Undersize solar panel charging Li-Ion?
- Thread starter AilSnail
- Start date
Doug S
Flashlight Enthusiast
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AilSnail said:
If I made a portable setup with very small solar cells to charge a Li cell, would the li be damaged by being charged too slowly?
I'd use a charger chip to limit current and voltage, for instance bq2057 or something.
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I have seen nothing in the literature that suggests that there is any problem with charging Li-ion at very low rates. Since these are "very small" solar cells, one charger solution to consider that would be a very simple one would be a shunt voltage regulator. A shunt regulator absorbs the solar cell output once the battery voltage has risen to the full charge level. It can be implemented with just a few components: a shunt regulator IC, a couple of resistors to set the voltage, and a power transistor to absorb the excess power.
AilSnail said:
If I made a portable setup with very small solar cells to charge a Li cell, would the li be damaged by being charged too slowly?
I'd use a charger chip to limit current and voltage, for instance bq2057 or something.
[/ QUOTE ]
I have seen nothing in the literature that suggests that there is any problem with charging Li-ion at very low rates. Since these are "very small" solar cells, one charger solution to consider that would be a very simple one would be a shunt voltage regulator. A shunt regulator absorbs the solar cell output once the battery voltage has risen to the full charge level. It can be implemented with just a few components: a shunt regulator IC, a couple of resistors to set the voltage, and a power transistor to absorb the excess power.
I don't advise it. Here's why. Li-Ion batteries need a very specific charging cycle and they have to be held at the fully charged voltage for a specific period. Not following the manufacturers specs means shorter battery life.
The best solution in any case is to use the designated charging chips like the LTC4052 which works very nicely.
I've found that the charging chips don't work as well with less current but I don't know how much this shortens battery life.
Rob
The best solution in any case is to use the designated charging chips like the LTC4052 which works very nicely.
I've found that the charging chips don't work as well with less current but I don't know how much this shortens battery life.
Rob
andrewwynn
Flashlight Enthusiast
having just built a charger with the LTC4052 (practice soldering an ant.. wow that thing is small!).. and knowing how it works, i'd not do it any other way..
I can set it to charge at 300mA max... probably can go lower with a higher programming resistor... but DJ said it got weird i think...
in any event.. yeah i guess.. 1.5W is a little steep for a solar cell... i just did some searching and for $10-15 you can get a solar panel that'll output enough juice to run a LiON charger, i think i'll be getting one.
-awr
I can set it to charge at 300mA max... probably can go lower with a higher programming resistor... but DJ said it got weird i think...
in any event.. yeah i guess.. 1.5W is a little steep for a solar cell... i just did some searching and for $10-15 you can get a solar panel that'll output enough juice to run a LiON charger, i think i'll be getting one.
-awr
AilSnail
Flashlight Enthusiast
Doug_S, I like the sound of what you are suggesting. Will solar cells be destroyed if they are exposed to light when open cirquited?
Do you have any suggestions for a shunt regulator IC?
I found a neat looking TI charger, bq24200, specifically suited for low current wall warts, might work with a tiny solar cell too? Very low parts count as well.
Do you have any suggestions for a shunt regulator IC?
I found a neat looking TI charger, bq24200, specifically suited for low current wall warts, might work with a tiny solar cell too? Very low parts count as well.
