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.

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iceng4 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
iceng iceng10 months ago

Trying a better video


Josehf Murchison (author)  iceng4 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.
SammanthaC1 month ago

dont know nowt about what your all talking about except your all after getting something for nothing which is all good.Any body out there want to get involved with researching and building the power unit that will earn trillions.35 Kg unit that produces 15 metric tonnes (150,000 Kg..min) its electric powered but produces its own power after start up.Will be a replacement power source for ALL internal combustion ,jet,rocket engines,but I think the cream on the cake and would be that zero gravity is achieved,... and we all know what that would bring. Steve

Josehf Murchison (author)  SammanthaC1 month ago

What we were talking about is how big of a gas motor would we need to run an alternator.

I was having a hard time finding the efficiency of an alternator.

iceng solved a power problem for European lath by driving a 50 cycle generator with a 60 cycle motor, giving him the right power for the lath.

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.

I'm from Missouri... show me... got a video?

ByronB2 psron7 months ago


iceng psron10 months ago


I don't have a video, but, here is the kicker. I designed a system and was very lucky to find a motor of the correct rpm. I bought a 2.5 hp 180 vdc motor from Ebay for $100. It's rpm is 7000rpms. It is a really strange speed, but, here is how it is done. Find a high rpm dc motor like this and gear it down with a 2:1 gear reduction, then, buy a northern hydraulics 3000 watt rms generator head/ 3500 w peak. The electric motor doubles it's hp when geared to a 2:1 ratio, but, you reduce the speed. The generator will be operating at 50hz instead of 60 hz, but, it won't hurt anything. The generator is supposed to run at 3600 rpms, but, when it is reduced by 2:1, it goes to 3500 rpms and gives you 5hp instead of the needed 5.5 hp, so, you have a 5% reduction in wattage out, giving you like 2850 watts instead of 3000 watts rms. , the electric motor literally is operating at 1800 watts at start up and once it is up to speed, it operates at 1250 watts rms without any additional electric loads, so, once it's up to speed, you can switch it to self power from the generator head, but, you have to either build or buy a boost transformer good for 3kVA.

The system will operate all by itself and it is safe to use this to generate an additional 1500 watts of the 1600 watts left over without overloading or overheating anything.

Be sure to use it from only the 240 volt output and wire a box with 120 volt breakers and if you need, you have to use one of these systems to power a well pump alone, as well, another to run each ac in your home. They are extremely expensive to build, but, if you maintain them, these will replace every 15 amp circuit in your home and run completely free if you maintain and lubricate the gears on the gear box, lube the bearings in the motor and generator, and keep the circuits barely loaded, remembering you don't have a massive power handling capability like from the power company!

If you can find a 10kW generator that operates at 1500 rpms, you are in because you would be able to reduce the speed of the motor and get a gain in hp with the use of the same load , ultimately driving the 10kW generator at 12.5 hp, when the generator needs and actual 13.5-16hp to run it. The electric motor does a bit better than a gas engine because it has more torque and doesn't have too much trouble doing it's job.

My motor was a European motor that was much more efficient and you will find they do not have hp tags because the hp is much higher than american dc motors. I have a 550 watt motor from europe that is moving a generator head with a gear reduction like it's nothing. The electric motor should only be producing 3/4 hp but it is running more than 7hp worth of generator head and it isn't running hot or straining, in fact it is effortlessly generating power to provide for a refrigerator and two freezers.

They cost about 4k for all parts to build if the motor and gear box and gen head are new, but, if you find treadmill motors, you can get 2.5 or 2 hp motors for like 80 bucks with 5000-8000 rpm specs if you find them anyway. Good luck. I won't upload any vids because I won't show location to get these taken away. They cost way too much, but, trust me, they work. Jesse McQueen uses this and many others do as well. Scrap hunt and you may get lucky.

While I'm not a OU critic, reducing the speed of a 1HP motor by a 50% (using a 2:1 reduction drive) does not double its HP... you might want to look up how HP is calculated... but for a Motor, it's calculated as a given amount of work (torque) over a given amount of time (RPM).

(RPM x Torque in lb/ft) ÷ 5252 = HP

Halving the time by 2:1 (the speed reduction) will give us a RPM of 2500. At the same time, it will double the torque by the exact same 2:1 ratio... therefore the calculated HP remains the same (less the losses of the 2:1 reduction drive).

Example: If the DC motor is rated for 2HP at 7000 RPM:

2(HP) x 5252 = 10,504 ; 10,504 ÷ 7,000 (RPM) = 1.5 lb/ft force (Torque)

If we reduce that 2HP at 7000 RPM to 3500 RPM, the Torque increases by 2:1 to 3 lb/ft - so:

3500 RPM x 3 lb/ft = 10,500 ; 10,500 ÷ 5252 = 2.0HP

Your assumptions seem to be off... just because you can spin the
Generator at the required RPM, and just because it's rated for 3000
Watts, in no way means that you will be able to deliver full-rated power
from the Generator to Loads. As you require the Generator to provide
more Work (more Watts output), the drive requirements will increase
beyond the DC motor's capacity to maintain the shaft speed.

