bigfarmerdave
New Member
I've got a little 12 volt DC circuit that I built which gets its power from the battery on the tractor. I guess the function of the circuit isn't of importance here so I won't go into detail. Anyway, what I wanted to do was protect it from a reverse polarity hook up and also protect it if a direct short were to develop. So, what I did was put a 7 amp polyswitch and a 6 amp, 200 volt rectifier diode in series between the battery and my circuit. When I reverse the polarity to my circuit, the diode does its job of protecting the circuit. When I directly short something within my circuit, the polyswitch drops the voltage from roughly 12.5 volts to about 1.2 volts and the current draw is limited to 7 amps. The problem is that the diode gets VERY hot. My question is this, is the diode getting hot because it is only rated at 6 amps and there is a 7 amp draw or is the voltage being dropped so low that there isn't sufficient voltage to forward bias the diode? I thought that the min voltage required to forward bias a diode was somewhere in the neighborhood of .4 to .7 volts depending on the diode. I'm thinking my problem is that I simply need a higher amperage rated diode and not the latter. Anyone agree?