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Solar Lithium Ion/Polymer charger - Charge rate Question
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Solar Lithium Ion/Polymer charger - Charge rate Question

by oby_one on Sun Nov 20, 2011 1:06 pm

Hi,
I bought a USB / DC / Solar Lithium Ion/Polymer charger - v1.0 http://www.adafruit.com/products/390

It works fine except I can't get faster charge rates out of it.
This is how I tested.
I discharged my Lithium Ion Battery Pack - 3.7V 4400mAh http://www.adafruit.com/products/354
and then connected it the the solar charger but with an ampermeter between the charger and the battery.
As a power source for the lipo charger I used in one test the Large 6V 3.7W Solar Panel in full sunlight an on the other test my computers power soruce 5V line (that has many amps available).
In both cases I had about 230->250 ma flowing between the charger and the battery.

Then I soldered an 1K ohm resistor on the prog pad of the solar charger and now I have a charge rate of about 330 ma on both tests.
I was expecting a 1000ma charge rate and not just 330ma.

Can you please guide me on obtaining the desired charge rate of 1amp?
Ps: yes I did desolder the default resistor from the prog pad.

oby_one
 
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Re: Solar Lithium Ion/Polymer charger - Charge rate Question

by adafruit on Sun Nov 20, 2011 8:03 pm

the charge rate depends on the battery state and voltage from the USB port. it will be MAX 1000mA when the battery is in the optimal state. check the datasheet for more details

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Re: Solar Lithium Ion/Polymer charger - Charge rate Question

by oby_one on Mon Nov 21, 2011 2:42 am

1. At what voltage will the charger consider the battery is empty and deliver a full charge rate?
My battery is now at 3.2 volts.. should I discharge it some more?

2. Isn't 5Volts enough to power the solar charger? ( the pc's power source can deliver many many amps)
I thought it would want 6Volts but that I can only provide that with the solar panel and my panel 3.7W can only give ~350ma

Please tell me exactly how I should try it.

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Re: Solar Lithium Ion/Polymer charger - Charge rate Question

by adafruit_support_bill on Mon Nov 21, 2011 7:15 am

The charge cycle has several phases based on voltage, current and temperature feedback. It does not necessarily start off at maximum charge current. The details are in the data sheet here: http://www.adafruit.com/datasheets/MCP73871.pdf

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Re: Solar Lithium Ion/Polymer charger - Charge rate Question

by oby_one on Mon Nov 21, 2011 3:16 pm

You didn't answer my questions :)
I read the datasheet and now I know that 5V are enough and are not the problem.

I further discharged the battery until 2.82 V and repeat the charge test but the results are the same.

The factors that can modify the charge rate are:


The resistor on the prog pad ( I already have installed the 1k rezistor )
The temperature is not an issue because the charger and the battery are at 21Celsius.
The battery current charge level, again not an issue because it is discharged.
The battery internal resistance, not an issue because the battery is brand new.
The power supply of the solar charger, not an issue because I have 5 steady Volts and 80Amps available.
The charging phase, I monitored for about 15 minutes and the charge current dropped from 0.34 amps to 0.29 Amps...

So you see ? I got all the factors covered and still got a low charging current.
Have you done any tests regarding this matter? if not then I will kindly ask you to do one test and tell me your results.
Any other advice will be greatly appreciated.

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Re: Solar Lithium Ion/Polymer charger - Charge rate Question

by adafruit on Mon Nov 21, 2011 4:27 pm

Check page 25 of the datasheet, there is a graph showing charge rate and battery voltage. Also, there is the temperature of the die which you cannot directly measure - that is the temperature of the chip itself which is what will limit the charge rate at high currents.

We test every design, it is possible to get to the charge rate advertised but that is a 'high limit' - the charger chip will do its best to not destroy itself or the battery, that may require lower current charging

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Re: Solar Lithium Ion/Polymer charger - Charge rate Question

by oby_one on Mon Nov 21, 2011 4:42 pm

Are you referring to FIGURE 6-2 ?
I saw that graph and I understand it... however I don't see how it helps me ?
I am at the beginning of the charge cycle and I should have 1 amp.. but instead I have only 0.3amps

Please trust me I am in NO limiting mode because everything is cool.
The chip is NOT warm and I even opened the windows to get the -2 degrees Celsius onto the chip and battery... everything is cool ( my digital thermometer says 17Celsius(62.6 ºF) at the chip surface.

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Re: Solar Lithium Ion/Polymer charger - Charge rate Question

by adafruit on Mon Nov 21, 2011 4:52 pm

no, figure 6-3

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Re: Solar Lithium Ion/Polymer charger - Charge rate Question

by oby_one on Mon Nov 21, 2011 4:57 pm

The preconditioning phase has finished a long time ago.
I started with a voltage of 2.82 V and now I am at 3.57V at ~ half way through the charging process.
I monitored it closely and noticed that the charging current actually dropped from 0.34 to 0.25 Amps, contrary to the FIGURE 6-3.

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Re: Solar Lithium Ion/Polymer charger - Charge rate Question

by adafruit on Mon Nov 21, 2011 8:15 pm

OK post clear, detailed photos of each part of your setup - battery, charger, supply, mods, etc.

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Re: Solar Lithium Ion/Polymer charger - Charge rate Question

by oby_one on Tue Nov 22, 2011 5:49 pm

I made a few pictures here https://picasaweb.google.com/radu.boboc ... bPjn4jPpQE

Please tell me if you want something in more detail.

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Re: Solar Lithium Ion/Polymer charger - Charge rate Question

by adafruit on Tue Nov 22, 2011 7:10 pm

what is the precise voltage at the DC IN solder points

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Re: Solar Lithium Ion/Polymer charger - Charge rate Question

by oby_one on Wed Nov 23, 2011 2:47 am

The precise voltage in Dc in port is : 5.08 Volts in load and 5.10 V with no load

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Re: Solar Lithium Ion/Polymer charger - Charge rate Question

by adafruit on Wed Nov 23, 2011 2:01 pm

do you have an oscilloscope?

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Re: Solar Lithium Ion/Polymer charger - Charge rate Question

by oby_one on Wed Nov 23, 2011 4:42 pm

Unfortunately I don't have an oscilloscope.

Ps: the charging was not yet complete after 24 hours, when I disconnected it because I needed the power-source.

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