Battery Life

[yojo98]

Look at my other question for the full thing, sorry.

[mahjongg]

Are you from korea? I hear they are fanatical about playing starcraft there. LOL?

just kidding, but you should know there isn't a native Linux version of starcraft, so I wonder what version you want to play, and how?

Not that it matters much.

The R-PI use 5V at an average current of about 400mA (depending on what the CPU and GPU are doing), but really they run off 3.3 Volt, the 5V is only used to power the regulator (for 3.3V) and for the USB devices. But say the average energy consumption is 2 Watt @ 5Volt.

because the header of the post is "battery life", I assume you want to run the R-PI on a battery, well first you have to output of the battery to a useable voltage for the system (actually that mainly means for the USB deices, because the R-PI itself will probably run on something like 3.6Volt fine, but not  the keyboard and mouse!

Say you are using NiMH rechargeable batteries, these output 1.2 Volt, so for 5V you would theoretically need 4.166666 batteries, which is a bit difficult, but if you use 4 you would only get 4.8 Volt, which most keyboards wouldn't work with and soon the batteries would drop to say 1.0 Volt, so you need 5. But then you would get 6 Volt when fully loaded, and (again) the keyboard would have a hard time. Also each battery will supply about 2000mA/H Or 2 Ampere for one hour, even when using 5 of them they would be depleted in 5 hours, and you still would need to convert 6 Volt to a steady 5V which is difficult. Instead use 10 of them for 12Volt, and use a "cigarette plug converter" (which are cheap and plentiful), which take 12V or 10V which they convert to 5V at the required amperage (so use one that can supply at least 600mA). These convert the energy with a reasonable efficiency of 70% or more (unless you buy a garbage one with a passive regulator "7805 style" in a TO220 package, do not buy those!) So with ten AA NiMH batteries you could have something like eight hours, just for the R-PI (and maybe keyboard and mouse) alone. The display is another matter entirely.

[yojo98]

What do you mean by the display? Also would these battries work (with more of them)

Duracell 74787 – AA Cell NiMH 8 Pack

Also could you please recommend a converter to me?

Also, is there anyway I could do this without a car battery or other battry, just running off the batteries?

[wallabybob]

If you have some basic electronic tools and knowledge you could use a DC switchmode step down converter which will take (say) a voltage between 6v and 20V and convert it to 5V. You could use this a 12v car battery or at least 5 NiMh batteries. These converters are readily available from eBay sellers - just look for LM2596 or MP2307 (the type number of switchmode converter chips commonly used in theses sort of applications).

[RaTTuS]

http://www.amazon.co.uk/TeckNe.....m_sbs_ce_1 may be what you need to run it over long periods YMMV

[Don Stewart]

Just a couple of points;

The Amazon USB power supply is a good idea but the one in the link is out of stock and looks as though it's not coming back. plus it would only power the Pi B for about an hour and twenty minutes.

The link below is for a 7000mAH version which is in stock and would power the Pi B for 10 hours (not allowing for mouse and keyboard)

http://www.amazon.co.uk/TeckNe.....pd_cp_ce_0

If your planning to build a power box yourself then please note that the voltages talked about in earlier posts for NiMh and NiCd batteries are the discharged nominal voltages which are written on the batteries.

When they reach 1.2V they are flat and should not be taken down to 1V to avoid damaging the cells.

The fully charged voltages for these types are 1.44V so any calculations should take this into account

[RaTTuS]

Don Stewart said:


Just a couple of points;

The Amazon USB power supply is a good idea but the one in the link is out of stock and looks as though it's not coming back. plus it would only power the Pi B for about an hour and twenty minutes.

The link below is for a 7000mAH version which is in stock and would power the Pi B for 10 hours (not allowing for mouse and keyboard)

http://www.amazon.co.uk/TeckNe.....pd_cp_ce_0


Don the one I posted was a 10k one 3k more than the one you posted but there are 11k ones and more [all depends on price]

e.g.

http://www.amazon.co.uk/New-Tr.....m_sbs_ce_2

YMMV and as to how long - until someone tries we don't know.

