Overvoltage Protection Problem

Hey all,

I am trying to design a circuit which to rectify and boost the back-emf of a 3-phase BLDC motor (on a bicycle)to charge a 48V battery. As of now, the circuit works great, it can accept input voltages ranging from 5-56V and boost them to a Vout of 56V to charge the battery.

However, if the speed of the bike increses too much, the back emf will exceed 56V and this could potentially damage my circuit. What I would like to do is add a protection scheme such that if the back-emf increases over 56V, the rectifier is disconnected from the boost circuity and battery so as not to damage them. Schematic of my system and what i want to add is below.



I have tried putting a MOSFET between the rectifier and boost stages and using a gate driver to control it, but this did not work great. I am able to disconnect the stages by applying 0% duty cycle to the FET, but a 100% duty cycle (to leave it connected i.e. normal operating mode) causes my gate voltage to drop out completely instead of Vg=Vs+12V. :-?

Someone has suggested to me that i should use a dual-coil latching relay but I am not sure how this would work. Dont relays usually connect circuits? how will i use them to disconnect the stages?

If anyone can explain how the dual-coil method might work or if anyone has any other ideas I would really appreciate it.

Thanks a lot! :grin:

hi there is another option by using pic16f676 or any other pic having built in adc. u have to make coding in this manner that when voltages acceeded above limit it switch switch relay to cut i/p.

allstartyper said:

Hey all,

I am trying to design a circuit which to rectify and boost the back-emf of a 3-phase BLDC motor (on a bicycle)to charge a 48V battery. As of now, the circuit works great, it can accept input voltages ranging from 5-56V and boost them to a Vout of 56V to charge the battery.

If anyone can explain how the dual-coil method might work or if anyone has any other ideas I would really appreciate it.

Thanks a lot! :grin:

Click to expand...

Do not cut of the circuit suddenly . It can throw you out of control as the breaking effect get released suddenly.
Here is another option . After the bridge divide the potential by Two using two series caps across the supply and charge the battery using two separate circuits connected to each capacitor.