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I want to make a system with a dynamo where the dynamo can be made harder to turn (as a fitness device) and I want to be able to use an electrical signal from an arduino or similar to control the turning difficulty.

I guess that if I put a lot of small ohm resistors in parallel then this will make the dynamo harder to turn as more power is required, then relays could be used to connect and disconnect these resistors, with more resistors being connected to make turning harder?

Or is there a simpler way to do this with transistor control?

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  • \$\begingroup\$ Transistors could replace the relays (less noisily!). OR you can use a big transistor (2N3055) or several on a VERY big heatsink as a variable resistor (for up to 100W per transistor) by modifying the base current. \$\endgroup\$ – Brian Drummond Feb 28 at 12:25
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Or is there a simpler way to do this with transistor control?

Yes, this can be done with a power transistor switching on and off a load resistor using pulse width modulation (PWM) techniques in order to give the effect of a variable load current on the dynamo. The PWM signal can be sourced from the "arduino or similar" controller.

It's simpler if you know how and, more reliable in terms of longevity and accuracy of loading.

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