dannydebont
Posts: 6
Joined: Mon Sep 05, 2016 6:56 pm

Pi3 car battery source

Mon Sep 05, 2016 7:17 pm

Hi,

I have 2 Pi 3 B's that I can only power from car batteries (remote location). I have not hooked them up yet ... just wanted to know if it would be safe to bring the voltage down from 13.8v to 5v without damaging the Pi's?

Thank you

Danny

mosespi
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Re: Pi3 car battery source

Mon Sep 05, 2016 7:45 pm

Sure, you can use an off the shelf lighter plug USB adapter, or use one of many available DC-DC converter modules.

Input power either through the original micro USB port or feed it from the 5v pins on the GPIO. Remember you bypass the polyfuse if you power from the GPIO, so add your own if you want to maintain the fuse.

Note, if you have actual car starting batteries, remember they don't like to be discharged too much before recharge. You will damage them quickly if you deeply discharge and recharge them about a dozen times. If you will be doing this often, get a deep cycle battery.

Regards,
-Moses
Power problems? MoPower UPS for the Pi
http://www.allspectrum.com/mopower/

klricks
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Re: Pi3 car battery source

Mon Sep 05, 2016 8:53 pm

dannydebont wrote:Hi,

I have 2 Pi 3 B's that I can only power from car batteries (remote location). I have not hooked them up yet ... just wanted to know if it would be safe to bring the voltage down from 13.8v to 5v without damaging the Pi's?

Thank you

Danny
Doing anything other than converting from 13.8 to 5V will destroy the RPi.
It is best to use a switching or buck type converter. Do not use a linear regulator such as a 7805. Do not attempt to divide voltage with resistors alone.
Google [UBEC 5v] these are very popular with battery powered RC applications.
Unless specified otherwise my response is based on the latest and fully updated Raspbian Buster w/ Desktop OS.

PiiPatient
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Location: Cornwall, Ontario, Canada
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Re: Pi3 car battery source

Mon Sep 05, 2016 11:22 pm

You could always use something like this to get power converted from 12 VDC to 5 VDC with 10amps
Image

Myself I got one that has a plug that is on the output side of things that plugs directly into the Raspberry Pi3 with a factory plug attached, the other end, i.e., the input has the two stripped and tinned wire ends that you need to figure out a wiring solution for that gives you protection from any power surges etc....
Certified Glazier/Metal Mechanic, Certified Chef, Hobby Electronics enthusiast. Audiophile

dannydebont
Posts: 6
Joined: Mon Sep 05, 2016 6:56 pm

Re: Pi3 car battery source

Tue Sep 06, 2016 12:31 pm

I did get a deep-cycle battery ... not cheap though ... thank you moses ;)

I also managed to get a UBEC from a local hobby store ... I got one that has a 3A rating ... hope it won't bake the Pi ... thank you klricks for the tip on how to NOT connect the Pi ... (like your write-up on the Pi)

PiiPatient Thank you for replying

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davidcoton
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Location: Cambridge, UK

Re: Pi3 car battery source

Tue Sep 06, 2016 4:48 pm

dannydebont wrote:I also managed to get a UBEC from a local hobby store ... I got one that has a 3A rating ... hope it won't bake the Pi ...
As long as the UBEC has the correct voltage (5 +/- 0.25V), and can supply the current your equipment needs, there should be no problem.
Low voltage may cause problems, depending on what is connected and what it needs.
High voltage risks causing serious damage.
Low current capability will lead to low voltage.
High current capability is fine -- the equipment will only draw what it needs. 3A should be enough, since 2.5A minimum is usually recommended.

Think of electricity in a wire like water in a pipe:
If the pressure (voltage) is low, you may not get enough.
If the pressure (voltage) is high, things will break.
If the flow is limited, for example by a thin supply pipe (cheap USB cable), you may have problems.
A good fat supply pipe (good thick USB cable) is fine, as long as the pressure (voltage) is right only the amount of water you want will flow.
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ejolson
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Joined: Tue Mar 18, 2014 11:47 am

Re: Pi3 car battery source

Tue Sep 06, 2016 5:36 pm

davidcoton wrote:Think of electricity in a wire like water in a pipe:
If the pressure (voltage) is low, you may not get enough.
If the pressure (voltage) is high, things will break.
On the other hand electric motors may draw more current and overheat when voltage is low.

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davidcoton
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Re: Pi3 car battery source

Tue Sep 06, 2016 9:20 pm

ejolson wrote:On the other hand electric motors may draw more current and overheat when voltage is low.
At this time of night, I can't work out whether you've just pushed my analogy too far, or whether there's an analogue of that of hydraulics. Or both. :? :)
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ejolson
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Re: Pi3 car battery source

Wed Sep 07, 2016 1:41 am

davidcoton wrote:
ejolson wrote:On the other hand electric motors may draw more current and overheat when voltage is low.
At this time of night, I can't work out whether you've just pushed my analogy too far, or whether there's an analogue of that of hydraulics. Or both. :? :)
I never thought about the fluid flow analogy. Maybe at the transition from laminar to turbulent flow, a lower pressure could lead to laminar flow with an increased rate of mass transport compared to a higher pressure that leads to turbulence.

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