Pulsating sound from inductive coil...Uh-oH!

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pendragon_01
 
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Pulsating sound from inductive coil...Uh-oH!

Post by pendragon_01 »

hello
I have been working with the inductive coils set and it charges very, very slowly, but that is another issue. What is concerning me most is a low buzzy sound that lasts about 2 seconds and occurs every 5 seconds as the coils are aligned and the charge is happening. Any thoughts as to what this sound is? is it normal..like related to the inductive effect? Is it related to the absolutely glacial charging speed? should i put a oscilloscope on it?

Thanks!
pendy

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zener
 
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Re: Pulsating sound from inductive coil...Uh-oH!

Post by zener »

I will guess that is when the charge is happening. Do you have a scope or meter? Maybe you can verify that.

pendragon_01
 
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Re: Pulsating sound from inductive coil...Uh-oH!

Post by pendragon_01 »

Yes, the sound only occurs when the charge is happening. I have confirmed it with a multi-meter. I just wanted to get some insight into the nature of that sound. Is it dangerous? perfectly normal? related to the slow charge? any help would be much appreciated.

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adafruit_support_bill
 
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Re: Pulsating sound from inductive coil...Uh-oH!

Post by adafruit_support_bill »

It is not unusual for an inductive coil to generate audible noise. The waveform fed to the transmitting coil creates a varying magnetic field which is picked up by the receiving coil. The varying magnetic field causes the coils themselves to vibrate. If that happens at an audible frequency, you have sound.

pendragon_01
 
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Re: Pulsating sound from inductive coil...Uh-oH!

Post by pendragon_01 »

adafruit_support_bill wrote:It is not unusual for an inductive coil to generate audible noise. The waveform fed to the transmitting coil creates a varying magnetic field which is picked up by the receiving coil. The varying magnetic field causes the coils themselves to vibrate. If that happens at an audible frequency, you have sound.
So this sound could be completely normal and unrelated to the slow charge rate. OK, thanks.

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adafruit_support_bill
 
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Re: Pulsating sound from inductive coil...Uh-oH!

Post by adafruit_support_bill »

buzzy sound that lasts about 2 seconds and occurs every 5 seconds as the coils are aligned and the charge is happening.
I suspect that the slow charge is due to the fact that it is only charging 2 seconds out of every 5. That is probably the problem that needs to be solved.

pendragon_01
 
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Re: Pulsating sound from inductive coil...Uh-oH!

Post by pendragon_01 »

adafruit_support_bill wrote:
buzzy sound that lasts about 2 seconds and occurs every 5 seconds as the coils are aligned and the charge is happening.
I suspect that the slow charge is due to the fact that it is only charging 2 seconds out of every 5. That is probably the problem that needs to be solved.
So you believe that the sound should be constant not intermittent?

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adafruit_support_bill
 
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Re: Pulsating sound from inductive coil...Uh-oH!

Post by adafruit_support_bill »

The sound is a side-effect. I would expect the charge current to be constant. From your statement, I inferred that the charge is only happening 2 out of 5 seconds.
buzzy sound that lasts about 2 seconds and occurs every 5 seconds as the coils are aligned and the charge is happening.

pendragon_01
 
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Re: Pulsating sound from inductive coil...Uh-oH!

Post by pendragon_01 »

I am powering the coils using a custom power supply i built not the recommended adapter. its kinda similar to minty boost. I am supplying 9v to the transmitting coil but without detailed specs for the induction coil kit(not available - i know) it may be nigh on impossible to troubleshoot if the inconsistent charging is a current (amp) issue or a power quality/conditioning issue.

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adafruit_support_bill
 
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Re: Pulsating sound from inductive coil...Uh-oH!

Post by adafruit_support_bill »

These things are only about 40% efficient - even that assumes optimal coil alignment. So the input power needs to be substantially higher than what the load is trying to draw. It may be that your power supply is cutting out periodically due to overload.

pendragon_01
 
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Re: Pulsating sound from inductive coil...Uh-oH!

Post by pendragon_01 »

adafruit_support_bill wrote:These things are only about 40% efficient - even that assumes optimal coil alignment. So the input power needs to be substantially higher than what the load is trying to draw. It may be that your power supply is cutting out periodically due to overload.
Im supplying the 9v the coils need. the phone should only draw 5v. I will check the current supply from all points in the transmission as well as confirm the phone draw.

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adafruit_support_bill
 
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Re: Pulsating sound from inductive coil...Uh-oH!

Post by adafruit_support_bill »

Most phones need at least 500mA @5v (2.5W) to charge. To get that, you will need 9v@ ~700mA (6.3W) on the input side.
2.5W * 2.5 / 9V = 694mA

pendragon_01
 
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Re: Pulsating sound from inductive coil...Uh-oH!

Post by pendragon_01 »

Thanks!
One more question - i have been shorting the data pins together, but the net result has been impractically slow charging. Should I add a few resistors on the data lines ala minty boost to try to get the charging phone to draw higher current? Should i use the exact same resistors in the minty boost or does that depend on the charging phone?

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adafruit_support_bill
 
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Re: Pulsating sound from inductive coil...Uh-oH!

Post by adafruit_support_bill »

The charging protocol depends on the phone. http://en.wikipedia.org/wiki/USB
Two types of charging port exist: the charging downstream port (CDP), supporting data transfers as well, and the dedicated charging port (DCP), without data support. A portable device can recognize the type of USB port; on a dedicated charging port, the D+ and D− pins are shorted with a resistance not exceeding 200 ohms, while charging downstream ports provide additional detection logic so their presence can be determined by attached devices.[75]
...

Before the battery charging specification was defined, there was no standardized way for the portable device to inquire how much current was available. For example, Apple's iPod and iPhone chargers indicate the available current by voltages on the D− and D+ lines. When D+ = D− = 2.0 V, the device may pull up to 500 mA. When D+ = 2.0 V and D− = 2.8 V, the device may pull up to 1 A of current.[76] When D+ = 2.8 V and D− = 2.0 V, the device may pull up to 2 A of current.
But it doesn't matter what you do on the phone end if the power supply can't provide the power. If you are seeing it charging only 2 seconds out of 5, you are probably overloading something.

pendragon_01
 
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Re: Pulsating sound from inductive coil...Uh-oH!

Post by pendragon_01 »

Noted.

The sound is more of a hiss and in checking the forums others have heard a similar sound using atypical power supplies. The intermittent nature of it is still suspect so i will try to track it down.

Thanks!

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