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

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.



Best Answer 7 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


Trying a better video


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.

JOseph or iceng.what if i use a flywheel,can a 1hp motor run a 5kw alternator,ill use my hand for to initiate motion.would this be possible?

Not to full power.

A 5 kw alternator needs 5 kw plus efficiency.

So if your alternator is 50% efficient you need a 10 kw motor minimum to get to full power. About 14 horsepower.

1 horse power is 746 watts.

A flywheel doesn't add horse power it only adds stable load torque.

When synchronized 5kva alternator and driven motor are same frequency,speed,& rating how to needs ?

Hello please can any body help my how to construct flywheel free enargy? I have 3kva altanator 1500rpm and 2hp 1400rpm

an alternator with AC and DC phase, can the DC output use to charge a battery that is powering DC motor that is driving the same alternator effectively?

That would be perpetual motion.
Not possible with what we know today.
Friction loss in bearings alone would prevent it.

You know; I originally asked this question because, I wanted to power an alternator with a gas engine, and wasn't sure about gas to alternator efficiency.

Please, am a student, my project is to produce 5kva using DC motor,
What HP or motor do I need to drive 5kva alternator

Ok 5kva to watts is 5000 watts.

1 horse = 746 watts.

5000 / 746 = 6.7 horse.

So for a 5kva alternator that is 100% efficient you need a 6.7 to a 7 horse motor. However most alternators are not even 90% efficient, most are only 50% efficient so you may need a 14 horse to power that alternator.

What is the efficiency of your alternator.

Please I find out that the output from the alternator was not enough to drive the motor(DC) continually, as the battery went down.

So what do I do to ensure that that the alternator charges the battery very well and generate 5kva

Of course not; you are using up to 10,000 watts, to make 5,000 watts.

Alternators are only 50 to 80 % efficient; for a 5,000 watt motor to drive a 5,000 watt alternator then to power a 5,000 watt motor it would need to be 100 % efficient. Then to do some other work the alternator would need to be 100 % + efficient.

The only thing over 100 % efficient is geothermal heating; and it dose not convert electricity to heat, it just moves the heat from one place to another, so you put 1,000 watts in and you get 3,000 watts heat out of the system.

You are correct, that is a more realistic value for efficiency !

Paulo you will need 14 of these devices pictured below ;-)


OK I have got to ask, What did you google to get that PIC.?

Nine years ago I was a good skier..

Now I'm building this using a 1/3 HP 3 Phase Motor

Sinv.jpg1in Tumbler.jpgStrong2.jpg

What about a racing bike air tube some of them can be quit small in diameter.

Water hose but it was new wound and has bumping..

I may have to search out old garden hose.


5000 VA / 746 HP/W = 6.70 HP

Now assume 80% conversion efficiency.

6.70 / 0.80 = 8.38 HP DC motor is your answer.


BTW next time ask your own question, so you may award the best answer and more iblers will see your comment rather then the few who have left a watch command to a 6yr old question.

Please, am a student, my project is to produce 5kva using DC motor,

What HP of motor do I need to drive 5kva alternator


Hello. Please give us advise on our school project.

We are trying to make a generator using motor and alternator. If our target is to produce minimum of 1000 watts of electricity, is an 85amps alternator already good enough? what is the compatible volts, amps and hp of motor do we need to find? We'll appreciate any expert response from anyone in here.

- Student Ianne

You are going to need about a 3 to 3 1/2 horse power motor depending on the alternator. Some car alternators are only 50% efficient. So 2000 watts / 746 watts = 2.68 horse + 1 for mechanical.

I'm in need of some help, I'm working on a project including a steam powerer tesla turbine which I want to harvest surplus energy going into a boiler, it'll also serve as backup power generator in winter when the P.V.s slow down.

I'm looking at a 2m long, 300mm dia boiler witha 100mm dia flue running through it, not sure what sort of pressures I'm looking at. This comes after a thermal mass rocket stove style combustion pipe burning wood. The tesla turbine will be ally plates in oil drum based housing (572mm, 22.5" dia).

Any ideas what sort of alternator would be suitable and should I be thinking about any gearing?

Since Tesla turbines are very efficient and high RPM you should be able to connect an alternator direct to the turbine.

I wouldn't go with a car alternator most of them are only 50 to 60% efficient.

I would go with a brushless alternator or a brushless generator some of them are 80 to 90% efficient.

I have a technology for produced
the free energy by alternator...i can do
that..but still working for the experiment.

how much current produce when a DC altinetor works 1800rpm or 1200rpm and volt 60vlt or 120 volt

How many pounds is the alternator weigh ?

how much current produce hen a altinator work 1800 rpm and volt 120volt or 60 volt

i know from experience as i had a 35 amp alternator combined with a 3.5 hp b&s over 20 years ago. if i had a huge amperage draw the engine would stall as the alternator came up to match the output. i used this to charge the race car battery between rounds and had 1- 500 watt halogen floodlight and a box fan to cool me off. Just about any other device such as a small tv connected to it would stall it. purchase a 5-6.5 hp engine and a 350 sbc crankshaft pulley then connect to the ( i'd run a 6.5hp harbor freight engine on it) engine and this would overdrive the alternator. i've viewed the diy generators on youtube but what they don't tell you is the engine has to be started in a no load alternator situation.

Not surprised combine 50% efficiency with up to 25% mechanical loss and you do not have much left for generation.

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

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?


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.