Hello,
Ok great. I'll see what i can throw together for you using those parts.
Dont give up if your interview fails, they may call you later, or you may get another interview at another place and then get hired there instead. In any case though good luck with it.
Oh yes! Actually it has 4.30V output. But how it won't overcharge (more than 4.2V) if supply is more than 4.2V? Why we cannot set output to 4.2V?A Lithium charger has a Maximum output of 4.20V.
But I don't know why it has such low charging current. I am charging now Li-ion cells rejected from cell phone. Will these rejected cell take such less current like 50 or 100mA while charging? (I think it take more current than this.)It also has a Maximum output current, you said yours is only 50mA. Then if you try to charge a defective or completely discharged battery its output current will be limited to 50mA but the load (the battery) determines the output voltage that can even be zero volts if the battery is shorted.
4.3V is too high. Either your charger or your meter is WRONG. Is the charger a Chinese one? Enough said.Oh yes! Actually it has 4.30V output. But how it won't overcharge (more than 4.2V) if supply is more than 4.2V? Why we cannot set output to 4.2V?
A new lithium battery cell will try to take a very high charging current which will destroy it. Therefore a charger limits the current.But I don't know why it has such low charging current. I am charging now Li-ion cells rejected from cell phone. Will these rejected cell take such less current like 50 or 100mA while charging? (I think it take more current than this.)
Yes.4.3V is too high. Either your charger or your meter is WRONG. Is the charger a Chinese one? Enough said.
I found good Li-ion never discharge lower than 3V (approx.) or something like that in ideal operation. Then how 'battery level indicator' can sense the level of battery? (on cell phone or laptop or on analog devices). May be due to its tiny decreasing voltage...right?A new lithium battery cell will try to take a very high charging current which will destroy it. Therefore a charger limits the current.
An old battery might have such a high internal resistance that it will not take more than 50mA of charging current.
Thank you for your wishes and encouragious words. If I felt depressed or totally sad then I use to busy with electronics (discussion forum, repairing or creating new device myself), it make me fresh. So I think I never will give up electronics.
One thing- I talked about before I have a Li-ion charger from China (220V IN and 4.2V OUT tiny supply) Its output current is VERY low than normal (50mA to 100mA almost) but it is amazing--
It just has LM358 and only few transistors (two or three) as a special components. Main amazing thing is its LEDs-
1st turns ON if I connected battery there. It also turns ON if I connected the charger to 220V to power it. But It turns of if it is connected to 220V but bad battery (totally discharged) or opposite polarity or short occurred on charging terminal.
1st LED- it starts to glow if battery terminal voltage is higher than 1.5V or more. So it can work as a opposite terminal detector (LED turns OFF) or damaged battery detector (LED turns off because damaged battery has zero or just only few mV).
I turned ON the charger and connected damaged cell to charge. When turned ON the charger, the 1st LED was glowing fully, but when I connected damaged battery there I got it turned OFF instantly. I measured the charging voltage and got just 500mV. (I charged this fully damaged cell few hour carefully But charger didn't get hot, charging current & volts was 50mA, 0.5V ). I don't know how 4.2 charging voltage decreased to 0.5V automatically, I guessed charging voltage determined by battery voltage level.
Yesterday mistakenly I connected opposite polarity and charged on same situation almost half an hour, but luckily happened nothing. Charger and battery both did't get hot. It means it has opposite polarity protection too, wow.
2nd LED- it starts to blinks frequently while charging. I don't know how it it blinks. I didn't see pair of transistor to blink it, but there is a single transistor near of it (I didn't see other in detail)
It turns OFF (with dim) if charging is full
3rd LED- It glows (starts from dim) if charging is full.
Nice indication! Can we have few too in your upcoming circuit too?
Sorry for my long post, actually I did two mistakes with Chinese charger- charged fully discharged Li-ion and charged with Opposite polarity but there is nothing wrong happened! So I was just excited with it.
But there are two resistor in series with battery from Gnd- 0.6 ohms and 2 ohms. This '2 ohms resistor' is confusing me. So I calculated output current like this way as before- 0.6V/(2R+0.6R)=230mAHi again,
The first current setting is the same as before, it's the max current output and that is set with the 0.6 ohm resistor.
0.6 ohms gives 1 amp max output, 1.2 ohms gives 0.5 amp max output, etc.
The second current setting is the low level min current. That's like around 20ma to 50ma or around there. That is set with the 10k pot so no need to change the 2 ohm resistor. It's better not to change the 2 ohm resistor anyway because we need a certain level of voltage for the LM358 to work properly given the various imperfect spec's for that chip.
Hi,
Well actually the new 2 ohm resistor does NOT affect the max current setting (with proper input voltage of course). Only the 0.6 ohm resistor changes that. So the output current limit is set ONLY with the 0.6 ohm resistor as before. Again, 0.6 ohm will give about 1 amp max, 1.2 ohm will give about 0.5 amp max. For 750ma then it would take about 0.9 ohm, and check the wattage making the rating in watts equal to P=2*I*I*R.
I assumed you wanted a minimum current indication but if you want a max voltage indication that's every simpler. I'll draw that next and add that to the circuit so you can have an LED come on when the voltage reaches say 4.15v or whatever you want to set it for. Of course when you set the output voltage itself it has to be a little higher than that though so the adjustment might get a little tricky. You might set the voltage to 4.16v and then set the LED to come on at 4.15v or something similar to that.
I'll try to get the new schematic drawn up tomorrow sometime, probably afternoon. It's just going to be a comparator, voltage reference, pot, couple resistors.
Do you still want the min current indicator LED too?
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