That is not the whole story!Cancelor wrote:I run my RPi of a small 12v lead acid battery using one of these**:-
http://www.ebay.co.uk/itm/New-Ultra-Min ... 565cec5c7f
The battery is rated at 12Ah and I can quite reliably get 24 hours use out of it.
Amps x hours = 500mA x 24 = 12Ah
To run for a week 500mA x 24 x 7 = 84Ah
A 100Ah battery like the one below should cover it.
http://www.ebay.co.uk/itm/019-100Ah-4-Y ... 27df812d83
** adjust the output voltage before going anywhere near the RPi
50% of its nominal capacity ? No.ghans wrote:Don't you damage a car bettery if you discharge it over 50 % ?
Code: Select all
We got about 60 – 90ma of current at 15MPH
*makes a mental note to check under my local bridges for free RPi and car battery *Blender wrote:Thanks Guys.
The Pi will be left on the underside of a bridge, monitoring a potential probe within the concrete in mV to find out if the reinforcement is corroding or not.
I currently have it hooked up to a 12V 110Ah battery for a trial. I have connected a cigarette lighter socket to the battery, then a standard usb stepdown to 5V connected to the cigarette lighter.
Seems to be working great so far.... I let you know how it goes.
A cheap cigarette-lighter -> USB adaptor may well be using an inefficient linear regulator (and even then the output might not be very well regulated if it's only designed to be a 'phone charger'). Much better to use a proper 12V -> 5V switching regulator, which will be more efficient and therefore give you longer battery life.Blender wrote:I have connected a cigarette lighter socket to the battery, then a standard usb stepdown to 5V connected to the cigarette lighter.
I was thinking just about all the 12V to 5V (USB) car adapters would be switchers. A linear would generate too much heat for that application.redhawk wrote:To follow up from previous poster I would suggest you carefully take apart the ciggy power adapter and inspect the circuit.
Some cheap and nasty regulators are linear, if however you find a IC with 8 legs (sometimes with #34063 markings) then it's safe to say you have a switching mode regulator.
Hi, just saw this post. The 60-90ma is off the 50W wind turbine, not the 15W wind turbine. Sad but true.mikerr wrote:Just read an interesting project using a tiny 15W turbine for wind power and pi:
http://www.switchdoc.com/2014/07/wind-p ... pberry-pi/
http://www.switchdoc.com/2014/01/small- ... open-loop/We got about 60 – 90ma of current at 15MPH
a bit short of the 150ma needed for a model A