Will this solar charger work with the Libre Pro

[Gardenman]

Does anyone know if this charger would work with the Aluratek Libre Pro?


http://www.ebay.com/itm/Solar-Power-...#ht_4060wt_716

[MLXXXp]

If it actually performs as specified, then yes, it should work.

Note, though, that if using solar power only, it may take days or even weeks to build up enough charge in the charger's internal battery to fully recharge the Libre.

[Ken Maltby]

You can get a larger 12v "Battery Maintainer" solar panel (1.8w should be enough for
just the one device, the larger 3w panel for a couple of such devices) they come with
a cigarette lighter plug output option.

http://www.northerntool.com/shop/too...s-solar-panels

Then something like this:
http://www.geeks.com/details.asp?inv...-TX013&cat=MP3

Then a 3.5" piece of 3/4" copper pipe. Slide the cigarette lighter plug from
the solar panel in one end and the 12v to 5.5v 1000mA adapter into the other
end, insuring that the center contact points are touching.

The regulated power from the adapter should be able to provide enough charging
current for your device even as the solar input fluctuates.

Luck;
Ken

P.S. as has been mentioned that 0.7w panel is ridiculously low for charging the internal
battery of your ereader.

[MLXXXp]

Originally Posted by Ken Maltby

The regulated power from the adapter should be able to provide enough charging current for your device even as the solar input fluctuates.

Not likely.

I have a number of the 1.8W panels mentioned. On a bright, cloudless summer day, with the Sun directly overhead and the panel perfectly aligned with the Sun, the most I've ever seen is about 1.5W. They must rate these panels based on standing on a mountain top at high noon in Arizona.

The Libre charger is rated 1A at 5V, which is 5W. But, USB is only specified to provide 500mA at 5V, which is 2.5W. When charging via USB the Libre probably draws the full 2.5W when the battery is low, so that's what the panel has to provide to maintain the 5V required.

So, given perfect efficiency in the USB adapter, we need the panel to provide 2.5W under normal conditions. By "normal" I mean no clouds but the Sun at about 45 degrees and the panel reasonably but not perfectly aligned.

My experiments show that a 1.8W panel can average about 1W under the above "normal" conditions, so we would need about a 2.5W x 1.8 = 4.5W solar panel to maintain charging the Libre.

However the 12V to USB adapter mentioned won't be 100% efficient in converting to 5V. It will probably more like 80% efficient, or worse, so we have to increase the panel output by that factor to compensate, which brings us to needing about a 5.6W or greater panel.

If you're not going to be around to re-align the panel with the Sun every half hour or so (or build yourself a Sun tracker mechanism, which would need additional power), then even the above "normal" conditions are quite optimistic.

Also, every time the Sun goes behind a cloud the voltage will probably drop such that charging will cease.

To compensate for these problems, it's best to use a "buffer" battery. I.e. use the panel to charge a 12V battery and then charge the Libre using the USB converter attached to that battery. However, depending on the output of your solar panel and type of 12V battery, you may also need a charge controller to prevent frying your 12V battery. This introduces additional inefficiencies, so your solar panel now needs to have even greater output, to charge the Libre with the same amount of "Sun hours".

[Ken Maltby]

First, I am willing to concede that my experience here in San Antonio, TX may differ
somewhat from yours in Toronto, Canada. Perhaps as much as mine does from a
certain poster powering his home in Hawaii.

The specs for the example adapter show an output at 5.5v @ 1000mA (1.0Amps)
USB2 specs allow for 1000mA and you can usually draw 20% more than that without
encountering problems. Not that the power circuitry for the eReader's builtin battery
would allow drawing an excessive amount while charging.

The OP was starting with a $2 kit that had a tiny solar panel with an output of 5.5v
@ 80mA. The components that I described offer the closest to his initial kit, in terms
of panel size, and price - that would provide reasonable, if longish, charging times.

