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I'm trying to make my own alternator & study the physics behind it.

So I have a circle of magnets rotating over 4 coils, forming a square (90 degrees each).

When I remove 3 coils from the square and only rotate magnets over 1, the coil produces ~6 volts AC.
However, with 4 coils, each coil produces only ~3 volts AC.
I even tried with 8 coils (in a circle configuration), and they seem to generate each ~1.75 volts AC.

Why is that?

More infos:
The coils are connected in parallel, not series.
Each coil has between 30-40 ohms of resistance.
They are very close to each other (~ 5 mm of distance between 2 coils).
Their winding are all in the same direction, and the magnets all have the same polarity.
The coils are NOT connected to a load, only to a multimeter (1 coil at a time).

Update:
To clarify: I test the voltage 1 coil at a time using 1 multimeter. Thus, the coil being tested is not connected to the circuit, only to the multi meter.

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    \$\begingroup\$ can you draw a circuit diagram with the circuit tool? edit your question and push the circuit tool button. \$\endgroup\$
    – Voltage Spike
    Mar 31, 2023 at 16:59
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    \$\begingroup\$ A picture of your setup would also be helpful. If your coils are in parallel, you have one generating an EMF as it links the magnetic flux while the others are loading it or possibly generating an opposite EMF? \$\endgroup\$
    – John D
    Mar 31, 2023 at 17:30
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    \$\begingroup\$ Yes, please show a photo or a drawing of the apparatus. As I understood the description, you shouldn't be getting any current at all \$\endgroup\$
    – user253751
    Mar 31, 2023 at 18:29
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    \$\begingroup\$ each coils produce only ~3 volts AC. ... how do you know this? ... you said that multiple coils are connected together \$\endgroup\$
    – jsotola
    Mar 31, 2023 at 18:48
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    \$\begingroup\$ A sketch indicating positioning including distance between magnet poles and coils as well as axis of rotation and interconnections (if any) would help me significantly. Or a picture. \$\endgroup\$
    – greybeard
    Apr 1, 2023 at 2:37

2 Answers 2

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The coils are connected in parallel, not series.

As described, the coils will be able to produce positive as well as negative voltages so, if one coil is individually peaking positively, it might be "held-back" (or restrained) by other coils producing a negative voltage or 0 volts. You just can't parallel coils and have a sensible result unless, the outputs are all pretty-much in phase with each other.

Alternative idea; connect the coils in parallel using diodes forming a rectifier.

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Nevermind, found the culprit.

If the distance between the magnets and a coil is event 1 mm differents, the voltage can differ significantly. (1mm adds 50% voltage in my case).

So the weight of multiple coils , believe it or not, is pulling down the plate of 1 or 2 mm.

Thanks again for all your excellent suggestions guys !

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  • \$\begingroup\$ Yes, the magnetic gap is critical. Most generators use a rotor and stator where the gaps are very consistent and unable to be influenced by mechanical conditions. It's good that you found the reason. Could you provide a picture of your machine? \$\endgroup\$
    – PStechPaul
    Apr 1, 2023 at 23:27

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