raspberry pi --> power consumption + battery design

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Hi to all.

I need to create one off grid IP video intercom with RSP model 2 B.

In this project i will use
- wifi connection ( usb )
- 12V DC doorlock
- two relay board
- button for triggering call and doorbel
- USB video camera ( 320 x 240 )

The whole system is set but now i want to make the offgrid version with  
some small solar panel.

Real time scenario:
- call will be triggered on button press
- at the same time, wifi connection should be activated
- camera will start to stream "low" quality stream.
- voip will be started
- automatic disconnect in 10 seconds ( or until next button click )
- trigger DC lock ( 12V, 20ma ) for 5 sec.
- dc lock will be triggered 3 times per day and that's max.
- shortly, I'm planning to use rsp in lowest possible power consumption
mode
- daily power consumptions : up to 600mA ?

The idea is to set some small 10W solar panel +rechargeable battery set  
but i dont know if this should do the job because it's not quite sunny  
this days :-)

Suggestions ?

Re: raspberry pi --> power consumption + battery design
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It helps when you can keep it powered off until the button is pressed,
but of course then have to wait for Linux to be booted.  You could
try optimizing the boot to have your system functional as fast as
possible but it depends on your requirements if it is possible to
get it fast enough.

Re: raspberry pi --> power consumption + battery design
On 1/9/2017 1:47 PM, Rob wrote:
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PCs can go into hibernate mode where everything is saved to disk and the  
PC will restore to operation much more quickly.  Isn't there anything  
like this for Linux on the rPi?

BTW, I've cross posted to the rpi group.

--  

Rick C

Re: raspberry pi --> power consumption + battery design
following:


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    Considering how much power is consumed to write to flash memory, and
that you'd basically need enough spare flash memory to write the entire RAM
contents along with various processor registers (all the GPIO states, for
example), I wouldn't hold out much hope <G>
--  
    Wulfraed                 Dennis Lee Bieber         AF6VN
     snipped-for-privacy@ix.netcom.com    HTTP://wlfraed.home.netcom.com/

Re: raspberry pi --> power consumption + battery design
On 1/9/2017 7:01 PM, Dennis Lee Bieber wrote:
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What does the power of writing to Flash have to do with anything???

--  

Rick C

Re: raspberry pi --> power consumption + battery design
On Monday, January 9, 2017 at 4:54:07 PM UTC-8, rickman wrote:
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That would have been a poorly designed embedded system (i,e, Windows) in the first place.  All *nix (going back to the first ?nix) have separate prog and data spaces.  Absolutely no reason to save prog space and data space is usually much smaller.

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A little bit more power and time.  Yes, insignificant.


Re: raspberry pi --> power consumption + battery design
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The Pi will draw less power when it is doing less (like a PC) but I
think there is no real "hybernate" mode from which it can be woken up
without fully restarting.  That is why I mentioned booting it at the
time the button is pressed.

Of course when you have a task for a Pi that does not need a full-fledged
OS to be running it would be possible to run a simple OS or even a single
program stored on the flash card.  However, it looks like the poster
requires networking, camera driver, audio streaming etc and it could be
a lot of work to code all that on the bare hardware.

Re: raspberry pi --> power consumption + battery design
On 1/10/2017 3:22 AM, Rob wrote:
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Hibernate is not really a "mode".  It is just a matter of shutting the  
processor down after saving an image of the RAM and other details to  
mass storage.  The idea is that restoring from hibernation is faster  
than booting from scratch.  I know on the PC restore from hibernation is  
much faster than booting from scratch.


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I found mention of OpenELEC which is intended for home entertainment  
systems and a version for the rPi exists.  I read that it boots much  
faster than raspian.

Here is something else I found.  An add-on board that lets the pi power  
down cleanly and back up automatically.  I am sure this can be  
configured to bring the pi back up with a button push, but this may be  
more useful when waking up on a timer.

http://www.buyapi.ca/learn/01-raspberry-pi-extended-time-lapse-camera-with-battery-power/

--  

Rick C

Re: raspberry pi --> power consumption + battery design
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Maybe "suspend" would be a better possibility.   It means the processor
is stopped and peripherals are turned off but the RAM is powered
(and supposedly refreshed).  It should be quick to recover from as
the "only thing" required is re-powering and re-initializing the
peripherals (not easy at all when not foreseen in the drivers...)
and the execution can just continue where it was suspended.

However, the Pi does not offer that.

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OpenELEC is just a stripped down Linux with Kodi installed.
It is in the category "make the Linux start as fast as possible by
omitting unused services and doing as much as possible in parallel".

However, the WiFi is really slow to initialize so I don't think this
will ever bring down the startup time enough for good user experience
on a doorbell  (say 3 seconds max).

