# So, I've got this alternator, right?

Discussion in 'The Projects Forum' started by roadwaystrybran, May 26, 2015.

May 9, 2015
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... And I plan to hook it up to an angle grinder, or some kind of motor to act as a generator. Honestly, I have no idea what I'm doing, I'm an electronics novice. Basically, in trying to learn this I figured I'd start at the source- the actual production of electricity. I've built a few of those science fair-y coils with a neodymium magnet rotating near them, but had negligible results. I just want to generate, like, 1 volt dammit! I figured that I'd go with the golden standard of electricity generation to see if I can spot my failure. As I understand it, alternators put out a small amount of voltage, at least compared to their amperage output. I have about half a clue what I'm trying at here, and was wondering if someone could help me out/ stop me before I fry myself. Anything from the complete knowledge of electricity to hurtful naysaying would help immensely. Thank you in advance for your help!

2. ### Kermit2 AAC Fanatic!

Feb 5, 2010
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750 watts is one horsepower in electrical power.

How many horse power is that angle grinder? 1/2 maybe?
That means with losses calculated in, roughly of course. you could generate about 250-300 watts of electricity max.

Next problem is what type of alternator you have. Most will need an 'exciting' current to generate the magnetic field that is the driving force of AC current from the alternator. Cars have control electronics that tweak the exciting current to keep the voltage output of the alternator fairly even over a wide range of engine RPM's and loads.

You, sir, need to do some serious researching on the topic of automotive alternators before proceeding further. otherwise, it is a good way to learn about all the problems in power generation!

Finding a DC motor and driving that with another motor would be a better place to start, if you are just beginning.

Jul 18, 2013
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Most angle grinders are Universal series wound motor and do not make for a alternator or generator.
You could either obtain any DC brushed P.M. motor that requires no external supplied excitation or pick up a Auto alternator and apply a varying DC to the rotor while under rotation, this produces rectified three phase.
Max.

4. ### blocco a spirale AAC Fanatic!

Jun 18, 2008
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He wants to drive an alternator from an angle grinder, not convert an angle grinder into an alternator.

I don't know why he would want to do this when he could just spin a small PM DC motor and generate few volts, as that is the stated objective.

5. ### Dodgydave Distinguished Member

Jun 22, 2012
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You're going to need a 12 v battery/psu to exite the field winding, then you can spin it to create 14v or so,

show pics of the alternator..

Jul 18, 2013
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IIRC a typical auto alternator will put out over 60v - 70v with straight 12vdc on the slip rings.
It comes up to full voltage at a fairly low rpm.
Max.

7. ### shortbus AAC Fanatic!

Sep 30, 2009
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Used to be ~120V three phase AC. Remember from the 1970's when you could buy a "box" to mount in the engine compartment of a car. The internal electronics then converted to single phase.

May 9, 2015
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Yeah, I should have specified, the grinder is to drive the thing. I was reading about alternators, and just learned about the meaning of "3 wire"... Maybe I could replace the electromagnets on the rotor with neodymium or something? If not I guess I could find a way to power the electromagnets in there... huh.

May 9, 2015
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IIRC? 12 volts on slip rings? Full voltage at low rpm? Care to elaborate?

May 9, 2015
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I would also like a fuller understanding of what you're talking about.

Jul 18, 2013
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A auto alternator is rectified 3phase generator that has a rotating DC field (the rotor) provided from the battery via the slip rings , but regulated in order to maintain the Alt output at 14.5vdc regardless of load.
If you apply 12vdc and rotate the alt, the subsequent output is unregulated and hence will be what ever the load is and the rpm of the alt.
Max.

12. ### tcmtech Well-Known Member

Nov 4, 2013
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Depending on the alternator many are now designed to self excite like a normal DC generator does. Most of the Delco SI series are that way or can easily be made into a one wire self exciting unit by changing out the internal regulator module.

BTW the Delco 10 and 12 SI units when converted over to a low RPM exciter regulator systems will usually self excite at under 2000 RPM. Some as low as 1200 RPM.

13. ### shortbus AAC Fanatic!

Sep 30, 2009
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Don't think it can be done with today's alternators. Back when those boxes were sold in the back of magazines like Popular Mechanics, alternators had external regulators. And you hooked into those wires. Today's alternators have internal regulators or some use the ECM to regulate.

14. ### shortbus AAC Fanatic!

Sep 30, 2009
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Some people have done this to make "bicycle motors". The press the shaft out of the rotor and put round speaker magnets in place of the rotor coils.

Some people do the permanent magnet thing for windmills. If you change the rotor to permanent magnets you then can't regulate the out put easily or effectively.

May 9, 2015
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Oh, sweet, thanks man

May 9, 2015
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Hold on, Self-excite? This sounds relevant to my interests. If you have any literature or wisdom on this, please share

Jul 18, 2013
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Self excitation uses the residual magnetism that may be present in the field, if it is present and you rotate the armature or rotor, and in the case of an alternator the stator will start to output an ac signal, if this is rectified in the usual way and the resultant DC fed back to the rotor (field) , it then becomes truly self exciting and will gradually increase if not regulated.
Max.

18. ### tcmtech Well-Known Member

Nov 4, 2013
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Pretty much self explanatory. The alternator only has the main power wire going out so there are no other wires to send a start signal to it. Spin it up and it goes.

Delco SI series alternators are the most common ones to use being they are cheap and easy to work with. Old three wire units are easily converted to one wire units by replacing their internal three wire voltage regulator with a special self exciting one wire unit.

There are also low RPM self exciting regulators for them as well now so they don't have to be spun up to several thousand RPM to get them to excite.

In fact if you take a common Delco 10SI or 12SI 60 - 75 amp three wire type of alternator put in a low RPM regulator and reconfigure the windings from the typical three phase Delta configuration to a three phase Wye you will get a alternator that can self excite at around 800 - 1000 RPM and put out up to around 35 - 45 amps!

I have a old John Deere A that I may convert over to alternator one of these days and I will more than likely have to do the low RPM one wire regulator conversion and internal Wye change over to get the alternator to excite at a low enough RPM to work properly.