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charger circuit issues

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aliyesami

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I put this circuit together that charges the 3.7V Lipo battery and also produces 3.3v at the output .
An LED indicates the charging status .
I am getting 3.3v output but the LED is not lighting up and the status pin is showing zero volts .
is the charging part of the circuit correct ?

bat_charger_Circuit.jpg
 

Hi,

Please post the MCP7381 datasheet.

Klaus
 

Hi,

A link is O.K.

But pleas confirm part name:
Is it MCP73831
or MCP7381 ?

Klaus
 

Hi,

power up your circuit properly.
Then measure the voltage of STAT pin directely at the IC pin. with reference to GND.

Klaus
 

If you built your circuit *exactly* as shown, it is correct.

You either have an intermittent contact or a defective component.
 

is there another way other than the LED to find out if the battery is being charged?
also if the MCP73831 chip is toasted will I still get the 3.3v output?
 

Hi,

Do you find it easier to look for new issues, new methods than just take a DVM and measure at the voltage?
Even writing my post here takes more time.

Klaus
 

KlausST said:
Hi,

Do you find it easier to look for new issues, new methods than just take a DVM and measure at the voltage?
Even writing my post here takes more time.

Klaus
Click to expand...
hi Klaus
I already measured the voltage and I am getting 3.3v but I asked the question cause I am not sure if the charger chip MCP73831 is working or not , how can I know?
regards
 

Hi,

We need your feedback.
I don't expect it to be 3V3. What is the USB voltage? What is the exact LED type..exactely i need to know the LED forward voltage at low currents.

****

Do the tests step by step.

****
To your question:
* disconnect USB, wait some minutes, measure battery voltage.
* connect USB, wait some minutes, measure battery voltage. If it rises, then chargin works.

But maybe the battery is full...then it won't charge.

You could use an amperemeter to measure charge current.

Measure every IC pin and tell us the voltages.

Klaus
 

KlausST said:
Hi,

We need your feedback.
I don't expect it to be 3V3. What is the USB voltage? What is the exact LED type..exactely i need to know the LED forward voltage at low currents.

Klaus
Click to expand...

ok I let the battery die and then connected the usb cable and the battery was fully charged so I know th charger circuit is working ., so it means the LED is not working .
now I tested the LED out of circuit and it lights up but in circuit even with power removed it doesn't light up .
the LED is a digi-key part nr 404-1033-1-ND , FV 1.7v and 20mA, the USB voltage is 5v.

- - - Updated - - -

also I removed the LED and the STAT pin is measuring -0.25 volts ? how is it getting negative voltage?
 

Hi,

Good informations.
Be sure the LED was not connected the wrong direction.

Negative voltage:
I wonder... is it a PCB with proper GND plane...or a breadboard?

What voltages did you measure with empty and full battery?
How long did it take to charge?
What charging current? And what Ah rating is the battery?

Klaus
 

To see why the LED is not lighting then you must measure the STAT pin voltage with the LED and its series resistor connected and the battery fully charged.
Did you measure the resistance of the resistor to make sure it is correct?
 

KlausST said:
Hi,

Good informations.
Be sure the LED was not connected the wrong direction.

Negative voltage:
I wonder... is it a PCB with proper GND plane...or a breadboard?

What voltages did you measure with empty and full battery?
How long did it take to charge?
What charging current? And what Ah rating is the battery?

Klaus
Click to expand...
my current meter is not working so i couldnt measure any currents but the battery charges pretty quickly to 3.3v , in about 10 mins .
i have made a pcb and there is ground plane below.
the battery i think is rated at 3.1Ah
oh and i checked the LED is connected correctly, i used a cell to light it up before soldering.

- - - Updated - - -

Audioguru said:
To see why the LED is not lighting then you must measure the STAT pin voltage with the LED and its series resistor connected and the battery fully charged.
Did you measure the resistance of the resistor to make sure it is correct?
Click to expand...

the STAT pin shows 0 volts with resistor connected and -0.25v with LED disconnected.
i havent measured the resistance of the resistors , will do it this evening .

- - - Updated - - -

how does the STAT pin work?
 

Hi,

When the STAT pin is low and the Led /resistor is connected to 5V_USB, then the led should be alight.

Please measure all voltages from STAT, Led, resistor, 5V. And tell us.

Klaus
 

The Lithium battery will be 4.2V when it is fully charged and its charging current should have slowly dropped fairly low. The LED should light during preconditioning and charging then turn off when the battery is fully charged. It the battery was discharged too low (less than about 3V per cell) then the battery is probably destroyed and the charger will stay in the preconditioning very low charging current mode and the battery probably will not charge properly. If the battery was stored fully charged for about 6 months or longer then its capacity is ruined.
 

the diode was connected wrong . it has a bar on underside and I thought the bar was the cathode as in normal diode symbol but the bar means Anode for this diode .
so now the led is on and battery is charging ,so when the battery is fully charged the led should turn off I understand? with 3.1Ah how long will it take ?
also can we find out from the data sheet or circuit as to what is the charging current of this circuit?
 

The datasheet has the charging current in writing and it has it on a few graphs of programming resistor (yours is 2k ohms) and chip temperature. I didn't download it but I think it says about 500mA charging current, then it slowly drops for the last 1/3rd of the total time to about 50mA, then it is fully charged.
 

Hi,

how does the STAT pin work?
Click to expand...

what is the charging current of this circuit?
Click to expand...

Read the datasheet.

Usually the parameter "charging current" is urgent to know before you connect a battery..to be sure it does not destroy the battery.
Wrong charging parameters may easily bring the battery to explode and catch fire!


Klaus
 

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