One thing I liked about my old Asus EEE (not, alas, it's resistance to full cups of coffee over the keyboard) was the ability to not only charge itself but to run off a 12V power supply - ie my house battery.

I was surprised to find the low-power smartbook coming with a 19V supply. I think I have one I may be able to use but I'm curious as to why. Surely, a 12V source would make it more accessible for off-the-grid situations?

I probably have a 12V-19V adapter (not particularly efficient) but is there a better way of powering it?

Hi.

The reason for the higher input voltage at the adapter is because you need that higher voltage to be able to charge a 12V battery. It could have been designed with a little step-up converter inside, but that would have expanded the circuitry and cost, and probably wouldn't have been as efficient. A 19V adapter is small, common and cheap.

By the way, most netbooks and laptops run on 19V for this reason.

The solar set-ups we've done in the past (running off the grid) used a combination of Netbooks and Nettops. In this case, you need a DC/AC converter anyway (to power the monitors you need 110V/230V).

You could probably get away with running the netbook from 12V, but I think you would need to unplug the battery to prevent a possible brownout caused by the charging circuit.
I'm not entirely sure of this since I don't have the schematics at hand right now, but I'll see if I can find out later and update this post.


Johan.

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Johan Dams, Genesi USA Inc.
Director, Software Engineering

Yep, I have a blog... PurpleAlienPlanet

I just did some checking and the voltage of the EEE battery is 7.5V vs 11.1V for the Smartbook giving, in both cases, enough of a voltage difference to charge the battery. What components need the extra voltage? I would have thought the low-power design would have rendered it unnecessary on the main board (I know, Volts vs amps but even so).

From the board design, do you have any idea how "clean" the 19V needs to be? I have 17.5V solar panels and a few prototype generators producing somewhere in that vicinity.

Don't get me wrong, I love the machine and I've been looking for it for years (since the mid-'80s if you include my desire for a non-Intel based, practical machine). I just want to figure out how to make the most of its capabilities.

Hi.
No, not really. You can see the voltage difference on the Asus EEE is the 12V from the charger minus the 7.5V from the battery. This gives a 4.5V difference. This is required to overcome the voltage of the battery while in rest, which can be higher than 7.5V.
This same reasoning holds true for the smartbook: 0.9V voltage difference between battery and charger is not enough.

For example, let's imagine a lithium-ion battery consisting of a single cell. This cell has a nominal voltage of 3.7V (The netbook is a 3-cell battery, making 11.1V). However, the maximum charge the cell can hold is 4.2V per cell, giving 12.6V max charge.

Charging a lithium-ion battery is done by using a current source, rather than a normal voltage source. This means that for charging, a current is generated and kept constant until the the 4.2V per cell is attained, after which a constant voltage is applied until the current reaches zero.

A typical charging circuit for a single cell battery consists of for instance a LP2951 IC which does exactly that. The input voltage at the IC ranges between 6 to 10 Volts DC to charge a single 3.7V cell.

I think you can get away with operating the Netbook at 12V, but only when the battery is not connected. I don't have a variable DC power supply at hand to test this; but will try to run some tests after the weekend.

Johan.

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Johan Dams, Genesi USA Inc.
Director, Software Engineering

Yep, I have a blog... PurpleAlienPlanet

Thanks for that, I'll look up the details of recharging LIon batteries. In electronics, I'm the sort of person I hate in software - a circuit scrip-kiddy who knows just enough to assemble pre-designed stuff but lacking a full understanding of the background.

Flooded lead-acid, I'm familiar with as well as simple drop-down circuits to power computer peripherals but LIon batteries apparently work differently. I live full-time in an RV and most of the time we're plugged in but sometimes we're dry-camping for long periods of time (hence my interest in low-power computers - even my desktop machine is a 12V mini-itx rather spoiled by the 19V monitor).

I'm looking forward to hearing the results of your 12V test.

Any news on this? Spring is here and I'm looking to head into the mountains and do some writing which means running/charging the machine from 12V.

What are the dimensions of the DC plug? I have a 12V to 19V power supply for an old Toshiba that I might be able to use if I swap out the plug.

I don't know if this is helpful to you at all, but he does mention which plug on this adapter fits the smart book. I suppose worst case you could always just plug in an inverter to charge your smartbook. I tested this with a 12V deep cycle battery and a very small dual solar panel setup last summer and it worked OK.

http://www.powerdeveloper.org/forums/vi ... php?t=2255

I'm not looking for an inverter - I actually have one of those that a well-meaning relative got for me. Converting DC-AC-DC, unless there's a transmission issue, just rubs my sense of design the wrong way.

I have a 12 to 19V step-up transformer that used to charge up (not enough juice to power it while running) a Toshiba Satellite. The POS Toshiba has gone now but if I can get the correct plug, I can rewire it for the Efika.

that's why I linked the thread that I did, it looks like that one has many plugs one of which fits the efika.

DC to DC converters that step-up the voltage already are DC-AC-DC converters. They just put it all in one box, eliminating a socket, plug, and cord.

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--

Science, n. Investigation of natural phenomena.
Engineering, n. Domestication of natural phenomena.
Technology, n. Domesticated natural phenomena.

--

\"It is essential for automatic computation that, instead of containing every single instruction necessary to carry out the program, the coded program include methods for generating instructions which are needed to carry out the program. ... One measure of the extent to which an automatic digital computer is used effectively is given by the ratio of the number of instructions formed in the machine to that of the instructions inserted into the machine initially.\" Mathematical Machines Volume I Digital Computers ©1961 Francis J. Murray

If so, then why is this ratio zero on most modern computer software?

I'm wondering why Genesi even bothered with making additional power supply in the first place? Efika is very similar to mobile phones we have today, and most of them are charged via USB. Ok, Efikas battery is a bit bigger, but you still can use power USB to get up to 24 V. It would strikeout charging problem all at once.

19V is just what most Netbooks used at the time (I have a Lenovo, Acer Aspire, EeePC all with 19V supplies - in fact they are *identical* 19V supplies almost down to the part markings).

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Matt Sealey