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Truth or BS?

jjoerger

jjoerger

Veteran Expediter
Owner/Operator
US Army

My neighbor just told me this story.
He said a few weeks ago his car battery was dead.
He had no way to jump start it or a charger. He claims he removed the belt from the alternator, attached a 1/2 inch electric drill to the alternator and spun it a full speed for 30 minutes to charge up his battery.
It seems plausible and I have never known him to tell stories but it also has a BS feel to it.
 
Murraycroexp

Murraycroexp

Veteran Expediter
I'm thinking the battery wasn't 100% dead. I think alternators need electricity to generate electricity. But maybe plausible????
 
Turtle

Turtle

Administrator
Staff member
Retired Expediter
Alternators that are belt driven receive no electrical input with which to generate electricity. ;)

Use a drill to power an alternator? It's possible. That's exactly how many alternators are bench tested (alternator, vice, drill with correct size socket). You spin the alternator and as if by magic electricity is generated. That's how it works.
 
jjoerger

jjoerger

Veteran Expediter
Owner/Operator
US Army
But would a 1/2 inch drill have the power to turn an alternator under load? I just read that it takes approx. 1 HP for every 25 amps. This was on an older jeep so I'm guessing a 60 amp alternator or bigger.
 
Turtle

Turtle

Administrator
Staff member
Retired Expediter
Depends on the RPM of the drill, and the load, but yeah. It's unlikely that a cordless drill would have enough power in its battery pack to spin the drill at full speed for half an hour under a load like that, though.
 
paullud

paullud

Veteran Expediter
You can spin the pulley by hand, I believe the 1hp for 25 amps is in reference to parasitic drag.

Sent from my SCH-I535 using EO Forums mobile app
 
BobWolf

BobWolf

Veteran Expediter
Owner/Operator
Turtle said:
Alternators that are belt driven receive no electrical input with which to generate electricity. ;)

Use a drill to power an alternator? It's possible. That's exactly how many alternators are bench tested (alternator, vice, drill with correct size socket). You spin the alternator and as if by magic electricity is generated. That's how it works.
Click to expand...

But you for got the magic words. As the Amazing Mumford from Sesame Street used to say....
I will waive my magic wand, and say the magic words, it will make electricity..

A LA PENUTBUTTER SANDWICHES!!!!


Bob Wolf.
 
RLENT

RLENT

Veteran Expediter
Turtle said:
Alternators that are belt driven receive no electrical input with which to generate electricity.
Click to expand...
Are you sure about this ?

To clarify my question: is that true before the alternator actually starts to produce an output ?

IOW: Does the alternator require an electrical input ... in order to start producing an output ... even if the output is self-sustaining once it starts ?

I think that your statement, as constructed, is not (necessarily) entirely accurate ... ;)

Alternator - Wikipedia, the free encyclopedia
 
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jjoerger

jjoerger

Veteran Expediter
Owner/Operator
US Army
So I can plug my 1/2 inch drill into my inverter, remove the belt from the alternator, spin my alternator with the drill, and charge my batteries? Would the drill and inverter draw more power than the alternator can produce? 160 Amp alternator. 1750 watt inverter. Drill is 10 amps.
 
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Murraycroexp

Murraycroexp

Veteran Expediter
RLENT said:
Are you sure about this ?

To clarify my question: is that true before the alternator actually starts to produce an output ?

IOW: Does the alternator require an electrical input ... in order to start producing an output ... even if the output is self-sustaining once it's starts ?

I think that your statement, as constructed, is not (necessarily) entirely accurate ... ;)

Alternator - Wikipedia, the free encyclopedia
Click to expand...

Ya, I was told otherwise when I worked in a shop as a kid. Not that I'm sweatin' it. LOL!!
 
spongebox1

spongebox1

Expert Expediter
jjoerger said:
So I can plug my 1/2 inch drill into my inverter, remove the belt from the alternator, spin my alternator with the drill, and charge my batteries? Would the drill and inverter draw more power than the alternator can produce? 160 Amp alternator. 1750 watt inverter. Drill is 10 amps.
Click to expand...

If you try this please make me a video

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mugurpe

mugurpe

Seasoned Expediter
the HP rating is dependent upon the size of the pully, it's about gear ratio. For racing applications they make different sized pulleys which will reduce the alternator's output, but also rob less HP from your performance. This would also affect the alternator's output, so running the alternator at a slower speed, with a weak drill motor would mean it would take longer for the battery to charge. Also, a lot of alternators do connect back into the charging system via a 3rd wire but that's just to test the charge on the battery so that the alternator will release the clutch on it's pulley when the battery is charged (and therefore freeing up HP in the engine). So, I think the story is plausible. I would also suggest that the battery wasn't all the way dead as I think it would take more than 30 minutes to charge a totally dead battery to good enough to start a car with a screwgun, but it making the difference between not enough to start and enough to start? you bet.
 
RLENT

RLENT

Veteran Expediter
mugurpe said:
Also, a lot of alternators do connect back into the charging system via a 3rd wire but that's just to test the charge on the battery ...
Click to expand...
It is not just to "test" - it is required for the (some ?) alternator(s) to (initially) produce any output at all ...

From the Wikipedia link I provided that describes how automotive alternators function ... specifically a portion of the 4th paragraph under the "Automotive Alternators" heading, which describes the process:

"The field windings are supplied power from the battery via the ignition switch and regulator. A parallel circuit supplies the "charge" warning indicator and is earthed via the regulator.(which is why the indicator is on when the ignition is on but the engine is not running). Once the engine is running and the alternator is generating power, a diode feeds the field current from the alternator main output equalizing the voltage across the warning indicator which goes off. The wire supplying the field current is often referred to as the "exciter" wire. The drawback of this arrangement is that if the warning lamp burns out or the "exciter" wire is disconnected, no current reaches the field windings and the alternator will not generate power.
Click to expand...
 
Deville

Deville

Not a Member
jjoerger said:
So I can plug my 1/2 inch drill into my inverter, remove the belt from the alternator, spin my alternator with the drill, and charge my batteries? Would the drill and inverter draw more power than the alternator can produce? 160 Amp alternator. 1750 watt inverter. Drill is 10 amps.
Click to expand...

You would need an 18 amp drill.
 
Turtle

Turtle

Administrator
Staff member
Retired Expediter
RLENT said:
Are you sure about this ?
Click to expand...
Yes

I think that your statement, as constructed, is not (necessarily) entirely accurate ... ;)
Click to expand...
No, you're right, it's not entirely accurate. Within the charging system of a vehicle the exciter wire is absolutely necessary for the system to work. But you can bench test an alternator with a drill just the same, and when you rotate that copper coil around a magnet, electricity is generated every time.
 
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