As to the overall experiment, been there, done that... MUCH time invested, but I have not given up yet. I have a 4400W (peak) gen head (240/120), and a Johnson 2.25HP peak, 2.0HP continuous DC motor from a large treadmill, with a variable speed drive controller. I have used many drive ratios to drive the Generator, as well as using the variable speed controller. This motor is only capable of about 5000 RPM or so.

I even modified the Generator to use radiant energy to become "self-exciting", so that it does not require any input energy to the Exciter coils (this happens only at the self-resonance frequency/speed of the generator).

I have tried "Earthing" the system at various points, to no avail. I have also tried adding an "antenna" (50' of wire, suspended well above ground) to help collect more radiant energy.

I know MANY people have claimed to have this working... I keep looking for more helpful information.

Well then,

if it doesn't double the hp at the end of the shaft (of the gear reduction), then please explain why the generator works to provide a small fraction of wattage less than the rated power. I'm no genius, but I am starting to think that some modifications in mathematics have been ,made over the years to accommodate the overunity suppression we have been silenced over, in fact, just like the original Maxwell Equations that have been edited, and deleted by JP Morgan who financially persuaded Lorenz to erase and rewrite the equations so publsihers could provide physics books and formulas that have stated overunity was impossible now for over 135 years.

In fact, nearly one year after Maxwell's death, these equations for asymmetric magnetism, asymmetric transformers, and any asymmetric system that basically stated an outcome of overunity have been suppressed. It's pretty damn obvious that the equations are blatently wrong for HP if I have come up with this based upon what others are doing. Jesse McQueen holds the patent, not me. He had to use the excuse that the additional energy came from lightning strikes so the patent office would have some sort of explanation of where the additional energy came from when the lightning has nothing to do with it, nor has ever been necessary.

If you know a thing about history, you'll know this is exactly why Tesla was financially confined to a hotel room... Because his theories and experiments were criticized by those who had millions. Hell, I'd shut up too if JP Morgan gave me billions or even millions to keep quiet. The sad matter is this.. i won't be shutting up unless somebody does shell out money to shelf my ideas because I have a technology called Pelex that creates more energy pound for pound than any other device on the planet, and I'm not putting it away for any less than 10 billion.

If I can't sell it, I will be open sourcing it before long. Check out PELEX on youtube. It is very real and it is available now for the right spender.

ByronB2 belangers7 months ago


ByronB210 months ago
ByronB2 ByronB210 months ago

Correct, you can not run a load off the same battery you're charging at the same time. Alternating charge/discharge with switching works. The more efficient way is discharging a battery bank whilst charging a separate bank. Switching out multiple banks, the more banks the better. If volts can be amplified and if amperage can be amplified and volts and amperage can be amplified then watts can be amplified, period. "Magnification" (Multiplication) is not breaking any laws. The reason why 'motor turning generator running motor' does not work is because of the 1:1(and less) ratio. What does work is 1:1xHz/s. 1 Coulomb ten times per second = 10 Amps per second. Hit me up on Facebook, guys. mx6maximus

iceng ByronB210 months ago

In the interest of electrical engineering, your comments and assertions are Totally Invalid and Incorrect !

ByronB2 iceng10 months ago

I'll leave it up to you to prove it wrong since my hands are busy doing just watt I said. I'm not doing anything 'new', just going on what Tesla did and he got it from Volta is all.

iceng ByronB210 months ago

No need to prove what you can not see, WWW words wrong words.


I Have added a working You-tube video .... show us yours ;-)

ByronB2 iceng10 months ago

We understand when a switch is turned off, such as is in a relay, we get a EMF spike. As Paul Babcock says "Mother Nature gives us a 'freebie" so that's what we're doing; 'catching that spike', storing that high voltage static, chopping it through a transformer coil. To do the 'chopping' (makes and breaks) we use a rotary SWITCH (not rotary gap) in the middle of the shared motors axle. One motor is externally powered to run (This is a temporary primer to start the motor). The generator motor is DC output which we run positive to the rotary and come out the rotary through transformer primary back to generator negative. What the rotary switch is doing is increasing the rate of makes and breaks (Hertz). The more of these chops per second the more charges per second that can be used (I prefer storing charge during the makes and discharging the stored during breaks). It's simple Coulomb math; 1 Coulomb = 1 Ampere for 1 second. Add-in Hertz per second (number of times within the second 1 Coulomb is chopped) If you have 1 Coulomb 100 times per second you have 100 Amperes per second, the number of times inside a second a Coulomb is made the amps compound per second. You're the only one responding here and if there are others interested in this it has to be understood firstly; when we speak of step-up transformers we're only looking at low-volts transformed to high-volts (we understand a step-up transformer takes in high-amps and outputs low-amps). You have to look at both volts and current as separate scales; volts go up, amps go down (volt gain/amp loss). If we reverse the step-up transformer, input the high voltage we get volt loss/amp gain. Many experimenters understand this seeing the output coil at that point burning up. I understand your your education in electricity may be extensive but I assure everyone there is another side to it that is not taught in schools. Just because I understand a thing doesn't make it new, this is just old almost forgotten technology. My partner posted a vid in ytube showing potential difference increase after we hastily built a rotary switch. I personally try to avoid sharing vids and drawings because in this if someone does not understand what is going on in it first, does something wrong it can be deadly (we're talking excessive amps & one mistake WILL be the last). Message me through gmail; mx6maximus and I'll give you that vid link)

iceng ByronB210 months ago

Discuss in the open or not at all.

