Alternator design

[PTwizz]

Hello good people,

I would like to know if it is possible to convert a dynamo (field wound, not permanent magnet type) to operate as an alternator. The hardware appears to have the required elements, suggesting that I might be able to convert from commutator to slip rings, and excite the field windings from a suitable regulator circuit.
I don't fully understand the workings of an alternator regulator. Can anyone direct me to a website which explains the circuit and its function? The dynamo is fitted to a motorcycle, and will be required to output 12V at around 100W.

Pete.

 

[maged541946]

Hi,It depends on the model, they all are coil(s) rotating in magnetic field which results in AC not DC, then the use a way or another to make it DC, so you may find yourself using one coil from the set in the device, this will reduce the power out, or you may get a frequency changing with speed too.

Maged A. Mohamed

http://magedm.freeyellow.com

http://www.magedsoft.com

 

[Whiteknight]

Hi,

Essentially, no it is not a practical proposition. All alternator is of 3-phase design terminating into a full wave bridge. The output is DC in nature, all be it 'dirty DC'. The other point to remember is that the staor windings are kept live and the armature is selectively energised to 'live' up the alternator when running.

You could I guess build something cia the two pole structure that you would have in the dynamo and then dc rectify its output but then you would not have any shunt regulation in position and it would most likely run up to about 18v. So sorry but no.

 

[felixc]

Out of curiosity, why do you want to make it an alternator?

 

[PTwizz]

Felix,

I am not too concerned about it being an alternator, so long as I can get the required power from the device. I was under the (possibly misguided) impression that an alternator was easier to control/regulate than a dynamo.
I have been experimenting, turning the armature at 1000rpm, with 12V DC across the field windings, the armature was able to produce 11 amps at about 7V when loaded. This power was taken off at the commutator, where I assume an oscilloscope would show a heavily clipped sine wave. My reasoning is that if I were to change to slip rings, I could feed into a multi-phase rectifier and extract more of the available power.
I may never make a useful alternator, but I'm interested now, so I'll keep tinkering and see what I can learn.

Pete.

 

[felixc]

I'm not sure that you could get more efficiency after making it an alternator. In both cases the battery is what smoothes the peaks into a clean DC. IMO, going to an alternator was a matter of reliability as the slip rings are gentler on the brushes.

Or was there something about a stator/rotor principle that makes it more efficient in one way or the other? Is there anyone old enough in the forum, who remembers what was behind the move from generators to alternators in the cars? The advent of power diodes for sure, the reliability of the sliprings for sure, but anything about better efficiency?

I guess that there is no room on your motorcycle to try to fit a bigger one than the one you already have. 100 watts is not such a high output. Is your gen running at the same RPM as the engine? 1000 rpm is a low speed for a generator. How does it fare at higher revs?

 

[PTwizz]

Felix,

I could fit a standard car alternator on the bike, but it is a custom project, and I would like to preserve the appearance of the original mag/dyno setup. The generator runs at approx 2X crankshaft speed, but the bike is a '53 Panther 600cc single, which doesn't do rpm! I am testing at 1000rpm because that's the top speed of my lathe. There is a commercially available alternator that is a direct replacement for my dynamo, but it's a permanent magnet type with a regulator that simply dumps excess power as heat. If possible, I'd like to build something slightly more refined.
I have heard that dynamos can be persuaded to run at higher voltages than they were designed for, does anyone know how?

Pete.