tony1812
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6V power supply on pi3?

Sat Oct 07, 2017 1:20 pm

Hello, I have a battery pack rated 6V 2000mah, I really like to use it on the pi3 due to its small form factor and light weight. but I know that pi3 takes 5v on its usb plug. Is it necessary to regulate it down to 5v so that it would not demage the pi. Can the pi tolerate 6v without being demaged? After all, It is only 1 volt difference. Thanks.

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Re: 6V power supply on pi3?

Sat Oct 07, 2017 1:26 pm

tony1812 wrote:
Sat Oct 07, 2017 1:20 pm
Hello, I have a battery pack rated 6V 2000mah, I really like to use it on the pi3 due to its small form factor and light weight. but I know that pi3 takes 5v on its usb plug. Is it necessary to regulate it down to 5v so that it would not demage the pi. Can the pi tolerate 6v without being demaged? After all, It is only 1 volt difference. Thanks.
NO. You risk damaging the RPi. The specification is 5.00V +/- 5% or 4.75 to 5.25V
Use a USB battery bank instead.
Unless specified otherwise my response is based on the latest and fully updated Raspbian Buster w/ Desktop OS.

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rpdom
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Re: 6V power supply on pi3?

Sat Oct 07, 2017 1:27 pm

The Pi requires a supply of 5V +/- 5% (so 4.75V to 5.25V). The best range is 5V to 5.2V. Below that range the Pi or its peripherals may fail to work correctly. Above that range the Pi can be damaged. The microUSB input is designed so that the on board polyfuse will blow if the voltage reaches 6V.

Martin Frezman
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Re: 6V power supply on pi3?

Sat Oct 07, 2017 1:29 pm

An ordinary silicon diode will drop 0.7 volts. Wiring that in series with your 6V power supply may well do the trick.
If this post appears in the wrong forums category, my apologies.

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Re: 6V power supply on pi3?

Sat Oct 07, 2017 1:36 pm

i guess, even when the RPi would accept 6V as inputvoltage - that i don't know if it would - you will be not really that happy about it, because
without a DC-DC regulator/booster/charger module, you will only be able to suck that energy of the battery until the voltage dropps below, lets say, 4.8V.
that is not very much.
there is "much" more unused energy left in the battery, you never will be able to use,
a DC-DC booster module will suck even more energy from the battery that is left and transform it as long as enough energy is left in the battery to opperate up to the required 5V.

and remember, a fresh charged battery will maybe have more than 6V at the beginning, that may be finally too much to the RPi.
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tony1812
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Re: 6V power supply on pi3?

Sat Oct 07, 2017 1:40 pm

Thanks all for your reply.

The battery comes in 5 cells, 6 volt for 5 cells, so I suppose it is 1.2 volt a cell. If I take out one cell, that makes 4.8 volt in total, that will be safe for the pi?

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Re: 6V power supply on pi3?

Sat Oct 07, 2017 1:53 pm

if you only want to use your RPi to boot up, then the voltage is droppes below the absolute minimum...
with burning away the overvoltage by a diode or removing a cell, you are already at the minumum limit when you start the RPi.
then you immediately run out of required voltage and the RPI "browns out".

you didn't read the others posts. the RPi is working well only in a very limited smal range from 5V +/- 5%.
Last edited by beta-tester on Sat Oct 07, 2017 2:06 pm, edited 2 times in total.
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Re: 6V power supply on pi3?

Sat Oct 07, 2017 1:55 pm

tony1812 wrote:
Sat Oct 07, 2017 1:40 pm
If I take out one cell, that makes 4.8 volt in total, that will be safe for the pi?
No, because 1.2V is the average voltage per cell. Batteries vary in voltage. When fully charged they may give 1.4V or more for a short while, which will mean 5.6V+ into your Pi.

There is a reason that you have been advised to use a regulated supply like a 5V battery bank.

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Re: 6V power supply on pi3?

Sat Oct 07, 2017 2:02 pm

rpdom wrote:
Sat Oct 07, 2017 1:55 pm
There is a reason that you have been advised to use a regulated supply like a 5V battery bank.
i also recommed you to use a "usb battery bank" from the shelf.
specially if you are a beginner.
it is easier, more safe and maybe even cheaper than using a separate DC-DC-regulator/booster/charger module.
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tony1812
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Re: 6V power supply on pi3?

Sat Oct 07, 2017 2:36 pm

I am trying to use what is available in my dad's treasury trove. So I resist the temptation to buy additional parts :)

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Re: 6V power supply on pi3?

