Will 5V 1A power supply enough for RPi 2 MOD B ?

[curious-pi]

My new RPi 2 MOD B reached me today. I did not order a power supply as I was determined to use my smartphone charger to power RPi. But now I realize that it is 5V 1A but the instructions tell me that i should have atleast 1.8A power supply. Will using my smartphone charger cause any problem if I'm going to use a usb keyboard, mouse and a HDMI to VGA adapter ?

[FTrevorGowen]

My new RPi 2 MOD B reached me today. I did not order a power supply as I was determined to use my smartphone charger to power RPi. But now I realize that it is 5V 1A but the instructions tell me that i should have atleast 1.8A power supply. Will using my smartphone charger cause any problem if I'm going to use a usb keyboard, mouse and a HDMI to VGA adapter ?

It depends upon how "good" the charger is ie. can it supply 1A and (still) 5V? Also whether it's uUSB cable is of good quality (low resistance). What model of charger is it? (It may be one I've measured the characteristics of). If the keyboard and mouse are (both) wired USB devices they will not require excessive current but some (older) HDMI-to-VGA converters can be "power hungry".
Are you (going to be) using a NOOBS-based install of Raspbian (pre-installed uSDHC card?) or another method/O.S. (which)?
You could try a quick test with just the keyboard installed and if the red PoWeR led does not flash**, but remains lit then you have a "fighting chance". If you do that wait for all green led ACTivity to cease for 10 seconds at least before removing power to minimise any risk of uSDHC card/file system "corruption". (Worst case scenario, you may have to re-write the uSDHC card)
NB: However, should you wish to use any additional USB devices, it will probably be better to invest in a PSU that can supply more than 1A.
Trev.
** An odd flash or two before green led ACTivity shouldn't cause any issues - I've had that happen when (first) testing a P2B using a good "powerbank" but YMMV.

[curious-pi]

This is the Converter I use http://www.amazon.in/gp/product/B00L67Z ... 1_1&sr=8-1
and about the charger, I don't know much about it
If I use the charger, will it blow my RPi and render it useless ?

I will be using NOOBS in micro sd

And my keyboard and mouse are wired.
And, can you explain "fighting chance" ? I'm not that much good in english.

[fruitoftheloom]

My new RPi 2 MOD B reached me today. I did not order a power supply as I was determined to use my smartphone charger to power RPi. But now I realize that it is 5V 1A but the instructions tell me that i should have atleast 1.8A power supply. Will using my smartphone charger cause any problem if I'm going to use a usb keyboard, mouse and a HDMI to VGA adapter ?

This board is littered with inadequate PSU issues, the RPF even have an official and recommended PSU:

https://www.raspberrypi.org/products/un ... wer-supply

[FTrevorGowen]

This is the Converter I use http://www.amazon.in/gp/product/B00L67Z ... 1_1&sr=8-1
and about the charger, I don't know much about it
If I use the charger, will it blow my RPi and render it useless ?
I will be using NOOBS in micro sd
And my keyboard and mouse are wired.
And, can you explain "fighting chance" ? I'm not that much good in english.

The converter is similar to one I've used** and is probably one of the newer "low power" devices. You are unlikely to damage the Pi by using the charger but it may not boot up properly**** - "fighting chance" means that it may work but not in all circumstances or, to put it another way, by using an underpowered PSU you may find some things don't work as expected or, eventually, files may get corrupted etc. and you have to work harder (fight) to keep the system stable.
Trev.
** http://www.cpmspectrepi.webspace.virgin ... rter2.html
**** More info. about the causes/symptoms of boot failure here:
viewtopic.php?f=28&t=58151

[curious-pi]

Thank you all, the posts were useful and My charger is enough to power my minimal setup

[trakannon]

Searching for similar things.. Would a USB plug work to power the pi like this one..http://www.belkin.com/uk/p/P-BSV103%20/

Or am I completely missing something? I am certainly not up to speed on power supplies.

Cheers

[W. H. Heydt]

Searching for similar things.. Would a USB plug work to power the pi like this one..http://www.belkin.com/uk/p/P-BSV103%20/

Or am I completely missing something? I am certainly not up to speed on power supplies.

Cheers

The specifications are more than adequate. Assuming that it will deliver what it promises, it should power any current Pi even at maximum settable current to the USB ports.

[JimmyN]

The problem with that type of adapter is finding a USB to microUSB cable with decent sized conductors. You need to look for a "power" or "charge" only cable that actually lists the wire size.

This is a good example. http://www.amazon.com/PortaPow-Micro-US ... ower+cable

It uses 20AWG conductors, which even at 5' long will work OK. Most of the ones on the market use a standard USB "cable" and have 4 conductors, plus a foil shield, plus a woven mesh shield and an outer jacket, so they only have 30 or 32 gauge wire to keep them flexible. A power only cable only has two power conductors and no need for shielding (no data flowing) and it can use larger conductors and still be flexible and about the same physical diameter.

20AWG conductors with 5V DC at 1A and 5' in length (total 10' conductor length) will only drop ~.1V. If the supply is outputting 5V then you'll have 4.9V at the RPi with a 1A load. If the supply is outputting 5.25V then you'll have 5.15V at the RPi.

Compare that to a "normal" USB cable with 32AWG conductors and let's say it's only 3' long, that's a pretty typical length. Then with the same 5V PS and 1A load you'll have a voltage drop of ~.98V, and you'll only have 4.02V at the RPi. If the PS is outputting 5.25V then you'll have 4.27V at the RPi, still not enough.

If the cable is only 1' long you'd still have a ~.33V drop and only 4.67V at the RPi. If the supply is putting out 5.25V then you'd have 4.9V at the RPi and that would work if a 1' cable is long enough for your use. But if you start plugging in peripherals and current goes to 1.5A total then voltage drop increases to ~.49V, so even with a 5.25V supply you'd only have 4.76V at the RPi.

The size of the conductors in the cable is just as important as the amp capability of the power adapter.

[W. H. Heydt]

I don't want to quote all of JimmyN, but make a couple of additional points...

Monoprice gives wire size in there USB cable specs. Most of them are 28/28 ga., but the better ones are 28/24 ga. I've had no issues with the 28/24 ga. cables up to six feet long. (I haven't needed to try longer ones.) The other thing that can be done is to put something like the Belkin plug on an extension cord, so the AC side is closer to the PI, thus allowing a shorter USB cable. Even then, I'd go for the best grade of USB power cable you can get your hands on, but you needn't go to extraordinary lengths to get the very best.

[trakannon]

Cheers guys. Sorted out a better cable and now no rainbow square showing. Great stuff!

[W. H. Heydt]

Cheers guys. Sorted out a better cable and now no rainbow square showing. Great stuff!

Good to hear it. Besides inadequate PSUs, poor cables are a major cause of power problems for Pis. I dearly love the folks that brought us the Pi, but they were a bit optimistic in the beginning with the idea of using any old phone charger.