Regenerative Braking (DC Motor)

Thread Starter

Loutr

Joined Mar 7, 2019
4
Hello to all!
I am interested in building an all electric go kart and i have been thinking about different features that it could have and i came across regenerative braking. The motor I will be using is a 48V 1kW DC motor. While I do have some experience with electronics, I have no clue about how stuff in the car industry works. For example should I take 4 smaller 12V batteries to match the 48V and simply PWM or should I take one bigger 12V battery and use a step up converter? Because a car battery has more than 12V and I don't know if the motor can handle this overvoltage. The one thing that concerns me most though, is how I could implement regen. braking. Because if I would connect 4 batteries and then just feed the current back to the battery it wouldn't work, because of the batteries higher voltage, right? Or if i use one battery and step down the 48V to 12V it wouldn't work for the same reason, or am I wrong?
Please share any experience you have with me!
Thanks in advance
 

mvas

Joined Jun 19, 2017
538
21 amps = 1,000 Watts / 48 Volts
21 amps (avg) is a reasonable amount of current

AT 12 volts you will need to control 84 amps

Buggies Gone Wild ...
 
Last edited:

Thread Starter

Loutr

Joined Mar 7, 2019
4
Okay thank you, didn't think about that... I still need a solution for my regen braking problem though
 

djsfantasi

Joined Apr 11, 2010
5,841
For a go-cart, do you need to save the energy or just brake the vehicle?

One simple way is to cut off the battery and connect the motor to a resistive load.

The problem here is the current. You need to be able to switch up to 21 Amps when cutting off the battery. And assuming you’re using 48V, consequently, you need a resistive load to drop 48V at 21 Amps. You could build a resistive load from power resistors and a huge heat sink. (that’s how early diesel locomotives did it).

Using Ohm’s law, V=IR and 48V at 25A, we get the following:

R=48/25=1.92

You can use a higher wattage resistor, such as a 50W or 100W. The links show a couple of possible choices from Amazon.

To switch the power to the motor, you can use an appropriate set of MOSFETs. If you switch the ground connection, look for a >48V and >21 Amp n-channel MOSFET. Perhaps these!

You should use a center-off SPDT switch as your brake, to prevent a direct short when braking. Or perhaps someone can provide more information than I can at the moment regarding switching One MOSFET will connect the motor to ground. The other MOSFETS are used to invert the brake signal and drive the third MOSFET.

Hope this gives you some ideas.
 

Thread Starter

Loutr

Joined Mar 7, 2019
4
For a go-cart, do you need to save the energy or just brake the vehicle?

One simple way is to cut off the battery and connect the motor to a resistive load.

The problem here is the current. You need to be able to switch up to 21 Amps when cutting off the battery. And assuming you’re using 48V, consequently, you need a resistive load to drop 48V at 21 Amps. You could build a resistive load from power resistors and a huge heat sink. (that’s how early diesel locomotives did it).

Using Ohm’s law, V=IR and 48V at 25A, we get the following:

R=48/25=1.92

You can use a higher wattage resistor, such as a 50W or 100W. The links show a couple of possible choices from Amazon.

To switch the power to the motor, you can use an appropriate set of MOSFETs. If you switch the ground connection, look for a >48V and >21 Amp n-channel MOSFET. Perhaps these!

You should use a center-off SPDT switch as your brake, to prevent a direct short when braking. Or perhaps someone can provide more information than I can at the moment regarding switching One MOSFET will connect the motor to ground. The other MOSFETS are used to invert the brake signal and drive the third MOSFET.

Hope this gives you some ideas.
Thank you, originally I wanted to store the energy.
 

mvas

Joined Jun 19, 2017
538
Are you designing and building the ESC - Electronic Speed Controller or will you be purchasing an off-the-shelf ESC with Regenerative Braking built-in?
Regenerative Braking can work very well - when designed properly it does not prohibit coasting
Also check out ... Buggies Gone Wild ... for a wealth of information regarding small electric vehicle design.
 
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