Location of TVS & clamping voltage

The closer to the origin of the spike, the better. 

Some place them across the transformer terminals.

Some place them at the track hookup and that would be closer to the spike. 

Some sprinkle them about the rails around the layout.

Some put them in the engine - can't get closer than that.

If they fail, they can fail open and it won't be an issue other than you no longer have protection... or they can fail as a short.  If they short and are distributed around the layout it could be a real challenge to find the cause of the short. 

The TIU has tvs built in, having more does no harm though.

If you have a main bus or busses that you pull your track feeds from, I'd place them there.

Actually, the closer to the item being protected is the best place.  However, since that's a rolling locomotive in most cases, the only way to accomplish that is to open them up to install them.

I'd sprinkle a few along the track, you really can't have too many.

I have 22 track blocks, each with one or two feet of wire drop to a two position terminal strip which connects to one of two main terminal strips for each TIU channel. I have a TVS at each short  track feeder wire connection. It's never more than six track joints away from a spike. If one shorts out, it will probably be the 22nd one I disconnect.

Probably.

  With PS2 and PS3 boards between the red and black at the wire nuts i believe.

If you're putting them inside the locomotive, you're correct, right across the track pickups to frame ground.

WARNING, bad joke ahead:

Rad400, you should put your TVs everywhere in your house so you are never far from Fox News, CNN, Lifeline, ME TV etc. 

Sorry, couldn't resist. I have the capacity to induce laughter (electrical types will get this sentence)

OK we now return to serious electrical problems.

Anyone have a photo of the typical TVS installed in a locomotive?

I never thought to take a photo, but right across the roller and frame ground is the correct placement. 

Just to add to what John says. The power source is what produces the spikes. The engines are what you are trying to protect. The closer to the power source the more likely you are going to blow the TVS. Some of the energy is dissipated in the wiring and tracks so reduces the energy the TVS has to dissipate.

Think of a lightning strike that hits the power line to your house vs one that hits a line 3 miles away. The former will likely take out every electronic device plugged into the wall. The latter probably not.

Pete

Pete, spikes can be generated by other components as well.

What I was trying to point out is the transformer is the source. Without the transformer no spikes, right? The closer to the transformer the greater the risk. A derailment two feet from the transformer presents more energy to a TVS then one twenty feet away all things being equa given a TVS unstalled in that engine. Reactive components in the circuit are going to attenuate the effects of the derailment.

Pete

What I'm saying is that the transformer is NOT the source of all spikes.  The transformer powers the layout, but any coil with a collapsing field can directly generate a voltage spike. The source of the spike would be the coil and not the transformer.

John

A quick question so the IR senor and other track relays should have a TVS attached to them as well?

Well, you can get carried away.   All I'm saying is that voltage spikes "can" be generated by any accessory, locomotive, operating car, etc. that has a coil that is energized and then deenergized. 

When I was working in aerospace, we put transient protection everywhere, that was a significant part of our design effort.  Of course, it's bad with some of that stuff stops working!  If you have a couple TVS diodes around the track, that's an excellent start.

It's hard to have too many, but then it's a PITA to track one down if it shorts.

Thanks for all the responses on the location for the TVS.  Has anybody tried to put a 18v light bulb in series with a TVS, so if the TVS shorts out, then you will have a lit bulb indicating a shorted TVS.  I am thinking of this configuration for a large layout and it would make it easier to trouble shoot when a ZWL/Z4000 indicated a short due to a TVS. Locations I would place the TVS in series with a light, is at the TIU output terminal block and at the ZWL/Z4000 output terminals.  I don't think this would interfere with Legacy or DCS command signal.

Also, does anyone know what is the rating of the TVS that is in the TIU.  I have had a lot of power output FETs blow in our TIUs, but never a TVS or blow fuse. So I am not sure how effective the TIU TVS's are.

Thanks,

RAD400

The resistance of the bulb would negate any benefit of the TVS.  The TVS counts on a very low impedance path to shunt the spikes to ground.

The TVS in the TIU is a 1500W unit, and it's the same rating as one that I've recommended many times.  The power FETs would die for a totally different reason that the TVS diodes, probably why you don't see TVS diodes dying.  An overload on the variable channel FETs can take them out, but the TVS doesn't care at all you're cooking our output circuits.

Dear John

Thanks for the reply. With your suggestion and other input SOP on my layout is always have a 22 ohm choke and TVS connected first to any accessory on the layout. For the engine it is PTC and then the TVS.

Sounds like you have about as good a protection scheme as possible.

John sorry to hijack but i put a forum under Lionel o gauge for a Lionel motion detector which  need a 10 k pot but need to be miniature to fit in the housing do you know where i can get the delay pot 10k minature

model number 6-14111 153irblue three leg pots.

Any help would be appreciated as no one has answered my forum

I checked digikey but only find square

Thanks Alan

A picture would help.

Something like this?

Lots of these style on Digikey: http://www.digikey.com/product...d=0&pageSize=500

John, thanks for your additional information on TVS.  One of the items I am trying to protect besides engine electronics, is the FETs in the TIU.  Do you have any suggestions on how to protect the TIU FETs from a burnouts?

Also the thread from Kris talks about putting a 22 ohm choke in for protection.  Can some one describe this further.

Thanks 

RAD400

For the engine it is PTC and then the TVS.

Where are you installing the PTC and what value?

RAD,

Back to the OP.  Lots of good data here from the experts.  Here is what I've done.  Like others, I put a TVS across each transformer terminal as well as across each track hookup.  I'm hoping the TVS at the track hookup will be close enough since I don't have them in the engines.  The one across the transformer terminal is a back up incase one of the TVSs at the track fails open.  I'm using the 1.5KE33Ca size because when I bought them way back when I was told the 18V max 180 PH transformers didn't need more than this (older transformers and some newer MTH ones go to a higher voltage, so the 1.5KE36Ca is better for them).

