1970's alternator test, HP loss.

How much more horsepower does it take to turn a high amp alternator over a lower amp one? The reason for the question is due to a test I recently did. I'm using a 1/3 horsepower electric motor on my test, when checking voltage output with a 37 amp compared to a 50 amp alternator, the 50 amp kills the 1/3 HP motor. I can't seem to get the video to load on here so go to youtube, type in, detrick 50 amp alternator and then, detrick 37 amp alternator to see the difference between the two. Wonder what a 100 amp would do?

1 horsepower = 746 Watts (approx).

HTH

What are you using to load the alternator?

12 volt car battery.

If my math is correct it would take 1 HP @ 12v would to crank out 62 amps.
50 amps would take about .8 hp.

No wonder it killed a .33 Hp motor.

What was the state of the battery's charge before each test? I would expect a discharged battery to create more alternator load than the available hp could overcome. IOW, if the battery was fully charged at the beginning of each test, would the hp required to merely maintain a charge be the same for both alternators?

That's what I was thinking. An alternator will never generate more current than is needed by the demands of the electrical system. The 37 amp alternator and the 50 amp alternator will put out the same current when connected to identical loads (up to a point). If the load is sufficiently large, e.g., somewhere above 37 amps, the 37 amp alternator will hit its limit while the 50 amp alternator will continue to deliver .

Are you measuring output current with an ammeter? I think you need to measure the output current to know what is going on. If you aren't measuring current then it could just be friction load that you are looking at.

And wouldn't pulley ratios play a role also?

Somewhat, the alternator has to spin a minimum amount to make the power required and cannot spin so fast it comes apart. But generally, the regulator controls the output. In the OP's setup he has the alternator full fielded, which is a wonderful way to blow up a battery.

My advice to the OP is to not play like that. There is a reason the FSM tells you to use a carbon pile as a load.

Two things I see possibly wrong on your testing is no regulator and no load for the regulator to load that alternator and no amp gauge or volt meter to see the output from it
I've watch many stock Mopar amp gauges work when I accidently flooded a motor at the races and saw the amp gauge almost peg for 2 to 5 minutes charging the battery back up.
I have also disconnected the field lead at the races when testing and tuning to see if the car would slow down or pickup without the alternator charging, it would slow down a small amount in ET and MPH That was with a stock single field 1963 Alternator with new brushes and charging the battery up with a battery charger in the pits before starting it up and getting in line to run

If my math is correct it would take 1 HP @ 12v would to crank out 62 amps.
50 amps would take about .8 hp.

No wonder it killed a .33 Hp motor.


I can afford 1 horse, so I run an alternator.
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An alternator will never generate more current than is needed by the demands of the electrical system Exactly!!!! For example, if the steady state load is say 21 amps on a 37 amp alternator, you can put a 200 amp alternator on the car and it will output the same 21 amps. You only need a larger alternator if you are adding things like fuel injection, electric fans etc. that are beyond the capability of the stock one.

Even the stock alternators will put out more than their rating. My 69 340 Cuda with AC has a 46 amp factory alternator and when Dixie Restorations did the final test, it cranked out 55.8 amps while charging up a battery.

Jim

This is incorrect. If you full field an alternator, like the OP apparently did, it will put out maximum output regardless of load.

What controls the output of the alternator is the regulator and in the case of this setup there is no regulator and the alternator is hard wired to provide maximum output.

I once had a regulator fail on my and full field the alternator. Blew the over pressure caps off my Optima.

Also correct!!!

The statement " An alternator will never generate more current than is needed by the demands of the electrical system" is correct.
The regulator regulates voltage, not current. Current is the product of Voltage and resistance. The misunderstanding here is semantics.

CURRENT IS THE RESULT OF (Voltage level and resistance)
Assuming the circuit resistance total (Rt) is fixed, then current will rise and fall as voltage rises and falls. Voltage goes up=current goes up. Voltage goes down=current goes down.
Now, assuming voltage if fixed, current will rise and fall as Rt falls and rises. Resistance goes down=current goes up. Resistance goes up=current goes down.
The regulator regulates the duty cycle of the field from monitoring the voltage. If voltage is low then the regulator will increase the duty cycle of the field (more on-percentage, less off-percentage). If voltage output is high then the regulator decreases the duty cycle of the field.

Regardless, the amount of current that moves is directly controlled by the resistance in the circuit and the electrical pressure ie. Voltage.
E= Electromotive Force/measured in Volts
I=Intensity/Current/measured in Amps
R=Resistance/measured in Ohms

E=IxR (Voltage = Amps times Resistance)
I=E/R (Amps =Voltage divided by resistance)
R=E/I (Resistance = Voltage divided by Amps)

Ohms Law.

What happens to a full fielded alternator?

It goes to max output regardless of load.

I do not misunderstand the semantics, I fully and completely understand the relationship between voltage, current and resistance. It's been my job since 1985.

What you fail to consider is that the regulator measures the load and controls the output of the alternator. So when an alternator is full fielded, as in the OP's test or with a failed regulator, the alternator is being told to go to maximum and it does.

Don't believe it, go full field one and see. Go measure the voltage, measure the current then come back and tell us what the real world tells us about your theoretical one.

Your discussion above is about how the charging system is supposed to work, that is NOT what we are talking about. We are talking about how the OP has set up his test.

Technically, the voltage regulator doesn't measure the load directly, it measures the voltage drop created by the load.

Yes, let us play the semantics game.

Technically an ohmmeter doesn't measure resistance, it measures the voltage drop across the load and infers the resistance from that.

Still want to play?

Touchy, touchy. You want to correct other's semantics but you get offended when............

You can’t push in amperes from an alt ( or any other kind of source ) if there is no devices sucking out around.