TVS from Scott's

Dale Manquen,who I consider an expert on electronics,evaluated the unit as I remember and said it offered inadequate protection from voltage spikes even compared to a 50 cent TVS. Perhaps he changed his opinion but I did not read about it here if he did.

Dale H

Bob:

Yes, there is a complete set of installation instructions with the unit along with a fuse block and the necessary hook-up hardware.

Dale:

Dale M had reviewed the earlier model quite a while ago. That first model was replaced with the new TVS model that Dale M said was fine.

Neil

Taylor

you may wish to ask Scott what you can expect from the unit relative to safety. Your layout sounds large, power wise. You should be sure it will serve your needs. 

When I looked into them, I found that they were 'bashed' from units used in the home security application. They are very low amp/volt tolerant. You may be putting more amp/volt than it can secure.

There is the added thought that installing multiple TVS units that Dale H describes, 85 cents per I think, at multiple spots around your layout might be an added security measure you should consider. 

Ralph

Ralph:

How long ago did you look at them and were they the TVS model?

Here's an excerpt from an email by Scott of Oct 11,2012...

Dale Manquen had complained about our previous product, the DTK-2 and DTK-4 (a product that was made for us by a 3^rd party).  However, when we came out with the TVS-4 he wrote us a nice email and endorsed the product.  Maybe he is thinking of the old one… 

Neil

I think the anemic TVS protection was upgraded in the new product to the 1500 watt units we generally recommend.

gunnerjohn,is this the same tvs we was talking about on a different thread for surg protecter to put on the hot side of the transformer to track.. and on the pickup rollers on our train?  does dig key carry s them?

Yes and Yes.  Both Digikey and Mouser have them.

I only evaluated the original unit (which I found inappropriate), and I don't recall ever seeing or endorsing any of Scott's subsequent TVS products. Perhaps Scott could refresh my memory if there is an email to the contrary.

If he would like to send me one of his latest units, I would be happy to examine it and render an opinion.

GTW- This may have a newer version of a TVS componenent, but it is still the same home security type device. Note that the wire diagram shows that a ground goes into the outlet's connection screw. Home security systems most times connect this way. 

Not my cup of tea. Gentleman on another forum - mr electronics - advised me against anything that needs go to a power outlet this way and led me to the TVS solution I describe later.

Note that the TVS should be close to the place where the spike would occur. Some suggest putting the TVS into a loco for full protection.  INHO, there should be multiple TVS located, one each, at each feeder drop from the power bus. At $50 a pop vs 85 cents Scotts is pricey Plus complex with its wiring requirements.

Currently, I run conventional - until I work out Legacy connection issues. The TVS at each feeder drop and glass break fuses has worked well for me. Where this Scott's device fits in with the TMCC environment Taylor has should be understood. The diagram omits the data and comm serial cable. The power - amp/volt - needs that drive his TPC and other boxes should be examined or they may stop blinking - this serial data comm signal is a mystery and gets mor foggy when Legacy gets there, if Taylor plans that upgrade.

In any event, different strokes for different folks.

Ralph

Just looked up the hookup after reading The above post. I would not use anything that hooks up to the house electrical ground,shown this link

www.scottsodds-n-ends.com/wiring_diagrams.htm

Really not needed for suppressing spikes generated off a transformer secondary IMO.

Dale H

That's the same connection as you get with the ground plug on a 3-wire plug.  Every power strip that claims to provide surge protection connects to that ground.

John

That is for surges primary input surges on the 120 VAC line. How is it needed for spikes generated off the secondary?

Dale H

Good point Dale, I have no idea what he's doing with it.  Perhaps a good question for them.

This was my original beef with Scott's products.  I even had a conference call with Scott's supplier and Scott, but it was obvious that the supplier was a manufacturer of products for data line protection where a ground is a proper reference into which a surge can be dumped.  We don't want to reference our secondary power wiring to ground.

If you don't use the ground, at least on his old products you just wound up with two TVS units in series across each output pair.  This means that it does nothing until a spike reaches more than 60 volts.  Who wants that?

Dale:

Would you be interested in doing another evaluation of the current model TVS-4? Please let me know and I'll send you one.

