Instructables

How powerful of a motor do you need to run an alternator?

From questions I have read and step by step’s I have read a question came to my mind.
How powerful of a motor do you need to run an alternator?
I checked the Delco Remy alternator series from 10SI in 37 Amps, to the 40SI durable brushless model, in 240, 275, and 300 Amps.
All their performance charts show rpm’s at the alternator not the motor.
The pulley on the crankshaft is considerably larger than the pulley on the alternator, giving you more rpm’s at the alternator than at the motor.
All their performance charts show rpm’s from 1200 to 8000 rpm’s.
All their performance charts show at 3000 rpm’s you get 13/16ths of max power.
The last 5000 rpm’s only gaining 3/16ths of power.
The thing is none of the performance charts say the horsepower to drive the alternator.

I decided to approach the problem from a different direction
Typical alternator efficiencies are in the 54%-60% range.
Brushless alternator efficiencies are in the 60% 70% range.
A typical 12v 60 Amp alternator produces 720 watts at 55% efficiency.
It needs just 1310 watts to drive it or a little under two horsepower at 1492 watts.
This does not account for mechanical efficiency of connecting the alternator to the motor.
With this in mind a three horsepower motor should drive a 12v 60 Amp alternator.
This is just an educated guess but I would like a horsepower chart.

720 watts would do well at charging a battery bank while you sleep; however I could not run my microwave and charge batteries at the same time.

iceng3 years ago
Here is my mechanical 60 Hz  to 50 Hz sine wave  frequency changer.  
A 50 cycle MG set ( Motor Generator ),  The alternator has been modified
( no diodes ) to output 120 VAC at 50 Hz by virtue of the belt pulley diameters.
The drive is a 115 VAC induction motor drawing 9.6 Amps 60 Hz at 1725 RPM,
that's over a Kilowatt about 1½ HP of input Power. 
The alternator was rewound deliver over 6 Amps at 110 VAC 50 Hz. about 700 Watts.
There is a step-up 600 VA transformer is used to provide 220 VAC at 50 cycles.

The dual duplex outlet on the left provides 220 VAC and 110 VAC at 50 Hz.
The single duplex and motor power switch on the right is the 115 VAC 60 Hz side.
Efficiency of the whole system is a whopping 60%  but with it I can qualify designs
for the rest of the world including the UK :-)
There is a 12 sec video of it running.  The last pic is where it helps hold down a
Chinese metal lathe.

In my opinion a Transformer Rectifier would be a much better battery charger
then an MG setup...........................   A
ALT1.JPGmotorNamePlate1.JPG
Josehf Murchison (author)  iceng3 years ago
Now that is neat, years ago I worked for a company that rebuilt electric motors.
We would get brand new motors from manual lath’s imported from Europe that ran on a variety of voltages and cycles, our job was to convert them to 600v 60cy. (Canadian Industrial Power) large electric motors are cheaper to rebuild then they are to buy.
That looks easier to build than a variable power inverter or rebuilding the motor without the specialised equipment. Especially if you cant buy just the right motor.
Yeah going through the demoic incantations to work out what is the BEST RPM to run an alternator at under full load.

Unfortunately the Delco Remy site has more or less only the current models and their specs on site - but the "Spec Sheets" say nothing more than "Clean the battery terminals with baking soda, water and a wire brush..."

(Doh!!!! - grinds teeth a little - why????)

No maximum / Minimum RPM and output curve.....

Since I figure that using the alternator to charge up a battery bank - for the odd occassions I need to do light gauge welding, and usually not a whole heap of it, in conjunction with a small solar array - may in fact be better value than actually paying to keep the power connected at my place.

That is currently !$90 for 90 days..... THAT is an awful lot of fuel for a generator.- like about 65 litres - or 30 hours of continuous welding.... actual running an arc time..

2 or 3 minutes running a weld... 8 to 10 minutes charging up the batteries....

Might be worthwhile.....

Delco won't tell you because they don't want us to know that the alternator will put out more than an AC motor will output, which can run the alternator to charge the battery bank at more than what the electric motor draws. The alternator speed , depending on alternator only needs to be 2500-3000 rpms for 80% of it's output. The alternators are pretty much all rated at 20% higher than their capability which is said to be their maximum, which is absolute maximum to compensate for peaks and valleys of the environmental energies that are accumulated (induced) by the alternator while in motion , which is completely dependent upon the ionized particles in the air, elevation (from sea level) of course will play a part in how much output you have coming from the system, and of course, the depth of the earth ground used to develop this phenomenon.

