Electronics > Beginners
Power Raspberry with DC/DC converter
german77:
I want to power a raspberry pi3 from two car batteries in series. The maximum voltage will be 30v and minimum 21v. Right now I have a XL4005 DC-DC converter that lowers the input voltage to 5.2V. It should deliver up to 5A witch should be more than enough to power the raspberry through its microusb power conector.
At first the power LED on the raspberry stays on. Then turns off while the ac Led still blinks. After some investigation I found that the voltage drops slowly to 4v with a lot of noise on the 5v rail of the raspberry pi. And the output of the DC-DC converter stays always at 5.2v and the current consumption hardly goes up from 300mA.
I added some decoupling capacitors but the results where the same. The weird thing is that I have the same DC-DC converter on another raspberry that has been working since December without problems. The raspberry works fine with a 5.3v 2A usb charger.
Anyone knows why the DC-DC converter is not working properly. I make sure that the input voltage is solid as a rock, and everything is soldered .
mariush:
The microUSB connector can barely a bit more than 2A of current. They claim their connector is up to 2.5A and supply the pi with a 2.1A wallwart adapter.
Your USB cable must also have thick wires inside otherwise the higher the current, the more voltage drop.
It's not realistic to do 5A through the usb connector and cable.
maginnovision:
What happens if you connect some wires to the 5V header pins instead. That's how I've done external supplies.
Bratster:
That sounds like crappy micro USB cable.
There are some test pads on the bottom of the pi where the micro USB connector is, what voltage do you measure on those two pads when you're seeing the 5.2 volts on your DCDC converter?
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german77:
--- Quote from: mariush on April 26, 2019, 08:41:32 pm ---The microUSB connector can barely a bit more than 2A of current. They claim their connector is up to 2.5A and supply the pi with a 2.1A wallwart adapter.
Your USB cable must also have thick wires inside otherwise the higher the current, the more voltage drop.
It's not realistic to do 5A through the usb connector and cable.
--- End quote ---
The raspberry is rated at 5W roughly 1A continuous. No one said that I will draw the 5A that the converter is able to deliver
--- Quote from: maginnovision on April 26, 2019, 08:56:35 pm ---What happens if you connect some wires to the 5V header pins instead. That's how I've done external supplies.
--- End quote ---
I'm worried about lack of some sort of protection. That will be my last resource.
--- Quote from: Bratster on April 26, 2019, 09:39:02 pm ---That sounds like crappy micro USB cable.
There are some test pads on the bottom of the pi where the micro USB connector is, what voltage do you measure on those two pads when you're seeing the 5.2 volts on your DCDC converter?
--- End quote ---
I use the same cable to power the raspberry with the phone charger. It will be a little hard to test on the pads. But after some test I found that with the DC-DC the voltage does drop to 4v, while with the with the phone charger stays always at 5v. It's the same cable on both test.
I'm starting to think that the problem resides on the usb conector of the DC-DC converter. I will solder a thick cable and clean the contacts to see if that makes a difference
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