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TideMan
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Most 1A power adaptors are rubbish

Wed Feb 19, 2014 7:53 pm

In the last few days, I've been through 4 different power adaptors that look like this:
279356707.jpg
279356707.jpg (11.55 KiB) Viewed 1895 times
All were rated 1 A, but none could produce enough current to run my RPi.
Fortunately, it's my 3rd RPi, so I have other power supplies I can try, otherwise I would have suspected a faulty RPi.

This is by way of a warning for beginners: don't trust the current rating on cheap power adaptors - most of them are crap.

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FTrevorGowen
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Re: Most 1A power adaptors are rubbish

Wed Feb 19, 2014 9:05 pm

TideMan wrote:In the last few days, I've been through 4 different power adaptors that look like this:
...
All were rated 1 A, but none could produce enough current to run my RPi.
Fortunately, it's my 3rd RPi, so I have other power supplies I can try, otherwise I would have suspected a faulty RPi.
This is by way of a warning for beginners: don't trust the current rating on cheap power adaptors - most of them are crap.
Some "branded" and "not so cheap" ones may not be suitable either - depends upon whether they were "designed" to be PSU's or "chargers". The "specs." may be "the same" but the interpretation and requirements are different.
FWIW, you may be interested in my measurements here:
http://www.cpmspectrepi.webspace.virgin ... plies.html
and here:
http://www.cpmspectrepi.webspace.virgin ... dPSUs.html
Trev.
Still running Raspbian Jessie on some older Pi's (an A, B1, B2, B+, P2B, 3xP0, P0W) but Stretch on my 2xP3A+, P3B+, P3B, B+, A+ and a B2. See: https://www.cpmspectrepi.uk/raspberry_pi/raspiidx.htm

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jojopi
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Re: Most 1A power adaptors are rubbish

Wed Feb 19, 2014 10:39 pm

There is an extra problem with the type in the original picture. Even if it meets its specifications, it only needs to provide 5V 1A at its socket. USB A to µB cables are only required to carry 500mA at the allowed voltage drop. (Even assuming they are are not themselves rubbish!) So if the supply provides 1A, the voltage may be out of spec at the other end of the cable.

Power supplies with a captive cable are likely to be better because then their specification applies to the plug end.

(Having said that, I have several Pies powered from PCs and TVs using USB A to µB cables. That is technically out of spec. It requires cables that exceed the USB specification. No seller ever specifies the resistance of a USB cable, but if you buy enough you find that some are very good and some are very poor.)

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FTrevorGowen
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Re: Most 1A power adaptors are rubbish

Wed Feb 19, 2014 10:50 pm

jojopi wrote:There is an extra problem with the type in the original picture. Even if it meets its specifications, it only needs to provide 5V 1A at its socket. USB A to µB cables are only required to carry 500mA at the allowed voltage drop. (Even assuming they are are not themselves rubbish!) So if the supply provides 1A, the voltage may be out of spec at the other end of the cable.
Power supplies with a captive cable are likely to be better because then their specification applies to the plug end.
(Having said that, I have several Pies powered from PCs and TVs using USB A to µB cables. That is technically out of spec. It requires cables that exceed the USB specification. No seller ever specifies the resistance of a USB cable, but if you buy enough you find that some are very good and some are very poor.)
I'd not come across the "500mA requirement" (but then, being retired, I don't read "formal specs." much these days :) ). You may be interested to discover that (at least for the ones I've measured) USB A to mini-B cables are worse - FWIW, my, fairly basic, measurements of a number of cables can be found at:
http://www.cpmspectrepi.webspace.virgin ... esChk.html
Trev.
Still running Raspbian Jessie on some older Pi's (an A, B1, B2, B+, P2B, 3xP0, P0W) but Stretch on my 2xP3A+, P3B+, P3B, B+, A+ and a B2. See: https://www.cpmspectrepi.uk/raspberry_pi/raspiidx.htm

lifebeginsatsixty
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Re: Most 1A power adaptors are rubbish

Wed Feb 19, 2014 11:34 pm

About the time I got my Pi the flea markets in my area started having piles of old adapters/chargers and so with judicious choosing and bargaining I have what I need and more, learning a little along the way. The older ones come apart easily and the output cable is usually a simple 2 wire one, soldered to two holes on the pc board. I buy several (cost should be negligible), check them out at home and then put a heavier cable from one on a good brick of another and there we are. Your voltmeter on the checkpoints on the Pi board will tell you if it's getting what it needs.

