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Old 11-15-2006, 01:05 PM   #1
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ENGINEERING ABOUT DIODE

I have a question that was unable to be answered by any technical department of two Speed Control Manafacturer's which will remain nameless but not shameless. Anyone want to give it a shot????????
A Diode is wired in parallel with the motor and is supposed to keep electical spikes from feeding back into the speed control. Now for the tough part. Anyone who knows parallel circuits would know that the spike does not have to go through the diode because it is not in series and has a direct wire into the speed control, therefore making the diode useless. What does the diode do when wired in parallel?
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Old 11-15-2006, 01:16 PM   #2
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The forward voltage drop of a Schottky diode is so low that the back emf uses that path rather than the path offered by the brake fets.

Well, that's what I always thought, be glad to hear if I have it wrong/too simplistic
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Old 11-15-2006, 01:19 PM   #3
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The diode will only carry current in one direction, right. So, it will "short circuit" the current/spikes/whatever with the wrong pollarity. The current with the correct polarity will not be shorted and flow back to the speedo....

Hope you got that?
Not so good to explain things in English
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Old 11-15-2006, 01:40 PM   #4
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Eirik is right. By wiring it in parallel with the motor, it provides a path for flow from one pole of the motor to the other, which allows the energy to be dissipated. It literally takes the path of least resistance, and that the diode. Its also why a schottky is used. Schottky's are diodes having superior characterisics in this regard. If you wired it in series, yes it would block reverse current flow, but it would not allow that flow to go somewhere. Voltages would spike higher. Its like a by-pass in that configuration, as opposed to just a one way check valve, talking in terms of fluid flow analogy. As well, if it was wired in series, it would reduce the efficiency of the system by being a source of voltage drop in the supply to the motor. It would get hot, and use energy that would have been used to make you go faster.

Last edited by Iceracer; 11-15-2006 at 01:55 PM.
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Old 11-15-2006, 05:09 PM   #5
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Very well put. It's like a ground loop isolater. When I drew out the schematic on paper I used power and ground going to the motor but never took into consideration the schematic of what is inside the speed control. Now I can sleep at night!
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Old 11-16-2006, 03:47 AM   #6
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Quote:
Originally Posted by "Spanky
Now I can sleep at night!
I just hope you didnt wake up at 3am one morning with the thought of starting this topic
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Old 11-16-2006, 08:42 AM   #7
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It is just something that always bothered me because I know its supposed to be there I just wanted to know how and why. Now that I know and understand I will take the extra time to make sure everything is perfect.
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Old 11-16-2006, 08:52 AM   #8
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I'd love to know why i've been damn unlucky in the last two meetings i've been to, 2 siezed diffs, a cooked motor, a wheel coming off and two unfinished finals later wasnt exactly how i'd planned to see things work out....

Then I think about a diode and think, gee I wish thats all I had to think about - i'll trade you some bad luck if you want?
3rd time lucky then?
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Old 11-16-2006, 09:45 AM   #9
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Are there any other performance advantages to running a diode, other than keeping your speed control from letting the smoke out? I keep hearing that they aren't necessary in stock or 19 turn brushed motors, just for mod.

What else does the diode do? Does it restrict power at all? If so, I won't bother with it for stock. Some believe that it stores power somehow and gives you more punch. I don't see much difference with or without.

Help me understand.
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Old 11-16-2006, 10:05 AM   #10
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If it restricted the power I dont think many people would be using them at all!

I have tried with and without on various motors and not "felt" any difference.

I would err on the safe side though,so if your esc instructions say use one then I would. Better safe than sorry....
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Old 11-16-2006, 10:10 AM   #11
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A diode is not restriction, thats what a resistor is. A diode acts as a valve to
prevent electrons from flowing in one direction there by preventing any
electrical spikes from feeding back into the power feed. You will not feel any performance difference, it is simply an insurance plan if you will.
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Old 11-16-2006, 10:21 AM   #12
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It is claimed to reduce arc across the brushes, radio interference and improve braking. Since it does no harm unless its installed backwards, I see no reason not to run one. Don't forget that a dc motor spun quickly enough is a generator. That energy has to go somewhere.

Quote:
Originally Posted by Motor City Hami
Are there any other performance advantages to running a diode, other than keeping your speed control from letting the smoke out? I keep hearing that they aren't necessary in stock or 19 turn brushed motors, just for mod.

What else does the diode do? Does it restrict power at all? If so, I won't bother with it for stock. Some believe that it stores power somehow and gives you more punch. I don't see much difference with or without.

Help me understand.
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Old 11-16-2006, 10:32 AM   #13
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so what diode to run?
I have thousands of diodes at work, but I dont know their values.
Would there be identification numbers that would work better than others, and would anyone know these part numbers and their values so one could go to the local electronic supply store and buy some rather than shelling out 15 - 30 bucks for a much more or equivalent?
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Old 11-16-2006, 01:15 PM   #14
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Minimum 45 volts (higher is ok)
At least 9 amps rating (higher is ok)
no more than 0.4 volts forward voltage drop (higher number is worse)

and that will meet or exceed the typical shottky sold for rc motor purposes. Diode specs are available online to find some typical numbers.
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Old 11-16-2006, 01:19 PM   #15
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Novak describes function and characteristics of schottky diodes uses in conjuction with their speed controllers:

http://www.teamnovak.com/tech_info/m...o/schottky.htm
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