Muller Dynamo

[chalamadad]

I don't have magnets on the back of the coils yet, I tried with ferrite magnets but no difference.

This is exactly why I suppose the magnets are being used for cogging reduction. Equalizing the drag can become more important if you are putting your coils closer to the rotor magnets.

[mondrasek]

@mondrasek
each coil is 3.9ohm, about 8 ohm for a pair.I use 4 fillar connected as tesla style, but I am not sure about the wire type... maybe 26 awg. If I connect a capacitor 10uf AC in series before the bridge then I get speed under load.unfortunately I have only one AC capacitor and I cannot test all coils with a capacitor connected.I tried a 10uf DC capacitor and is not working.

David

Are you using a dump cap on the o/p from the FWBRs?  If so, what size?

[mondrasek]

@Mondrasek:

I don't know what kind of scope you are using, but if it's a USB-type
DSO scope try disconnecting the AC plug from the PC/laptop.
It can give you funny readings. I had like 20 Volt P2P coil voltage waveforms when i touched the coil physically (groundloop).

You might not need more than 7 Volt per coil.
The voltage might add up when you parallel multiple coils, the effect reported earlier when adding many coils.

When you have your final coil figured out, try Plengo's series cap circuit.
It works, i tested it and the rotor does not slow down when the load gets connected.

My o-scope is a stand alone analog CRT type.

I have 3 pairs of coils mounted (so far).  When I hook only one up through the FWBR to the dump cap the cap will charge to a value ~same as the value on the scope across a single coil.  The final voltage is lower by about what you would expect for the drop due to the diodes.  When I hook up the other coils in parallel, the voltage does not go up.  But the cap will achieve it's highest voltage much more quickly after being shorted.  This is as expected if paralleling the outputs is only increasing the current.

[mondrasek]

This is exactly why I suppose the magnets are being used for cogging reduction. Equalizing the drag can become more important if you are putting your coils closer to the rotor magnets.

With the rotor and coil spacing getting even closer in my last set of tests I was able to confirm that the coil's reaction to backing magnets has returned.  Since the effect was not evident at the farther spacings, and was definitely very strong when I had preliminary tests with the coils as close as possible, I would say the effect increases as the rotor/coil spacing decreases.

While looking at the voltage wave form while introducing a backing magnet I could see that the wave shape changed slightly, but did not gain appreciably in amplitude.  It appeared that the "flip" portion of the voltage curve that happens when the the rotor magnets passes TDC of the coil becomes steeper.  I was planning to get scope shots but ran out of time yesterday.

As I recall from my previous testing at minimal rotor/coil spacing, the change in the voltage curve begins with that same flip portion of the curve becoming steeper and then the amplitude being increased as the magnets are brought in from far away towards the back of the ferrite cores.  At a critical distance the effect begins to reverse.  At too close, the voltage is even decreased.  If in contact with the ferrite, the voltage is decreased dramatically.

In that previous testing I noticed that the strength of the backing magnets also played a part.  But the distance from the back of the ferrite for maximizing the effect did not appear to change.  Once a magnet was placed at the correct distance, the voltage could be increase further by increasing the strength by adding more magnets to a point of diminishing returns.  But changing the distance at all could not improve the voltage further.

Please note that those preliminary tests were fairly gross and there may be some fine adjustments possible that I did not witness.

[mondrasek]

@mondrasec . How to make a variable load . Get some Nichrome wire . This is used in the heating elements of electric fires , toasters , dryers , also cooker elements but is harder to get out . Get it from a scrapyard or recycling centre . This wire can run red hot without damage . Now , with a length of this wire and 2 crocodile clips you can fine tune the resistance to within 1 ohm or less . You can add a series resistor to get it into the right range . Mount the nichrome on a fire proof mounting , or use it on its original mounting .

Excellent.  Now to convince the wife we need a new toaster...  Much appreciated!