Well my picture file is way too big. Sorry. Trust you get the general idea. I average about 75% success with negligible outlay so the money's no problem. Besides, more fun to do it yourself.

lifebeginsatsixty

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chrisryall
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Re: Most 1A power adaptors are rubbish

Thu Feb 20, 2014 8:26 am

Coming into PiLand in December I was struck by the number of "power supply" posts here; Yet they continue …

Doesn't seem rocket science compared to some of the issues on the board, and with 1 million pi-lettes sold it seems extraordinary that there aren't several "guaranteed suitable" stable 5V,1+A supplies out there from the burgeoning electonic factors industry.

. Why hasn't this been bottomed? If so, where? If not why not?

Having said this, my own little pi has run happily and stably on the USB charger that came with the (admittedly expensive) Maplin UK package … though I never got its wifi dongle to work ;)

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Jim JKla
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Re: Most 1A power adaptors are rubbish

Thu Feb 20, 2014 8:45 am

Ayt least there are a number of posts around flagging up the issue of flaky power supplies and theres a whole flock of stuff on the Wiki. I suppose I got lucky when my first wall wart PSU worked perfectly and within a fortnight I was onto a USB hub with loads of amps to spare.

I did notice RS are now advertising a cheap HDMI to VGA converter for the RPi there's no reviews as yet but I do know there are a lot of VGA Monitors out there probably nearly as many as there are flaky 1A PSU's. ;)
Noob is not derogatory the noob is just the lower end of the noob--geek spectrum being a noob is just your first step towards being an uber-geek ;)

If you find a solution please post it in the wiki the forum dies too quick

hampi
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Re: Most 1A power adaptors are rubbish

Thu Feb 20, 2014 8:57 am

chrisryall wrote:. Why hasn't this been bottomed? If so, where? If not why not?
I guess the user community is quite diverse and there are different needs for the power supply. And those more into coding are not always very good in the hardware. There is a wiki page on this

http://www.elinux.org/RPi_5V_PSU_construction

The power electronics is different from RPi board since it does not need very high level of integration, but a rather different design approach.

Edit: For comparison to RPi how much engineering has been done in the desktop PC power supplies

http://en.wikipedia.org/wiki/ATX_power_ ... wer_supply
Last edited by hampi on Thu Feb 20, 2014 9:11 am, edited 1 time in total.

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Douglas6
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Re: Most 1A power adaptors are rubbish

Thu Feb 20, 2014 8:58 am

I've been very happy with the supplies from Adafruit. 1 amp, and 5.25 volts, which overcomes most cable problems. 6 bucks US; not too much for peace of mind. The blue indicator LED is bright enough to attract UFOs, but that's par for the course. You could land an airplane in my apartment at night.

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Jim JKla
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Re: Most 1A power adaptors are rubbish

Thu Feb 20, 2014 9:40 am

Douglas6 wrote:You could land an airplane in my apartment at night.
How long is the runway ;) ?
Noob is not derogatory the noob is just the lower end of the noob--geek spectrum being a noob is just your first step towards being an uber-geek ;)

If you find a solution please post it in the wiki the forum dies too quick

johndough
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Re: Most 1A power adaptors are rubbish

Thu Feb 20, 2014 1:13 pm

Hi

Model MWUSB3UK 5v 2100ma Premier Farnell et al. Six quid plus Vat.

What more do you need?

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