[RaspberryPie]

for those looking in the us, i found this link for the same product:

Dual-Port-Sensation-Thunderbolt-Blackberry

for $40, free shipping, gonna pick one of these up once my pi gets delivered.

[samgray111]

Don't mean to hijack but I am looking at doing the same thing and didn't want to start a new thread,

I have a couple of 6x D battery packs lying around, would a voltage regulator such as the 5 volt one here at maplin work (QL31) to step down a stack of 6 Ds proving 9v to the 5 required by the Pi?

http://www.maplin.co.uk/1a-pos.....tors-46475

Thanks

[jbeale]

If you've got a 9V battery, using a 5V linear regulator wastes almost half your power, and if it's running at 700 mA it probably wants a heatsink (4V*0.7A = 2.8 watts).  With a switching converter, you can get better efficiency and less heat (costs a bit more though).

For example, here's a switching step-down supply module that takes as input anything between 5V and 23V and gives you 5V out at up to 3 A current, so it could even power a hard drive as well as the Pi.  http://www.pololu.com/catalog/.....oduct/2177

[error404]

Work? Yes. It'll waste a ton of power and generate a lot of heat (you'll need a heatsink) though. You're much better off getting one of the previously mentioned buck converters from eBay for a couple bucks. They should be 80+% efficient.

I got a stack of 10x KIS-3R33S modules (MP2307 based) for about $0.30 each. Put a 10k resistor from the ADJ pin to ground to set the output to 5V and you're set. You can get them here: http://www.digole.com/index.ph.....ductID=458 (or all over on eBay).

[samgray111]

Thats great, thanks, using a heatsink isn't a problem but didn't realise linear regulators were *that* inefficient (just googled) will go for something like that instead.

Thanks

[samgray111]

Just bought one of these, coming from Hong Kong, will probably beat my Pi thanks a lot guys

http://www.ebay.co.uk/itm/LM25.....256f6905d4

[RaspberryPie]

jbeale said:


If you've got a 9V battery, using a 5V linear regulator wastes almost half your power, and if it's running at 700 mA it probably wants a heatsink (4V*0.7A = 2.8 watts).  With a switching converter, you can get better efficiency and less heat (costs a bit more though).

For example, here's a switching step-down supply module that takes as input anything between 5V and 23V and gives you 5V out at up to 3 A current, so it could even power a hard drive as well as the Pi.  http://www.pololu.com/catalog/.....oduct/2177


Found this on ebay:

DC DC Converter Step-Down Buck Module 12V to 5V 3A 15W,5V usb output power adapt

for less than $10 US. just need usb to miniusb cable and good to go..

on power question (n00bish here) can i use this here: 600 mAh Lithium Ion Battery ($13.00) and use one or two of those with the buck converter/cable mentioned above?

[jbeale]

The module you mention is intended for use in a car with a 12 V battery. It specifies an input voltage "DC8-20V" but your "9v" type lithium battery actually starts at 8.2 V (two 4.1V cells in series) and runs down to 6 V. So you would get only a small fraction of the nominal 600 mAh capacity.  You can find other switching converters which accept lower voltage inputs and would work better. Remember also, that particular battery wants to be disconnected from the load when it drops below 6 V, or you risk damage.

