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ferrite ring question

Old 01-01-2012, 11:41 PM
  #1  
craigrs84
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Default ferrite ring question

I have a ESC with a switching BEC built in that has a ferrite? ring with the cord wrapped around it to help reduce interference.

I also have a seperate, external UBEC that I am using in place of the built in BEC on the ESC. The UBEC is also switching and also has a ferrite ring... so I have 2 ferrite rings.

My question is do I need them both? Can I remove the ferrite ring from the built in BEC on the ESC since I am cutting the red power cord. I'm guessing there's no need for it if power is not being supplied but wanted to make sure.

Thanks.
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Old 01-01-2012, 11:51 PM
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payne9999
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Originally Posted by craigrs84 View Post
I have a ESC with a switching BEC built in that has a ferrite? ring with the cord wrapped around it to help reduce interference.

I also have a seperate, external UBEC that I am using in place of the built in BEC on the ESC. The UBEC is also switching and also has a ferrite ring... so I have 2 ferrite rings.

My question is do I need them both? Can I remove the ferrite ring from the built in BEC on the ESC since I am cutting the red power cord. I'm guessing there's no need for it if power is not being supplied but wanted to make sure.

Thanks.
The reason they use the ring is because the wires tend to be an antenna radiating unwanted RF created by the switching frequency. Since you will still be using the white and black wires for motor control signals I would think you would still want the ferrite ring because the two remaining wires could still radiate some RF. Better safe than sorry. I am not certain by not connecting to the switching power supply that the circuit that potentially is making RF noise is not still active in some way.

Dave
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Old 01-02-2012, 06:56 AM
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kyleservicetech
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Originally Posted by craigrs84 View Post
I have a ESC with a switching BEC built in that has a ferrite? ring with the cord wrapped around it to help reduce interference.

I also have a seperate, external UBEC that I am using in place of the built in BEC on the ESC. The UBEC is also switching and also has a ferrite ring... so I have 2 ferrite rings.

My question is do I need them both? Can I remove the ferrite ring from the built in BEC on the ESC since I am cutting the red power cord. I'm guessing there's no need for it if power is not being supplied but wanted to make sure.

Thanks.
It might be that the switching power supply is radiating electrical noise, and the ferrite rings reduce this effect. But, that radiated signal would also be radiated from the INPUT of the uBEC, so it's a good question. It could send switching signals directly into the battery circuit of a receiver though. I've checked the output of a Castle Creations 10 amp uBEC, and it did have a lot of high frequency electrical switching noise on its DC output. My models have 5 of the CC uBEC's on five Spektrum AR7000 receivers, absolutely no bad issues have ever been observed with this combination.

At any rate, the switching power supplies I've checked operate at below about 100 Kilohertz, and as such might be radiating radio noise up into the IF frequencies of a typical 72 Mhz receiver. So, I'd be a little reluctant to use any uBEC on a low quality 72 Mhz receiver. Not that it might not work just fine, just personal policy.

If you're using that uBEC on a 2.4 Ghz receiver, wouldn't worry about it. No switching power supply can radiate electrical noise any where near 2.4 Ghz. (Thats 2400 Megahertz, or 2,400,000,000 cycles per second!)
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Old 01-02-2012, 01:32 PM
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What is the I F of GIGA sets ? If they use one ?

Servos with long leads can pick up noise & do random moves. Rub 2 pieces of metal together nearby. About 3' away. On my 72mhz systems & Hitec servos.
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Old 01-02-2012, 01:45 PM
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Something to remember about switching & non switching BECs

Non- switching does not cause noise. It may cause overheating shutdowns.
& a loss of power & lock the servos in place untill cooldown. 50 50 chance of a crash.

Switching BECs cause active random noise that will swing servos all over or into a stop. Total loss of control untill the plane comes close to the pilot again. More than a 50 50 chance of a crash in my opinion.
Never remove any Ferrite rings. They are a " Band Aid " for a VERY SERIOUS control problem at various flying distances.
I grew up on Ferrite Rings in USN radar systems.
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Old 01-02-2012, 03:11 PM
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payne9999
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Originally Posted by kyleservicetech View Post
It might be that the switching power supply is radiating electrical noise, and the ferrite rings reduce this effect. But, that radiated signal would also be radiated from the INPUT of the uBEC, so it's a good question. It could send switching signals directly into the battery circuit of a receiver though. I've checked the output of a Castle Creations 10 amp uBEC, and it did have a lot of high frequency electrical switching noise on its DC output. My models have 5 of the CC uBEC's on five Spektrum AR7000 receivers, absolutely no bad issues have ever been observed with this combination.

