From this thread I think we learned that PTC's on the 3rd rail power of a TMCC engine are a good idea.
Would there be an advantage to installing a TVS inside the engine between the roller and the ground?
Any advantage to installing a TVS and a PTC or both?
If both than which goes closer to the roller TVS or the PTC?
I've been installing 3 Amp PTC's in my and TMCC engines and TMCC upgrades for years with good results - no boards lost since.
Plenty before.
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I believe some here have stated they do install a TVS in their engines when they have them open for other maintenance or repairs. I have always heard voltage spikes (and static from handling the boards) were the most feared cause of board damage. So that is a good idea. I don't know about order of placement? Maybe gunrunnerjohn or someone else more knowledgeable will be by to provide input on which to place where.
The TVS simply goes right across the pickups to the frame.
The PTC installations I'm doing currently are when using the new ERR Cruise Commander Lite boards. They work great, but are susceptible to cooking the motor drivers if you have a motor stall and go overcurrent on them. I use a 1.3A trip PTC for those, it's a .65A hold 1.3A trip. As you probably know, the PTC will handle considerably more than the trip current for a spell before it trips, and I've yet to see these trigger on any of my installations. I also use a PTC between pickups in passenger cars, between the tender and locomotive for load sharing of the pickups, etc.
I understand how a TVS is connected normally but if I were to use a TVS and a PTC inside an engine would it make any difference which is closest to the roller? I'm guessing not. The TVS should protect against voltage spikes and the PTC against over current. They are small enough to easily fit and cost less a couple dollars per engine. Putting the PTC between the motor and the TMCC board doesn't protect the entire board if the smoke or light shorts out
You're right about the PTC location. My reasoning for locating it in the motor leads of the Cruise Commander Lite was that they seem a bit more sensitive to a stalled motor overheating the drivers pretty quickly. Even though it's almost the same in the power lead, the capacitance of the power supply does add a little energy to the mix before the PTC kicks in. As far as other shorts, the good thing about the TMCC R4LC is that it's ground referenced, so a smoke unit or lighting short only takes out a cheap and easily replaced triac on the board, not the entire board.
In the spirit of protecting against a failed TVS, I'd probably put it after the PTC in the power lead. If the TVS shorts, you just trip the PTC, and that locomotive just stops. That results in less current for less time through the pickups and from the transformer, less chance for arcing across the pickups or wheels.
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