PiGraham
Posts: 3577
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Location: Waterlooville

Re: How long will it stay on with a external battery?

Fri Mar 29, 2019 11:01 am

B.Goode wrote:
Fri Mar 29, 2019 10:48 am
Having been directly criticized twice for my reply, can point out again that the OP only provided two "facts' as a the basis for their question:
i have a raspberry pi 3 b+ and i have a 20100 mah external battery

I tried to indicate, perhaps too gently, that a reliable reply could not be provided from those supposed 'facts'.

My tl;dr summary was
Your experience with the battery in question and with the RPi running its anticipated workload is the only thing that matters.
I hope you don't take my reply as a criticism, direct or otherwise. I was only expanding on the calculation and offering some broader context.

[ETA] I see the posts you are referring to now.

You are quite right in pointing out the limitations of calculations from limited data and the importance of real world tests.
Last edited by PiGraham on Fri Mar 29, 2019 3:26 pm, edited 1 time in total.

MarkTF
Posts: 297
Joined: Tue Mar 03, 2015 4:59 pm

Re: How long will it stay on with a external battery?

Fri Mar 29, 2019 2:19 pm

Andyroo wrote:
Thu Mar 28, 2019 7:49 pm
Androsmeq wrote:
Thu Mar 28, 2019 7:05 pm
Thank you so much for all the help!
:?:

No one has actually given you an answer. The calculated example is exactly that - a mathematical answer and is worth the paper it’s written on (no disrespect meant).
The calculated example(s) tell one the necessary parameters and the procedure to find the answer, which is arguably far more valuable than a simple result.

lewmur
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Re: How long will it stay on with a external battery?

Fri Mar 29, 2019 5:31 pm

MarkTF wrote:
Fri Mar 29, 2019 2:19 pm
Andyroo wrote:
Thu Mar 28, 2019 7:49 pm
Androsmeq wrote:
Thu Mar 28, 2019 7:05 pm
Thank you so much for all the help!
:?:

No one has actually given you an answer. The calculated example is exactly that - a mathematical answer and is worth the paper it’s written on (no disrespect meant).
The calculated example(s) tell one the necessary parameters and the procedure to find the answer, which is arguably far more valuable than a simple result.
Great reply!! :lol: "Instead of giving a hungry man a fish, teach him how to fish." All the nit picking in this thread was getting tiresome.

LTolledo
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Re: How long will it stay on with a external battery?

Fri Mar 29, 2019 8:31 pm

SO does anybody have any real-world data on this?

Calculation(s) are good for reference only
Real-world values, made/acquired during actual testing/use is much preferred

If none is available (or nobody is giving it) better acquire one yourself by doing actual test.
Then your question will be answered.
"Don't come to me with 'issues' for I don't know how to deal with those
Come to me with 'problems' and I'll help you find solutions"

Some people be like:
"Help me! Am drowning! But dont you dare touch me nor come near me!"

W. H. Heydt
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Re: How long will it stay on with a external battery?

Fri Mar 29, 2019 8:41 pm

LTolledo wrote:
Fri Mar 29, 2019 8:31 pm
SO does anybody have any real-world data on this?

Calculation(s) are good for reference only
Real-world values, made/acquired during actual testing/use is much preferred

If none is available (or nobody is giving it) better acquire one yourself by doing actual test.
Then your question will be answered.
I haven't done the specified scenario (Pi3B+ and 20Ah powerbank) but I do use a setup with a Pi2Bv1.1, RPF 7" display, keyboard, mouse, and WiFi dongle powered by either a 10Ah or 10.4Ah powerbank. I get run times of 5 hours.

PiGraham
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Location: Waterlooville

Re: How long will it stay on with a external battery?

Fri Mar 29, 2019 9:55 pm

LTolledo wrote:
Fri Mar 29, 2019 8:31 pm

Calculation(s) are good for reference only
Real-world values, made/acquired during actual testing/use is much preferred
Accurate calculations are far more useful than individual anecdotes. Unless someone else is using the exact same parts and running the exact same tasks their run time can't be relied on to predict your runtime. But it you have accurate data on capacity, efficiency and power consumption you can actually work out whatever you need to know, and do so before you buy, or send your rover into the wilds or whatever.
It's the difference between engineering and bodging.

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Imperf3kt
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Location: Australia

Re: How long will it stay on with a external battery?

Fri Mar 29, 2019 10:28 pm

True, but let's assume you bought a car from a car dealer and you ask how far it travels on one tank of fuel.
Would you prefer him to tell you "average results seem to indicate about 900km" or "you'll have to try it and see"

Now apply the same logic to a Pi and a battery. Nobody asked for an exact time, an approximate would be good enough.
55:55:44:44:4C
52:4C:52:42:41

Leoj03
Posts: 1
Joined: Fri Mar 29, 2019 10:26 pm

Re: How long will it stay on with a external battery?

Fri Mar 29, 2019 10:36 pm

For some measure of comparison, I have a 20,000 mAh power bank that outputs 5V/3A. It runs a Pi 3B with Raspbian Lite, a keyboard, and a 7 inch display for 9-10 hours, and Raspbian with keyboard, mouse, and same display for at least 8.
Never go up against a Sicilian when death is on the line.

Heater
Posts: 13111
Joined: Tue Jul 17, 2012 3:02 pm

Re: How long will it stay on with a external battery?

Sat Mar 30, 2019 3:35 am

Imperf3kt,
Now apply the same logic to a Pi and a battery
You can't. The analogy is wrong.

In your car case the car and the gas tank are one complete product form one manufacture and it's reasonable to expect such a specification.

In the Pi case it has no "gas tank". The battery is an unknown part of unknown capacity/quality from some unknown vendor.

Car analogies are always terrible. Best to avoid them.

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