Will this solar charger work with the Libre Pro

[Ken Maltby]

Estimated delivery Jan 11.

Arrived Jan 10.

[Ken Maltby]

OK, Set up the panel and the USB charging adaptor as I described and tried it out on
my PDA. It is working fine with that. (Its "Input" is listed as "5v 1A)

On the first try with the Libre Pro:
09:00 am CST
The Libre Pro just out of the box. The manual states that it takes 7 Hours to charge
the Libre from a USB source (Don't know if that is based on the USB source not
providing the 1Amp of the power adapter that comes with the Libre. The USB adapter
I'm using in these tests is also rated at 1Amp.)

With everything setup and the panel pointed at the sun;
The USB adapter's indicator light is lit.
The indicator light on the panel is blinking. (I have no Idea what that is meant to
indicate.)

The panel's small print shows "Up to 1.8 watts/125mAmp under ideal conditions"

The Libre won't turn on so I have no indication that it is charging or not.
I don't know if the Libre is working, I may have to charge it up normally, and insure
that it works, before draining it and running another test. I'll give it two hours as it is,
that should be a little over a quarter of the 7 hr charge mentioned in the manual.

-------------------
11:15am
OK, after removing from the setup, reseting and starting again, the Libre started and
showed two of the three bars in the charge indicator. (It has 20g as the firmware)
Placed it back on the setup and realigned it with the sun.

12:15am checked it, and it is still showing the two of three indication (what a stupid
charge indicator, only three elements). Will check every hour, I guess.
Oh, and I had to remove it from the setup and reset the Libre before it would start up
again.

4:30pm still the same 2 of 3 bars, there does seem to be a drain on the panel, going
by the response of the indicator light, so I think that some charging is taking place, but
at a much slower pace than I was hoping for. That's enough for today, I would have to
admit that this panel just won't cut it for the Aluratek Libre Pro, the adapter worked out
and I may try a larger panel at some point. As it is, the panel and adapter seem to work
well with my PDA/GPS so its not a total loss.


Luck;
Ken

[MLXXXp]

Originally Posted by Ken Maltby

Oh, and I had to remove it from the setup and reset the Libre before it would start up
again.

I've found that my Libre doesn't like to get a "gradual" power up or down for charge supply. If it doesn't get a near instantaneous stable 5V on the USB port and then an immediate drop to 0V to remove the power, it sometimes will lock up and require a reset, as described above.

I've seen this happen with the supplied charger if you first plug it into the Libre and then into the A.C., or remove the A.C. with the charger still pluged into the Libre. To avoid this I now always plug the charger into a live A.C. outlet and then next plug the mini-USB cable into the Libre. I also unplug the mini-USB connector from the Libre before removing the charger from the A.C. outlet.

Since using a solar panel directly connected to a 12V to USB adapter, without a buffer battery, could cause the voltage to drop below 5V whenever the Sun went behind a cloud, etc., it's possible that these lockups may occur.

[MLXXXp]

Originally Posted by Ken Maltby

[...] I may try a larger panel at some point.

In an earlier post you said "I already have a couple of those panels.". Instead of using a single larger panel, you could double your power by using two of your 1.8W panels with something like this:
12-Volt-Outlet-Splitter

Or 3 panels with something like this:
3-WAY-ADAPTER-AUTO-SPLITTER

I'm still not sure that you'd get very good results, though.

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.

[Ken Maltby]

I would think that these splitters are wired in parallel:

http://partsonsale.com/learnwiring.htm

So it would likely be a good answer. It looks like you would need 8 of these small panels
to get near what the power adapter provides (or the USB plugin adapter could provide).
That would make using the splitter with larger panels a real possibility. Two five watt
panels might be a workable compromise with size, cost, and flexibility.
Perhaps two of these:
http://www.northerntool.com/shop/too...4313_200494313


It is looking like you will need a surface area of panels (given the stats for these panels)
of about that of a 24" monitor, to have something that can charge up a device like the
libre, in a reasonable time. As you mention a battery in the circuit is a major improvement
(but an added weight) and your project is sounding like a good "transportable" option.
For this sized project you might consider any unused UPS batteries that you might have
on hand.

Luck;
Ken

[MLXXXp]

Originally Posted by Ken Maltby

I would think that these splitters are wired in parallel:

Yes, the splitters mentioned are wired in parallel. As long as the panels have built in protection diodes, they work fine wired this way.

(For my project, I'm not using these 12V car style splitters. I've removed the lighter plugs from the panel cables and replaced them with small barrel connectors, which plug directly into my electronic control box.)

For this sized project you might consider any unused UPS batteries that you might have on hand.

