h bridge for diy riding cooler

Hello everyone,

I am starting to plan to make my own riding cooler here shortly and have a few prelim questions that i am hoping someone can assist me with. My budget only allows me to buy some parts at a time so this project is probably a few months out but I was thinking for the controller I could design my own H-bridge. Before I jump to the questions my system is as follows:

DC motor: 500-750W
Battery: 24V, 12AH

With these parameters I can expect to see a full drive @750W of around 32A with possibly inrush spikes higher. I wanted to rate my H-bridge to around 40A continuous just for some buffer. So I want to do P-FETs for my high side switches and N-FETs for my low side switches. I will have anti-parallel diodes to handle the EMF of the motor when the field collapses and it shuts off. I will have a cap to limit and battery spikes of the battery. I will have heatsinks on all the switches and drive the switches with a micro configuration (either direct, with small transistors, or drivers). I am thinking I can do it with an arduino since all I have to do is drive the high side to low and the low side to 12V above the gap voltage.

So my questions are:

Is there a way I can determine the EMF current to size my diodes correctly?

What will be the voltage seen at the N-FET on the negative side of the motor? I guess I have always been confused a little about the actual voltage. When the high side is on there is only a small voltage allowed across the source drain junction and a high current (2V on max and 30A). I guess any clarity on this topic in general will help.

Going along with the one above, what voltage will I need to activate the N-FET? This will determine if I need a driver or not to turn on the gate.

Does anyone have an example on how to use the back EMF for regenerative breaking? So I turn off the motor and allow a single path to stay open with a rectifier and put it to the battery?

Worst comes to worse I can buy a 750W controller made for scooters or what not but I think if it was simple enough I could manage to make it myself. So far all I see is:
4 switches
4 diodes
Cap
Driver (probably micro or transistors)
Various resistors

Any help would be appreciated. Thanks in advance.

I think all the mosfet's have internal diodes, which can handle the back emf..

That is true but i am not sure if they can handle a possible surge that a 750w motor can produce.

surge current handling is one thing.
but will 24v , 12AH battery give atleast the running power of 500W?

Well it should since those systems and batteries are currently used in e scooters. I can also implement PWM control to extend life so it doesn't have to be all the way on or off. Why wouldn't it? 24v would pull 30amp continuous at max but would kill the battery pretty fast. I could jump up to the 36v model or 48v for battery life.

Hello c10greg
u can use more fast Diodes for handling the back emf as the internal diodes are slow relative to MOSFETs
i prefer using All N channel mosfets especially in high power applications. U can use IRFP064
i see that u must use a driver to fire your MOFSTs especially if u use high frequency PWM for gatting. u can use IR2110 driver
For regenerative breaking u can simply turn off all your MOSFETs and the stored mechanical energy in the motor will go back to the supply "battery" charging it.

Hz2020