If you look back at Tesla's radiant energy inventions, this is basically how this qmogen or qed effect is done. The electric motor of course is an AC motor, and it is belt driving the alternator. The pulley on the motor needs to be smaller than the alternator, but, not by much, and the motor rpms are really necessary to know the output you are going to obtain from the generator.

The difference in potential from the Earth's ground will actually give the alternator the additional voltage that is needed to give you more than you have coming into the system. The motor needs to start up and run at full speed, then, the drive motor needs to be pulsed at 3 times per revolution on, and 3 times off of course so 1/2 of the energy used is from the power feed, and, the other half of the power needed to drive the alternator will be from a flywheel that will be added to the system which will drive the alternator by inertia. This inertial assistance is needed to provide the overunity needed as Jesse McQueen does to output more than it draws.

This will allow you to draw energy in it's off time from the motor's windings as Back EMF which can be directed back to the feed of the motor, as well, you can wind a reverse polarity coil around a bar magnet and add a magnet of the opposing magnetic phase to the "inertial flywheel" as John Bedini does to produce a high amount of counter emf from the winding you have created, which will be pulsed by the flywheel of course, and this will be self generated back emf which can be thrown into the motor, during the "off" period of switching, so it eliminates the majority of input current. When all said and done, you will be able to self loop the system, but, when you do, you have to feed the power from the system to a battery bank. The battery bank will lose it's ability to hold a charge eventually if you do not run a light bulb created to absorb the high voltage peaks that the back emf creates, so, it is highly recommended to add the old neons used for high voltage sensing in parrallel with the feed to each inverter used from the battery bank. One inverter will need to loop and drive the motor, and the other inverter can be used to power whatever you wish. It is actually a patented system by Jesse McQueen, and it is being developed to be used right now in 3rd world countries that can not afford fuel for electricity.

Good luck, there are many people having success with this, so, if you wish to be successful, do not listen to the critics or skeptics as they will shoot down the method and brainwash you into shielding yourself behind a physics book. Believe it or not, you would not be violating any of the good laws, because the additional source is the drawing in of ionized particles, which derive from atmospheric electricity, so, it really is not doing more than adding the induced atmospheric electricity by adding the deep Earth ground to the electric motor, even though there is no physical connection other than air!

Be sure the motor to drive the system has the correct sized shaft, then, look at the amperage and the rpm. If the motor uses 1.5 amps and is driven at 110 volts, the motor has the ability to run the system using 110 x 1.5 = 165 watts, and HP of course. If the motor will not spin the alternator, try to pop start the belt by hand and see if ti maintains it's speed. If this is the case, you may need to add a starter capacitor and a run capacitor. See then if it'll start by itself. If it does, then, you will need nothing more than the correct ratio by utilizing the right rpm with pulley sizes.

When the alternator is finally spinning at the max power, or say 3000 rpms, take the max amperage and multiply this times the voltage out. so, if you have a 105 amp alternator, 14.4 volts times 105 amps= 1512 watts.

If you could get a very small motor to spin the alternator at the correct speed, it will make more than it consumes, just as long as the electric motor starts up, even if you have to pop start it, AC has more torque, and is more efficient, but, when we take AC voltage and rectify it, it becomes a larger voltage. This is what happens in the alternator because of the atmospheric energy. So, the alternator maybe only producing 9 volts ac, but,when we rectify it, it makes 14.4 volts dc. Add this to the batteries, and you are able to power a really heavy ampacity load, such as a welder, etc., through a large inverter. Even if you do not create more than you use, you will certainly reduce the massive draw from your home's electrical system because you will have a massive gain in efficiency by using the back emf created from the differences in the systems. (which is an AC motor to drive a converted AC to DC system.)

