TVS and Fast Acting Circuit Breaker help

For those who have never "seen" a TVSS operate, here is a screen shot of an oscilloscope trace of our standard OGR TVSS. Green trace is applied voltage, yellow

trace shows the effect of the TVSS, limiting voltage to about the peak value of a 20 VRMS voltage.

This was done with an isolated variac and a 1k resistor in series with the TVSS.

I turned up the supply voltage and let it run until the TVSS would boil water but it kept working just fine.

Just for giggles.

Nice picture, shows the operation well.

@PLCProf posted:

For those who have never "seen" a TVSS operate, here is a screen shot of an oscilloscope trace of our standard OGR TVSS. Green trace is applied voltage, yellow

trace shows the effect of the TVSS, limiting voltage to about the peak value of a 20 VRMS voltage.

This was done with an isolated variac and a 1k resistor in series with the TVSS.

I turned up the supply voltage and let it run until the TVSS would boil water but it kept working just fine.

Just for giggles.

You like your Rigol O scope?   Looking for an inexpensive one for my vintage audio repair hobby.

Gunrunner,

I am very sorry, but as usual, I am confused.  I want to install a 5 amp TVS.

You mentioned above that,  "The TVS goes right across the track feed from hot to common"

This sounds like I connect one side of the TVS to the hot wire, and the other side of the TVS to the common wire.   But, can that be right?

Or, do I install one TVS directly in the hot wire, and another TVS directly in the common wire?

And, if this is installed, do I also need a separate pop-up or glass tube breaker in the system?

Thanks,

By the way, I went to the TVS link you posted above, and when I clicked on the product description it said "Manufacturer's lead time 18 weeks!"

Mannyrock

@Mannyrock posted:

Gunrunner,

I am very sorry, but as usual, I am confused.  I want to install a 5 amp TVS.

You mentioned above that,  "The TVS goes right across the track feed from hot to common"

This sounds like I connect one side of the TVS to the hot wire, and the other side of the TVS to the common wire.   But, can that be right?

Or, do I install one TVS directly in the hot wire, and another TVS directly in the common wire?

And, if this is installed, do I also need a separate pop-up or glass tube breaker in the system?

Thanks,

By the way, I went to the TVS link you posted above, and when I clicked on the product description it said "Manufacturer's lead time 18 weeks!"

Mannyrock

It seems than you may be mixing up the Airpax breakers and TVS diodes.  They are both currently available from the following links:

Airpax Instant Breaker 5 Amp   PP11-0-5.00A-OB-V   https://www.onlinecomponents.c...00aobv-10090638.html

TVS diode 1500W 33.3V TVS at Digikey

The breaker is wired in series (inline) with the Hot feed from the transformer output.

The TVS diode is wired in parallel with (across) the hot and common.

@Mannyrock posted:

By the way, I went to the TVS link you posted above, and when I clicked on the product description it said "Manufacturer's lead time 18 weeks!"

What about the 25,000 they have in stock? Did you need more than that?

Manny,

In order for the TVS to clamp voltage transients it has to act like a short-circuit -- but only when the voltage amplitude  of these transients exceeds the specified voltage of the TVS.  For this reason you wire it across hot and common.

(It's seems odd because you wouldn't normally do that with a wire, or a resistor, or most other components because doing so with them would create a definite short circuit -- but the TVS is a special kind of short-circuit, to higher-voltage transients only, so it's fine.)

Mike

Thanks for all of this clarification.

And Gunrunner, you got me again!  " (24,920 in stock)"

Mannyrock

There are many ways to do it, but I use these intermediary black terminal blocks to connect my power feeds from the transformer distribution block to the track at each power drop.  The blocks are screwed to the underside of the layout at each drop location. 14 gauge wire from distribution block to one side of the black terminal block and then 16 gauge feeder wires from the block to the track.

You can also see that there is a TVS soldered across the hot/common on each terminal block.

I got the blocks and TVS from Del City.

@Mellow Hudson Mike posted:

Manny,

In order for the TVS to clamp voltage transients it has to act like a short-circuit -- but only when the voltage amplitude  of these transients exceeds the specified voltage of the TVS.  For this reason you wire it across hot and common.

