Hi
I am building a bicycle generator using a hoverboard motor, running the output through a rectifier to get DC voltage. Now it is quite easy to get to 80-100V for somebody with some "ambitions" and the my step down module allows only 72V max. What would be the easiest way to limit the voltage, so I don't fry the module? One option was to cut off the current with a relais, triggered by an Arduino that measures the voltage (with voltage divider)... Any easier solutions that I have not thought about?
Thanks

 

Welcome to AAC!
What is the step-down module used for? Can you post a link to its spec?

 

Is the ambitions 80-100V under load or no load?

 

You've given no information on the character of the Load that You expect to Power.

Regarding your "Module" ( what ever that might be ) ...........
I'm assuming that it's basically a Voltage-Regulator of some sort,
and You want a "Pre"-Voltage-Regulator to regulate the Voltage
going in to the Input of your Voltage-Regulator so that You don't smoke it.

If all the above assumptions are correct,
then You need to build, or purchase,
a Voltage-Regulator that can accept a higher Input-Voltage,
and skip using your existing "Module" all together.
Any other solution will just waste more Power and Money.

How much Current, at what Regulated-Voltage,
do You require for your Load ?
.
.
.

 

You could make a power Zenner and place it across the rectified output of the alternator..

This will clamp the voltage to about 70V max, but have no effect at lower voltages.
Make sure the transistor is on a heat sink.
I've made similar devices in the past but you may have to play with the values a bit.

 

You need negative feedback.

Maybe electrocute the cycler when he peddles too fast.

 

Hi.. Thanks for your suggestion, I like the negative feedback suggestion
The buck converter is this
DC 12-75V to 2.5-60V DC-DC Buck Converter 600W Buck Regulator
https://a.aliexpress.com/_mt1ENw0
No overvoltage protection. I need 12v and max 5A current. I will actually have to try it under some load, I suppose that it will not be quite as easy to get to 80V anymore.

 

Well, I ordered a buck converter 15-100V to 12V 10A. That seems the easiest solution.
https://a.aliexpress.com/_mqClIBe

 

Well, I ordered a buck converter 15-100V to 12V 10A. That seems the easiest solution.
https://a.aliexpress.com/_mqClIBe

Great, time to start working out for the maybe 150Wh per two hour session on the bicycle generator.