The "gel cell" battery from a UPS is exactly what I'm using. My charge control circuit is designed specifically for this type of battery and generally wouldn't work properly with any other type.

[Ken Maltby]

I am charging an Aluratek Libre Pro with a 10Watt panel the same size as my 23" desktop
LCD widescreen monitor.
http://www.northerntool.com/shop/too...6972_200496972

The adapter can handle the output of two of these panels, I think. I have
two of these panels now, and a "Y" cable auto power plug on order.

Here are some pic:

[MLXXXp]

Originally Posted by Ken Maltby

The adapter can handle the output of two of these panels, I think.

What method did you use to calculate this?

The adapter output is rated 5V at maximum 1A, which means it can provide a maximum output of 5V x 1A = 5W. (If the Libre follows USB rules, it will only draw a maximum of 2.5W, which lowers requirements even more, but we'll ignore this.) If the adapter is 100% efficient in converting the input power, the most it would pull from the panel is 5W. Therefore, a single 10W panel would be capable of providing twice the power required.

However, the adapter won't be 100% efficient in converting from 12V to 5V. I'm guessing it's more like 75%. With a 75% efficiency the maximum input required would be 6.67W. This is still less than the panel's 10W rating.

Then, I'd bet that under normal sunlight and alignment situations, this panel will probably only provide about 8W. Still, this is more than the maximum that the adapter can handle, so under bright sunlight a second panel would not provide any benefit.

But, as long as the "no load" voltage of the panels never exceeds the 24V maximum specified by the adapter, then two panels in parallel can do no harm. The extra panel would allow the system to continue to charge under lower light or poorer panel alignment.

So I say go for it. It can't hurt.

P.S. I wouldn't recommend leaving your Libre in direct sunlight. It could possibly overheat and be damaged. I'd put it in some shade. Maybe behind the panel?

[Ken Maltby]

The spec that are listed in the little pamphlet that comes with the panels:

"Power Rating: Up to 10 Watts - Maximum rating - Under optimum conditions.
Current: 667 mAmps @ 15Volts."

So while 2x667=1334mAmps and the adapter is rated with an output of 1000 mAmps,
I am hoping that it can handle the input.

Luck;
Ken

P.S.; the setup was just for the picture taking, the libre can be in its neoprene sack
and in the shade, normally.

[MLXXXp]

Originally Posted by Ken Maltby

So while 2x667=1334mAmps and the adapter is rated with an output of 1000 mAmps,
I am hoping that it can handle the input.

This shows that you don't seem to have a proper understanding of basic electrical theory.

Of course the adapter will be able to handle the input. What do you think would happen if you plugged the adapter into the lighter socket in your car? A car battery can provide 60000mA (60 Amps).

You have to look at things in terms of power (watts) requirements, not current (amps). Power is calculated by the formula:
power (watts, W) = voltage (volts, V) X current (amps, A)

Note that power is usually signified by the letter P, current by I, and voltage by E or V, but I'll use the unit letters: W, A, V.

You can rearrange the formula to get:
V = W / A and A = W / V

The electronics in the adapter will do whatever it takes to provide a fixed 5V to the device connected to its USB output (in this case the Libre).

The Libre will draw whatever power it requires to run and charge its battery. You've stated in a previous post "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", so let's assume that the Libre will draw a maximum of 900mA (0.9A). Since the adapter will always regulate the output voltage to 5V, we can use the formula to derive the maximum power that the Libre will draw: 5V X 0.9A = 4.5W

The job of the adapter is to convert the high input voltage (12V to 24V) to a fixed 5V output voltage. In a perfect world, it would do this 100% efficiently, so that the power that goes in would equal the power that goes out. Let's assume that the panel's output voltage will be 15V, as is stated in the little pamphlet (although this will vary depending on current draw and light available). Since the panel voltage is higher than 5V, less current will be required to provide the required power: 4.5W / 15V = 0.3A (or 300mA).

So, to charge the Libre, the panel need only be rated 300mA @ 15V. Any extra capacity that the panel could possibly provide will be wasted as heat; the panel itself will get hotter. Adding a second panel will just mean that this second panel's potential power will also be wasted as heat, with no difference in the Libre's charging speed.

However, as I've previously stated, the adapter won't be 100% efficient (even the red LED on it will use a little power) and the panel(s) won't normally be running, as the little pamphlet puts it, "under optimum conditions".

