Car SMPS Project

badboy_6120

New member
If you want to check that the gate resistors are good just check the voltage at the gate to source with the scope. If the voltage is above 10 volts than the gate resistors are good at that value. 50 degrees on the fets is not so much you can add fan to cool things up. You may be pulling around 60 amps from the battery at 600w at 80% efficiency. Are you pulling a continuous load? or with amplifier?

Regarding current trafo it may be the case that you have too much turns on the secondary of the current trafo. Make less turns and put a load resistor according to the tripping voltage wanted in your smps. It is not the current passing but the load on it with the secondary turns and load resistor.

I will check the gate voltage of the fets as soon as I get home

about the current trafo
The core gets really hot (only when smps is under load) without any secondary winding on it ( just the primary winding of the ETD59 going through it)
I tested a few core that I have and the only core that didn't get warm was a green core but when I test this green core, the protection board kick in as soon as I release the high load from the output of the smps (when I connect a low resistance to smps output and hold it there, it dosen't triger the protection board but as soon as I release the load protection board react and cut the power)
I tried different secondary turns on current trafo but with same result
This only happened when I use the green core

thank you again for all your helps
 
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Silvio

Member
I will check the gate voltage of the fets as soon as I get home

about the current trafo
The core gets really hot (only when smps is under load) without any secondary winding on it ( just the primary winding of the ETD59 going through it)
I tested a few core that I have and the only core that didn't get warm was a green core but when I test this green core, the protection board kick in as soon as I release the high load from the output of the smps (when I connect a low resistance to smps output and hold it there, it dosen't triger the protection board but as soon as I release the load protection board react and cut the power)
I tried different secondary turns on current trafo but with same result
This only happened when I use the green core

thank you again for all your helps

Current trafo

It could be the case due to the high current involved you can use a low value resistor (current shunt) instead or even a piece of wire to form a small loop or a small coil to get to the desired length. This all depends on the material used for the high current resistor.

A few suggestions for the material are:- Brass brazing rod, A piece of eurica wire from a thick heater filament, a piece of copper wire, piece of stainless steel wire, piece of steel wire etc.
These type of shunts that I am mentioning will bring the need to alter the protection circuitry as the voltage drop across the shunt is very small and I guess the circuit will have to be altered a little to adjust the reference voltage at the LM393.

One other option is to sense the output instead with a small resistor like 0.1 ohm and measure the voltage across instead. Here it would be easier as you only have DC to deal with and there will not be the need for a diode to rectify the voltage thus avoiding the the voltage drop in the diode itself. You have less current to deal with at the output.

Regarding the false trigger during the load release well this may be cured with a small capacitor across the load resistor (secondary coil) like 1uF or so. Use the minimum until you get rid of this false trigger as the capacitor will somehow delay the operation of overload. You can also try to change the small 330pf cap entering pin 2 of LM393 to 0.1uf.

Silvio
 
Last edited:

badboy_6120

New member
Current trafo

It could be the case due to the high current involved you can use a low value resistor (current shunt) instead or even a piece of wire to form a small loop or a small coil to get to the desired length. This all depends on the material used for the high current resistor.

A few suggestions for the material are:- Brass brazing rod, A piece of eurica wire from a thick heater filament, a piece of copper wire, piece of stainless steel wire, piece of steel wire etc.
These type of shunts that I am mentioning will bring the need to alter the protection circuitry as the voltage drop across the shunt is very small and I guess the circuit will have to be altered a little to adjust the reference voltage at the LM393.

One other option is to sense the output instead with a small resistor like 0.1 ohm and measure the voltage across instead. Here it would be easier as you only have DC to deal with and there will not be the need for a diode to rectify the voltage thus avoiding the the voltage drop in the diode itself. You have less current to deal with at the output.

Regarding the false trigger during the load release well this may be cured with a small capacitor across the load resistor (secondary coil) like 1uF or so. Use the minimum until you get rid of this false trigger as the capacitor will somehow delay the operation of overload. You can also try to change the small 330pf cap entering pin 2 of LM393 to 0.1uf.

Silvio

Fix the problem with just letting a quarter of primary winding going through the yellow current trafo
now the protection board working perfectly and there's now heating on current traso as well
 
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