Thank you.

Neil 

Neil, yes I would.  That will clarify everything.

My address is in Contact at www.trainfacts.com .

Do you need a TVS if yrun run the power and common through a circuit breaker and then to the track.

Yes.  The circuit breaker only protects the wiring and transformer source from damage due to overcurrent.  If the circuit breaker (or fuse) "pops" due to a short such as a derailment, the interruption of the large surge current will create a voltage spike that can damage electronic components.  The TVS (on the Track side of the breaker) will clamp the spike to about 40 volts maximum.

Dale:

Thanks

Neil, I received the sample of Scott's unit today, and I took a quick look inside.  It still has the totally inappropriate fantasy that there is some kind of "ground" that is in the middle of the swing of the two power wires - Track and Common.  In other words, there are two TVS units in series connected between each channel's Track and Common pins.

I measured the TVS characteristics at DC:

1mA @ 17.5V

5mA @ 17.7V

10mA @ 17.8V

20mA @ 18.0V

40mA @ 18.4V

70mA @ 18.7V

100mA @ 19.2V

I also tried setting the voltage at 19.1V to test all 8 TVS units in turn.  When I applied 19.1V, I got a ramp of current that started at about 160 mA and dropped to 100 mA in about 5 seconds.  There is significant heating in the devices at this power level, and perhaps that is causing the change.

I have not yet determined the size/power of the surface mount TVS units.  We use 1500W devices for the leaded version, which means these would need to be at least 750W devices to give a similar capacity.  Does anyone have the "code book" for translating surface mount markings - MCC  BM ?

I am worried that this scheme cross-connects all of the power channels together via the shared ground bus.

I designed the TVS4. I was asked to post a reply to this post to help clarify any questions regarding its' intended operation. The TVS4 in question does use 600W Transorbs. There are two 15V devices in series across each AC wire pair. 15V only means that they begin to conduct at that voltage (1mA of current @ 15V). The "hard clamp" vlotage is different for each manufacturer, but most 15V devices “hard clamp” around 25V. There are two devices in series accross each AC wire pair. I have tested the circuit boards to 20A with no measurable heat detected. I don't know if systems need more than that, but the quick connects are rated at 20A and those are the limiting factor of the TVS4 device. I suspect that is conservative and they will handle more. I guess the next limiting factor would be the wiring you use. The transients that this is meant to clamp come from inductive loads such as solenoids that might make something in your layout move. Yes, the closer to the solenoid the TVS device is, the better the protection, but not having one will allow these transients to dissipate their energy in whatever device they can, including circuitry connected to the lines. A transorb with the proper value anywhere in the circuit will help and probably protect sensitive components. Regarding the common connection, I don’t recommend using it. It was on the original and I was asked to supply it on the TVS4. It was meant to be tied to earth ground (the third prong in many outlets). The problem with it is that the earth ground this tab is meant to connect to, is supposed to be tied to AC neutral somewhere in the building. If it is, there is a short (through wires) between this earth ground and the AC neutral connected to the wall plug your transformer is plugged in to. If this is connected to the transformer secondary you may create an auto transformer in your system. That, in itself, may not cause a problem. I have heard of people connecting the secondary of the transformer to AC neutral from the wall. If they do that, and the earth ground tab is connected, they may effectively short out one of the two transorbs in series in the unit making it a 15V unit, not a 30V unit. When they apply power, they let the spoke out of the remaining transorb in the circuit and I get it back. If you have electronics connected the the AC power in your layout, it is a good idea to have TVS devices across the AC to protect any solid state devices that might be vulnerable to voltage transients. The TVS4 was designed to achieve the transient protection these low voltage systems should have.

If an earth ground wire is attached to the TVS-4, aside from the cross-coupling and safety grounding issues, half of the TVS units would be connected directly across the Track signal output of the TMCC/Legacy Base (which is between earth ground and track Common.)  This would not be a problem when the TVS is not clamping, but it could do strange thing when it starts to clamp.

I'm not really a train guy, so I'm not familliar with the details of the controllers. I would just not recommend connecting the secondary of the transformer isolated system back to the input because you cannot be sure of what will happen with all of the devices in the layout. I would not connect the common of the TVS4.

