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automobile alternator?

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squeak63d

New Member
Can you change a alternator from dc to ac ? I'm a mechanic and know of the diode that lets the current flow one way and not the other. but can you wire a alternator to produce ac current to run a drill? I know you can buy converters but I have been told there is a simple way to change the alternator. I was planning on powering a 100amp alt. with a 10hp. gas motor. Can someone tell me or give me a web site with the info.
 

kinjalgp

Active Member
Alternator itself generates AC output and is converted to DC in the car using diode to charge the batteries. The previously used Dynamos gernetares DC output. You can remove the rectifier diodes and use the output of the alternator directly.
 

squeak63d

New Member
Thanks :D So if I remove the rectifier diodes do I need to wire anything in it's place? I have two kinds of alternators, One with the built in regulator and one that uses the external regulator, Which one would be better to use? And do I still have to hook up a 12 volt power source long enough to energize the feilds? I was thinking of using the internal regalotor alt. and take the diode trio out of it that conects up to the rectifier bridge[looks like a big heat sink and the diode trio hooks to it in three places with the windings, and go to the internal reglator] Is there a wiring digram for this on the net or can you draw me up one so I can be clear on this? again thanks al-lot.
 

kinjalgp

Active Member
You can directly hookup the output of your alternator to the drill after bypassing the rectifier. But before that be sure that it generates voltage equal to that required by the drill or it will overload your alternator or may be the drill will just not produce enough torque.

I don't think it will make any difference in using either kind of alternators.
 

Sebi

Active Member
I f i understand well,it`s a three phase generator for cars. When You removed all diodes and regulator,no more DC voltage for field. When You connect 3 wires direct to AC phases, You can powered a 3 phase motor with about 13...14V 400Hz AC if the diodes and regulator existiert.
With regulator adjustment You can go up to cca.20V because the reverse voltage of diodes about 50V.
 

kreed

New Member
Sebi is correct the alternator is three phase and the voltage is determined by the input of dc into the rotating fields. More dc volts in the more ac volts out. Most alternators are not insulated or designed to handle more than 180% of nominal voltage so most are 14 volt so the max volt availabel is around 25 volts. You will probably want to bring the input wires out for external input (so you can control the voltage)
Hope this helps.
kreed
 

bogdanfirst

New Member
hey, i went and asked someone, you can remove the diodes and have a 3 phase alternative curreent and he mesured it 14.* Volts, almost 15. but i found out if you puit more votage to the alternator, you wouldnt get more than 30V out, even for 36 input.
and if you use it to power a single phase consummer, it gets quite bad, because the laternator sounds quite nasty, i dont know if it is a problem with that.
but also the frequency generated depends on the engeine's turation, so it depends if the drill can handle it
 

squeak63d

New Member
I would like to say THANKS for all the replies. This forum is the best I've come across, All the others I've visited, I never got a reply or It was wrong. You all helped me understand it, thanks :D

squeak63d
 

spikegds7

New Member
Car Alternator Project

Hey,
For my shop project I decided to make my own generator from an old car alternator. I found a way to convert the output to 3 phase, but I need to know how to go back to a single phase. I would also like to know how to make the alternator supply its own input juice.

Thanks
 

pooey

New Member
alternator generator

hi all,

i have gained a lot of experience using car and truck alternators for all sorts of purposes over the years.so here's my 2 cents.firstly to run power tools you do not need ac if the tool is equipped with a universal motor as most are.they run just as happily on dc.the only exception are those with fancy speed control triggers.therefore you can rectify the 3-phase ac from the alternator to dc and use it to run power tools.use an external rectifer with good beefy diodes on decent heatsinks.remove the regulator and internal diodes from your alternator.this will aid cooling also.the output voltage is dependent on field strength and rotor speed.to get 110v output (assuming thats what you require) , put an 8 inch pulley on your engine and a 2 inch on the alternator and set the engine to about 2000rpm and supply 12 volts dc to the rotor.play with the throttle till you get the voltage just right.remember it doesn't have to be spot on as most tools tolerate +/- 10% voltage change anyway.

hope this helps.let me know if you need more details.
cheers.
 

micahd02

New Member
Related to this question, if I have correctly assembled the drive source/alternator/regulator, and I lose contact momentarily with the load, is it likely to blow either the alternator or the regulator?

Micah
 

Willbe

New Member
Watch your freq. A lot of stuff only likes 60 Hz.
 

RODALCO

Well-Known Member
Your alternator will put out 3 phase. e.g. your voltages and currents are 120° apart.

You can not make this a single phase supply.
You can of course use this as 3 times a single phase supply , each on it's own fused circuit.

For a 100 Ampère alternator the current will be 33.3 Ampère per phase at about 14 to 16 volts.

You can use a step up transformer e.g. 12 to 120/240 Volts at a reduced current of 3.3/1.6 Ampères per phase.

The frequency depends upon the speed of the prime mover, the pulley ratio and the amount of poles of the alternator.
 

Analog

New Member
An alternator puts out a frequency that is proportional to the rotating speed. As your car changes RPMs, then the frequency also changes, but this is irellevant to the car, since its being rectified regardless. In your case, you will not be able to reliably get 60Hz at all, as the frequency will be significantly higher and of a variable nature.

Secondly, an alternator puts out maximum amperage when its field voltage is Zero. This is a fail safe for a faded battery.

Thirdly, this is generally not going to work very well, I would say that it would be easier to buy something that is meant for the job, instead of hacking this, which won't work right in the best case.
 

Willbe

New Member
Secondly, an alternator puts out maximum amperage when its field voltage is Zero. This is a fail safe for a faded battery.
You mean field current? How can it do this?
 

Analog

New Member
You mean field current? How can it do this?

The current through the field winding is directly proportional to the voltage on that winding. The field winding is wired to oppose induction, perhaps you thought it was the other way?
 

Willbe

New Member
The current through the field winding is directly proportional to the voltage on that winding. The field winding is wired to oppose induction, perhaps you thought it was the other way?
I thought zero field current = zero output, otherwise the voltage regulator would have to do some gyrations to regulate the alt. output.
I've never heard of zero field current equaling full output and the gizzards of the regulator don't seem to be wired to do this, but I've never specifically looked for it, either.
 

Ross Craney

New Member
A car alternator is a three phase generator. Normally these 3 phases are full wave rectified by two diodes on each phase which also isolates the phases from each other. The regulator provides voltage to the rotor ( field ) at the correct level to generate 13.8v. It would be more accurate to call it a rectified AC rather than a DC. Your battery is like a HUGE capacitor & smooths it out to be usable by your car electrics. If you remove the diodes and use one phase you will cause a load imbalance and physical damage to the alternator. Similarly if you join the three phases together - well I would hate to think. Remember they are OUT of phase with each other - big no no.
The design of the alternator is what limits the current , the voltage to the field (rotor) AND the speed is what determines the voltage o/p.
As previously mentioned most handtools will work quite ok on DC. The best way to achieve what you want is to leave it as an alternator and arrange for the feild voltage to be adjustable. A simple formulae to help out.

Alternator speed = RPM of drive motor X Diam of drive pully divided by the diam of alternator pully
 

Ross Craney

New Member
Secondly, an alternator puts out maximum amperage when its field voltage is Zero. This is a fail safe for a faded battery.

.

So if the input to the alternator is zero , where does this magic o/p current come from ?
 
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