Words don't show the circuit and I'm only talking why it wont work from the engineering you have not considered. Your rotary switch is nothing more then an armature commutator. Many word inventors have gone the next step and built a single machine that is both a motor and generator with a many pole armature using two or four quadrature contact brushes.

Coulomb math does as you point out involve current flow ( very dandy ) but inductive reactance which you refer to EMF ( Electro Magnetic Force ) is always there and limits your current buildup especially as speed increases. These engineering restrictions will always conspire to keep your generated output much less then 99% efficiency.

Fool yourself but don't try to fool me and our knowledge thirsty inventors.

If you had a working device and could be a rich why would you need to convince us of what does not exist :-)

ByronB2 iceng10 months ago

Well, I see where this is going. Of course I get ridicule and insult from people whom can not get off the 'it won't work because...' I HAVE considered all angles in what YOU understand and you're right, from your perspective, knowledge, understanding and explanations I absolutely agree with you. However, all arguments aside the devices have already been patented many years ago. I am not here to fool anyone (I also do not stick around to retaliate, name-call and argue over words), I just happened to stumble upon this thread by accident and made 10% effort into responding just based from my understanding of a thing, no more, no less. Where I stand there are no such thing as inventor, only re-discoverer. I'm merely pointing to a historical 'fork-in-the-road' in time. We could also say because I do have a working device, of which I have not gone into extensive details of the thing, if I share its drawings I guarantee that I would not be rich at that very moment. I humbly ask; "How does one RE-patent a device as his own, protect what they built as instructed from the old patent for the same reasons you have just said?" If what I have can do what you say (make me rich) could you direct me to that goal? I am curious.

iceng ByronB210 months ago

When I worked for Bill Lear ( Lear Jet, Steam Bus, Auto pilot, Cartridge 8Track, etc etc ) one of my functions was to examine the greater then unity power inventions that came to Lear to get rich.

It was an easy job, I had to measure power input and power output.. They always watched the relatively easy and quick test. As a general rule most never reached 80% efficiency.

The amazing part was, that the inventors / discoverers and their investors like you never accepted reality and moved on to continue promoting their particular ideas else where.

Go and make a working model. Demonstrate it can do 101% plus efficiency. Have people you trust sign ten identical one page disclosures and register mail them to yourself. Make and show a video and you will be rich.. I will come and work for you, if you let me..

ByronB2 iceng10 months ago

Ok but you and everyone has to understand there's no such thing as 'over unity' we're merely getting gain on this side as opposed to loss we currently use. Using 120vac house outlet get a 230vac HVAC RUN CAPACITOR and series that with the outlet hot. You're going to get roughly up to 170 volts coming off that cap so you have to trim that voltage down to 120v. Keep in mind what your polarity sign into the cap is you're going to get the opposite polarity sign out (we don't care since it's AC) Now that your voltage is back down we're at just using current output (voltage can not get through the cap from the grid; what comes into the cap goes right back out). During the volt peak cycles the current peak output of the cap is 1/4 wave AHEAD IN TIME and available for work in here & now as we catch up in time. What I like to do is connect the cap output to a diode bridge rectifier and connect the DC- direct to house ground so the cap isn't sucking to implode (relief valving). This is one-half of a Tesla Switch, you can route your circuit back to another cap to the bridge to get double DC+, smooth out that and use or convert to AC at any Hertz you wish. This is called 'Hairpin' and there is absolutely no voltage closing through the capacitor.

iceng ByronB210 months ago

Thank you

"everyone has to understand there's no such thing as 'over unity'"

ByronB2 iceng10 months ago

https://www.youtube.com/watch?v=ICH0ceJe_AE (Watch the volt meter)

iceng ByronB210 months ago

Watched it twice.

iceng iceng10 months ago

is this where we were going ?


it hits all the spots ;-)

akumar1992 years 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)  akumar1992 years 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.
akumar1992 years 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
lemonie4 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?

iceng lemonie3 years ago
MG sets run many an older elevator and before inverter technology got
Reliable that was the best conversion technique..
lemonie iceng3 years ago
That's a frequency or phasing conversion then?

iceng lemonie3 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...

Ragnarr3 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) 4 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

Josehf Murchison (author)  iceng4 years ago
Ha Ha Ha Ha Ha
Josehf Murchison (author) 4 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.
Vyger4 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.
seandogue4 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.
orksecurity4 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.