The adapter might be 70% to 90% efficient in power conversion but lets assume it's not very good, and therefore can only convert 60% of its input power to output power. So we need to multiply our output power by 1/60% = 167% to get input power requirements: 4.5W X 1.67 = 7.5W. Calculating input current: 7.5W / 15V = 0.5A (500mA). This 500mA is still within what a single panel can provide, even under slightly less than optimum conditions.

To summarize:

• The current that the panel needs to provide will be determined by the current that the Libre draws, but will be less (disregarding adapter inefficiencies) because the panel provides 15V and the Libre runs at 5V.
  
• As far as what the adapter can "handle", the only concern is that the panel(s) don't exceed the maximum 24V that the adapter specifies, and that the Libre doesn't try to draw more than the maximum 1000mA that the adapter specifies (both of these cases are probably true).
  
• One panel will be sufficient under optimum or somewhat less than optimum conditions. Two panels will allow charging under conditions that are less optimum than with one panel, but won't make any difference if conditions are sufficient for operation with one panel.

[Ken Maltby]

OK, you got as far as Ohm's Law. Maxwell's Equations should be coming soon.

Much of what you presented is accurate, just based on some mistaken assumptions.
Partly as to my understanding and partly as to how a source effects the calculations.
The panels get hot from being in the sun, not from any undrawn power build up.

You know, I've found that it is useless to get into a discussion about theory when it
comes to likely experimental results. The theorist will always assume that all
conditions are accounted for in their application of the theory they have learned.
I have often found that, that is not always the case and that the actual practical
results will often be greatly effected by factors not considered in a theoretical
approach to the subject.

Yes, one panel does put the Libre into charging mode when placed in full sun. I have
not yet timed the recharging from a known state to a full charge, using the one panel.
Until I've done that, I don't have anything to compare with a two panel setup.
So at some point we will see.

Luck;
Ken

[MLXXXp]

Originally Posted by Ken Maltby

OK, you got as far as Ohm's Law.

Nope, sorry. Ohm's Law deals with the relationship between resistance, voltage and current. I didn't use it at all. I only used the electrical power law (I don't think it's named after anyone since it's derived from Ohm's Law and Joule's first law).

The panels get hot from being in the sun, not from any undrawn power build up.

Now we need to get into the first law of thermodynamics.
http://en.wikipedia.org/wiki/First_l...thermodynamics

Light is a form of energy. When that light hits the panel, it is either reflected off the panel or absorbed and converted into some other form of energy. If the panel isn't connected to anything, then almost all the absorbed light is converted into heat (which is another form of energy).

However, if the panel is connected to an electrical load, then some of the absorbed light is converted into electrical energy, so given a constant amount of light, the panel will remain a small amount cooler. That electrical energy will be converted into heat by the load (or stored as chemical energy by a battery), thus satisfying the first law, requiring the conservation of energy.

The only reason that the panel heats up is because it's not 100% efficient in converting light to electricity (probably more like 10%) or the load is not capable of accepting all the electrical energy.

What do you think would happen if a solar panel could convert 100% of the light to electrical energy and that energy was completely supplied to an external resistive load? The answer is that the panel wouldn't heat up at all and remain at the surrounding temperature. (Though, the bezel would still heat up and possibly transfer some of that heat to the panel). The resistor would then heat up instead.

You know, I've found that it is useless to get into a discussion about theory when it comes to likely experimental results.

Well, I was right when I predicted that the 1.8W panel wouldn't be sufficient, before you tried it experimentally

[MLXXXp]

Originally Posted by Ken Maltby

I have not yet timed the recharging from a known state to a full charge, using the one panel. Until I've done that, I don't have anything to compare with a two panel setup.

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.

Measure with one panel connected and then connect the second panel. If nothing changes then the second panel isn't helping any.

[jlg432]

- Over the last couple of years I bought 4 of those 1.25 watt maintenance S Panels when they went on sale for $10 at Canadian Tire. I have set them up so I can place all four in parallel with the output to an automotive cigar lighter. I haven't done any measurements but I found that it will charge most of my devices - no problem here in Ottawa Canada. As you stated you do need an usb adapter that does provide enough current rating to make the charge time reasonable.

I have used the set-up to charge various GPSr's.

Just giving my input.

John

[Ken Maltby]

Actually, 3 of them (125mA x 3 = 375mA) could supply the 12v 300mA that my MAHA
MH-C204GT runs on to quick charge (2.5 - 6 hrs) 4ea AA NiMH batteries. A fourth
might make up for your latitude issues, though.

The charger has an input spec of DC 12V 300mA and an output spec of DC 2.4V 500mA x
2 Ch. So a any "12 volt" source that can supply the 12V 300mA will be sufficient to power
the two channels of 400mA 2.4V charging.

Luck;
Ken