Regenerative braking

Hello, I am using a pic12c508 to control a 24v 250w motor and wish to add regenerative braking via a second mosfet. My problem being that I am unable to find any data for the inductance of the motor (unbranded). I am wondering what ballpark frequency would be required for the 12c508 to switch the second mosfet between motor short circuit and open to allow sufficient time for the voltage to build up and then with the motors inductance charge the battery.
Any advice in this matter gratefully received.
Many thanks
(would monitoring the voltage in the motor windings via a shunt and then say at 12v (hopefully with the motors inductance pushing the voltage to battery above 24v) open the mosfet be a viable option)

My old-time knowledge about your question is.....
The energy to charge back in-to the battery comes from the DC motor acting as a generator, and the actual E x I power (watts) is derived by stopping/slowing the inertia of the physical load.
If your motor has a shunt winding, that winding can be used as a field to boost the generated voltage (as the motor slows) higher than the battery voltage to charge back. You probably know that the only way to charge is to have a voltage higher than the battery voltage
You were basically talking about a "boost converter" so you could calculate and use your own inductor/frequency/switching network just figuring on a DC voltage from the motor ranging from say 5 to 25 volts as the motor slows and stops.
What about all that junk?
good luck
don
amgen

After some sleepless night trying to get the old grey matter firing i think i might be making progress. It certainly would have been easier knowing the motors inductance, but i think i have a ballpark figure for the freq to reduce battery ripple and duty cycle to prevent continuous mode. (going to test with a different chip using hpwm)
Many thanks for your reply