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Old 04-13-2012, 06:56 PM   #31
MLXXXp
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With the right equipment, you don't have to get the Libre into a known charge state or do any timing. Just use a voltmeter and an ammeter (preferably at the same time, or alternatively a wattmeter) to measure the voltage and current (or power) going to the Libre, from the output of the adapter.
In case Ken, or anyone else, is still interested in this topic, I've done some work to determine the power requirements for charging an Aluratek Libre.

I built a Mini-USB breakout box to allow me to measure the current that the Libre is drawing while charging.
Details of the box are at this link

Here's a link to a picture of my measurement setup

The device with the large black heat sink, at the lower left, is a DC voltage regulator circuit that I built. It's being used to provide a nice stable voltage (I set it for 13V) to a lighter socket. The regulator is being fed from a 15VDC unregulated "wall wart" adapter that's not in the picture.

A white 12V to 5V USB adapter is plugged into the silver lighter socket to the right of the regulator. The adapter is rated maximum 1A output, 12-24V input. The meter at the far left is measuring the voltage on the lighter socket (thus the adapter input) and the meter next to it is measuring the current drawn by the adapter.

The USB cable that came with the Libre is connected between the adapter and my break out box, and the box's plug goes to the Libre. The beige Beckman meter is measuring the voltage on box's plug cable (thus the Libre's input) and the meter to the right of it is measuring current drawn by the Libre.

During these measurements, the Libre's battery was quite low.

Calculating power to the Libre:
4.81V X 0.54A = 2.60 Watts.

Calculating power to the Adapter:
13.00V X 0.28A = 3.64 Watts.

Calculating the efficiency of the adapter:
2.60W / 3.64W = 0.71
(The adapter has a conversion efficiency of 71%)

For use with a 12V solar panel, the power into the adapter (overall power) is the important value. To operate in this set up, in place of the regulator, a panel would need to be able to provide 3.64 Watts. (A panel capable of providing more power wouldn't hurt, but it wouldn't speed up charging any.)

Now, if you look at the AC adapter that came with the Libre, you'll see a diagram that indicates that the negative output goes to both pins 4 and 5 (pin 4 is what I call pin X for my break out box). In other words, pin X is grounded.

I moved the pin X jumper on my box so that pin X was grounded.
Here's a link to a picture of this setup

Notice that the Libre is now drawing more current, since it sensed that pin X is grounded and thinks that a high power charger is attached.

Calculating power to the Libre:
4.51V X 0.84A = 3.79 Watts.

Calculating power to the Adapter:
13.04V X 0.43A = 5.61 Watts.

Calculating the efficiency of the adapter:
3.79W / 5.61W = 0.68
(Here, the adapter has a conversion efficiency of 68%)

So if you had a way to ground pin X (like I do) and wanted to use a solar panel, the panel would have to be able to provide 5.61 Watts.

If your 12V to USB adapter was more efficient than mine, your panel power requirements would be reduced proportionately. And actually, there's a very small amount of power lost in the ammeter measuring the Libre current, so slightly less power would be required if the meter is removed.

Last edited by MLXXXp; 04-13-2012 at 07:04 PM.
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Old 04-14-2012, 06:34 AM   #32
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From calculating my Jetbook which had a 3.6V battery, 800mAh,which ran 24hours, it uses 0.12W on average.

Most of the time the system is in standby while the display uses some power.

I think the 5W is well overestimated! A 1W will be more than enough. The problem is you need more when the device tries to charge at the same time.
But when you are not using the reader, it might charge from the 1W solar panel, while when you are using it the 1W is not enough to charge, but it is enough to provide the device with energy.
That way, unless you're reading/writing a lot of data to the card, while flipping pages like crazy, you'll never run out of battery.

That'd be what I'd think... The device itself uses very little battery. If you have a lite version where you can remove the batteries, or where you can direct the device to use USB power but not charge, you could perhaps run the device without batteries.
I say USB because I had hoped the solar panel could plug straight into the USB port!
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Old 04-14-2012, 05:14 PM   #33
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Hmm... I'll have to see if I can rig a ground for the adapter's USB connection at pin 4.
(If there is not one there already.)

You wouldn't want to have the unregulated output of the solar panel go directly to
the power pins of the Libre's USB port. The power regulation of the charging circuits
are likely limited. Having a properly sized solar panel go directly to a battery is less of
an issue. Having even a number of small panels go to an adapter, designed to regulate
the power from the much greater amp capacity of an automotive electrical system, is
a simple and inexpensive measure to insure compatible power for your device.

Luck;
Ken

Last edited by Ken Maltby; 04-14-2012 at 05:16 PM.
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Old 04-14-2012, 09:37 PM   #34
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Quote:
Originally Posted by Ken Maltby View Post
Hmm... I'll have to see if I can rig a ground for the adapter's USB connection at pin 4.
(If there is not one there already.)

You wouldn't want to have the unregulated output of the solar panel go directly to
the power pins of the Libre's USB port. The power regulation of the charging circuits
are likely limited. Having a properly sized solar panel go directly to a battery is less of
an issue. Having even a number of small panels go to an adapter, designed to regulate
the power from the much greater amp capacity of an automotive electrical system, is
a simple and inexpensive measure to insure compatible power for your device.

Luck;
Ken
The input to a USB port is certainly expected to be regulated and should not exceed 5.1 Volts, nominally 5.0 V.

Dale
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Old 04-14-2012, 10:39 PM   #35
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Originally Posted by Ken Maltby View Post
Hmm... I'll have to see if I can rig a ground for the adapter's USB connection at pin 4.
(If there is not one there already.)
Please carefully re-read the first section of my breakout box document.

