Which contact pad is positive?

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jimbob79

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#208117 27-Jan-2017 11:21

So I got the USB 5V 3A DC-DC buck converter from eBay and I've realised I don't know the polarity of contact pads. Experience has told me that the top corner is positive when looking down from the top view, but I just can't be sure. Normally the eBay seller has a diagram highlighting the parts. Any ideas?

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#1710584 27-Jan-2017 11:40

Keen to hear back about how well they work and if it has enough grunt to charge a Samsung S6 in less than 11 hours....

Handle9

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#1710590 27-Jan-2017 11:50

It looks like the top right is the positive as the big 4R7 thing is the inductor

jimbob79

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#1710593 27-Jan-2017 11:53

TimA:

Keen to hear back about how well they work and if it has enough grunt to charge a Samsung S6 in less than 11 hours....

I don't have a Samsung S6 to try but I do have a very fussy Raspberry Pi 3 which needs ~2.5A so I let you know my results.

jimbob79

673 posts

Ultimate Geek

#1710599 27-Jan-2017 11:58

Handle9:

It looks like the top right is the positive as the big 4R7 thing is the inductor

FOUND IT! Phew.

Also mentions About Apple and Sumsung devices for the USB output.

Coil

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#1710600 27-Jan-2017 11:59

jimbob79:

Handle9:

It looks like the top right is the positive as the big 4R7 thing is the inductor

FOUND IT! Phew.

Also mentions About Apple and Sumsung devices for the USB output.

That 1.5A trickle charge, id have a flat phone before it would charge?

jimbob79

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#1710891 27-Jan-2017 22:12

Unfortunately this eBay module is not powerful enough to provide suitable power for the Raspberry Pi 3 . The USB Doctor monitor show 5.1~2 volts and 0.68 amps. It's show a 'thunder bolt' in the top right hand corner. This is not going to work for my application.

More info Pi3 with a lightning bolt:

https://www.raspberrypi.org/forums/viewtopic.php?t=82373

djtOtago

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#1710917 27-Jan-2017 23:14

What input voltage / source were you using?

I have found some of these cheep 'BUCK' regulators, the input voltage needs to be at least twice the output voltage before they start to perform correctly.

Samsung

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jimbob79

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#1710920 27-Jan-2017 23:28

djtOtago:

What input voltage / source were you using?

I have found some of these cheep 'BUCK' regulators, the input voltage needs to be at least twice the output voltage before they start to perform correctly.

I'm using a 12V 6A power Supply.

Ge0rge

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#1711317 29-Jan-2017 14:02

May I suggest that you try soldering a bridge across the two data pins on the USB outlet? A lot of devices will see this connetion and in turn draw more current from the supply than if they are left open.

Unfortunately Apple devices are lookng for a specific voltage across the data lines, involving a resistor bridge circuit to make work correctly, but in this case the Pi shouldn't care.

richms

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#1711329 29-Jan-2017 14:30

If there is 5.1v at that end of it and that low current then its not the buck converters fault. Try another cable and see how you get on.

Richard rich.ms

hyperman

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#1711414 29-Jan-2017 18:13

Ge0rge: May I suggest that you try soldering a bridge across the two data pins on the USB outlet? A lot of devices will see this connetion and in turn draw more current from the supply than if they are left open.

Unfortunately Apple devices are lookng for a specific voltage across the data lines, involving a resistor bridge circuit to make work correctly, but in this case the Pi shouldn't care.

from the photo of the underside of the board they are already bridged

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Ge0rge

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#1711462 29-Jan-2017 19:49

haha so they are - my bad! Why things are seen...

jimbob79

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#1711464 29-Jan-2017 20:05

After trying to charge iPhones and iPads I was unable to get over 1 amp. I'm not convinced that the buck converter is able produce current over 1 amp nor the 3 amps as advertised.

Ge0rge

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#1711467 29-Jan-2017 20:14

Depending on the model/age of the i-device, it will never draw full current as the i-device is looking for specific voltage on the data line.

I can't post links yet due to being too green, however google "adafruit minty boost" - you'll need a few resistors and a soldering iron, then you'll be able to make a circuit that will tell the i-devie that it can indeed draw the current it wants from the charger.

richms

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#1712477 29-Jan-2017 20:54

idevices are a prick like that. When I briefly had an ipad it would do the useless not charging thing and still go flat if you were using it on any charger that didnt have the stupid apple voltages on the pins. Last I used a friends one it seemed to charge slowly off a non apple charger so perhaps they fixed that stuffup of a design a little bit?

Richard rich.ms

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