PWM Circuit Design for Regenerative Braking on 36V Mobility Scooter With 4 Motors

Using a 555 timer PWM or op amp PWM to feed a bank of MosFET's, electric mobility scooters have a hill hold/ regenerative braking to keep the scooter or wheel chair from running away going down hill. What circuit would I need so that when at full power starting down a hill, that when the power is reduced, regenerative braking will slow the scooter down, and when power is reduced to minimum, the scooter brakes automatically to a very slow speed? When power is increased the motor automatically powers up to the speed set with a 5K pot.

I am using 12V for the PWM control circuit to power the MosFET's for 36VDC batteries (42 to 43 V peak at full charge), with each motor (as many as 4 motors) pulling about 38 ampere each (yes I use a lot of high ampere MosFET's)

I am using relays to control direction since P-channel MosFET's are not adequate to use an H-bridge. This allows for ease of utilizing adjustable regenerative braking if I need to go that route.

I am considering an independent circuit dedicated for adjustable regenerative braking, but could use the automatic regenerative braking system. I am using a number of powerful motors, so off the shelf scooter controller will not due.

I had a bad heart attack 6 years ago that blew big holes in my memory, and some of these type of circuits are missing in my memory. Any information or schematics would be appreciated. I can supply a schematic for the PWM if needed. I have a number of PWM circuits if anyone is interested. And I have circuits for automatic battery charger circuits to maintain 12 V deep cycle batteries, and circuits for 8 to 12 LED battery monitors for 12V, 24V, and for 36V if someone would be interested that can help me with my project.

Thanks.
Jeff

Have you got any schematics at all Just one or two would be helpfull

I know what this does to you by the way if thats any concilation Not too many people seem to understand this iether

Hi Jeff,
Your motors need to work as generators to draw mechanical energy and so to slow down.
There are two ways. 1. you use a low high power resistor to burn the energy directly.
2. you can use a voltage doubler to take the lower generating voltage to feed back in the battery. Based on that trick you can use again a PWM to control the braking/feed back.

Mark,

Here are the basic power and braking circuits. I use relays to control Fwd - Rev - Braking.

The PWM001 shows the basic PWM speed control circuit. I also use capacitors across the diode. I tune them in using an oscilloscope. I am running about 16K frequency to reduce the audible noise.

Question – I have only seen one schematic showing a diode across the Drain and Supply. What is the purpose for this??

The Regenerative Brake is a simple full wave bridge system so the unit can be traveling in either direction, and the braking is still functional. I use a relay system for Forward – Reverse – Braking in either direction.

I still have a three week loss of memory before the heart attack, and big holes everywhere else. I am either too stubborn to quit, or too stupid to know when to quit... LOL ! I have permanent heart damage, but life goes on! Thanks for the concern.

Jeff

Peter,

Centuries (decades) ago, I called it dynamic braking. Either for DC motors, like in railroad locomotives or for AC motors through a full wave rectifier. I showed people how well it works on a glass factory line to test bottles just made coming out of the molds. They tried to use mechanical brakes and the bottles fell over a lot.. I set up a variable electric brake on a 3 phase motor to bring it to a gentle but controlled stop.


Here are the basic power and braking circuits. I use relays to control Fwd – Rev – Braking.

The PWM001 shows the basic PWM speed control circuit. I also use capacitors across the diode. I tune them in using an oscilloscope. I am running about 16K frequency to reduce the audible noise.

Question – I have only seen one schematic showing a diode across the Drain and Supply. What is the purpose for this??

The Regenerative Brake is a simple full wave bridge system so the unit can be traveling in either direction, and the braking is still functional. I use a relay system for Forward – Reverse – Braking in either direction

I have been considering usiing a boost to feed back into the batteries.

Curtis Instruments uses an auto braking in their controllers for mobility scooters and wheel chairs. How do they work, and how would I boost voltage to dump back into the batteries when I am only generating 3 or 4 volts with the motors?

Any information would be appreciated.

Thanks
Jeff

Simple circuit can be; use a switch to switch off DC supply to all the motors and short motor terminals, this generate reverse voltage in the motor and motor stops forward movement, this is how dynamic breaking can take place and electric mobility scooters stops or moves slowly.

Dont let that worry you Jeff Ive been through the same myself keep at it

You need to to keep brain active and open memory cells again

It does take time especially after sever shock mental or physical or both For me I found programming the art of bringing memory back together again so much so that my memory now extends back to the age of 3 which in some cases can be equally disturbing

Might pay to try your hand at that It defenately helps to improve memory not only this but I found it nessecary to keep at this as at one point I thought I was going mad So I kept at this to ensure that my mind was working logically and I wasnt imagining things, which if you are or have suffered from some type of mental illness people take advantage of and do thier level best to make your life a misery and they certainly seem to know how to do this alright

A liitle advice as to what helped me


So Nothing to worry about my friend or be ashamed off I understand exactly what your going through

The diode across the fet is normally incorperated into the mosfet anyway depending on the mosfet you use Typically its there to prevent back emf from the motor damaging the fet but i see you have one across the motor anyway If you were using an IRF540, IRF640, IRF1310 you will find the diodes inbuilt

If your concerned over this simply download a datasheet and that will normally provide those answers

AS far as the rest is concerened im about to study your diagrams in full so i understand what you are doing etc then ill get back to you

Mark