Also refer to these links:
http://en.wikipedia.org/wiki/Univers...cal_appearance
http://pinouts.ru/Devices/mini-USB_pinout.shtml

You can't do anything with pin 4 of the adapter's USB Standard-A connector, or that end of the cable. That pin is ground.

The pin that needs to be grounded, to affect charge current, is the additional pin (pin 4 or pin X, depending on which of the above links you refer to) that's only present in the Mini connector. In the USB cable that came with the Libre, and any other Standard-A to Mini-B cable, this pin won't be wired to the cable or anything else. The only way to get to it is in the Mini-B connector itself. (Or you could ground it in the Libre itself but I definitely wouldn't advise that.)
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Old 04-14-2012, 10:43 PM   #36
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The input to a USB port is certainly expected to be regulated and should not exceed 5.1 Volts, nominally 5.0 V.
Actually, the 5V for PC power supplies, and thus USB ports, is specified to be within plus or minus 5%. Up to 5.25V should be safe and it should work properly down to 4.75V.
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Old 04-14-2012, 11:02 PM   #37
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Having even a number of small panels go to an adapter, designed to regulate the power from the much greater amp capacity of an automotive electrical system, is a simple and inexpensive measure to insure compatible power for your device.
Simple and inexpensive, yes. Unfortunately not very efficient. As can be seen from my tests, these adapters don't do a great job of converting the 12V down to 5V.

My test adapter, and another rather more expensive Motorola SYN0847 adapter, were both only about 70% efficient. 30% of the power coming from the panel(s) will be wasted as heat in the adapter. The power output capabilitiy of the panel(s) has to be increased to compensate.
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Old 04-15-2012, 01:21 AM   #38
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USB ports are more flexible than you think. Just measure the voltage on a USB AC wall charger and you'll know it's seldom exactly 5V.

Connecting the solar panel to the battery might indeed be a better idea, as the battery will work like a capacitor.
The only thing I'd be worrying about is when the sun isn't shining, doesn't the panel consume some battery instead of providing power?

One thing I've thought of,is having a 6V panel, pasted on the back of the reader.
As long as the sun isn't shining fully on the panel, it'll never reach 6V.
Another thing is, that every device has a power LED, as well as this has an LED screen.
Both will dampen over-voltage (with over-voltage they perform better, and prevent the voltage from reaching too high). Before the power led would become unusually bright, or decolored, you'd be running at least 25-33% higher voltage. Also most of the internal CPU and stuff can handle a bit more than 10% overvoltage, especially with such low heat devices.
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Old 04-15-2012, 05:42 AM   #39
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The solar panels almost always have a diode, to prevent that.

The potential benefit of a panel of the same size as the device would be as a trickle charger, to
extend or maintain a charge level, despite selfdischarge. But, then you would need to leave it
out in the sun.

Luck;
Ken

Last edited by Ken Maltby; 04-15-2012 at 05:46 AM.
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Old 04-15-2012, 09:45 AM   #40
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It really depends. I've seen solar panels that would be able to over charge the device.
All panels provide voltage, even if the sun isn't shining directly on them.
I don't know to which extend, but it may be that as long as you're holding the device, the panel would get enough light from it's environment to charge the device.

The only thing you would not want to do is put it in full sunlight,or put it in it's sleeve.

I have a gameboy charger, it consists of 2 solar panels of 2,5".
I also have a solar panel cellphone charger the size of an iphone (3.5")

The cellphone charger always provides voltage, in any room with more light than office light; it also has a built in battery. you can buy them on dealextreme:

http://www.dealextreme.com/p/solar-p...adapters-30047

If you have a sleeve like this one:

or this one:


you could easily paste 2 solar panels on the outside of it, with a wire connected to the reading device!
panels like these ones:

http://www.dealextreme.com/p/solar-p...-18168?item=15
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Old 07-18-2012, 07:15 PM   #41
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In an earlier post you said "I already have a

The solar charging system that I'm working on will use from 1 to 4 of those 1.8W panels but also includes a 12V gel battery along with charge control and low voltage cutout circuits that I've designed.
i simply opened up the libre and connected a 9 volt solar panel to the INTERNAL BATTERY DIRECTLY with a diode in series to prevent the internal battery discharging into the solar cell or causing short circuits.

result i got on a DULL day was 15 minutes of aluratec libre pro operation after 6 hours on a window ledge inside the house.i had totally discharged the battery beforehand.

the panal can output 200 milliamps short circuit current on a bright direct sunlight day.

the current flow varied between 10 to 20 milliamps on a dull day into the libra battery.

no doubt you can on better days you could get up to a 1/2 hour operation or longer.

this was a 0.7 watt panel.
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Old 07-19-2012, 03:06 PM   #42
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Yes, the batteries have an internal BMS; so it won't harm them.
Next time just try to get a higher power version (more Milli-amps), 6V, without diode.
Just as long as you connect the leads correctly.

I don't know about solar panel discharge; I should find a way to test it though.
DX sells Gameboy DS batteries for very cheap (like $3). You could try to connect one with panel, the other without to see if it loses energy over time.

I gave up on the solar panel, as I waited for 9 months, before cancelling the order (I had already sold the Jetbook, so no need for solar panels for a while).
ALthough I might want to install one on my EZ-Reader Pro.
15 minutes of reading time on the Jetbook equals about 15 hours on the EZ Reader PRO (has e-ink), and by the time you reach those 15 hours, the solar panel most likely has charged it even more. It could technically provide the EZ REader Pro with an infinite amount of energy, just as long as there is light.
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