Darki said:
It worked kind of... But the BU2527AF died when i connected it to a 12 volt 4.5 amp battery... And it was rated 15amp? Strange
Hi,
(the BU2527AF is rated at 12A continuos or 30A peak current, ok? from data sheet)
I assume your 12V 4.5Amp battery means for you 4.5 AmperHour, right? It means that you can load your 12V battery with 1 Amper for 4.5 hours or load with 4.5A for 1 hour and so on with the current-hour combinations to remain at or under 4.5AH, right?
SO the BU2527AF could be died for two reasons: either DC over current or inductive overvoltage. I suspect Over current through its collector-emmiter because when the transistor opens/switches on, its ON resistance is well under 1 Ohm and from your 12V battery the current through the switched-on transistor can be very easily higher than 12Amper (the continuous collector current limit). Because there is no any other resistance in your circuit which could limit the current not going higher than 12A. So the solution is to include a high wattage resistor of at least 1.2 Ohms in series with your positive battery wire which will let only flow about 10 Amper max towards the collector-emitter path, ok? (considering a full switch-on for your BU transistor, the 10 Amper max current limit will be within its 12 Amper capability)
Another possibility would be to reduce the duty cycle of your switching signal to reduce current through the switch (the less time you keep the switch ON the less current is able to flow that would distroy the switch) but in case of your present astable 2 transistor multivibrator it is not easy to reduce, in case of the 555 timer circuit I showed it is much easier with one of the variable resistors.
Do i need to change anything on the circuit to trigger the Motorola MGP20N40CL ?
Basically NO, but to be a 100% sure an oscilloscope would be needed to see the waveform on the collector of one the your astable multivibrator transistors and check if the transistor switches fully on or not: in case it switches fully on it means that the DC voltage on its collector goes down to as low as 0.2 to max 0.5V with respect to its emitter (which is the negative ground) because this low voltage would insure the full switch off of your IGBT (or MOSFET) device. (Because they switch on usually at a positive gate source threshold voltage of a few Volts, in case of MGP20N40CL this threshold is a minimum of 0.75 to 1V from data sheet.) And if your astable multivibrator transistor does not go under 0.75V at its switch-on time then it cannot correctly switch OFF the IGBT (though capacitive coupling instead of the present direct coupling from its collector to the gate of the IGBT may help on this situation a little). What I included in the schematics is two resistors, a voltage divider to help reach the situation of bringing the off voltage below 1 Volt for the switch. Some tinkering with the resistor values may be neccessary as I included in the schematics.
A notice: if you use the IGBT transistor rated for 20 Amper, it may still suffer from overcurrent, because the inner resistance of your battery usually is around or under 0.1 Ohm and AGAIN there is NO any current limiter in your circuit to protect the IGBT!
(Remember if you make a short circuit on you battery how much current is able to flow into the wires?)
unkarc