Voltage clipping help.

[kaarvannan]

Hi all,
I have a DC input from a battery (36V) to a motor controller. However, sometimes a fully charged battery has up to 42V. Since my motor controller is rated for 40V I need some kind of a clipper circuit that cuts off any excess voltage.

The only thing I can think of is a Zener diode with zener voltage of say 36V. Will this work? how much resistance do I need to add in series to the power supply if the current could be as high as 3 Amps.

Are there better ways to accomplish this?

Thanks in advance!!

Cheers,
kaar

 

[Grossel]

A zener will most likely just broke as the inrush current will destroy it any time the voltage exeed the zener break voltage.

But - a zener combined with a transistor to a relay will probably work.

 

[kaarvannan]

View attachment 65525


I am sorry I dint quite understand you there. I have attached a circuit diagram of what I have in mind. Please verify and let me know if this will work.

 

[Grossel]

Are the motor supposed to be connected directly in parallel to the zener?
If that's the case, the motor will probably not run because the resistor puts a limit to the current.

Anyway, the zener will get hot unless it have some cooling. Depends of its physical size.

 

[ronsimpson]

Kaarvannan, In you circuit the 100 ohm resistor will limit the power to you motor. You need a circuit that will allow the motor to run under full power at 36 volts but remove only the voltage above 40 volts.

Look at these parts: LT4356, LTC4360, 61, 62, 63, 65, 66
https://www.linear.com/product/LTC4366

These parts limit voltage and some also limit current.
The LTC4366 limits the voltage with a MOSFET. At low voltage it only adds a fraction of a ohm. At high voltage it limits the voltage to any value you want (40V).

https://www.linear.com/product/LTC4366

 

[WTP Pepper]

Either way you are sailing a little close to the wind. You need a higher spec controller.