Voltage Clamp Resistor for motor braking with the Sabertooth

I have a Sabertooth 2x32 motor controller, which will be used to drive a load with a lot of rotational inertia.  It will be battery powered, with Lead Acid batteries. I am a little concerned about the issue of feeding a lot of current back to the batteries, when the regenerative braking is used.  Also, for testing, I am using a power supply and some small motors without much of a load on them, and the power supply should not be permitted to get any voltage back from the regenerative braking.

I imagine I should consider using some "voltage clamp resistors" as a place to dump my back EMF from the motors, when I am stopping them.  I see that is an option with the Sabertooth motor controllers, but they don't go into detail.  I see that there are two connectors for powering a electromagnetic brake, or to connect the voltage clamp resistors.  But, it is limited to 8 Amp.  If the motors can be driven with 32 amps, then if I stop them at the same rate that I accelerate them, I may be needing to dump current in the range of 32 amps x 2.  Though, I am doubting it is that simple.

My drive system will be a v-belt drive, so that I can deliberately permit the belt to slip to protect the gear motor from being back-driven too much.  I.e. a cheap over-dive clutch.  So, that may also protect me from getting an extreme amount of current from the motors as they stop.

Perhaps, when I am in my final version, with the batteries installed, I should have both the regenerative braking and the power resistors there, so that I can have them both function as my current dump.  But, I have no idea if this is something that can be configured on the Sabertooth.  Perhaps I can do it with components, by simply putting a resistor in series with a diode at the battery wire.  So, when the current is driven back into the battery, the resistor will be acting in parallel, and so take some percentage of the current.  When I am drawing power from the battery to the motors, the diode would allow the current to bypass the resistor.

I don't have much experience with this stuff, so I felt it would be wise to run this by you all, and see if my thinking is reasonable.


Hi Joe, just wondering how

Hi Joe, just wondering how you got on with this? I have a similar question?

- Nathan

Me too - any joy?

Me too - any joy?

Regenerative braking

I’m also using a Sabertooth controller on my large robot Jazzy. I have found these controllers to pretty much be bulletproof and don’t need any modification. I’m pretty sure you can turn off the regenerative braking by the DIP switches if neccessary. Putting a diode & resistor in series with the battery isn’t going to do anything but severely limit the power available from the battery. If you’re drawing more than a few hundred milliamps run current from the battery, the drop across any diode and / or resistor combination will be huge.

I am not sure exactly what

I am not sure exactly what regenerative braking is but on the assumption it’s the braking system used on wheelchair motors yesterday I managed to get my setup working.

I am using a Raspberry Pi connected to a Sabertooth 2 x 32 via USB.

I connected the brake power cables to P1 and P2 on the Sabertooth and this appeared to switch the brakes off so that when a signal was applied to turn a motor on they worked. If it didn’t work I guess the motor would have produced an amp stall current higher than the meager 20 Amp Fuse that I fitted on the battery power line?


** Regenerative braking is**

 Regenerative braking is used to turn the braking enerty into electrical power, that is used to re-charge the batteries.  This is possible becuase motors are also generators.  That is, if you spin the motor, it generates electricity.