Richard Smith recently answered questions about the XO-3 power requirements, with an illuminating video of the similar XO-1.75 running directly off a 10W solar panel (without a battery). Below is his update to olpc’s devel mailing-list:
> Q: What are the XO-3 power consumption and charging requirements?
It’s still too early to lay out exact claims for this. These are A1 prototypes. This is the stage where we start finding all the things that use more power than we would like, and reduce them. The exact size of the battery is also changing as we maximize the space in the battery cavities.
We won’t make exact claims on power until it moves well into B- and C-series builds. That said, a lot of internals are almost identical to the 1.75, so things I’ve previously said about 1.75 are a good approximation of the XO-3.
- The traditional display consumes more power than the Pixel-Qi.
- The maximum runtime power draw of the 1.75 is 5W. (Not including the extra 5W you can draw from the USB port.)
- The power input front end of the XO-3 is identical to the XO-1.75 and XO-1.5: an 11V-25V input range and a maximum input rating of 25W.
- The XO-3 can also be powered by USB OTG (On-The-Go).
- The XO-3 would survive long term if you connected it directly to a car/motorcycle 12V power system (with no adapter).
(I don’t think any other tablet made so far could say that.)
Here’s a video showing a 1.75 powered completely by our 10W PV panel. This is a raw panel, with no power controller or internal battery; there is no battery in the XO. The laptop has suspension turned off. Chris Ball and I shot it yesterday, on a sunny winter day in Cambridge. More notes and details below, for the power geeks.
Unlike the XO-1.5 the XO-1.75 almost never gets to the 25W maximum because its runtime power is much lower. So peak power draw only happens when charging a very low battery.
OTG has a strict 5V/7.5W power specification so charging via OTG will take longer. No, I’ve not yet measured how much longer. Sadly its not a nice linear thing that you can just do the math and figure out. There are many variables some of which will change with the next prototypes.
Having a robust, wide voltage range, high power input is an important feature when using alternative power sources. Alternative power can be very unclean and very sporadic. You must be very forgiving on what you allow and when its available you want to maximize your input.
> Has it been demonstrated to be chargeable by “solar panels,
> hand cranks cranks and other alternative power sources?”
> [Sources] not requiring systems that cost more than the laptop,
> nor someone with XO-green skin color to crank?
The claim of being chargeable by alternate power sources isn’t new. Every XO generation we have made to date matches this claim, and in each generation we make an improvement.
It’s always been possible to charge an XO from alternative power sources. Sites in Rwanda, Peru, Haiti and the Solomon Islands (just to name a few) are powered entirely by solar. These use XO-1’s and XO-1.5’s. Some use a commercial-type solar system and some are just solar panels that connect directly to the XOs. Read more:
The XO-1 and XO-1.5 had maximum runtime peak power draws in the 10W range. Running things like the camera activity which keep the system busy would draw that power continuously. If you didn’t have 10W of input you’d go backwards. Most people don’t really realize how much work 10W of continuous power is. The physical size of a 10W solar panel isn’t huge but its still pretty large and you need perfect solar conditions for that 10W. So what you really need is a larger solar panel that so a wide range of solar conditions still work.
The XO-1.75 and the XO-3 tablet have a runtime peak power draw in the 5W range and they idle even lower. So power sources with peak production in the 5-7W range can fully power the new XO devices in a variety of conditions. A 10W panel would almost certainly have no net power draw unless the solar conditions were really terrible.