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Current hogging prevention

eligri

May 29, 2017
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Hi!

I've got a RC receiver and a FPV camera/transmitter wired upp in parallel. I have a 3A 5V powersupply going to them both, but when I power on the device only the camera works correctly; the receiver needs rebinding. I am quite sure this is because of the camera hogging all the current for a split second.

The camera needs about 0.5-1A 5V.

Would it be enough to add a 5ohm resistor between the camera and powersupply?

Cheers
 

Harald Kapp

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Nov 17, 2011
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Welcome to EP.

This won't work: 5 Ω * 1 A = 5 V -> all the voltage drops across the resistor, nothing left for the camera :(

As the camera needs 5 V, you should not place any resistor between camera and power supply. An inductor may help as it limits current rise.
If the receiver works with less than 5 V, you could add an RC filter between power supply and receiver. This will filter the disturbance caused by the camera and the capacitor (if chosen big enough) will support power to the receiver to mitigate short interruptions in the power supply (such as teh ones you assume are the cause for the failure).
 

eligri

May 29, 2017
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I'd be getting the camera onto it's own supply.
Not possible, running lightweight stuff here ;)

Welcome to EP.

This won't work: 5 Ω * 1 A = 5 V -> all the voltage drops across the resistor, nothing left for the camera :(

As the camera needs 5 V, you should not place any resistor between camera and power supply. An inductor may help as it limits current rise.
If the receiver works with less than 5 V, you could add an RC filter between power supply and receiver. This will filter the disturbance caused by the camera and the capacitor (if chosen big enough) will support power to the receiver to mitigate short interruptions in the power supply (such as teh ones you assume are the cause for the failure).
Would it be possible to just use a 16V capacitor infront of the receiver? Think I have some of those in a drawer somewhere..
 

Harald Kapp

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Give it a try. But if the camera draws too much current it will draw this curent from the capacitor, too and the voltage at the input of the receiver will drop. Then the receiver may need rebinding as before. I recommend you put an impedance between the power supply and the capacitor, in effect a low pass filter as I noted in my post #2. The impedance will limit the current the camera can draw from the capacitor, thereby reducing the voltage drop across the capacitor. Use an inductor instead of a resistor for lowest DC resistance but higher impedance with respect to the current pulse.
 

Audioguru

Sep 24, 2016
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An RC receiver uses a battery, not a power supply.
Nobody makes a 5V battery, it is probably two Li-PO cells in series making 8.4V when fully charged and delivering a massive current, much more than a puny 3A. My very small and lightweight two-cell Li-PO batteries are rated for a continuous 22.75A or momentary 45.5A. My RC receiver detects "low battery" when the voltage is less than 6V.

Maybe your receiver and camera are designed poorly and do not work together.
 

Harald Kapp

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An RC receiver uses a battery, not a power supply.
I challenge that. A battery is a form of a power supply: it supplies power to a load, doesn't it?

Just a test to get some info on the problem: Use separate batteries, one for the camera, one for the receiver. Connect '-' together, but lead '+' separately to camera and receiver. If the problem persits, it is not the current drawn by the camera but some other effect. If the problem goes away, filtering may help.
 
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