Input protection for an analog read with a wide voltage range

[rmills]

Need some advice, I need to measure the voltage from a hand crank generator on a teensy 4.1 that has an average use voltage of 0-6V however in some cases such as really whipping the handle around I have measured a peak as high as 16-20V and in theory could spike higher but unlikely. I'm unsure where the line is for protecting the input and isolation overkill. Assuming 25V is near impossible, could I drive an analog pin safely with just a 20V Zener and a voltage divider as shown below? I added a ~5V safety margin. The bridge rectifier is a 50V schottky. I think generally there should be an op amp buffer or maybe it's "more correct" to buffer it with an additional ADC before the teensy input but on paper it seems like this would be fairly safe and avoid extra parts and cost?

I spent some time on digikey and google but did not see any sort of all-in-one package to safely read/monitor a voltage in these ranges, if there is a better way I'm open to suggestions.

Any thoughts or criticisms welcome.

 

[thebigg]

I would use something like an INA219

 

[rmills]

I actually did use an INA219 for a very similar project a few years ago. While it worked I had one out of the 4 die and then they were impossible to find for 6 months before I could get it running again, client was less than happy with me. I have to go back and see what I did on that one but it also has a 26V limit so I would need to add protection for the "protection" and while I'm using the teensy to design it the final will likely run on a PIC that does not have I2C. Was really hoping to find a simple analog method if possible. I feel like i'm adding so much extra for a simple thing but maybe it is the best way.

 

[MarkT]

The zener will blow as there is no current limiting before it. Perhaps split R1 into two parts, one before the zener, one after?

Measuring after the rectifier will mean there is some lost voltage compared to the actual output of the dynamo.

The low resistor values mean you may have to chose higher than 1/4W devices - do the math to be sure.