beaglebone white doesn't work when powered from the barrel connector

[scm...@gmail.com]

hello everybody from a newbie,

well, happily, my beaglebone white works just fine when connected to my pc via usb. The power led is on and everything is fine, therefore  i suppose that my bb board is still functional.
The case is though that i am going to need to provide external power supply because i intend to connect my bb (through it's header pins) with an external circuit and thus power from usb is not enough. While trying to do so i face a power problem (i guess).
Let me explain you in short what's going on. As i said before the board is working fine when powered from usb (and thus my pc). The problem is when i power it from external power supply.
In specific when i supply 5V through a power supply the result is that the power led doesn't turn on and the board is not functional.

So, do you have any suggestions about what is wrong? Let me emphasize that in the past my bb was working just fine when powered from ac.

Thanks for any help in advance!

[evilwulfie]

Time to grab a volt ohm meter and do some troubleshooting.

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[scm...@gmail.com]

first of all thank you for your reply..

If you could suggest me though something more specific (i.e what voltage should i test?) i would appreciate it..
Now, what i noticed has really driven me crazy...
Since i have the bb RevA6, i checked in the system reference manual (http://beagleboard.org/static/beaglebone/latest/Docs/Hardware/BONE_SRM.pdf) that power can be supplied via a 2.1mm x 5.5mm center connector when connected to a positive power supply rated at 5VDC +/- .1V and 1A.
So i used a power adaptor with nominal voltage output 5V which though, as i found out later by using a volt meter, it actually provided 5.26V...and miraculously the beaglebone power led turned on and the board was working...If i am not mistaken i accidentally exceeded the voltage limits (not the current though) and it worked..
Now the question is..what is the actual functional power supply for the bb white?

[scm...@gmail.com]

[John Syne]

Are you measuring the power supply voltage with the BBB connected? You need to load the power supply to measure the output voltage. 

Regards,

John

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[scm...@gmail.com]

first thanks for your reply.

i am measuring without the BB connected since i want to know if i am able to provide the required voltage..Also if i am not mistaken the BB white has a voltage regulator so there is no reason to count with the BB connected because there will be a voltage drop if i supply more (but not too much). Am i wrong?
In any case i can give it a go and measure with the BB connected..
But again..does anyone know what is the supposed voltage to be supplied?Is it the one i mentioned in my previous post?(5V +/-.1 ? ) Cause as i have already said it seems that my bb works when provided with 5.26V and not with 5V..(hope i won't destroy the board..)

Thanks again

[Gerald Coley]

5V

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Gerald

 

ger...@beagleboard.org

http://beagleboard.org/

gco...@emprodesign.com

[evilwulfie]

Measuring a power supply with no load will not give you a good reading.

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[John Syne]

Clearly you have to load the power supply to get an accurate voltage measurement. You could use a purely resistive load for a current of about 100mA and that would give you an accurate voltage measurement. Using the formula R = V/I, select a resistor that would give you close to 100mA. Remember the power dissipated in the resistor must be considered so given P=VI, a 100mA load will dissipate 1/2 watt, so the resistor size is important. 

Now Gerald says the power supply needs to be 5V, but I think he is being overly restrictive here. The datasheet for the TPS65217C shows the AC input should be between 4.3V and 5.8V, so my way of thinking is 5.2V should be fine as long as there are no noisy pikes that cause the voltage to exceed 5.8V. However, Gerald is the original designer and he has set the input voltage parameters for a reason. 

Regards,

John

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