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Resqueline
- Jul 31, 2009
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Yes-yes.. The higher the internal ESR of the battery is the more pronounced this effect will be. Just try to lower the current capability of the charging system and see.
Ok, I got my hands on a pretty good bench
I tried it on another brand of mobile powering with a AC/DC converter at 9V 2A+7805
The quiescent is about 5mA and the current measured at the adapter and the 7805's input leg is approx 350mA, the LED is OK
With the same settings, I changed power source to 9V battery and the measured current was 100mA (approx, the battery was near dead so I don't expect much from it) and the LED is OK only when the current was measured >100mA.
As the current falls, the LED starts blinking and dims
Then I hooked up my old mp3 (again, the internal battery is probably worn down but it is fine enough for testing).
With the AC/DC adapter, the current starts at around 140mA and dropping, pretty fast, to around 50-60mA. The LED, again, starts blinking at around <100mA
Then I changed power source to 9V. It's pretty much dead, so.... Current starts at around a bit more than 100mA and slowly dropping to 50mA. But the LED starts blinking only after significant current drop, something around 70-80mA but it is brighter than when the power source was AC/DC converter at around the same current
The mentioned AC/DC adapter/converter is a big box that you can adjust voltage and max current, I don't know what it is called...
What I don't understand is:
Why does it blink? I thought I hooked up the comparator as a SPST switch to ground...?? The LED should be just ON or OFF. I understand that when the current is lower than 100mA, the voltage at negative of the comparator starts to get lower than that of the positive. I also understand that there is a range when the power isn't completely out but dropping to 0, and said range is short enough (according to the datasheet, it is only 5mV). But it seems to blink even when the current is very low....
The second test case, is it because the battery is worn down? That the current output from the converter gets decreased over time. I set the charge mode to 500mA, so why doesn't it draw 500mA but instead only 140mA and then dropping?
Sorry if I sound confusing, I'll try explain better if you don't get what I meant
One more,
I forgot to put in a diode to prevent backward current. When will backward occurs? (The battery can't supply enough voltage/current so the current flows from the device instead?)
What happens during backward? Can you show a simple diagram of how things go? Like the battery changes into a cap instead and the device turns into power source or so (Just my imagination)
How can I know if the power is actually going backward? Not by the device's battery indicator please, I don't trust it
If the current actually goes backward, will the LED lid?
I tried it on another brand of mobile powering with a AC/DC converter at 9V 2A+7805
The quiescent is about 5mA and the current measured at the adapter and the 7805's input leg is approx 350mA, the LED is OK
With the same settings, I changed power source to 9V battery and the measured current was 100mA (approx, the battery was near dead so I don't expect much from it) and the LED is OK only when the current was measured >100mA.
As the current falls, the LED starts blinking and dims
Then I hooked up my old mp3 (again, the internal battery is probably worn down but it is fine enough for testing).
With the AC/DC adapter, the current starts at around 140mA and dropping, pretty fast, to around 50-60mA. The LED, again, starts blinking at around <100mA
Then I changed power source to 9V. It's pretty much dead, so.... Current starts at around a bit more than 100mA and slowly dropping to 50mA. But the LED starts blinking only after significant current drop, something around 70-80mA but it is brighter than when the power source was AC/DC converter at around the same current
The mentioned AC/DC adapter/converter is a big box that you can adjust voltage and max current, I don't know what it is called...
What I don't understand is:
Why does it blink? I thought I hooked up the comparator as a SPST switch to ground...?? The LED should be just ON or OFF. I understand that when the current is lower than 100mA, the voltage at negative of the comparator starts to get lower than that of the positive. I also understand that there is a range when the power isn't completely out but dropping to 0, and said range is short enough (according to the datasheet, it is only 5mV). But it seems to blink even when the current is very low....
The second test case, is it because the battery is worn down? That the current output from the converter gets decreased over time. I set the charge mode to 500mA, so why doesn't it draw 500mA but instead only 140mA and then dropping?
Sorry if I sound confusing, I'll try explain better if you don't get what I meant
One more,
I forgot to put in a diode to prevent backward current. When will backward occurs? (The battery can't supply enough voltage/current so the current flows from the device instead?)
What happens during backward? Can you show a simple diagram of how things go? Like the battery changes into a cap instead and the device turns into power source or so (Just my imagination)
How can I know if the power is actually going backward? Not by the device's battery indicator please, I don't trust it
If the current actually goes backward, will the LED lid?
Last edited:
Resqueline
- Jul 31, 2009
- 2,848
- Joined
- Jul 31, 2009
- Messages
- 2,848
I had to take a rest before commencing on this one, hope this helps..
Both charging scenarios are exactly as I'd expect. The dimming of the LED may be caused by a PWM circuit in the phone, but I'm only guessing here.
A PWM can only adjust itself so low, sooner or later it has to turn itself off completely. If you apply an infinite current to a battery then the voltage will rise infinitely fast too, and then you will have to turn off said current infinitely fast. But the battery won't be fully charged so the cycle will start over again, causing infinitely fast blinking of the LED.
In the beginning of an ordinary charge cycle the battery is able to hold down the voltage due to resistance in the charging circuit, but as the voltage rises to 4.2V the current has to be shut off. The lower the current is at this stage the slower the blinking will be. Try reducing the PSU current limit and you should be able to slow it down - even to a steady light.
It's called a bench power supply, or a lab power supply.
Yes, a worn battery will only draw so&so much current due to its own internal series resistance.
Backward current is unlikely to happen. The phone's charging circuits are likely to prevent this, as it's usually a damaging circumstance. Not supplying enough current/voltage is not enough to make it happen, you'd have to short the input.
No, you can't tell it with the LED in this circuit. You'd have add another comparator/LED circuit, or put an instrument across the current sensing resistor.
Both charging scenarios are exactly as I'd expect. The dimming of the LED may be caused by a PWM circuit in the phone, but I'm only guessing here.
A PWM can only adjust itself so low, sooner or later it has to turn itself off completely. If you apply an infinite current to a battery then the voltage will rise infinitely fast too, and then you will have to turn off said current infinitely fast. But the battery won't be fully charged so the cycle will start over again, causing infinitely fast blinking of the LED.
In the beginning of an ordinary charge cycle the battery is able to hold down the voltage due to resistance in the charging circuit, but as the voltage rises to 4.2V the current has to be shut off. The lower the current is at this stage the slower the blinking will be. Try reducing the PSU current limit and you should be able to slow it down - even to a steady light.
It's called a bench power supply, or a lab power supply.
Yes, a worn battery will only draw so&so much current due to its own internal series resistance.
Backward current is unlikely to happen. The phone's charging circuits are likely to prevent this, as it's usually a damaging circumstance. Not supplying enough current/voltage is not enough to make it happen, you'd have to short the input.
No, you can't tell it with the LED in this circuit. You'd have add another comparator/LED circuit, or put an instrument across the current sensing resistor.
Resqueline
- Jul 31, 2009
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I'm afraid I don't understand at all how you can think the blinking can damage the LED in any way..
The blinking just shows the way the phones (simple) charging circuit works. I believe you should see it change character as the battery approaches fully charged.
The blinking just shows the way the phones (simple) charging circuit works. I believe you should see it change character as the battery approaches fully charged.
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