At any rate, the switching power supplies I've checked operate at below about 100 Kilohertz, and as such might be radiating radio noise up into the IF frequencies of a typical 72 Mhz receiver. So, I'd be a little reluctant to use any uBEC on a low quality 72 Mhz receiver. Not that it might not work just fine, just personal policy.

If you're using that uBEC on a 2.4 Ghz receiver, wouldn't worry about it. No switching power supply can radiate electrical noise any where near 2.4 Ghz. (Thats 2400 Megahertz, or 2,400,000,000 cycles per second!)
I should have said in my original post that the interference issue could be from radiated or conducted signals and the ferrite ring could be used to suppress both.

The thing is the switching frequency is not necessarily the primary issue and it doesn't have to get to 2.4 ghz to cause issues. However, if the rise time of the switching signals is quick enough it will cause a lot of odd harmonics up to and beyond 2.4 ghz. Theoretically it will cause an infinite number of odd harmonics. 1/t = the effective frequency of a waveform and not really it's primary clock frequency.

All this random looking noise can be troublesome and it is hard to predict the effects. If wires happen to be just the right length (like 1/4 wavelength) at one of these frequencies it becomes a very efficient antenna or at some frequency an inductor and the unwanted signals can then cause lots of problems.

Anyway, to make a long story short don't remove the ring, the original designers had a reason for putting it there....

Dave
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Old 01-02-2012, 06:20 PM
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kyleservicetech
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Originally Posted by cyclops2 View Post
What is the I F of GIGA sets ? If they use one ?

Servos with long leads can pick up noise & do random moves. Rub 2 pieces of metal together nearby. About 3' away. On my 72mhz systems & Hitec servos.
Good question, don't know if these 2.4 Ghz receivers use an IF frequency. At any rate most of the circuitry on these receivers is internal to a single microwave chip. Then add a few electronic components, and a microcontroller to control the microwave chip.

Take a look at the Microchip line of stuff. Their demo unit is about the size of a dime.

http://www.microchip.com/stellent/id...cName=en536084
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Old 01-02-2012, 06:27 PM
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Originally Posted by payne9999 View Post
However, if the rise time of the switching signals is quick enough it will cause a lot of odd harmonics up to and beyond 2.4 ghz. Theoretically it will cause an infinite number of odd harmonics. 1/t = the effective frequency of a waveform and not really it's primary clock frequency.

Anyway, to make a long story short don't remove the ring, the original designers had a reason for putting it there....

Dave
I've looked at the rise time of the switching circuit in my Castle Creations 10 ampere uBEC with my 100 Mhz Tektronics 2236 oscilloscope. The rise time of the switching circuit is many orders of magnitude less than 2.4 Ghz. The observed rise time was well within the capabilities of that 2236 scope.

You are correct though, leave the ferrite ring in the uBEC. My Common Sense uBEC's have the ferrite ring, and their output is very clean. My Castle Creations uBEC's do not have the ferrite ring, and the switching frequency of the switcher shows up as a low level AC signal on the CC uBEC's DC output. That's why, for me at least, I would not use one on a 72 Mhz receiver. Just my opinion though, it would probably work just fine on 72 Mhz systems.
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Old 01-02-2012, 07:46 PM
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Kyle

Remember over the years CC had screeching of the ICE ESCs. Timing had no effect on the problem. CC tried lots of things to stop the problem.

Problem could have been the UBEC & high load combining to randomly misfire the ESC outputs. I never followed the ICE problem to a conclusion.

So much switching power, on so tiny a PCB.
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Old 01-02-2012, 09:52 PM
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Originally Posted by cyclops2 View Post
Kyle

Remember over the years CC had screeching of the ICE ESCs. Timing had no effect on the problem. CC tried lots of things to stop the problem.

Problem could have been the UBEC & high load combining to randomly misfire the ESC outputs. I never followed the ICE problem to a conclusion.

So much switching power, on so tiny a PCB.
I've only got one CC ICE ESC, that unit is a 80 Amp ICE HV unit running on a 12S2P A123 pack on a Hacker A60-16M motor. Will be buying another 80 Amp HV unit this spring for another Hacker A60-5 motor now in another model.

Never had a screeching problem with the CC unit. But CC does have a recall on it, so I'll be sending it in soon.

As for tiny ESC's, note that the 80 Amp HV unit can handle over 3000 watts. Compare that to 120 VAC power, 3000 watts is 25 amps out of your 120 VAC outlet. That will kick out most main panel circuit breakers for outlet use. Amazing.
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