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I have four mini generators run by a blower. Each generator generates about 2 to 3 volts. When I connect all the four generators I get about 10-11 volts of AC. I convert the AC into DC using a bridge rectifier and get about 9-10 DC volts.

The moment I connect the DC into a 3 or 6 volt DC motor the four generators slow down or stop. What is happening here and how do I correct it?

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    \$\begingroup\$ Welcome to EE.SE. Your generators are too weak to drive the load (motor). \$\endgroup\$
    – user105652
    Feb 5 '18 at 23:05
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    \$\begingroup\$ You are taking too much current from them, increasing the torque load on them, which slows them down. That's what happens. There is nothing to correct. If your generators can supply more power, just blow harder. Otherwise, reduce the load or find better generators. \$\endgroup\$ Feb 5 '18 at 23:06
  • \$\begingroup\$ Why are you calling it "back flow"? \$\endgroup\$
    – Transistor
    Feb 5 '18 at 23:34
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You are witnessing the loading of your generators. It's one of the things that ruins perpetual motion schemes such as connecting a generator to your car to power the electic motor that's driving it. The electrical load on your generators will put a mechanical load on their rotation and slow them down.

You have another problem too. You are series connecting four alternators that are not synchronised in phase. If they are running slightly different frequencies then they will "beat" as they go in and out of phase with each other.

enter image description here

Figure 1. The sum of two sinewaves of different frequency. The "beat" is the difference between the two frequencies. Sourc: Vibration School.

If your voltages were a bit higher I would recommend rectifying and smoothing each generator but with such low voltages the diode losses will probably be unacceptable.

schematic

simulate this circuit – Schematic created using CircuitLab

Figure 2. Conversion of each alternator output to DC solves the phasing problem but voltage drops on the bridge rectifiers will be very significant at low output voltages.

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  • \$\begingroup\$ I thought when I connect the motor the current may be flowing back and work against the rotor in the generator - so I called it back flow with a question mark. I am just a high school student trying to do a project and trying to learn from experts like you. \$\endgroup\$ Feb 5 '18 at 23:58
  • \$\begingroup\$ Can I connect them in parallel and use one bridge rectifier to get rid of the "beat" problem? \$\endgroup\$ Feb 6 '18 at 0:08
  • \$\begingroup\$ No. That would not solve the problem. If one is trying to output a positive voltage and the other a negative they will cancel out to give zero. If you put a small load such as a bulb on your existing system you might be able to see the beat - the bulb will slowly fade on and off if the frequencies are close. Maybe try it with just two alternators and a 6 V bulb or even a pair of LEDs connected back to back. \$\endgroup\$
    – Transistor
    Feb 6 '18 at 0:15

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