Uninterruptable Power Supply (UPS)
This thread about using a auto battery to power RPi (http://www.raspberrypi.org/phpBB3/viewt ... =41&t=5385) got me to thinking: People want to use a cigarette adapter to USB power the Pi, but what if the power is cut? My car's been having power troubles recently so suppose I'm using a RPi for some reason in the car and the worst happens. abd what then? My first thought would be to have a backup battery for when the power from the cigarette lighter drops, but then, why not just have a UPS backup power source? It could connect to the micro USB and it is itself charged by the power from the car adapter. What would it take to convert or build a UPS to supply power to a microUSB port?
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mahjongg
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Re: Uninterruptable Power Supply (UPS)
An uninterruptible power supply (UPS) Is a complex system that takes energy from the net, then stores it in a battery, then converts it to AC (net voltage) again when needed.
Not a right solution, if you already have half the solution (the car battery), and you devcie is power from low voltage DC..
Just power the PI from the battery (using the ubiquitous "cigar plug" converter), and at the same time use a battery charger to keep the battery charged. The same thing happens with the battery in a car while its driving, so this is perfectly acceptable.
Not a right solution, if you already have half the solution (the car battery), and you devcie is power from low voltage DC..
Just power the PI from the battery (using the ubiquitous "cigar plug" converter), and at the same time use a battery charger to keep the battery charged. The same thing happens with the battery in a car while its driving, so this is perfectly acceptable.
Re: Uninterruptable Power Supply (UPS)
Really? I didn't know UPS were so complicated. That was my second choice but I don't know of what batteries to go on because of the concerns about current and my local choices aren't very great in that regard.
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mahjongg
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Re: Uninterruptable Power Supply (UPS)
Oh, UPS'es are much more complicated than I described, because the switch from net powered to battery powered (and back) must be essentially immediate, and that is technically very difficult.
Essentially every 12V battery should be fine, such as those found in motorcycles that are so often used in African (and Asian) countries, and the charging current needs to be essentially just a little bit more than the average current draw of a raspi. A raspi uses (for normal operation) about 2.2 Watt, or at 5V 0,44 A (440mA), so any 1A 12V charger would suffice (if the net power is mostly on, otherwise just double the amperage if the power is on half the time etc.) Don't worry about "overcharging" on a lead battery like the ones used in card and motorcycles the charger would just put enough power in the battery to keep it charged, no more.
The only point is that the bigger the battery is the longer the PI will be powered from it without it being charged. But a typical motorcycle lead battery will hold about 30 Amperes/hour, so at 0.44 Amperes it will power the Raspberry PI for at least 68 hours! (more, as the average cigar plug converter will generate much more output current at 5V than it draws input current at 12v)
Essentially every 12V battery should be fine, such as those found in motorcycles that are so often used in African (and Asian) countries, and the charging current needs to be essentially just a little bit more than the average current draw of a raspi. A raspi uses (for normal operation) about 2.2 Watt, or at 5V 0,44 A (440mA), so any 1A 12V charger would suffice (if the net power is mostly on, otherwise just double the amperage if the power is on half the time etc.) Don't worry about "overcharging" on a lead battery like the ones used in card and motorcycles the charger would just put enough power in the battery to keep it charged, no more.
The only point is that the bigger the battery is the longer the PI will be powered from it without it being charged. But a typical motorcycle lead battery will hold about 30 Amperes/hour, so at 0.44 Amperes it will power the Raspberry PI for at least 68 hours! (more, as the average cigar plug converter will generate much more output current at 5V than it draws input current at 12v)
Re: Uninterruptable Power Supply (UPS)
So could I do this without the car? I'd just need a motorcycle or equivilent 12v battery, a charger and something to convert it to 5v usb? I suspect I'm missing something it sounds too easy...