Author Topic: Powering baby monitor with power through battery connector  (Read 423 times)

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Offline AjkzaTopic starter

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Powering baby monitor with power through battery connector
« on: September 23, 2021, 07:55:18 pm »
Hi All

I have a Motorola baby monitor, and after lots of wear and tear on the portable monitor (let's you view the camera), the micro USB port (used to charge and power the device) seems to have lifted from the board or become damaged in some other way, and the monitor stopped working unless you hold the USB cable at the correct angle.

I ordered a new micro USB port to replace the one on the board, but unfortunately my surface mount soldering skills aren't great, and I lifted the pads and made a big mess of the USB input - it's totally disconnected from the device now.

The monitor also has a rechargeable battery (3x Ni MH cells) which allowed it to be portable. Since the battery connector is nice and big, I thought I could just remove the battery and provide approx 3.8V - 3.9V into the battery connector on the circuit board. I tried using a bench power supply and the monitor worked fine - if I lowered the voltage to about 3.6V, its starts warning about low battery.

My plan is to get a simple buck converter to provide 3.8V from a 5V USB wall power plug.

I don't need it to be portable, so removing the battery isn't a concern for me.

Am I missing something that could cause problems by powering the device through the battery input? The micro USB port is disconnected from the circuit board, so there isn't a concern of someone plugging in a USB cable and the monitor trying to charge the battery (which is actually my new power source [buck converter]).

Thanks in advance
Ajk
 

Offline Manul

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Re: Powering baby monitor with power through battery connector
« Reply #1 on: September 24, 2021, 12:30:03 am »
It is fine. If internal circuit does not have enough bulk capacitance at battery terminals, you could add some. Like 220uF, something like that. Often you can get away by using 5V directly. It is not unsual for NiMh cell to go 1.6V or above if fast charging, so 5V should be tolerated by circuits designed for 3 cells. If you are concerned, just add a series diode. With a diode drop you will get 4.2-4.4V which is for sure in the safe range for anything designed for 3 NiMh cells. So in my opinion, no need for buck converter in this case. Series diode and electrolytic capacitor would be my go.
 

Offline AjkzaTopic starter

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  • Country: za
Re: Powering baby monitor with power through battery connector
« Reply #2 on: September 24, 2021, 06:21:30 am »
Thanks so much, will give it a try.
 


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