mattmiller
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Anyone tried 4xAlkaline AA batteries on PiZero?

Wed Sep 21, 2016 9:34 am

Just before I decide to test to see if this is going to work - I thought I 'd ask :)

I know the volts is too high but it would be very handy for a throwaway type project that I'm thinking about if it could run off 4 alkaline cells

JFMI The PiZero will have a WiFi dongle but no other peripherals attached

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Re: Anyone tried 4xAlkaline AA batteries on PiZero?

Wed Sep 21, 2016 9:59 am

Try 8 batteries and a DC-DC buck converter, that will work fine and wont destroy the zero
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Re: Anyone tried 4xAlkaline AA batteries on PiZero?

Wed Sep 21, 2016 10:10 am

I love it when someone answers a different question :)

scotty101
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Re: Anyone tried 4xAlkaline AA batteries on PiZero?

Wed Sep 21, 2016 10:12 am

I have tried 4x AA cells.

Works fine when connected through the ZeroBorg
https://www.piborg.org/zeroborg
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Re: Anyone tried 4xAlkaline AA batteries on PiZero?

Wed Sep 21, 2016 10:15 am

it's too high - it will kill it - use a buck converter
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Re: Anyone tried 4xAlkaline AA batteries on PiZero?

Wed Sep 21, 2016 10:21 am

I can see this is going well :)
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This has the following additional features:
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mahjongg
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Re: Anyone tried 4xAlkaline AA batteries on PiZero?

Wed Sep 21, 2016 10:35 am

mattmiller wrote:Just before I decide to test to see if this is going to work - I thought I 'd ask :)

I know the volts is too high but it would be very handy for a throwaway type project that I'm thinking about if it could run off 4 alkaline cells

JFMI The PiZero will have a WiFi dongle but no other peripherals attached
NO! don't do this!

Nominally this will mean you are (initially with batteries full) putting 4 x 1.5V = 6V on both the PI Zero, AND the WiFi adapter.
If this doesn't destroy the Zero it probably WILL destroy the WiFi adapter, which is designed for USB power, with a maximum of 5.25V.

Use a low drop regulator that can handle 6V to 5V, like the LM1117-5V or equivalent to create a suitable power voltage.
But do realize that if the alkaline cells drops below the working input voltage of the 1117 regulator the regulator will stop working, most need a least a few tenth of a volt more on the input than the output. So you may be better off with 5 alkaline cells.

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Re: Anyone tried 4xAlkaline AA batteries on PiZero?

Wed Sep 21, 2016 10:36 am

mattmiller wrote:I love it when someone answers a different question :)
He did answer your question! You just didn't like his answer, but he is right!

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Re: Anyone tried 4xAlkaline AA batteries on PiZero?

Wed Sep 21, 2016 10:37 am

scotty101 wrote:I have tried 4x AA cells.

Works fine when connected through the ZeroBorg
https://www.piborg.org/zeroborg
The zeroborg acts (is) the low drop regulator.

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Re: Anyone tried 4xAlkaline AA batteries on PiZero?

Wed Sep 21, 2016 11:14 am

mahjongg wrote:
scotty101 wrote:I have tried 4x AA cells.

Works fine when connected through the ZeroBorg
https://www.piborg.org/zeroborg
The zeroborg acts (is) the low drop regulator.
Correct. Wasn't suggesting otherwise.
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Re: Anyone tried 4xAlkaline AA batteries on PiZero?

Wed Sep 21, 2016 12:01 pm

Well _ i'll tell you all how long it lasts - jsut powered one up - its managed to boot and I can connect to it over WiFi

I'm reading 5.82 on Pin1

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Re: Anyone tried 4xAlkaline AA batteries on PiZero?

Wed Sep 21, 2016 12:25 pm

Just set it to send a timestamp MQTT msg to topic pizero4aa topic on mosquitto.org once every 30 mins so everyone can see how long it lasts (in terms of battery life or actual PiZero life!)

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Re: Anyone tried 4xAlkaline AA batteries on PiZero?

Wed Sep 21, 2016 1:52 pm

mattmiller wrote:Well _ i'll tell you all how long it lasts - jsut powered one up - its managed to boot and I can connect to it over WiFi
Thanks for trying it and we now have an answer to the actual question asked.

AIUI the "5V" goes to a regulator which powers everything else, to the USB sockets, probably the HDMI socket, and GPIO power pins. Providing USB, HDMI and "5V" rails were not used it would seem entirely safe to use any voltage which doesn't exceed the regulator's input voltage or cause excess heating.

Using a USB device at over 5V would depend on its ability to withstand over-voltage. I wouldn't like to connect it via HDMI without knowing exactly what the Zero's HDMI interface was.

If we had a full circuit diagram of the Zero people could see exactly where "5V" went and wouldn't have to ask, guess or try to trace that out, but I don't expect to see that any time soon.

