Bon-86
Well-Known Member
No offense taken.
I don't have any facts about the old transistors but apparently you do. If they are 16 amp amp max transistors, fine. They do need to be derated somewhat for temperature though as they live next to a hot engine and do get a pretty good heat soak. I did see somewhat lower amperage through the COPS than the V/R would suggest. The on resistance of the power transistors, wiring and connectors account for the additional IR losses that you refer to in your experience. I'm not going to subject my TCI to the test to get a scope trace to prove differently.
yes, some designs are above the usual design criteria of 50% rated limit as most circuits are designed to cost above all. Component manufacturers derate and circuit designers derate again. It comes down to manufacturing tolerances and environment. Japanese automotive electronic design is extremely conservative and, for example, Chrysler is not. In the long run it makes all the difference between reliability and increased maintenance.
I have performed an autopsy on a dead TCI box and found it to be the driver rather than the power transistors. I looked and looked for a replacement chip but failed to find one as the part is long ago obsolete. I did find some sites listing it but none actually had any stock.
I don't have any facts about the old transistors but apparently you do. If they are 16 amp amp max transistors, fine. They do need to be derated somewhat for temperature though as they live next to a hot engine and do get a pretty good heat soak. I did see somewhat lower amperage through the COPS than the V/R would suggest. The on resistance of the power transistors, wiring and connectors account for the additional IR losses that you refer to in your experience. I'm not going to subject my TCI to the test to get a scope trace to prove differently.
yes, some designs are above the usual design criteria of 50% rated limit as most circuits are designed to cost above all. Component manufacturers derate and circuit designers derate again. It comes down to manufacturing tolerances and environment. Japanese automotive electronic design is extremely conservative and, for example, Chrysler is not. In the long run it makes all the difference between reliability and increased maintenance.
I have performed an autopsy on a dead TCI box and found it to be the driver rather than the power transistors. I looked and looked for a replacement chip but failed to find one as the part is long ago obsolete. I did find some sites listing it but none actually had any stock.