[RaspberryPie]

so if I were looking to the Li-ion set of batteries to use, what would be the preferred choice in that specific converter (trying to find the optimal liion battery and converter) again this is not my area of expertise

[jbeale]

Here is one example of a converter module that should work. Below module claims to take input anywhere from 3.7V up to 30V and can generate 5V output at 1 A or more. You could use a wide range of batteries: 4xAA NiMH, 2x Li-ion, or a 6V battery, or 9V, or 12V car battery for example. Don't forget to watch that battery and recharge it before it runs completely flat, to preserve the lifetime of the cells.

http://www.ebay.com/itm/DC-Buc.....1e6d62f986


Input 3.7V  Output 5V  0.5A  Efficiency 75%
Input 5V    Output 5V  0.5A  Efficiency 78%
Input 7.4V  Output 5V  0.5A  Efficiency 80%
Input 12V   Output 5V  0.9A  Efficiency 80%
Input 30V   Output 5V  0.5A  Efficiency 80%
Input 30V   Output 5V    2A  Efficiency 76%

[jbeale]

Or if you've decided on 2x Li-Ion cells in series, which gives you a voltage between 6 and 8.4 V (from discharged to fully charged), that's a good input range for a step-down (buck type) converter generating 5V. Check out the LM2596 converter modules on ebay; lots to choose from that will give you 5V at 1A or more output.

Not to put you off the project but if you are a beginner, I would recommend looking up "lithium ion safety" and consider if you might prefer to rely on a pre-built battery system. Commercial Li-ion packs are required to have built-in circuits to protect against overcharge, under-voltage and over-discharge all of which can have safety implications.

[RaspberryPie]

nah never kput off, this is all about learning.. no i hadnt considered the safety of doing the above...  would you mind recommending a good pre built system that would fit the bill..

many thanks

[MrRicheyRich]

Hi all,
I've been following the post with interest but now I have a question concerning after you have a battery system successfully set up.

How can you integrate a power management system into the Raspberry Pi? Is there a way of detecting the decay of the input voltage into the Pi in order to estimate how much remaining battery life you have? Useful additions would be a script that would drop the clock speed of cpu and memory when battery life is at 10%, and safely power down the system when battery life is at 1%.

I ask this because I tested my Power Monkey out on the Raspberry Pi and got about 4 hours before it switched off; but then I corrupted my SD card...

Rich

[pjc123]

Hi all,
How can you integrate a power management system into the Raspberry Pi?

I was wondering the same thing as I will be running on battery as well. I could add a circuit to monitor the battery voltage via a GPIO pin, but I am looking for a simpler way, perhaps somehow in software to internally monitor the pi's voltage or health.

[Mortimer]

Most modern laptop batteries have built in monitoring that talk via a I2C bus. The down sides will be having to come up with a safe and effective charging circuit.

[pjc123]

Most modern laptop batteries have built in monitoring that talk via a I2C bus. The down sides will be having to come up with a safe and effective charging circuit.

In my case at least, I have two 10AH batteries (vehicle batteries), so each will give me a long enough run time for what I need, and by keeping one charged via a Battery Tender battery charger I have, I will be able to swap it while I charge the other one. Although I don't need continuous operation, just a couple of days, I could connect them in parallel while swapping, so I don't have to shut down the pi to do a swap. I just need to know when to swap it out before erratic behavior or an unclean shutdown occurs.

[Mortimer]

In my case at least, I have two 10AH batteries (vehicle batteries), so each will give me a long enough run time for what I need, and by keeping one charged via a Battery Tender battery charger I have, I will be able to swap it while I charge the other one. Although I don't need continuous operation, just a couple of days, I could connect them in parallel while swapping, so I don't have to shut down the pi to do a swap. I just need to know when to swap it out before erratic behavior or an unclean shutdown occurs.

Are these car batteries, which shouldn't be discharged to any useful extent, or traction batteries designed for deeper discharge?

In either case, I would have thought a current logger, and hence a power consumption log. When the amount of power drawn from a battery has reached a preset limit, the batteries are swapped over, momentarily in parallel as you have suggested. Perhaps not the most elegant or simple solution, but could be an interesting project none-the-less.

[pjc123]

Are these car batteries, which shouldn't be discharged to any useful extent, or traction batteries designed for deeper discharge?

They are scooter/wheelchair type batteries, so they are designed for deep cycle applications. Regardless, I will not be letting them get too low because that still affects their MTBF.