running then blew the fuse, the alternator is charging. OP, And yes they run without the battery, just not starting. But the large question, what blew the fuse?

[sturgis 39]

I plan to run double circuits to everything . Two wires and double throw double pole switches with pilot lights before the switch, after the switch and at the appliance. There will be fuses at the start of each wire and at the end. Then each wire will all be run in a separate 1/2" heavy conduit and weather tight. All wiring will be 8 ga. The wiring will all be cooler coded and all conduit will be labeled for easy identification and also color coded. I plan to run two alternators and a two starters. The starters will be coupled together and this may be the only weak part of the system. The pilot lights will also be color coded and a color code chart will be attached to the dash and several locations on the car. A battery charge will be mounted in the car permanently and a wind generator for charging the battery will also be mounted on the left front fender with 1/2" carriage bolts after the fender is reinforced with 3/4" plate. The electrical switch board will be large and pretty much take up the passenger seat area. This will not make the car original but I feel the redundant circuits will make the car reliable and safe.



I no longer believe in the kiss principle.

[P.S.]

I admire your ability to over-engineer!

[sturgis 39]

Originally Posted by P.S.

I admire your ability to over-engineer!

Thanks

I have been thinking about adding a amp gauge on each circuit and of course they would be redundant too. I may now have to go with a four door body style to accommodate a co-pilot. He will be required to record all readings every half hour and these charts will eventually be down loaded by the home office clerk into a computer and will help predict future problems. I would install an on board computer but this might look tacky and not original.

A future addition will include temperature gauges on all bearings and gear boxes with analog readings to the co pilot which he will record on the pre printed log chart. These will also be redundant. I also plan to install vibration monitors on all rotating shafts. The plan is to use power plant type logic. This logic is one out of three must indicate a problem before the warning alarm is sounded and two out of three must indicate a problem before the power is shut off to the ignition switch.

I have never worked for Boeing or other airplane manufactures.

Strain gauges are also being considered but I have to get some work done before Mrs Sturgis comes home and the dog wants out. The dog does not understand "no".

[tbirdtbird]

People are not understanding how a GM 10si one-wire alternator works. There is no residual magnetism in any alternator that I know of. An OEM 10si needs to be excited and thus has more than 1-wire. The one-wire alt. is a 10si that has been modified by replacing the stock internal regulator with a special one that is 'leaky', thus accomplishing the required excitation without a separate wire. You need to rev the motor up a bit (perhaps 1000 rpm) to accomplish the initial 'leaking'. There are several web sites that go over this in detail

And maybe nothing blew the fuse. Fuses can just get tired. But certainly that issue should be investigated. He could be running close to the 30 amp rating since he is still 6V.

[tbirdtbird]

Sturgis I am just fully reading your post and I heartily agree, tho 8 ga is hardly sufficient, I would go with 4-ought on everything. And why limit yourself to weather-tite (or seal-tite, whatever you want to call it). Since the car will be at various gas stations, meaning near gasoline, and of course the car itself runs on gasoline, which is very dangerous, I personally would use explosion-proof wiring conduit, the same type that gas stations and refineries are required to use, where you fill the conduit with sealer via a wye fitting so that fumes can't get down inside the conduit and do bad things. Look carefully at your next gas station and you will see this type of conduit and a capped wye fitting.

[sturgis 39]

Thanks tbird tbird. I was on a sewage treatment project a few years ago. They used the explosion proof conduit that you mentioned. No cable trays on that job.