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Zilla707
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3B+ on a 9v?

Tue Nov 05, 2019 11:39 pm

Hello, I an wondering if the raspberry pi 3 b+ could be powered off of a rechargeable 9v battery with 680mAh. Would this work or would the pi need more power?
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pcmanbob
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Re: 3B+ on a 9v?

Wed Nov 06, 2019 12:15 am

So first off you can't power any pi directly from a 9V battery , as connecting 9V directly to the
I will kill it, so you would need a dc-dc voltage converter to reduce the voltage to 5V.

Second you wouldn't be able to power the pi very long from such a small battery, probably some what less that 1hour and may be less that 30min depending what you have connected to it.
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W. H. Heydt
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Re: 3B+ on a 9v?

Wed Nov 06, 2019 3:20 am

Rounding up to 700mAh, and making the (probably false) assumption that that is meant to be at 9v, would give you 6.3Wh. Assuming you can hold a Pi3B+ down to 2A, that is 10W. So--assuming the battery can even deliver enough current AND that you can get 100% conversion efficiency--it would run for 0.63h, or less than 40 minutes. Takeout the unrealistic assumptions and you'd probably be lucky to get it to run for 15 minutes...if it could be made to work at all.

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Zilla707
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Re: 3B+ on a 9v?

Wed Nov 06, 2019 3:48 am

Oh well. That's too bad, I guess i'll just have to use a USB phone charging bank. Thanks!
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W. H. Heydt
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Re: 3B+ on a 9v?

Wed Nov 06, 2019 3:58 am

Zilla707 wrote:
Wed Nov 06, 2019 3:48 am
Oh well. That's too bad, I guess i'll just have to use a USB phone charging bank. Thanks!
There are some things to watch for there as well. The Ah or mAh ratings given for powerbanks are at the nominal cell voltage of 3.7v, NOT the 5v output voltage. Make sure that the powerbank you select is specified to output at least as much current as you might possibly draw (2.5A for a Pi3B+). Convert to Watts (W) and Watt-hours (Wh) to determine if your choice of battery size will power your Pi for the desired time. Bear in mind that very few powerbanks can be charged and discharged simultaneously, and even if it can, it may not provide a seamless switchover between modes.

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Zilla707
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Re: 3B+ on a 9v?

Wed Nov 06, 2019 10:54 pm

I've been using this one for a while, and it seems to work pretty well, powering my pi3B+ and the official RPi touchscreen. It has a decent amount of usage time, and I don't get power warnings. The reason I wanted a 9V was that it's a bit big for my current project and I was trying to find something a bit smaller. Thanks for all the help.
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Imperf3kt
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Re: 3B+ on a 9v?

Wed Nov 06, 2019 11:04 pm

For the same size of a 9v rechargeable battery, you could get about 5 times as much power from a lithium ion or lithium polymer battery with a charge booster module as well...

For a slightly different shape a single 18650 lithium ion battery (a common standard) could give you up to 3400mA (about the absolute maximum they can hold. Others are fake) which is enough (with boost circuit) to power a Pi for several hours.

I am yet to test the extremes, but one of my Pi's (a 3A+) is powered by a genuine 2000mAh 18650 and it easily lasts over an hour. That's including a 5 inch touchscreen and a few low power usb devices as well.
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