Power Bank Circuit Diagram

[gauravkothari23]

Hi all.
I am planning to design my own power bank circuit. i have got one chinese power bank circuit for reference. it has only one IC, 2 capacitors, 1 inductors, and 4 LED's for indication to control the complete power bank. This IC is not available in india. so i want to use the IC's which are easily available and design it. Battery charger IC's are readily available but indication of battery status is quite difficult. i am planning to use MCP73871. how can i design the battery indication using this IC.

 

[Audioguru]

The datasheet for the MCP73871 shows three status LEDs and their functions are listed in Table 5-1. What is the function of your 4th status LED?

 

[gauravkothari23]

The datasheet for the MCP73871 shows three status LEDs and their functions are listed in Table 5-1. What is the function of your 4th status LED?

Actually i need 4 LED a to display battery status.
For example
25% = 1st LED Blinks.
50% = 1st LED Stable and 2nd LED Blinks.
75% = 1st, 2nd stable and 3rd blinks.
90% = 1st,2nd,3rd stable 4th blinks.
100% =. All LED Stable.
This is the feature what most of the power banks circuit has.

 

[Audioguru]

The percentage of charge in a Lithium battery cell is not simply its voltage. www.batteryuniversity.com shows a graph of the voltage and current of a charging Lithium cell. It is about 3.0V when it is almost dead and if it charges for about 1/4 of the total charging time then its voltage is at its maximum of 4.2V but it is far from being fully charged. Maybe you could detect the drop in charging current as it continues to charge.

Since the power bank IC is not available in your country then are you going to go into the past about 10 years and design and make one yourself? Do gardening instead of electronics.

 

[gauravkothari23]

you mean to say if the IC or module is not available in our country, i need to wait and watch for next 10 years for someone else developing the same thing and then buy it from him. Good sense of humor.
my question was how to show the battery status indicator using 4 LED's of the power bank batteries and not what to do instead of electronics.

Since the power bank IC is not available in your country then are you going to go into the past about 10 years and design and make one yourself? Do gardening instead of electronics.

This type of answers to any questions, forget about elecronics, we indian dont even keep them as a gardner.

 

[Audioguru]

I have never been to your country. I do not know why ordinary common electronic parts and many other common things are not available there.
Here everything is available.

 

[d123]

I hope you're well, gauravkothari23,

With all due respect, don't you think it's trying to put a size 5 right shoe on a size 7 left foot with this idea?

I thought you used MCs - wouldn't that make the idea of the four LEDs doing something at each stage of charging easier?

Why not rethink the basic idea, accept that as with all circuits you may have to make disappointing compromises here and there, and start with a different type of battery charger IC which you can get where you live, maybe looking for one that senses current and voltage (are they the "fuel gauge" type?)? And then, as an admittedly not-very-thought-out example at all, to say the least, use something like the LM3914 and a quad timer (I bet the 558 is available if nothing better) or whatever to have the LED's flash, using output 5 of the LM3914 to turn on all LEDs. ...Or any combination of easily available ICs to measure and convert to a logic output, a quad op amp and a quad logic device.
It's a poor idea, and not what you want, but just to take the conversation away from an unproductive thread and to suggest looking at the problem from a different angle...

 

[Audioguru]

d123,
I have never seen inside an IC that is a "fuel gauge" of the amount of charge in a Li-Ion or Li-Po battery cell. But I read on www.batteryuniversity.com that the voltage of a charging lithium battery does not show how much charge it has because the voltage rises to the maximum quickly and long before the battery is fully charged.

Also, a timer is never used in a Lithium battery charger because you do not know how long to charge, it might already be near a full charge. But a timer can be used if it has monitored and stored the amount of current and its duration for the last discharge.

 

[d123]

Hi Audioguru

Also, a timer is never used in a Lithium battery charger because you do not know how long to charge, it might already be near a full charge. But a timer can be used if it has monitored and stored the amount of current and its duration for the last discharge.

I was referring to a much more pedestrian use of timers to flash the leds using an e.g. 555 astables by controlling the reset pin, driven by the LM3914 outputs. Ooh, look flashing LEDs .

Surely guaravkothari23 can think a bit more about what is needed to sense the amount of charge going into the battery and use those levels of I and convert to V to drive an LM3914? Li-Ion charger ICs have features to turn off, LTC4079 uses C/10 or a timer feature.

 

[Audioguru]

I think that Linear Technology does not understand how to graph the charging cutoff of their LTC4079 charger IC.
Their graph is completely wrong. It shows the charge being terminated (with a simple timer?) when the battery has charged to its capacity.
How does the charger IC know how much charge the battery has at the beginning of charging if it simply uses a timer??
The graph is wrongly labelled "C/10" which is actually C1.
The voltage is shown to peak far too late.
The "charge status" simply lights an LED or an alarm but the datasheet confusingly says the charge is terminated only if the timer is used.

 

[d123]

Hi Audioguru,

I assume you're right about the graph (cloned copy/paste datasheet syndrome maybe?), as you know a lot about batteries; also, I suspect you haven't read the whole datasheet (nor would I expect anyone to for another person's circuit) because you missed the line in the preamble/description: Charging can be terminated by either C/10 or adjustable timer.

Just to add a picture:



It describes this feature on pages 9 and 12, at least.

"C/10 Termination
The LTC4079 supports a current based termination scheme, where a battery charge cycle terminates when the current output from the charger falls below one-tenth of the programmed charge current."

i.e. Just adding the above in case you missed it, however, I think I may not have understood the gist of your last sentence.

I guess the timer function is useful for circuits where the designer knows how much current the circuit should draw between charges, maybe something low power on for a few hours a day/365 days a year. Your point is understood - otherwise it would be a bit haphazard.

Thanks for explaining about the graph, useful to know what to look for regarding that difference.

 

[Kajunbee]

Digikey has a site "Designers guide to lithium battery charging". From what I understand you have constant current charging which switches to constant voltage charging to top off. From what I understand simpler chargers will use timers instead of current measurements for topoff only if I'm understanding correctly. I know nothing about the subject. Just you might be interested.

 

[Audioguru]

Linear Technology is confusing their term "C/10". Their graph might show Current/10 or Capacity/10 which are completely different.
Since their charging stops when the Capacity has reached the 500mAh rating of the battery then I think the graph terminates the charging of a completely dead cell with a simple timer. Then a cell with some remaining charge in it will become overcharged which might cause a fire or explosion.

But the datasheet says that the charging can be terminated when "the charging current falls below one-tenth of the programmed charge current."
So the graph shows a coincidence of capacity/10 and current/10.