If you went to the links I provided and looked around, at all, you could find larger and
higher priced panels that also could be used as I described, these might charge the
eReader a good deal faster. (Or a larger panel might not make any difference at all
depending on other relevant factors.)

The link to the adapter can also be used to find other adapters, (including one with two
Cigarette Lighter type sockets so you could double your panels) at various prices.

Luck;
Ken

[Gardenman]

Thanks everyone for the info.

[Ken Maltby]

This might give you some other ideas:
http://www.ladyada.net/make/solarlipo/

You might also consider for USB charging, your eReader already has the batt side of
the charge controller and the battery.

Luck;
Ken

[MLXXXp]

Originally Posted by Ken Maltby

The specs for the example adapter show an output at 5.5v @ 1000mA (1.0Amps) USB2 specs allow for 1000mA and you can usually draw 20% more than that without encountering problems.

Minor correction: The adapter is rated at 5.0V not 5.5V.
USB2 specs only allow for 500mA not 1000mA. USB3 can provide up to 900mA.
http://en.wikipedia.org/wiki/USB#Power

Not that the power circuitry for the eReader's builtin battery would allow drawing an excessive amount while charging.

It's not a question of drawing an excessive amount, it's being able to provide the minimum amount that the eReader wants to allow charging.

The recommended adapter is perfectly suitable for this situation. It's the 1.8W solar panel, which was stated would be sufficient, that's the problem.

The OP was starting with a $2 kit that had a tiny solar panel with an output of 5.5v @ 80mA. The components that I described offer the closest to his initial kit, in terms of panel size, and price - that would provide reasonable, if longish, charging times.

The OP's $2 kit included an internal battery that the panel can charge (over a possibly long period of time) and then the Libre can be charged from that battery, which can sustain sufficient current. The problem is that your solution didn't include this "buffer" battery and expects a 1.8W solar panel to provide sufficient charging current immediately and continuously on its own.

Even if the panel could provide its specified 1.8W, the Libre probably wants 2.5W. Wattage is calculated as volts times amps. When the Libre tries to draw the 500mA (0.5A) that it thinks it can get from USB, the 1.8W (in a perfect situation) from the panel could only be converted to 1.8W/0.5A = 3.6V. This voltage is out of spec and probably too low to charge the Libre.

My point is, that without a buffer battery, that can be charged via solar over a long time and then provide sufficient power over a shorter time for device charging, with a 1.8W panel you likely won't get any charging at all.

If you went to the links I provided and looked around, at all, you could find larger and higher priced panels that also could be used as I described, these might charge the eReader a good deal faster. (Or a larger panel might not make any difference at all depending on other relevant factors.)

I did go to that link. That's how I knew your recommended 1.8W panel was identical to the panel that I have been experimenting with. I also saw all the other panels there.

With just a panel and a 12V to USB adapter, any of those panels will either charge the device or not. None will charge "a good deal faster". It's the device itself that determines how fast it charges but you have to be able to provide at least as much "juice" as it wants.

Another thing to note. These panels tend to act more as current sources as opposed to voltage sources. They will vary their output voltage (within limits) in order to provide as much current as they can convert. I've measured voltages as high as 24V on the 1.8W panel under no load. When the device is fully charged it will stop drawing current. Without a buffer battery or other voltage regulator, the resulting higher voltage might damage the USB adapter, depending on its design.

The reason for my previous post was to point out that, without a buffer battery you will probably need a panel rated at at least 6W. A 1.8W panel, or even a 3W one probably won't work to charge the Libre directly, along with just a 12V to USB power adapter.

[MLXXXp]

Originally Posted by Ken Maltby

your eReader already has the batt side of
the charge controller and the battery.

Actually, your Libre already has both the charge controller and the batt side. Putting just another battery charge controller in front of this is not a good idea. What you need is something that looks like what is provided by USB (Regulated 5V at, at least, 500mA).

[Ken Maltby]

You claim to be experimenting with this 1.8w panel. Why not try one of the adapters,
with the same spec.s, and see how it handles a 5v 1000mA draw. You should see one
of the effects of going from 12v to 5v, that you seem to be ignoring.