JCM II, thanks for coming in to discuss the product, I suspect it'll help us understand the design and why decisions were made.

I agree with Dale on the ground terminal point.  If you connect that ground lead, once a transient is experienced, it could result in a greater amplitude pulse getting to the very item we're trying to protect.  Since both the track connections are floating for TMCC for sure, the ground doesn't seem to serve a function.

A dumb question, why connect the commons together in the middle?  I'm concerned this may cause issues with some of the control systems, though in my brief tests here, I didn't see any significant signal changes.

If you were to eliminate the ground, I'd probably like to see simply a single 1500 watt TVS across each input/output pair with no common connection of any kind between them.

As I have stated in my previous posts I would not connect the common to earth ground. This was designed about 5, or so, years ago. It was designed because the device Scott had been buying to resell was going up in price and was getting close to rediculous in price (and he wanted to make something). It was apparent that it could be made for this application for less than he was going to have to pay. At the time, Scott simply showed me the device he was purchasing from another manufacturer that was damaged. I took it appart and checked out the guts. It had two terminal blocks and 8 sidactors all connected to a common that was typically connected to earth ground. I didn't particularly like the idea, but he had been selling them and they weren't being damaged and were apparently working to the degree they could (Sidactors aren't as good of a TVS device for this application as transorbs). I didn't know much about the train system wiring (I still really don't) and Scott suggested that we hook up the new circuit the same as the one that he had. So I did. The only problems I have actually seen from this connection is when someone connects the common to earth ground and then connects one of the track lines to AC neutral. That's a problem. Otherwise I haven't seen any issues with the common connection in the box. If I make more PCBs I may change the layout to remove the common connection. I the mean time, as long as the common connection is left unconnected, things seem to work out OK. The earth ground connection by itself seems to not cause problems, but I don't think it improves performance either, so I wouldn't connect it.

If you're going to change the circuit board, I suggest eliminating any connection between the four circuits and just applying the protection to the individual circuit.  There is no upside to having that common path, and I can think of several downsides, as mentioned previously.  I'd be very happy to see a simple circuit that just ties a 1500 watt TVS across each through circuit with no connection of any kind between adjacent circuits.

Scott's previous version was designed, built and tested by a company that serves the telco and modem industry.  For their telco lines, earth ground is a good reference.  I talked with and even sent a sketch to the person I talked with at the manufacturer, trying to explain that we are dealing with a floating secondary that has no inherent ground reference, but the message never got across.  They "knew better" and convinced Scott that what they were doing was best.

I wish that point had been corrected on your version.  I would like to compliment you on a nice neat design.

Here is the schematic.  The other file is the explanation.

The system schematic makes sense. Kinda what I expected. The TVS 4 should protect these systems fine with no connection to the earth ground. While the suggestion about isolating the channels is valid, think about it. With the current design, it doesn't matter which quick connects you use for protection as long as the input wire is across from the output wire. Anyway, isolating the channels is simpler to follow.

It sounds like we're all on the same page at this point, right?

I am not an engineer but have a question.  Is the Scotts unit better or worse than simply using the 1.5ke36ca transorb as far as protection from voltage spikes?

Dale H

The suggested transorb isn't a bad choice. It would be easiest to use through hole and one per transformer output. and make sure to get the CA on the end.

The Scott's unit is basically the same protection as the TVS on the output, it's just in a convenient package with connectors and included fuse blocks.

Thanks all for the explanation. Since the TVS is cheaper and offers equal protection I will stick with them. What had me puzzled was the wire for the house electrical ground. Did not make sense to me and also brought up safety concerns. 

Dale H

As it turns out Dale, that wire doesn't make much sense, so your instincts were sound.

Thank you all for your research and input regarding the TVS-4. I appreciate your efforts and comments.

Sincerely,

Neil Knopf

Train Electrics, LLC

Not being all that familiar with electricity should the TVS be connected to the ground at the outlet says shown in the instructions

From what the  electrical engineers said, NO.

Dale H

Best place to get the quality  TVS, that is needed?  I am fused protected everywhere !!

need to do this neccessary item!

thanks