"spent" TVS

What does a "spent" TVS look like?

TVs devices do not need "resetting" it is good as long as the component lasts. Anyway the device is 1.5ke36ca can be purchased from Mouser for example.

www.mouser.com/ProductDetail/S...WKHmJCsiKCq6xrofg%3d

Dale H

Charlesp34

I just assumed that once the TVS prevents the damage that it needs to be replaced.  Actually "spent" is probably a stupid term to use.  It still looks the same as it did before.

Bob

Thanks Dale.

They can be destroyed without visual damage. You can measure it with an ohmmeter though. Exceeding the power rating usually shorts them out.

Pete

Thanks Pete.  Can you help an electrical novice - what reading should I look for when I hook the TVS up to an ohmmeter to tell me if the device is still working?

Bob

Given the very low price of TVS I would discard it as the most risk free solution and replace with new.

Good advice Dewey.  That's what I'll do.

Thanks

Bobby

Email me your address and I will drop a couple of TVS in a envelope and send.

Dewey,

I appreciate your offer but I have a few here.  How can I tell if the TVS is good - what reading should I get on an ohmmeter?

I don't know Bobby. A good question for gunrunnerjohn or go the the Manco website for Dale Manquen.

A TVS is simply 2 zener diodes manufactured in a single case --- cathode to cathode(- to -)   the + sides are attached across the voltage to be protected. The original TVS used 2 separate devices--- then the manufacturers figured out that they could make the 2 zeners on a single die--it's just more layers of silicon---

A TVS can fail in a number of ways, shorted, open, or simply degraded.  Obviously, shorted is easy to detect, and is the preferred failure mode, at least IMO.  Open or degraded are pretty difficult to detect, and only "out of circuit" tests typically would identify these.

I have seen pics of a few TVS units burnt in a TIU unit. Any electrical component can fail but TVS units are not more prone to failure than any other component. As John mentioned most often they fail shorted as they break down and conduct below the rated voltage. I would not loose sleep over it.

Most prone components IMO from most to least

Capacitors,connectors, transistors of all types, IC chips, diodes (not including the old selenium type which fail even with age), inductors,relays and resistors.  Resistors usually burn do to failure of other components.

Dale H

Been away for a while. As pointed out above a normal TVS would read close to infinity on an ohmmeter. One that has failed in the shorted mode would read under ten ohms. If you suspected one may be "spent" due to an abnormal incident then replace it. The only way to differenciate between a good TVS and one that is open is to apply a slowly rising voltage to the TVS while you monitor the current flowing through it and see if current flows as you approach the breakdown point. In this case between 32 and 34 volts for the recomended units.

I shorted mine out when I turned on my 500 watt homemade transformer with the throttle set to max. The power spike shorted out the TVS. Good thing they are cheap.

Pete

Can you please describe the event that you think damaged the TVS and the equipment involved?  Maybe we can understand the likelihood of damage from the scenario.

Do you have any symptoms that makes you think the TVS is bad?

Dale,

I was running my layout conventionally and had a derailment and short/spark on a switch.  In addition to the TVS the hot lead of the circuit was also fused and that fuse blew (10 amp). When I checked the circuit with a meter with the throttle off (a PW ZW) I got a reading of about 7.2 volts.  Once I removed the TVS the reading dropped to 0.0  I assumed the TVS had been "overpowered" (probably not the correct electrical term).

Bob