Sat Oct 07, 2017 5:17 pm

tony1812 wrote:
Sat Oct 07, 2017 2:36 pm
I am trying to use what is available in my dad's treasury trove. So I resist the temptation to buy additional parts :)
That is a good policy if the parts are suitable. A 6V battery is NOT suitable for a PI, it needs at least a 5V regulator (preferably a switching one, preferably one that can work with the full range of voltage from your battery, depending on its charge).
In the long run it is cheaper, easier and safer to use a part designed for the purpose. Be aware that not all USB powerbanks can be charged while powering the Pi -- if you want to do that, buy carefully.
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tony1812
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Re: 6V power supply on pi3?

Sat Oct 07, 2017 10:15 pm

I took a chance, took one cell out of the 5, disassembled the batter pack into individual cell, put the 4 cells into a regualar AA battery holder, it comes up as 5.4 volt and it powers up the pi like a charm, and it lasts about 90 minutes before I need to recharge it. :}

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Re: 6V power supply on pi3?

Sun Oct 08, 2017 2:27 am

rpdom wrote:
Sat Oct 07, 2017 1:27 pm
The microUSB input is designed so that the on board polyfuse will blow if the voltage reaches 6V.
that is not only wrong, what you say with that is actually: that RPI3B would be protected from overvoltage!
while a (ploy)fuse can not see / react on VOLT.
i think i read that it should shut off "blow" at a current of 5A.
but that does not protect a RPI, but possibly a powersupply,
and reduce the risk of fire ( on your breadboard circuit ).
Last edited by KLL on Sun Oct 08, 2017 2:56 am, edited 1 time in total.

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rpdom
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Re: 6V power supply on pi3?

Sun Oct 08, 2017 2:42 am

KLL wrote:
Sun Oct 08, 2017 2:27 am
that is not only wrong, what you say with that is actually: that RPI3B would be protected from overvoltage!
What I said is simplified, but correct. Yes, the Pi is partly protected against over-voltage on the microUSB power input.

There is a diode after the polyfuse that breaks down at 6V and shorts the power rails, that then causes the polyfuse to overload and shut off. It may not do that fast enough to protect the Pi, but should be enough to prevent a fire or anything like that.

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Re: 6V power supply on pi3?

Sun Oct 08, 2017 2:54 am

ok, thanks ( sorry )

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Re: 6V power supply on pi3?

Sun Oct 08, 2017 5:40 am

tony1812 wrote:
Sat Oct 07, 2017 10:15 pm
I took a chance, took one cell out of the 5, disassembled the batter pack into individual cell, put the 4 cells into a regualar AA battery holder, it comes up as 5.4 volt and it powers up the pi like a charm, and it lasts about 90 minutes before I need to recharge it. :}
that you are happy with it is the only thing that counts.

90 minutes, that is way longer than i expected.
specially with an RPi3 and 2Ah battery, i expected a quicker voltage drop, down under the minimum working limit of the RPi3.

at what voltage your RPi isn't working anymore?
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Re: 6V power supply on pi3?

Sun Oct 08, 2017 11:22 am

To be safe, before I modified the battery pack, I used one of those adjustable power supply. It measures 4.8 volt the minimun to boot up, I went up to 5.4 volt then didn't go any further. I do have quite a few sensors attached to the pi, on the amperage, it peaks to 1.25 A. I suppose when I add more sensors, it will draw more current.
And yes, I am delighted to see that it lasted 90 minutes. Joy :)

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Re: 6V power supply on pi3?

Mon Oct 09, 2017 2:27 am

At 5.4v it is only a matter of time until your Pi dies.
The limit is 5.25, going even 0.01v over this risks the Pi every time. You are likely causing unseen damage.
However it is possible you have a voltage drop before it gets to the Pi. What do the 5v rail and GND read?

Oh and as a tip, the Pi only requires 5v for peripherals. It will quite happily work at 3.7v
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Re: 6V power supply on pi3?

Mon Oct 09, 2017 4:27 am

Imperf3kt wrote:
Mon Oct 09, 2017 2:27 am
At 5.4v it is only a matter of time until your Pi dies.
The limit is 5.25, going even 0.01v over this risks the Pi every time. You are likely causing unseen damage.
However it is possible you have a voltage drop before it gets to the Pi. What do the 5v rail and GND read?

Oh and as a tip, the Pi only requires 5v for peripherals. It will quite happily work at 3.7v
Yes, voltage drop from the connecting cable is a factor. I've been running my Pi3 from a 5.3V supply for years. However, even with a relatively short, good quality USB cable a 0.05V loss would be considered good, so the input to my Pi3 is certainly within limits (one of these days I really should properly measure it). I do have a DVM on the USB output that is indicating 5.15V now (5.2V with nothing in the USB ports).

That being said, 5.4V is more than I'd be comfortable with. If it does die, at least it's not terribly expensive to replace.
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