solar charger for lithium battery

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EEdy
 
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solar charger for lithium battery

Post by EEdy »

Hi, i am looking for a solar charger for lithium battery. I found one from you site. Can i connect 4 lithium batteries in parallel to the USB / DC / Solar Lithium Ion/Polymer charger - v2?

My solar panel requirement is about 15x15cm, what suggestion do you have for me?

Thanks a lot

adafruit
 
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Re: solar charger for lithium battery

Post by adafruit »

Don't connect batteries in parallel, use a larger battery pack - we have a 6600mAh pack, it will take a very long time to charge but once its charged you'll have lots of capacity! :)

EEdy
 
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Re: solar charger for lithium battery

Post by EEdy »

Thanks, I have done some calculation on how long does it take to charge the 6600mAh battery pack. correct me if i am wrong, I will be using Large 6V 3.4W Solar panel - 3.4 Watt panel, for the 3.7V 6600mAh battery, its capacity is 3.7 x 6.6 = 24.42w. does it mean it will take about 7 hours (24.42 / 3.4 = 7.1h) to fully charge the battery in full sun condition?

Another question is what is the output voltage and current of the charger? my load will be a 5V, 55mA device. It works 24 hours a day.

Thanks

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adafruit_support_mike
 
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Re: solar charger for lithium battery

Post by adafruit_support_mike »

Most of the information you need is probably somewhere in this tutorial for our solar charger: http://learn.adafruit.com/usb-dc-and-so ... r/overview

You can't figure charging time simply on power. The charger has an internal limit of 500mA, so full charge would take at least 13 hours at full output, and even that oversimplifies things. The LiPo charging cycle is complicated, so there's a range of voltages where you apply constant current, then a range of voltages where you reduce the current to approach the ideal charge. The usable current you can get from a solar panel also varies with the available light, which is why we designed a charger specifically for solar applications.

Like I said, there's more information (including graphs!) in the tutorial.

EEdy
 
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Re: solar charger for lithium battery

Post by EEdy »

Thanks.

the tutorial doesnt say anything about the output voltage and current from the charger when there is no light for the panel.

My load will be a 5V, 55mA device. The device will be situated outdoor, it works 24 hours a day. I am wondering if there is no power going into the charger, will it supply power from the battery to the load? if yes, what is the output voltage and current?

Thanks

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adafruit_support_bill
 
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Re: solar charger for lithium battery

Post by adafruit_support_bill »

If there is no power to the charger, the load will be supplied by the battery for as long as the battery charge is sufficient.

EEdy
 
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Re: solar charger for lithium battery

Post by EEdy »

thanks, the output voltage should be 3.7V if it is coming from the battery. i guess i need a step up converter to boost the voltage up to 5V to power my sensor and microcontroller

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adafruit_support_bill
 
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Re: solar charger for lithium battery

Post by adafruit_support_bill »

i guess i need a step up converter to boost the voltage up to 5V to power my sensor and microcontroller
The Mintyboost works well for that: http://www.adafruit.com/products/14

EEdy
 
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Re: solar charger for lithium battery

Post by EEdy »

"The Mintyboost converts a low voltage to 5V USB standard. Because of this the first thing you must be aware of is that you cannot put a higher than 5v battery on the inputs to the circuit. If you do, it could damage the kit. "

"The smart load sharing means that the LOAD output can be as high as 6VDC if in direct sun because it will draw current directly from the 6V panel instead of from the battery. If using this with an electronic project, make sure it is OK for up to 6VDC input or use a low-dropout-regulator (LDO) to regulate the voltage down."

According to the smart load sharing, it would output 6VDC if in direct sun, so it might damage the Mintyboost converter, right??

Thanks

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adafruit_support_bill
 
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Re: solar charger for lithium battery

Post by adafruit_support_bill »

Yes. If you anticipate inputs greater than 5v, you should look for a buck/boost controller.

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kevinrs
 
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Re: solar charger for lithium battery

Post by kevinrs »

Ok, so, based on that, though several tutorials have the output of the solar charger connected to a mintyboost, it's sounding like that is not the best way to go. Since I went for the 5.6 watt panel, and the 6600 mAh battery, for max power, and my main purpose is for connecting to a power hungry phone, which seems to be too much for a mintyboost anyway, I'm thinking I need to rethink the mintyboost part of the project. Adafruit doesn't have a buck/boost converter, so I'm going to have to start looking at datasheets.

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adafruit_support_bill
 
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Re: solar charger for lithium battery

Post by adafruit_support_bill »

Ok, so, based on that, though several tutorials have the output of the solar charger connected to a mintyboost, it's sounding like that is not the best way to go
It is usually not an issue for panels of that size. Unless your panel is huge, the output voltage will start to drop as soon as you give it a substantial load.

But it is true. That latest generation of phones are pushing the limits of MintyBoost capacity.

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