raspberry pi --> power consumption + battery design

can you power it off while not needed?

assume 10 to 20 seconds to boot.

Maybe install a PIR sensor so it can boot up as the customer is potentially approaching the button. and shut down if nothing happens.

Passive infrared basically uses no power, I wireless PIR sensor that runs for a year on one of those horrible 9v batteries. 1000mAh or whatever.

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

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'.

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.

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.

I wasn't, but Dave Liquorice was allowing 50% for battery and conversion efficiency combined which sounds generous to me provided you use a decent converter (running a 7805 from 12 volts would be madness IMHO except for very small currents - and then it would be a 78L05). Conversion efficiencies in the high 80%s to low 90%s are cheap and easy these days.

would

Calculations "resonable ball park" rather than accurate. A high quality DC-DC convertor can get above 90% but a 70 cent jobbie or repurposed cheapy car 12 - 5 V USB may well struggle to get 80%. Similar sort of numbers for the battery effciency.

Where I think I'm being really generous is with the solar panel producing 50% of it's rated ouput for 6 hours/day. When daylight hours aren't much longer. 25% for 4 hours might be better which equates to a 150 W rated panel or nearer 300/400 W to provide cover for really dull days.

There are plenty of 5V output converters available that have no noticeably RF noise that can be placed inside many of the cheap plastic cases available. As a radio amateur who uses a Pi portable with it sat under the amateur antenna it was one of my main design criterias.

Its far far worse than that.

a solar panel averages 10 % over a year in UK. In winter on a dull day its the square root of SFA.

I applied instrumentation to my trusty old rpi-B (512meg) model, with a chinese made buck converter from a 12V feed; named "DROK". It has a network cable, hangs on a ~8 year old Apple monitor with HDMI, and has an 8G kingston extreme 30MB/sec SD card; plus a cat5 cable to an ethernet switch.

First I monitored the rpi side of things. I have the converter tuned to 5.2 volts, and have made a USB feedin cable from half a USB cable.

I exercised it while having a scope measure the current running through to the RPI. This gave a drop of 0.012 volts, so I tuned the converter up to 5.3 volts.

Initial turnon goes through a few steps, first second the current is 0.22A, then the video comes on at 0.28, then USB comes on and I see a 2-3 second spike to 0.53A. Then steady through the multiuser boot at 0.43-0.48A.

Then it drops to 0.40 when idle.

Then I exercised the rpi a little :

intensive sd card writing: 0.53A dd out over nfs: 0.48A (3 MB/sec) dd in over nfs: 0.52A (3 MB/sec) runnint netcat in+out, apt-get update, big compile : 0.47-0.54A stopping all non-essential daemons, down to

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:

// Christian

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.

Morten Reistad wrote: [snip]

I.e. something that consumes 10 watts left on continuously all year

This is on a domestic tariff where nighttime electricity is much cheaper than daytime. Other tariffs might cost somewhat more but it does at least give an idea of cost.

Now I swapped it for an RPI2, with the same environment except it has a SAMSUNG 8G "normal" micro-sd card.

This is a lot more frugal. It starts out at 0.17A, goes to 0.27 when the video/usb/net comes on, and then runs the boot at ~0.36A. Then drops down to 0.27 when really idle.

The plodding along barely lifts it, to ~0.29A. It maxes out easiler, but just at 0.36, with a few glimpses of 0.37.

I didn't do the 12V measurement with this one.

Watts used are 1.4 to 1.9, with a good average of 1.5.

By the rule of "a watt is a dollar" this should cost $1.50 for a year, it uses areoun 13 kWh/year; at the higher prices of 20 eurocents a kWh it should be a little less than three with the power supply included.

Other places have decent prices for electricity. In (most of) North America and Scandinavia this would cost quite less than $2/year.

Next up is the rpi3, I must just install an OS on it.

-- mrr

I haven't done an expensive power consumption test, but just going on my long term monitoring of CPU temperatures, the original Pi2 (over-clocked to 1GHz) runs the coolest of all 3 major revisions at idle and at moderate loads. At peak it exceeds the Pi1 (over-clocked to 900MHz) by a large margin although nowhere near the safe limit, but it is doing a lot more work on 4 cores so gets the job done faster.

The Pi3 (standard clock of 1.2GHz) on the other hand is the warmest at idle and gets far hotter under load, so much so it is worth adding a heat sink to stop it hitting the thermal limit and reducing the clock speed.

It can be up to 50% faster than the Pi2 so is getting the work done faster, but if power consumption and thermal stability in high ambient conditions is a concern, I'd go with the Pi2 rather than the Pi3.

But then I understand that now the Pi2's on sale now are using the Pi3 chip but without the Bluetooth and WiFi, so even under-clocked to Pi2 speeds you are probably going to see temperatures and power consumption greater than the original Pi2.

---druck

Or 11.4p/kWhr.

Trouble there is huge spread of units cost we pay from 5.446p/unit (E7 night, day is 13.828) to 16.884p/unit (a standard tariff with no standing charge but high unit cost but we don't use much...) via

But not overly relevant for a Pi, camera, WiFi etc all "off grid".

Yes, I know it's not accurate by any means but it gives me a guide as to how much it's costing, for example, to run my desktop server machine continuously. It consumes 18 watts when idle so it's probably

at least I'm pretty sertain it's not hundreds of pounds.

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...).

Would a 7805 provide those?