I've seen several people mention that some of the wall-wart power
supplies aren't well regulated and can produce power above 5.5v and
destroy the BB. What is a good power supply to use? I do not have an
oscilloscope to test for fluctuation.
Are the wall wart power supplies used to power USB hubs reliable
enough?
Just make sure the power supply is well regulated at 5V. There is one listed on the DigiKey site where you order the BeagleBaord. It works great.
Gerald
How can I tell that it is well regulated?
An unregulated one typically will measure much higher without any load on it. It will then regulate to 5V once a load is applied. You can take a voltmeter and measure the voltage and as you plug it in make sure the voltage does not exceed 5V even briefly.
Gerald
I've seen several people mention that some of the wall-wart power
supplies aren't well regulated and can produce power above 5.5v and
destroy the BB. What is a good power supply to use? I do not have an
oscilloscope to test for fluctuation.
I am using a surplus Palm branded power supply from BG Micro:
http://www.bgmicro.com/index.asp?PageAction=VIEWPROD&ProdID=12801
Cost is $4.95 and it works great.
Are the wall wart power supplies used to power USB hubs reliable enough?
Probably not. The hub has plenty of room for a low efficiency voltage
regulator to
clamp it down to an even 5v.
A good rule of thumb: If the wall wart accepts the full 100-240VAC
international voltage range, it probably has a good switching
regulator. This is the case for most cell phone chargers.
But always check it with a voltmeter. It's not worth risking a $149
BeagleBoard to save a few bucks on a power supply. If you're not
sure, get the Digi-Key supply.
A USB hub external power supply might work. From what I can tell, my
$5 Inland hub connects its +5V external power jack to the downstream
ports directly, except for a ferrite bead. So my hub must be powered
with a regulated +5V supply or it could destroy any devices plugged
into it. This implies that at least some USB hub external power
supplies are regulated.
Again, a voltmeter is your friend.
John
A good rule of thumb: If the wall wart accepts the full 100-240VAC
international voltage range, it probably has a good switching
regulator. This is the case for most cell phone chargers.
[snip]
Again, a voltmeter is your friend.
And you can normally get a cheap one for <$5 that will tell you whether or not
your seeing 5v on an unloaded power supply.
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=90899
Now I wouldnt recommend using this centech for all measurements
(because its super cheap) - but for checking battery voltages, power
supply votages, it works just fine =)
I used my voltmeter to test the USB hub power supply I had and noticed
that when it was plugged in the meter would read 8v for a split second
then settle at ~5.14v. Now, here's the weird thing, on a whim I
tested a couple batteries with my meter and right after connecting the
probes it would read 2 - 3v higher than the battery and then level off
at the battery value. For example:
* with a 9v batter it would read 14.75v for a second then level off
at 8.21c
* with a battery pack of 3 AAs it reads 7.73v and then 4.39c.
Could the voltage spike reading be something to do with my voltmeter?
Can I trust my USB hub power supply?
Thanks.
I used my voltmeter to test the USB hub power supply I had and noticed
that when it was plugged in the meter would read 8v for a split second
then settle at ~5.14v. Now, here's the weird thing, on a whim I
tested a couple batteries with my meter and right after connecting the
probes it would read 2 - 3v higher than the battery and then level off
at the battery value. For example:* with a 9v batter it would read 14.75v for a second then level off
at 8.21c
* with a battery pack of 3 AAs it reads 7.73v and then 4.39c.Could the voltage spike reading be something to do with my voltmeter?
That is what I would suspect. I have both analog and digital
multimeters and none of them behave like you describe when testing a
9V battery or 3 1.5V cells in series.
Also, with fresh alkaline batteries you should see around 9.5V on a 9V
battery, and around 4.8V for 3 1.5V batteries in series.
Can I trust my USB hub power supply?
That I cannot answer.
-Preston
Jeremy,
I just borrowed a friend's multimeter and the readings came back
correct this time, without voltage fluctuations or spikes. So I
suppose my meter is the problem. Thanks for all the help and advice.