Schotkey Diodes??
08-18-2003, 07:46 PM
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Schotkey Diodes??
Hello All,
I know what Shotkeys do but do we really need them for bashing, Will it hurt the motor if you do not use one? Will you get better runtime, punch, Etc. Etc. Thanks is advance.
RCDoon
I know what Shotkeys do but do we really need them for bashing, Will it hurt the motor if you do not use one? Will you get better runtime, punch, Etc. Etc. Thanks is advance.
RCDoon
08-24-2003, 12:24 AM
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Schotkey Diodes??
shotkey diodes are a good idea to use them. If you esc need them you will probably fry it if you dont use them.
These shotkey diodes are use as freewheel diodes as it is technically refers to their use in switching systems. Their use is to let the back emf from the motor decay exponentially on its own while protecting the mosfet devices from it.
This is why all mosfet devices that have been designed for switching have the diode inbuilt
Using the diode should not have any difference to the power of the system. It should though give slightly longer runs and cooler esc.
These shotkey diodes are use as freewheel diodes as it is technically refers to their use in switching systems. Their use is to let the back emf from the motor decay exponentially on its own while protecting the mosfet devices from it.
This is why all mosfet devices that have been designed for switching have the diode inbuilt
Using the diode should not have any difference to the power of the system. It should though give slightly longer runs and cooler esc.
08-29-2003, 12:29 PM
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Schotkey Diodes??
If you are using a forward only esc, not using them may cause the brake fet(s) to burn out.
You should not use them if you are using a forward / reverse type esc
Always consult your owners pamphlet that came with the esc (way to small to call a manual).
You should not use them if you are using a forward / reverse type esc
Always consult your owners pamphlet that came with the esc (way to small to call a manual).
09-04-2003, 06:33 PM
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Schotkey Diodes??
Most ESCs have them built in... and no motor requires one. I have been running RC cars for about 15 years, and have never seen a use for one, other then on ESCs that require one. In which case, you need a different ESC 
09-04-2003, 10:43 PM
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Schotkey Diodes??
The diodes are required for my mtronics prodigy and novak cyclone.
Here's an exerpt from Novak's website:
-------------------------
The following is a brief explanation of Schottky diodes and their use with electronic speed controls.
A Schottky diode is a special type of diode with a very low forward-voltage drop. When current flows through a diode, it has some internal resistance to that current flow, which causes a small voltage drop across the diode terminals. A normal diode has between 0.7-1.7 volt drops, while a Schottky diode voltage drop is between approximately 0.15-0.45 – this lower voltage drop translates into higher system efficiency.
At partial throttle, a speed control switches the battery power to full-on and full-off at varying duty cycles. The ratio of the duty cycle determines the throttle setting – for example: 50% on to 50% off is 1/2 throttle. The Schottky diode is used to carrying the re-circulating current from the motor during the 'off-time' while the speed control is at partial throttle.
Similarly, the motor in a car is like a big inductor. During the off-time at partial throttle, the motor will not allow the current to just stop. Instead, the voltage across the motor will reverse, and current will flow through the Schottky diode. If no diode is present, the current will flow through a parasitic diode built into the brake transistors. The current flows through the Schottky diode before it will flow through the brake transistor because the forward voltage drop of a Schottky diode is less than the brake transistor diode (this is why Schottky diodes are used and not other types of power diodes).
For the highest efficiency, during the off-time while the motor continues to flow current, the voltage should ideally be as close to zero as possible. One reason Novak uses an external Schottky diode is because the closer the diode is to the motor, the lower the voltage drop during this period. This is due to the voltage drop through the wires back to the speed control. This will also reduce some radio noise due to the current spike not having to travel a long distance.
Speed controls like the Hammer, Racer, Tempest, Atom and the Cyclone are racing speed controls. For the ultimate performance, an external Schottky diode is used (The Cyclone has one built-in also.). As a result, the speed control is smaller. Also, as a convenience to the newcomer, Novak's sport models have it built-in.
Another reason Novak uses an external Schottky diode is to prevent the brake transistors from overheating and losing brake power. When a Schottky diode is built into an ESC, it is positioned next to the brake transistor. As the Schottky heats up, it heats the brake transistor and consequently loses braking power (the on-resistance increases).
The hotter the motor that is used (i.e. the lower the number of turns), the higher the current that flows through the Schottky diode. In some cases, two diodes connected parallel must be used (connect both striped ends to motor positive and both non-striped ends to motor negative).
Here's an exerpt from Novak's website:
-------------------------
The following is a brief explanation of Schottky diodes and their use with electronic speed controls.
A Schottky diode is a special type of diode with a very low forward-voltage drop. When current flows through a diode, it has some internal resistance to that current flow, which causes a small voltage drop across the diode terminals. A normal diode has between 0.7-1.7 volt drops, while a Schottky diode voltage drop is between approximately 0.15-0.45 – this lower voltage drop translates into higher system efficiency.
At partial throttle, a speed control switches the battery power to full-on and full-off at varying duty cycles. The ratio of the duty cycle determines the throttle setting – for example: 50% on to 50% off is 1/2 throttle. The Schottky diode is used to carrying the re-circulating current from the motor during the 'off-time' while the speed control is at partial throttle.
Similarly, the motor in a car is like a big inductor. During the off-time at partial throttle, the motor will not allow the current to just stop. Instead, the voltage across the motor will reverse, and current will flow through the Schottky diode. If no diode is present, the current will flow through a parasitic diode built into the brake transistors. The current flows through the Schottky diode before it will flow through the brake transistor because the forward voltage drop of a Schottky diode is less than the brake transistor diode (this is why Schottky diodes are used and not other types of power diodes).
For the highest efficiency, during the off-time while the motor continues to flow current, the voltage should ideally be as close to zero as possible. One reason Novak uses an external Schottky diode is because the closer the diode is to the motor, the lower the voltage drop during this period. This is due to the voltage drop through the wires back to the speed control. This will also reduce some radio noise due to the current spike not having to travel a long distance.
Speed controls like the Hammer, Racer, Tempest, Atom and the Cyclone are racing speed controls. For the ultimate performance, an external Schottky diode is used (The Cyclone has one built-in also.). As a result, the speed control is smaller. Also, as a convenience to the newcomer, Novak's sport models have it built-in.
Another reason Novak uses an external Schottky diode is to prevent the brake transistors from overheating and losing brake power. When a Schottky diode is built into an ESC, it is positioned next to the brake transistor. As the Schottky heats up, it heats the brake transistor and consequently loses braking power (the on-resistance increases).
The hotter the motor that is used (i.e. the lower the number of turns), the higher the current that flows through the Schottky diode. In some cases, two diodes connected parallel must be used (connect both striped ends to motor positive and both non-striped ends to motor negative).
