Component RC snubber for speed controllers
Optional component snubber to limit voltage feedback to the speed controller.
This option for the RC snubber consists of components only; includes 1x .1uf 630V capacitor, and 2x 3W 15Ohm resistors.
Assembled and attached as per the wiring guide in the image gallery.
Although our speed controllers have on-board voltage protection (heavy duty 1200V diodes, the ones we don't build have a lot simpler protection) so if you plan to use those on a motor that feeds power BACK into the controller, you NEED a way to control the power feeding BACK into the controller, or you'll kill it. Its that simple.
There are circumstances where a high powered motor under heavy load can produce a sufficiently high voltage spike that feeds back to the controller and takes out the on-board protection (diodes or mosfets because they can't get rid of the voltage spikes that can accumulate, fast enough)
The way a PWM works, is that it turns the input voltage (say for example 12V) on and off very very fast, the motor only see's the average. So if you have a 12V PWM set at 50% speed, the controller is turning on half of the time, so the motor only ever see's 6v even though its being supplied with which is usually what the controller is powered by.
The speed is determined from the frequency as to how many times it fires per second. Now those spikes depending on the winding of the motor can exceed 2000V, and we can't have that feeding straight back into the controller because it will kill stuff quickly from these huge voltage spikes coming in via the motor controller outputs. They happen so quickly that a part can be fried in nanoseconds or even faster.
You can make your own, just don't try and use a wirewound resistor because this is also an inductor!
So why does this happen? Its because the large windings inside a motor are basically just huge inductors. When the field is fully charged and then collapses as the power switches off, the motor windings turn into inductors. The way an inductor works is to try and maintain a constant current, and because there is no more power being supplied, it increases its own voltage to keep the current the same. Unfortunately, this also makes the voltage rise to insane levels. Just as a fun fact, this is how they make voltage boosters or doublers!
Remember, when you're choosing a motor, you could take a 12v 40A model, or get the same results by using a 24V 20A model. While both the same, they each time you double the voltage, you half the current. Thats a super simplified version of the capacity of the simple inductor!
Some ways to reduce these huge spikes is to lower the frequeny of the controller (if possible) which will help reduce the amount of spikes coming from the motor. In these cases its best if at all possible to turn the frequency right down on your controller. And while this reduces the amount of spikes, it doesn't solve the issue of the high voltages feeding back to the controller!
Thats what this snubber does. The snubber circuit consists of two high quality metal film resistors and a single, non-polarized, metallized capacitor that are attached to the positive and negative motor terminals.
The reason its only a RC Snubber, rather than the better RCD snubber is because with the rcd snubber, your motor only goes in one direction. Whereas the RC Snubber can go in either direction. You would use a RCD snubber on the power input to the controller power input becase you can only enter the power in one direction. Its the controller itself that swaps the directions.
CAPACITOR DETAILS
- Rated Voltage: 630v
- Capacitance: 0.1uF (Microfarad, unless you ask for something different)
- For LARGER MOTORS, i.e anything above 300W (OR ANYTHING INDUSTRIAL) indicate in the notes which one you want!!! But for larger motors, please select the 0.1 Microfarad Capacitor, the 1uF takes too long to burn off if the frequency is too high
- 2 Metallized film resistors (3W, NOT wirewound, which creates its own induction!)
- Width = 27.5mm
- Height = 16mm
- Length of legs= 25mm