(It's seems odd because you wouldn't normally do that with a wire, or a resistor, or most other components because doing so with them would create a definite short circuit -- but the TVS is a special kind of short-circuit, to higher-voltage transients only, so it's fine.)

Mike

Mike, the TVS diode is a zener diode.  If working correctly, it will clamp (partially conduct) some of the voltage across it, while the remaining voltage across it would not be higher than its rating, which in this case would be 33.3V for the duration of the Spiking current flow.

Thanks Richie,

So, when these things "blow" ,  how do they cut-off the power flow from the power lines to the track?

Or, do you use them in conjunction with a standard breaker, and they only cause the breaker to trip more quickly?

Mannyrock

The Instant breaker trips quickly regardless of whether the TVS diodes are present or not.  Unless they fail, the TVS diodes don't blow (open) they partially conduct to help absorb part of the shock wave (Transient Voltage).  It might help to think of the TVS sort of like a shock absorber, kinda.  They may eventually wear out, but are designed to be re-usable.

TVS protection diodes have several failure modes.  The most common one is shorted, you'll know right away if you have that failure!

Less common is an open failure, there is no way you'll know if that happens without an out-of-circuit test.  Finally, in a few cases, the specifications simply degrade and the clamping voltage increases or decreases out of spec.

All of these failures are uncommon, in a normal situation a TVS diode will last many years.

Steve,

Yes.  One way to think of a TVS is that it's a resistor whose resistance depends on the amplitude of the voltage that appears across it.  At voltages below its rated clamp voltage it looks like a high resistance, thus it's not much of a short circuit.  At voltages above it automatically turns into a low resistance, which is a big short circuit -- only to the transients.  (Unless of course you somehow you're able to turn your transformer throttle up to exceed the clamp voltage.  Then the TVS is not only a short to transients its also a direct short to your transformer -- you'll get magic smoke from the TVS).

Mike

Mike, I mostly agree with what you're saying.  I was trying to point out that (unless is fails in a shorted state) it doesn't technically short, but instead briefly lowers its resistance , (like you mentioned) so that the voltage across the diode (voltage remaining on the tracks) is limited to the 33V clamping voltage.

I'm also wondering about the likelihood of a 20V transformer protected by an Instant breaker being able to smoke a 1500Watt TVS diode.  Was this just a hypothetical derailment scenario for a transformer with an output voltage higher than 20volts and a slow breaker, or have you experienced this with a 20V transformer and an Instant breaker?

Steve,

Not with an instant breaker.  Only with a traditional slow-acting breaker or fuse AND a voltage above the TVS's clamp voltage.  The farther above the worse it is.

My understanding is that 1500 Watts is inferred from the energy dissipation occurring when voltage spikes (which are narrow and tall voltage excursions) are clamped.  This can be quite different from wide and short (although still above the clamp voltage) voltage excursions.  These are not "spikes".  They are instead extended applications of overvoltage.

Handling 1500 W over very short periods is much easier than the same power over longer ones.  The heat generated in the first situation finds its way out of the device before its temperature rises to the point of damage.  In the second it builds up without escaping quickly.

Mike

Correct, the 1500 watts is an instantaneous rating, obviously the tiny package can't handle 1500 watts for more than a microseconds!  A continuous overload above the TVS device rated breakdown will pretty quickly destroy it.

Mike and John, thank you for the clarifications on the short vs. long overload time  - power handling capabilities of this diode.  In looking at the 1.5KE Series Datasheet, what you're saying is detailed.  Thanks for prompting me to read it.

This information, reinforces the benefit to using these TVS diodes in conjunction with "Instant" breakers to improve the diode's longevity, among other reasons already mentioned.

Agreed.

I found this topic today and want to buy some TVS diodes.  I went to this link (as above) and none are in stock:  TVS diode 1500W 33.3V TVS at Digikey

Does anyone know of a suitable replacement, perhaps from another source?

Mouser has these and these.

Got it.  Thanks!

Great information.  

Thank you all for the great lessons !!!