Hi all.
A long time ago, I read a very good and simple technical explanation why a plain 120VAC circular saw motor is perfectly capable to perform very well with 12V DC, and the proof from the writer; an electric bicycle he made with a 'Skil' saw and a car battery... or two.
Can someone explain the principles of similar POWER capabilities with such different voltages? Cannot find now the article on the net explaining it.
A circular saw is not among my toys, or I would have already tested with 12V DC to compare its POWER.
Thanks,
Miguel
Universal motor...
Universal motor...
 Abolish the deciBel ! 

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 Location: Buenos Aires Argentina
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No, at 120VDC it may take too much current and / or overspeed.Now, 120 VDC is another story!
An universal motor is just a series wound DC motor (that is, the field winding is connected in series with the armature), but it has two small differences:
>> As the field winding will have AC, the magnetic field it produces will be variable and so the iron should be laminated to reduce losses  a "real" DC motor may be built witt a solid iron stator
>> In a DC motor, the current is given by U = E  IR, where U is the applied voltage, E is the back EMF generated by the armature, R the resistance of the windings and (of course ) I is the current.
If you use the motor with AC, the resistance "R" gets replaced with the impedance "Z", (Z = R + jX), and the inductance of the windings reduce the current for a given voltage.
So, the "correct" DC voltage for the motor will be lower than its AC one, but the exact value deppends on the design of that particular motor (on the relationship betheen R and X)
To determine that "correct" DC voltage you should run the motor with an ammeter in series, both on AC at the rated voltage and at DC with the "desired" voltage. Be shure to use the same mecanical load (ie free running) in both cases.
E. Cerfoglio
Buenos Aires
Argentina
Buenos Aires
Argentina
Yes ! that is sort of what I remember reading a long ago;
Good, time to lean the details. Thanks,
Miguel
Then, from what I understand, such motor should be capable of developing the same power on a lower DC voltage.ecerfoglio wrote: <snip>
So, the "correct" DC voltage for the motor will be lower than its AC one, but the exact value deppends on the design of that particular motor (on the relationship betheen R and X)
To determine that "correct" DC voltage you should run the motor with an ammeter in series, both on AC at the rated voltage and at DC with the "desired" voltage. Be shure to use the same mecanical load (ie free running) in both cases.
Good, time to lean the details. Thanks,
Miguel
 Abolish the deciBel ! 
Anybody recall the switch box for sale that claimed, "Run any power tool off your car"? Essentially switched the regulator out of the alternator circuit, put full battery voltage on the field winding, and the armature output would then vary with engine speed. It did indeed power a Skil saw with the correct engine speed.
Let us know how it works, Miguel!
Let us know how it works, Miguel!
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