If you look around at your USB powered devices you will find plenty that draw between
800mA and 900mA, especially if they are charging batteries.

Luck;
Ken

P.S. As far as your "up to 24v" being a problem for the adapter, take another look at
the adapter's spec.

[MLXXXp]

Originally Posted by Ken Maltby

You claim to be experimenting with this 1.8w panel. Why not try one of the adapters, with the same spec.s, and see how it handles a 5v 1000mA draw. You should see one of the effects of going from 12v to 5v, that you seem to be ignoring.

I have no doubt, as I already said, that the adapter can provide 1000mA at 5V. However 1000mA (1A) at 5V is 5W. How can you get that 5W from a 1.8W solar panel? What happens when a device tries to pull 1000mA (or 900mA or even only 500mA) from the adapter and the panel can only provide it with 1.8W?

You should see one of the effects of going from 12v to 5v, that you seem to be ignoring.

I don't think I'm ignoring it, but I apologise that I might be ignorant of it. Please explain it to me or point me to somewhere with a explanation of this effect.

[MLXXXp]

I'll try to provide some help to the OP, instead of just my comments, arguments and criticism.

My question is, why are you interested in this charger?

Because it's really inexpensive and looks like it would be a cool thing to have?
I'd say forget it. The solar cell is too small to be useful and the battery is probably too small to provide adequate portable charging for an eReader. It might work somewhat but probably not as well as you expect.

Because you want to be environmentally friendly and use solar power?
I'd say forget it. The cost and materials and processes used to produce most small solar devices has a greater impact on the environment than what's gained by the subsequent use of solar power.

You don't really care about solar but want to be able to charge your eReader when you're not in a house or vehicle or other source of power?
Consider a device with a battery that can be charged up and then provide USB power such as:
http://www.duracell.com/en-US/produc...b-charger.jspx
http://www.energizerpowerpacks.com/c...rtablechargers

You want a portable solar solution that you can carry while biking, hiking, backpack camping, etc.?
Get something similar to the device you asked about but a quality product (expect to pay quite a bit more) such as:
http://www.goalzero.com/shop/p/57//1:1/
http://www.energizerpowerpacks.com/ca/products/sp2000/

You want solar but portablilty isn't an issue?
You could use Ken Maltby's first suggestion but add a car or motorcycle lead acid battery to buffer the power. You might also need a charge controller, depending on the battery and panel size. You should also consider "low voltage cutout" circuitry to prevent discharging the buffer battery too far and damaging it. You could also use a sealed lead acid "gel cell" type battery but probably would need a charge controller regardless of the panel size.

For this last case, you could also go with one of the many larger or non-portable commercial solar systems available. Some may not be as expensive as a portable solution because making things small and light can add cost.

Note that I have no connection with, or am endorsing, or have even used any of the products in the above links. They're just examples, and there are many similar products available.

[Ken Maltby]

Well... I just ordered an Aluratek Libre Pro ($39.99) and the adapter I provided the link to, so I can provide my experimental results, in a week or so. I already have a couple
of those panels.

Luck;
Ken

[MLXXXp]

Originally Posted by Ken Maltby

P.S. As far as your "up to 24v" being a problem for the adapter, take another look at the adapter's spec.

True, I missed that, but you said "something like" that adapter, and I said "might" damage the adapter.

[MLXXXp]

Originally Posted by Ken Maltby

Well... I just ordered an Aluratek Libre Pro ($39.99) and the adapter I provided the link to [...]

I look forward to hearing about your findings.

I don't have that adapter but I have some similar ones. However, one is a very cheap one (in all respects) from a "dollar" store. It may not be very efficient.

The other has a built in battery/charger/LED flashlight in addition to the USB port, so it may draw extra power itself, and thus make the results less valid.

Also with it being winter and me being so far north, the Sun remains quite low in the sky, so I probably won't be able to get much power from the panel but I may try anyway. I'll report here if I do.