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Old 03-26-2016, 04:11 PM
mbrownn mbrownn is offline
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Join Date: Jan 2011
Posts: 1,638
Originally Posted by marseye View Post
Yep, it does. But seems to me that this tranformer still needs big current to work.


The following is out of the main present subject, just about a dc motor-transformer effect, for the record :

I've been playing for long now with a dc 4-12v 2 magnets poles motor with 3 commutator segments (and as much drums) [dc drill type].

I had rewound it a star armature : all the ending terminals were connected to a ring belonging to the upper shaft, which was electrically connected to the frame by the shaft through the roll-bearings , thus making the frame a 3rd "permanent" contact (the 2 firsts are the brushes).

Having sanded the edges of the cover that holds the brushes, it can be rotated easily). But then, the maximun usable values (or it would burn down) was around 6v - 1.5amps. I generally fed it with 3 to 4 v.

Well anyway, I could at least observe a transformer effect : feeding one brush and the case, there's always a slight higher voltage, approximately 1/4 higher, between the 2 brushes (but less output current, of course). They could light a low dc bulbs (little cars's lamps) better than directly to the battery while it ran the motor. Plus, of course, the motor's shaft was running (I used to fit to it the long middle of a cork wine stopper, as a flywheel).

I estimate the electric transformation efficiency was maybe around 70% (maximum, depending on the extra load; from the half "maximum" real capacity of the AA Ni-Mh batteries perspective ) for 3v. The torque stayed anemic. Speed is then irrelevant.

Any capacitor was worsening the efficiency. This configuration couldn't recharge any "external" cell (as much as the diode for it didn't help it neither). So; really, just here for the record.
Generally speaking it is accepted that motors require current to work. (I accept that some do work on voltage with little current) The Universal motor requires current, doubling the current doubles the torque etc. Similarly transformers do the same. Donít be afraid of current unless it exceeds the capabilities of the windings. Not only that but our devices also require current.

I donít know where the excerpt is from so cant really comment on it other than this. When we have multiple coils on the same magnetic circuit, they will interact provided their circuits are closed. Ie transformer interactions. These interactions can be blocked or exploited as required. If blocked your efficiency will likely be low and if exploited as in the induction motor then efficiency will be relatively high.

I have run 12v motors producing significant torque at 3 or 4 volts because I used the motors designed current.

If you have a 12v motor held at stall, it only takes 3 or 4 volts to produce rated torque, so only 3 or 4 volts are needed to do the work. If we eliminate BEMF we can run a 12v motor at full power at 3 or 4 volts. So the voltage above does not surprise me.

Capacitors generally have a poor efficiency, generally 50% so saying that capacitors reduce efficiency makes sense.
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