With wired ethernet, maybe it is possible.  But even there it depends
on driver details, used switch, is DHCP used and what server, etc.

Re: raspberry pi --> power consumption + battery design
On 1/10/2017 6:41 AM, Rob wrote:
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Then why do you say it would be a "better" possibility?  If it doesn't  
have that feature, it is *not* a possibility.


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Yes, that is the point.


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Yeah, wifi sucks.  But 3 seconds should be adequate.  I have a hard time  
finding my phone or getting to the computer faster than 3 seconds or  
even 10.  How long does it take to get to the door to open it?


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--  

Rick C

Re: raspberry pi --> power consumption + battery design
On Mon, 9 Jan 2017 17:28:54 -0500, rickman wrote:

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It'll draw that sort of current but don't mix up "power" and
"energy".

600 mA @ 5V is 3 Watts of power or 3 * 24 = 72 Whrs of energy per
day.

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battery  
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quite  
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From the above you need 72 WHrs of useable enrgy for each 24 hour
period. Being a bit pessimistic about battery effciency and other
conversions(*) lets say 50%, so that's 144 Whrs/day input. Being a
bit generous about the solar panel, and say it'll produce 50% of it's
maximum rated power for 6 hours/day. So it needs to produce 144 Whrs
in 6 hours which means a power of 144 / 6 = 24 W but that's only 50%
of the rated power meaning the panel needs to be rated at  24 * 2 =
48W.

Rough and ready calculations but of the right sort of order. If you
want to be fairly sure of having enough energy to get through two or
three days
of dull winter days you can probably double or treble that rated
panel rating.  

Battery capacity for three days, 0.6 A * 72 hours = 43 AHr make that
50 AHr plus to take into accout charge/recharge effciency. Also needs
to be a battery designed for deep discharge, not a vehicle starting
battery.

(*) Pi's live on 5 V, easily available solar panels and batteries
tend to be 12 V.

--  
Cheers
Dave.




Re: raspberry pi --> power consumption + battery design
On Wed, 11 Jan 2017 20:06:12 +0000 (GMT)

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<snip excellent calculations>

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    That's for a 5V battery - make it 25AHr for a 12V battery.

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--  
Steve O'Hara-Smith                          |   Directable Mirror Arrays
C:>WIN                                      | A better way to focus the sun
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Re: raspberry pi --> power consumption + battery design
On Thu, 12 Jan 2017 11:39:16 +0000, Ahem A Rivet's Shot wrote:

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What efficiency are you assuming for the 12v -> 5v converter? It would be  
fairly dire if, say, a 7805 is used.  

I'd normally open up an eBay 'USB charger' designed to be used in a car's  
cigarette lighter, extract the switch-mode 12v->5v converter and put it  
in a more sensible box (Maplins metal or metallic sprayed if they still  
make them). This provides RF shielding and the possibility of using a  
connector that the converter won't suddenly eject itself from. However,  
I'm uncertain how efficient these are. Some get quite warm, so the answer  
may be 'not very'.

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I like Yuasa NP7-12 for this type of job but then again 7AH is plenty for  
my requirements. Yuasa batteries bought anywhere with decent pricing (not  
Maplins!) are generally pretty good value.


--  
martin@   | Martin Gregorie
gregorie. | Essex, UK
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Re: raspberry pi --> power consumption + battery design
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Those who still use a 7805 when you get a complete buck-mode DC-DC
converter from China for 70 cents deserve to be punished.

Re: raspberry pi --> power consumption + battery design
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There's also the apparently new MSR7810WUP family from MicroPower Direct;
pin-compatible drop-in replacements fro the 78xx regulators, with high
efficiency (up to 95% claimed) and supposedly low cost:

https://www.elektormagazine.com/news/miniature-voltage-regulators-boast-very-high-efficiency

// Christian


Re: raspberry pi --> power consumption + battery design
On 1/13/2017 7:51 AM, Christian Brunschen wrote:
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Similar devices have been available for some time from CUI.  I designed  
in the V7805-1000 and V7812-1000R around five years ago.  I see they  
have 2000 items at Digikey now.

--  

Rick C

Re: raspberry pi --> power consumption + battery design
On Thursday, January 12, 2017 at 6:10:36 AM UTC-8, Rob wrote:
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Well, almost complete.  If there's a lead/acid battery involved, you want a few
extras (like, a low-voltage lockout, a fuse, RF filtering, some cables/connectors...).

Re: raspberry pi --> power consumption + battery design
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Would a 7805 provide those?

Re: raspberry pi --> power consumption + battery design

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Load dump protection.

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No.

Re: raspberry pi --> power consumption + battery design
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My suggestion of a Chinese buck-mode converter is instead of the 7805.
Other circuitry would be required no matter what.
Ready made boards to run a Pi from a "car battery" most likely are
available off-the-shelf.

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