I would suspect that the biggest problem will not be running above 5V but what happens as battery voltage drops, as regulators fail to maintain their output voltages.

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Re: Anyone tried 4xAlkaline AA batteries on PiZero?

Wed Sep 21, 2016 2:20 pm

the "5V" goes to a regulator which powers everything else
There is no 5V regulator on-board any Pi.

There is a 3.3V regulator to power the main chips.

So it is over-cooking all the 5V bits on the Pi - which in this case is the 3.3V regulator (hopefully it will survive an extra 0.75 V) and the WiFi dongle.

The dongle I'm using isn't marked with any writing at all so I don't know what make it is but its not getting too warm (its a 5370 Ralink chipset according to dmesg_

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Re: Anyone tried 4xAlkaline AA batteries on PiZero?

Wed Sep 21, 2016 3:02 pm

The 3V3 regulator appears to be the same as used on A+ and previously discussed elsewhere. That looks to have a recommended input voltage max of 5V5, absolute max of 6V5 -

http://diodes.com/datasheets/PAM2306.pdf

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Re: Anyone tried 4xAlkaline AA batteries on PiZero?

Wed Sep 21, 2016 4:22 pm

Other stuff running off the Zero 5V rail: BCM2835 internal Vcore regulator, & the AP2331 current-limit switch for the 5V out on the HDMI socket.

In theory the latter should switch off the H5V source output & protect the connected monitor when the input is >5.3V - irrelevant if you are running headless, which you likely are if running off batteries.

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Re: Anyone tried 4xAlkaline AA batteries on PiZero?

Wed Sep 21, 2016 4:30 pm

irrelevant if you are running headless, which you likely are if running off batteries.
yep - no monitor -so prob just the WiFi dongles to worry about then :)

Note the measured volts are Pin 2 are down to 4.5 volt now so it looks like over-voltage problems are no longer an issue :)

Been running for 5.5 hours so not bad on a set of 4xAA

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Re: Anyone tried 4xAlkaline AA batteries on PiZero?

Wed Sep 21, 2016 6:00 pm

This is what is called "a kludge" it may, or may not work depending on the USB dongle.
This time you were lucky, I still would not trust it to work with just any USB WiFi dongle.
Most CMOS chips designed for 5V simply die if they get 6V, and many WiFi dongles simply stop working when their power drops below 4.75V.

Still, if all you want is a kludge, then go ahead.

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Re: Anyone tried 4xAlkaline AA batteries on PiZero?

Wed Sep 21, 2016 7:07 pm

Very tempted to test this too on my older, spare, pi zero. 4aa is just too convenient. Kludge can be a useful caveman.

mattmiller
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Re: Anyone tried 4xAlkaline AA batteries on PiZero?

Wed Sep 21, 2016 8:15 pm

Do I feel lucky punk - yes I do :)

PiZero still going after 9 hours - flashing an LED every 2 secs and sending an MQTT message out every 30 mins :)

I can still VNC in and do stuff

Pin 1 volts is down to 3.9 and still I'm rolling along :)

Gonna try this test again tomorrow with different WiFi Dongle and see how that goes :)

(I know its not legit but I have a need to use 4xAA batteries in a project - I will specify that they should be NiMH recharables but I needed to know what would happen if a user didn't follow the plan)

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Re: Anyone tried 4xAlkaline AA batteries on PiZero?

Wed Sep 21, 2016 9:37 pm

Its finally conked out :(

last MQTT message was at 22:32 so it lasted 10.5 hours off 4x Duracell Alkaline AA's

Going to try again tomorrow with a different WiFi dongle and we'll see how that goes

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Re: Anyone tried 4xAlkaline AA batteries on PiZero?

Wed Sep 21, 2016 9:44 pm

I had some charged £shop 1000mAh NiMh lying around so I'm just going to test 4 of them over-night just to see how long they last for comparison purposes

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Re: Anyone tried 4xAlkaline AA batteries on PiZero?

Wed Sep 21, 2016 10:36 pm

I don't recommend doing so, but if you're going to run from 4 x AA batteries without a regulator, rechargeable NiMH might be a better choice than alkaline. They're nominally 1.25 volts per cell (mitigating over voltage risks) and they have a flatter discharge curve than alkalines.

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Re: Anyone tried 4xAlkaline AA batteries on PiZero?

Wed Sep 21, 2016 10:53 pm

Yep - I know - I've run my Pi off 4 x NiMH for years

mattmiller
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Re: Anyone tried 4xAlkaline AA batteries on PiZero?

Thu Sep 22, 2016 7:53 am

Well those £shop niMh 1000maH (really????) only lasted and hour :(
So I've swapped dongles and using the official RPI White one this time - lets see how long this lasts - mosquitto.org topic=pizero4aa

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