Below is how I set mine up.  The choke is there to keep the PSX from messing up the DCS signal.

It's a 22 microhenry choke, he just used the wrong term.  

As far as protecting the FETs, good fast acting circuit breakers are the key.  I've had tons of shorts on my test tracks, the transformer runs through the TIU variable channel and to the tracks.  No damage to the TIU, but it's powered with the Lionel PH180 transformer with an electronic breaker, very quick action.

I've been reading these TV's treads for awhile and I really think a lot of you are really going overboard.  Like John has,  I deal with Transzorbs a great deal in Aviation so I know a thing a or too about them.  I personally think opening up every engine and installing a TV's is over kill.  Installing at TV's at the ouput of the transformer or TPC, TIU is good enough.

As for fast circuit breakers, unless it's electronic, there's no such thing as fast.  If you want good train protecting I'm a big advocate of the PSX circuit breakers.  Check out my Youtube video of me shorting the track.  I did that with engines on the track.  Ever since I've installed two PSX on my layout I have yet to blow any electronics, TIU, TPC, on any engine electronics.  Not to mention no more arc welding of wheels or pickup rollers to track.

http://www.dccspecialties.com/products/psx_ac.htm

https://www.youtube.com/watch?v=Mf-OVDKKGZk

I don't advocate open up all the engines just to install the TVS, but I do it when I have to open the engine anyway for other work. 

I consider the Lionel PH180 circuit breakers as fast.  They're not quite as fast as PSX-AC protection, but the difference is a couple of milli-seconds.  Since we're talking about shorts and heat buildup, and not trainsients (that's what the TVS is for), the PH180 breakers are excellent protection.

All the other thermal breakers take much longer to react to short circuits, especially if the current isn't multiple times their ratings.  I have a 2A thermal breaker on my test bench transformer.  I can put my VL-BB on the test blocks and turn on all the smoke features, it's drawing close to four amps.  It takes that 2A breaker about 30 seconds to notice there is a 100% overload and trip.

Trying to know when a TVS has failed with a light won't work, because the worst case scenario is the TVS just fails open.  It normally looks like an open so know way to tell with out testing.

A more dangerous failure is a short.  No light needed since you will know it.  The shorted TVS connects AC in and AC Ground.  So the transformer breaker will see it at some point.

This is the danger of putting TVS inside the engine.  If it shorts you will melt your internal wiring.  So if you want to do it, make sure you have the shortest amount of wire between the TVS and the track input power.

As far as TIU, the VAR channels already have additional TVS protection.  You have the output TVS and also internals specifically for the TIU VAR channels.  G

I don't see a significant issue with a TVS inside the locomotive.  Unless it's wired different than the standard MTH and Lionel wiring, the wiring should be able to trip the transformer breaker before it goes up in smoke.  The wire used is at least #22 wire, that has an enclosed ampacity of 5 amps, and so should handle the brief overload without issue.  Hopefully, you're not leaving the locomotive on the track and repeatedly resetting the breaker!

John,

Is the breaker in the 180 bricks, thermal or electronic?

Ron,

I see you are using PSX breakers, they do have TV's already installed.  If they ever blow or shorted out I'll remove them and add what have done.  Your setup is closed to what I have, except my TIU is in direct line not in passive mode and I'm using my own 20 amp transformer I built. 

How do you guarantee you will know.  I have seen plenty of loco with fused wiring either in the tether or at the engine.  Motor overload, and power.

5V boards are a perfect example of a hi current failure that would simulate a TVS short.  They can hold anywhere from 4 -9 amps.  Well below a trigger for some transformers.

A engine sitting on a powered siding as an example.

Frankly we don't have proof they make a difference one way or the other.  Though having the one at the transformer makes sense.

The tech note is really apples to oranges.  They are talking about protecting discrete components on a PCB.  TIU rev L with the SMD TVS added to protect a specific chip is a prime example.

I have one customer with TVS installed in the engine that lost a Audio amp to a derailment.  So he is questioning the benefit.

Folks are picking clamping specs with no specific data behind it.  TIU have 33, 39, 51 V TVS depending on model and location.  Transformers use 51.

But hey, it is a sellable insurance policy.   G

It's electronic, here's a schematic of the CW-80.

GGG, Thanks for your comments.   I wanted to install TVS's on a large layout (6000+sf) and my thought was that if there was light in series with the TVS and if the TVS shorted out, it would make it easier to located a short on a large layout with a lit bulb.  From previous replies, it seems that a light in series with the TVS will prevent the TVS from operating properly.  So I am back to the drawing board to find a practical way of implementing TVSs on a large layout.

As for protecting the TIU power FETs, looks like the PSX electronic breakers may be the way to go.

Thanks,

RAD400

John

Do you know if the circuit protection in the PH180 better than Z4000? We are using Z4000s and have a lot of TIU burn outs.

RAD400

Reference to 22 ohm choke...from rad400

http://www.digikey.com/product...32-2580-2-ND/2445590

When it comes to the electrical stuff I follow GuunrunnerJohn and Stan2004 and their advise on electrical stuff. I am new at this but a fast learner. John and Stan have covered TVS, PTC and 22 ohm chokes on other threads. Their also other fine folks that also give their advise as well. 

That's a specialty item, and it not what we use for DCS filtering.  A common mode choke is used to filter EMI from a power source typically.  A common mode filter or choke has two inputs and two outputs and is effective on common mode EMI, i.e. that which appears on both lines.

I don't know that it's the source of your TIU issues, but the breakers on the Z4000 are a pretty standard thermal breaker.  They work pretty well, but they're not in the class of the electronic sensing breaker that the PH180 uses.