Raspberry Pi off `12v battery


6 posts
by ahuk » Sat Jul 07, 2012 10:54 am
Hi,

I have recently been researching into portable options and projects for the RPI and have settled upon the fact that the voltage differences between the different hardware components is going to make this slightly difficult.

However, I can easily buy a 12v to 5v connector with current regulator, so this is not a problem, but I was wondering if it would be indeed possible to power the RPI and a screen from a 12v Lead acid battery such as those found in alarms etc?
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by alexeames » Sat Jul 07, 2012 9:03 pm
Yes it would be possible to do that. There are some fairly inexpensive switching regulators on ebay that would facilitate the 12V ---> 5V conversion fairly efficiently.
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by pjc123 » Sun Jul 08, 2012 12:19 pm
Here is a good blog of some of the possible options:

http://www.fanjita.org/serendipity/arch ... eries.html

I am looking into doing the same thing, run the pi off of either a sealed motorcycle battery, alarm battery, etc. because it is the only option that would supply a long run time. If I need super long run times I can even use a car battery, although lugging it around would not be too pleasant. I already have a trickle charger to recharge the battery. I am considering getting either a UBEC to convert the 12V to 5V or something similar to the following plugged into a cigarette lighter socket and wired to the battery:

http://www.amazon.com/Griffin-Technolog ... ds=griffin

What I like about this option is that it has a usb connector, so no building of cables. Since so many companies make similar products, the key is to find one with decent amperage output and good voltage/current regulation. I must say that I am currently powering my pi off an A/C outlet using one of the ports off a Griffin P1190R2 Dual 1 Amp Power Block and I have not had any power issues.
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by pjc123 » Sun Jul 08, 2012 1:34 pm
While looking at reviews of various USB cigarette lighter chargers, I discovered that it may be necessary to short two of the data pins on the charger in order to supply the necessary current to work with the raspberry pi. No big deal, as this is a simple modification of the charger. There are a few 1.0 Amp / 2.1 Amp dual port chargers available that would insure enough power for the pi.

Here is an explanation of the issue that someone else wrote:

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A little background on USB charging for those who don't know:

The USB power spec is for 0.5 Amps at 5 Volts... or 2.5 Watts. This was great up until the last couple years when devices have gotten really power hungry, particularly smartphones and tablets and to a lesser extent dedicated GPS's. Some of these devices use over 2 Amps, particularly the tablets like the iPad (or in my case the HP Touchpad).

Manufacturers of these devices therefore had a dilemma. If they had their devices pull more than 0.5 Amps, they risked damaging the power source, which could be a computer, that was only prepared to source 0.5 Amps. Thus the manufacturers have used tricks to determine whether their device is connected to an unknown source, at which point they purposely only draw 0.5 Amps, or to the dedicated charger that was provided with the device, where they can draw all the power they need.

There seem to be two common tricks used. The first is to short the two data-wires together in the charger. This is what most non-Apple devices do. Since a computer or older device wouldn't have done this, the device can assume it is safe to draw all the power it needs.

Apple seems to have taken a different approach, one that I don't fully understand but know can be seen by the fact that the data lines are neither open nor shorted when the charger is plugged in, and is more sophisticated and probably superior, because I suspect it allows the device to know exactly how much power it can use.

While Apple taking a better approach might be nice in concept, it's created chaos in the USB charger product category. What is the non-specific charger to do? They can't support both.
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by geezbeez » Mon Jul 09, 2012 12:20 pm
Just an Idea.

Id concider just using NiMh or even NiCd rechargeables.

Buy a 4 way USB hub taht takes a 5v-6v supply,
Buy 4 of 4 x AA BATTERY HOLDER (SQUARE) the kind that will attach to 9v snap connectors
Buy 4 of 9v snap connectors
Thats about 60p x 7 + hub so should be about £10-£15

If the hub takes 9v supply then alter spec for 6 x AA Battery holder.

Connect the 4 snap connectors in parralel to power the USB hub.
Snap on 3 of these battery holdes loaded with batteries to give 4.8-5v and power the 4 port USB hub from it.

Connect the hub to the Rasp PI and power the Rasp PI from one of the USB ports,
Put a WIFI dongle in another hub port, not in the Pi as you want to distribute power consumption across the hub.
Use a third hub port for your smartphone (when necessary).
Connect smart phone to Rasp PI over wifi. You need to configure your PI to accept connection from your phone.
Run VNC server on the Rasp PI
Run VNCClient App on the phone so your phone is now your screen and keyboard.

You should be able to hot swap the 4xAA Battery packs one at a time keeping the RaspPi and HUb working. attaching a 4th battery pack before removing a depleted one.
Youd want 12 new NiMh AA batteries and if you have any old NiCds you can charge the up and use them as backup.

Please feel free to pick at my logic if you see any problems with this.
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by alexeames » Mon Jul 09, 2012 5:55 pm
pjc123 wrote:While looking at reviews of various USB cigarette lighter chargers, I discovered that it may be necessary to short two of the data pins on the charger in order to supply the necessary current to work with the raspberry pi. No big deal, as this is a simple modification of the charger. There are a few 1.0 Amp / 2.1 Amp dual port chargers available that would insure enough power for the pi.


Yep, shorting the data pins tells the USB device it is connected to a charger and not a PC or other device. When I soldered up a 5.0V regulator for charging my phone, at first I didn't short the data pins. The phone thought it was connected to a computer. When I shorted them, it knew it was connected to a charger. I did this on the regulator output ports so I could use normal USB cables. Just a little dob of solder between the middle two pins. :D
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