Good luck, and let me know how you make out. I have created these systems to power lighting in a cabin and they worked for years.

akumar19911 months ago
well i also want to checkout that a low power DC motor can run heavy/semi-heavy alternator? to develop high power. if yes, on what parameters? what parameters should match in between them? thanks in advance.
Josehf Murchison (author)  akumar19911 months ago
In the case of what icing did he attached an AC generator to an AC motor to convert 115 volts 60 cycle to 120 volts 50 cycle. The same thing can be achieved with an AC PWM or a AC to AC converter but since at the time he did not have the skills to make one he found a different way, and it worked even though it worked at 50% efficiency it worked.
akumar19911 months ago
well i also want to checkout that a low power DC motor can run heavy/semi-heavy alternator? to develop high power. if yes, on what parameters? what parameters should match in between them? thanks in advance
lemonie3 years ago

I can't think of a good reason to connect two such electrical devices together.
There will be a better way to convert electricity-in to electricity-out, why do it this way?

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iceng lemonie2 years ago
MG sets run many an older elevator and before inverter technology got
Reliable that was the best conversion technique..
lemonie iceng2 years ago
That's a frequency or phasing conversion then?

L
iceng lemonie2 years ago
Yes, mine does frequency 60 cps to 50 cps.
And a Ward Leonard control used to do elevators with a much wider
speed change ie zero RPM...

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Ragnarr2 years ago
You can use the start with watts and convert that to horsepower and provide for the alternators efficiency, which averages about 55%. So rounding things off, a 100 amp GM 12si alternator at full load is approximately 3.5 hp just generating your electricity. The Denso square wire alts. are the most efficient design available now.
One thing a lot of people miss is how much hp it takes to turn the fan.
In working with alternators in racing applications, the 3.5hp is a small load. When you rotor is in the 5 to 6k range the fan can demand 15+ hp. When testing alternators in excess of 7500rpm, I have seen a 17 lb GM CS144 alternator with a 20 lb+ cage around it, rise off a test bench because the fan is moving so much air. Alternators with internal fans like Densos, the GM AD244, and Ford 3,4, and 6Gs use a little less power.
Josehf Murchison (author) 3 years ago
By the way this is a gas or diesel motor connected to an alternator.
Horsepower can be expressed in 550 foot-pounds per second, 746 watts, 746 Joules or 7.46E+09 Ergs.
From this you should be able to see why the international standard is watts.
I use 746 watts per HP a lot.
I know 550 ft_LB/sec, and 746 Joules.
But never had the 7.46+9 ergs to a HP,  thanks for that one.

I always referred to an erg as the energy of blowing one nostril
into a paper tissue without tearing the tissue, LoL

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Josehf Murchison (author)  iceng3 years ago
Ha Ha Ha Ha Ha
Josehf Murchison (author) 3 years ago
I already figured a governor on the motor’s accelerator would be necessary to compensate for load breaking. And my calculations are based on loaded output as near as I could figure. I just haven’t received an answer from the manufactures and it is not in their information brochures.
That is where I got, typical alternator efficiencies are in the 54%-60% range and brushless alternator efficiencies are in the 60% 70% range.
An ideal alternator and motor combo would be one horsepower in 746 watts out.
However real life does not always match theory.
In real life 1 horsepower in, .54 to .60 horsepower out, or 447 watts out, it should be an easy calculation.
Just cant get a conformation.
Vyger3 years ago
I know there have been people who have experimented with using alternators for wind power electric generation. (belt driven pulley systems). I would imagine that they have posted the info they have gathered somewhere. Try Google and see what you can find.
seandogue3 years ago
A rough calculation of the required minimum input power can be reverse-calculated from the output power.

1) Determine the maximum power you want out of the alternator.

2) Multiply the value ascertained from the above by a value of ~1.5 to conservatively account for mechanical and electrical efficiency losses presented by the alternator

3) Convert the result to units appropriate for the motor and you should have your tidy little answer.

To be more accurate, you'd need to know the specific losses involved.
orksecurity3 years ago
I think this comes down to how much torque it takes to keep the alternator running at that speed under full load (and, yes, load affects how much resistance there will be; that's the principle behind variable electric braking). The specs, and/or the manufacturer's help desk, should be able to give you that information.

Then, according to a quick websearch:
(Torque x Engine speed) / 5,252 = Horsepower
where torque is in foot-pounds.

Actually, if you contact the alternator's manufacturer, they can probably give you a horsepower number without your having to calculate it.

Caveat: This is a semi-informed guess.