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ko4nrbs

Solar Charging Lithium Ion Or Lithium Polymer Cells (updated! 1/26

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I have been experimenting and researching Solar charging Li-ion cells for some time now. Some of you are doing it successfully now. This board while expensive may provide better charging than what we are using now. In any event, it is interesting information and may help us understand what is going on with our chargers.

 

One of my ideas was to use a Solar Panel with a Lead Acid battery instead of just a Solar Panel. The Lead Acid battery would provide stable power to the charge board during periods of insufficient sunlight.

 

The following explanations were taken from this link about 3/4 of the way down the page. I have found them consistent with everything I have found while researching.

https://learn.adafruit.com/usb-dc-and-solar...w=all#downloads

 

 

Solar panels are a little different, the voltage and current vary constantly depending on sunlight available. They are unstable! That instability confuses battery chargers, which causes them to do one of two things: rapidly turn on and off as they try to draw more current from the panel than possible and/or draw much less current than they can, to keep the voltage from collapsing.

 

Now you can see what happens if you connect a 6V solar panel to a Lipoly charger. As long as the current being drawn by the charger is less than the panel's short circuit current at that light condition, everything is peachy. The moment the light changes even a little, and the current the lipo charger wants is higher than the short circuit current, the charger becomes unstable: it will draw too much current, which will cause the voltage to collapse, which causes the charger to turn off, which reduces the current draw, which makes the panel voltage recover, which turns on the charger again, which then draws too much current, and the cycle repeats.

 

Solar Optimization!

OK so how do we fix this problem? The issue we have here is that the voltage collapses during high current draw. We need to find a way to keep the lipo charger from drawing too much current, and backing off when the voltage starts to droop. We looked high and low and finally found a chip that has something like this built in. The MCP73871 calls it Voltage Proportional Charge Control (VPCC) and basically, it does precisely what we want. We can set the voltage to a point just above the battery charge voltage point (say 4.5V) and then instruct the charger to draw as much current as possible. It will automatically increase/reduce the charge rate to keep the voltage higher than 4.5V!

 

In this case, we set the voltage using two resistors, the voltage divider ends up stabilizing it at ~4.5V. Because the voltage collapse of a panel is really sudden, we still end up needing a little more help stabilizing the panel. We do that by adding a BFC (Big Freaking Capacitor).

 

Bill[/color]

Edited by ko4nrbs

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I am going to stick with these for now TP4056. $1 each. Most of these kinds of chargers call for a 5v input. And when I hooked a solar panel to one rated at 5V and had an 18650 hooked to it, it was over voltage and shut off saying charged. Then I found these with the 4V-8V input and seem to work nicely. I assume it has some kind of voltage regulator on the input and feeds the charger with a steady 5V.

 

http://www.ebay.com/itm/272459126851?_trks...K%3AMEBIDX%3AIT

 

Ordered some of these 3.3v-17v digital voltmeters to put in builds or monitor voltage on solar charged 4.2, 6, or 12v batteries.

 

http://www.ebay.com/itm/221602141455?_trks...K%3AMEBIDX%3AIT

 

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I am going to stick with these for now TP4056. $1 each. Most of these kinds of chargers call for a 5v input. And when I hooked a solar panel to one rated at 5V and had an 18650 hooked to it, it was over voltage and shut off saying charged. Then I found these with the 4V-8V input and seem to work nicely. I assume it has some kind of voltage regulator on the input and feeds the charger with a steady 5V.

 

http://www.ebay.com/itm/272459126851?_trks...K%3AMEBIDX%3AIT

 

Ordered some of these 3.3v-17v digital voltmeters to put in builds or monitor voltage on solar charged 4.2, 6, or 12v batteries.

 

http://www.ebay.com/itm/221602141455?_trks...K%3AMEBIDX%3AIT

Thank you for the links!!

 

Sure a lot of fun experimenting with Solar charging. Let us know about your new discoveries and findings.

 

Bill

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I have been experimenting and researching Solar charging Li-ion cells for some time now. Some of you are doing it successfully now. This board while expensive may provide better charging than what we are using now. In any event, it is interesting information and may help us understand what is going on with our chargers.

 

One of my ideas was to use a Solar Panel with a Lead Acid battery instead of just a Solar Panel. The Lead Acid battery would provide stable power to the charge board during periods of insufficient sunlight.

 

The following explanations were taken from this link about 3/4 of the way down the page. I have found them consistent with everything I have found while researching.

https://learn.adafruit.com/usb-dc-and-solar...w=all#downloads

 

 

Solar panels are a little different, the voltage and current vary constantly depending on sunlight available. They are unstable! That instability confuses battery chargers, which causes them to do one of two things: rapidly turn on and off as they try to draw more current from the panel than possible and/or draw much less current than they can, to keep the voltage from collapsing.

 

Now you can see what happens if you connect a 6V solar panel to a Lipoly charger. As long as the current being drawn by the charger is less than the panel's short circuit current at that light condition, everything is peachy. The moment the light changes even a little, and the current the lipo charger wants is higher than the short circuit current, the charger becomes unstable: it will draw too much current, which will cause the voltage to collapse, which causes the charger to turn off, which reduces the current draw, which makes the panel voltage recover, which turns on the charger again, which then draws too much current, and the cycle repeats.

 

Solar Optimization!

OK so how do we fix this problem? The issue we have here is that the voltage collapses during high current draw. We need to find a way to keep the lipo charger from drawing too much current, and backing off when the voltage starts to droop. We looked high and low and finally found a chip that has something like this built in. The MCP73871 calls it Voltage Proportional Charge Control (VPCC) and basically, it does precisely what we want. We can set the voltage to a point just above the battery charge voltage point (say 4.5V) and then instruct the charger to draw as much current as possible. It will automatically increase/reduce the charge rate to keep the voltage higher than 4.5V!

 

In this case, we set the voltage using two resistors, the voltage divider ends up stabilizing it at ~4.5V. Because the voltage collapse of a panel is really sudden, we still end up needing a little more help stabilizing the panel. We do that by adding a BFC (Big Freaking Capacitor).

 

Bill

 

One of my ideas was to use a Solar Panel with a Lead Acid battery instead of just a Solar Panel. The Lead Acid battery would provide stable power to the charge board during periods of insufficient sunlight.

 

On second thought that would defeat the purpose of the board in the link. Its design is meant to get around the problem of unstable voltage from the Solar Panel. The Lead Acid battery/Solar Panel combination may be useful with the rest of the charge boards. Those boards are meant to be supplied with a stable and consistent voltage source.

 

 

Bill

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