Nafihe
Posts: 1
Joined: Thu Sep 14, 2017 10:17 am
Location: Munich, Germany

Need of a battery

Thu Sep 14, 2017 10:26 am

hello guys,

i need a 12v or 9v battery for raspberry pi which runs atleast 1 day or 20 hours with bluetooth working.
also size matters it should be same of the size of pi or a little more. suggestions and thanks

W. H. Heydt
Posts: 7519
Joined: Fri Mar 09, 2012 7:36 pm
Location: Vallejo, CA (US)

Re: Need of a battery

Thu Sep 14, 2017 2:31 pm

You have two conflicting requirements. Any battery capable of running a Pi for 20 to 24 hours is going to be bigger than a Pi and any battery that is no larger than a Pi won't power it for that long, not even if it's Pi0W. It's a matter of energy density. In concept, the way around that dilemma ought to be a small Hydrogen fuel cell, but I don't know of any on the market, let alone affordable for casual use.

That said, rather than looking for a 9-12v battery (I presume you're going to use a UBEC or something similar as you *don't* want to connect such a battery directly to a Pi), why not use one of the ubiquitous 5v "powerbank" units? I can run a Pi0W with a 3.5" display attached to it for around 12 hours on a 4Ah powerbank so--depending on what you're doing--something in the range of 6 to 10 Ah ought to meet your run time spec.

W. H. Heydt
Posts: 7519
Joined: Fri Mar 09, 2012 7:36 pm
Location: Vallejo, CA (US)

Re: Need of a battery

Thu Sep 14, 2017 4:17 pm

Note...it is better to respond here than to send a PM. This is so that others, who may have the same or a similar problem will see where the issues and answers are. That said....

Even with your DAC needing 9v to 12v (and, again, DO NOT provide that high a voltage to a Pi...you'll let the "magic smoke" out), you still aren't going to find a battery with the required capacity that is the size of a Pi (or less). Current batteries simply don't have the energy density you need. Not even Li Ion or LiPO ones. You're going to have to either relax your run time requirement (probably by a *lot*) or use a much larger battery than you want. This is a matter of physics and engineering.

r3d3
Posts: 3
Joined: Fri Sep 15, 2017 9:07 am
Location: France
Contact: Website

Re: Need of a battery

Sat Sep 16, 2017 6:50 pm

Hi all.
I actually meet a problem to power any devices with a powerbank USB battery.
It is fully charged and I tried to power a simple LED with resistor (I've tried to get into VSS of a L293D before) through a micro-usb connector on the test circuit side.
When I connect the powerbank, the LED shines for about 30s, and then it stops suddenly, the voltage drops to 0V.
It seems to be a sort of electronic protection, or a lack of information from the device, back to the powerbank.
I've tried to short pinout DATA- and DATA+, put a 220ohm resistor between D-, D+, shorted D- and D+ to ground, but none of these "solutions" worked.
Is there anyone who know what is going on ?
Note : If I plug a "standard" device like a RPI, an electronic cigarette or a smartphone, it works without stopping the charge process after 30s... :shock:
Thanks.

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KLL
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Location: thailand
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Re: Need of a battery

Sun Sep 17, 2017 3:07 am

your power bank is too smart, your LOAD too small, so the power bank shut down.
?limit? min mA? use a bigger LED?

r3d3
Posts: 3
Joined: Fri Sep 15, 2017 9:07 am
Location: France
Contact: Website

Re: Need of a battery

Sun Sep 17, 2017 5:02 pm

Thank you for the advice.
So I've tried to power a more current-consumer load, such as 4 LED and resistors in parallel, without success, I also connected a 12V tungsten bulb lamp (to increase current flow) - no chance...
Still 30s of power coming from the powerbank, that's it.
I will soon get a different powerbank, so I'll give you results later - but it is a mystery for me.

Reference : "POWER BANK", PBS-16000, 16000mAH, Output1 : 5V 1A, Output2 5V 2A

W. H. Heydt
Posts: 7519
Joined: Fri Mar 09, 2012 7:36 pm
Location: Vallejo, CA (US)

Re: Need of a battery

Sun Sep 17, 2017 10:01 pm

Try putting a 15 ohm, 2W resistor across the power lines. You'll be drawing about 300mA. Use a 2W value becuase you'll be dissipating according to the formula W= I^^2 R (or W = v**2/R if you find the math easier).

r3d3
Posts: 3
Joined: Fri Sep 15, 2017 9:07 am
Location: France
Contact: Website

Re: Need of a battery

Mon Sep 18, 2017 5:08 pm

It works ! with a 12 ohms, 3W resistor (althought it became really hot !)
So I connected again the powerbank to the VS (pin 8) of a L293D IC and it works fine.
In fact I thought that motors first didn't rotate because of a power issue, but my first IC (L293DNE) burned out - I replaced it with a L293D and that's ok now : the battery gets in a sleepy mode when motors are down, but it wakes up straight away when I activate the logical +5V VSS pin from my python script.
Thanks again. ;)

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