b0ngokarl
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Battery power / USB power same time

Tue Dec 03, 2013 9:37 pm

Hi,

I finally got my PI. It is running 4 hrs ideling around on 4 Eneloop 2450 mAh cells.

I'm powering it through Pin 4 and 6.

What would happen if I attach my USB charger through the micro USB port at the same time? Would it be 10V then or is it parallel and it will only charge the battery? :)

Thanks!

Karl

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rurwin
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Re: Battery power / USB power same time

Tue Dec 03, 2013 10:24 pm

It will "charge the battery", but it will do so in an entirely uncontrolled way, dumping possibly several amps through the Pi into the battery. You could do serious damage to both of them. If the micro-USB voltage is lower, then the battery will discharge into the power supply, potentially damaging that too.

b0ngokarl
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Re: Battery power / USB power same time

Tue Dec 03, 2013 10:36 pm

Hi rurwin,

thanks for confirming :) approval progress took too long - I tried already.

Running at smooth 5.05 V even with 100% load.

Thats my PiBox :)

Image

Thanks again!

Edit: Do you think the 2A Walladapter and the 2450 mAh Eneloops could be dangerous? I seeit might f*ck up my Eneloops in notime anyways :)

smithg400
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Re: Battery power / USB power same time

Wed Dec 04, 2013 2:23 pm

Potentially it cause a fire!!

Ted
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Re: Battery power / USB power same time

Thu Dec 05, 2013 3:49 am

I have a usb power supply, but I would like to power my RPi by a battery connection alone. How's 3 AA batteries in series for 4.5V ? Which pins should I connect to?, and will it work that way? Or what about 2 AA batteries in series for 3.0V? I would like battery connection alone, without using the usb connector.
Thanks
Ted, Lake City, Michigan, USA

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rurwin
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Re: Battery power / USB power same time

Thu Dec 05, 2013 10:53 am

Read the FAQ. Battery operation is not supported. It is marginally possible using four rechargeable (NiCd or NiMH) cells giving 4.8V but the operation time would be short and the Pi would fail in unexpected ways as the voltage dropped. Dry-cells (non-rechargable) would not give voltages in the correct range (4.75V-5.25V) since they can only give 4.5V or 6V.

It is possible to use buck/boost voltage converters (known as UBECs in the Radio-Control world) but operation with 2 AA cells would be limited to a maximum of 3 hours with top-of-the-range alkalines or less than half an hour with zinc-carbon. Rechargables other than lithium wont get you any more time, and Lithiums can be difficult/expensive/dangerous (pick one) to charge.

The best solution is to use a mobile phone emergency charger battery. Those are Lithium-based and have all the complex charging and protection circuitry built in.

realworldnumbers
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Joined: Mon Dec 02, 2013 2:28 am

Re: Battery power / USB power same time

Fri Dec 06, 2013 12:59 pm

I have managed to power a Pi using 4 AA batteries directly. It may not be supported, but I also measure a very high 6.52 volts on the input (fresh batteries) and got as low as 4.6V before I pulled the plug on the experiment. I'll be playing with more battery types soon and adjusting my experiement to be more accurate and report the Pi's core voltage output. http://realworldnumbers.com/how-long-wo ... batteries/

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rurwin
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Re: Battery power / USB power same time

Sat Dec 07, 2013 1:13 pm

I've done a lot of foolish things in my life and got away with them. But I wouldn't recommend that others do the same.

Ted
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Re: Battery power / USB power same time

Sun Dec 08, 2013 3:01 am

OK, thanks for the replies, rurwin for the warnings and pointing me to the FAQ's, which I read completely, and realworld for the link which I read with interest. Formerly I powered pics with 2 or 3 AA batteries, and that worked out really nice.
But I can see from your replies that RaspberryPi is in a completely different category - more of a computer than a pic, and uses a lot more power. Battery power will probably not be practical for me.
I'm only about 3 weeks into my RPi, so I'm new to it. I appreciate that you took the time to help me with this question that was important to me.
Ted

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