I’m trying to help everyone here, but it’s not possible to fix every charger remotely; some require specific measurements and expertise that I’m unable to convey on the forum. People often ask what to do with a charger that isn’t charging, even though the green LED is lit… The answer is simple: no current is being supplied to the battery.
And the reason for this could be a fault with the charger or the battery itself.
I’ve noted at least four instances where the battery simply wouldn’t charge.
We’ll assume that all the chargers discussed here have a green LED that’s lit; if it isn’t lit, go back to the start of the post and read it carefully… there’s a problem with the MIP.
The first scenario is inserting the battery for a few seconds and hearing nothing; the current reading is 0.
The second scenario is when, after inserting the battery, the LEDs on the battery light up and the green LED goes out.
The third scenario is when, after inserting the battery, the fan starts up and you can hear the relay switching; current reading: 0.
The fourth scenario is: I insert the battery, the fan starts up, the relay engages, the current rises and then switches off after a moment.
I think I’ve done all my homework and finished drawing the schematic; I’ve drawn two more segments; today I’m presenting the final output of the battery charger – it looks like this: it could be improved, but this is the first sketch I’ve done and I don’t have time for any more… it’s about understanding the principle…
The second sketch will focus on the processor and its pins; it’ll be an interesting topic, but you’ll have to wait…
To summarise briefly, we have the main transformer T1, which generates the voltage for our battery, but before that happens, the current draw is measured by a shunt resistor and the circuit is ultimately switched on by relay RY2. The voltage measured across resistor R147 and Zener diode Zd107 is 30 V, and that across 108 is 10 V (checked with a multimeter) and R101 provide signals to the main converter circuit regarding its operation via the PC3 optocoupler (mounted beneath the main transformer; difficult to access – the transformer must be desoldered), which is often damaged when the IC1 L6599AD chip blows.
The PC3 optocoupler, which controls IC1 on pin 1, has a voltage of between 4.7 V and 4.8 V when the battery is not connected; this is because there is a 0.3 V drop across diode D124, which is supplied with a constant 5 V voltage, whilst the voltage at pin 2 is between 3.6 V and 3.7 V. When the battery is fitted and the circuit is operating correctly, the voltage at pin 1 rises to 5.1 V because, via R147, ZD107 and ZD108; R101 causes the voltage to rise, whilst on pin 2 the voltage is around 3.9 V and this varies depending on the battery’s charge level (this is determined by the IC103 operational amplifier; I should point out that if this is faulty, inserting a working battery will cause the green LED to go out). The PC3 optocoupler on the high-voltage side, when operating correctly, has a constant voltage of 1.9 V at pin 4, whilst pin 3, which controls transistor Q6 (BC817-40) and determines the operation of the IC1 circuit, fluctuates within a range of 0.08 V. If the measurements confirm these values, we can be certain that the charger is in good working order.
As soon as a working battery is fitted, the charger begins charging; you can hear the relay engage and the fan start, but after a few seconds it switches off; on pins 3 and 4 of the PC3 optocoupler, we will then read 0 V, which indicates that the main converter powered by IC1 is not operating correctly.
Having examined many faulty chargers, I have observed that there is a certain rule: when a working battery is inserted, the charger must engage the relay and start the fan, even if the main power converter is faulty! I had a case where, that after fitting the battery, there was no response, and the reason was cold solder joints near the processor, as it is the processor that triggers the charging process. The processor communicates with the battery via three wires: yellow, blue and green; these determine what to do with the battery. From my observations, I’ve noticed that the yellow wire is responsible for charging: as the voltage on our battery pack rises, the voltage on this wire drops to around 3V; without the battery, there’s a constant 5V there, whilst the green and blue wires read 0V. When the battery is present, the voltage on the blue and green wires fluctuates between 4.2 and 4.5 V; these are presumably signal lines.
At the heart of the charger is the MC9S08AC32 microcontroller, which has 32 pins, of which 2 are unused (pins 9 and 12).
Ground is on pins 13, 22, 26 and 30.
The +5V power supply is on pins 14, 21 and 25.
There is also a pin for programming the chip – pin 27, known as BKGD/MS (which carries 5V) – and the required pin 2, i.e. RESET (which also carries 5V).
I’ve tried my bloody best to sort this out… I’ll ask the admin to fix it, then I’ll describe these pins to you in detail because each one has its own function.
Here’s the processor and some interesting findings that might help someone repair a charger;
I’d like to point out that a problem with a battery that won’t charge, or the charger showing no response at all, is not related to the processor!!! Damage to the processor or its immediate vicinity is the least common fault; in these chargers, 90 per cent of faults are within the main L6599AD converter, and even replacing the chip with a new one will yield poor results, as the capacitors in its vicinity very often fail.
I have observed two different behaviours in the charger despite the lack of charging: 1) it switches off immediately after the battery is charged, and 2) it switches off only after about 30 seconds of the battery being inserted. The first shutdown indicates that a safety mechanism has been triggered – i.e. shorted switches, a faulty PTC1 thermistor (470R) or its components; for example, I had a cracked capacitor C5, no power at pin 7; the resistors R15/16/17 must be desoldered to take a correct measurement. The second scenario is more interesting because the converter starts up but does not supply voltage to the battery pack… but I’ll discuss that later.
The important thing is that at this stage we need to remove the transistors to find out more about how the converter works; their presence will quickly shut down the converter and you won’t learn anything about its operation. Even working switches won’t change anything here.
I’ll post the rest in a few days...
