Choosing the right TVS

[Konga Man]

I've read many of the posts about adding a TVS to wiring.  One that was recommended was the 1.5KE36CA.  From looking at the datasheet, the breakdown voltage is right around 36 volts.  I run older locos ('20's -30's), and I'm using a type R transformer (because it goes to 24V).

In light of that higher output, would I need to choose a different TVS with a higher breakdown voltage (e.g. 1.5KE43A)?

Also, can I just install this by wrapping the leads around the terminals on the back of the transformers?

On a related matter, how would one determine the rating for an added inline breaker on a circuit?  I have no idea what the current draw might be for one of these locos, or for a train with 5-6 lit cars.

Thanks.

[lionelsoni]

The peak voltage is the RMS voltage (24 in your case) multiplied by the square-root of 2.  This is 34 volts, still under 36 volts.  However, there is virtually no risk in going to a slightly higher rating and you eliminate any worry about the tolerance of the part; so go for it.

However, be sure you have the correct part number.  I notice that your example is the 1.5KE43A.  That is a unidirectional TVS, which is useless for an AC circuit and which your transformer will probably destroy immediately.  The "C" in the part number is essential, to get a bidirectional TVS.  So "1.5DE43CA".

Yes, the back of the transformer should work fine.

It is hard to estimate the electrical load of a train.  But I usually go with 5 amperes.  You should be able to find breakers with 5-ampere and 7-ampere ratings.

[Konga Man]

lionelsoni

However, be sure you have the correct part number.  I notice that your example is the 1.5KE43A.  That is a unidirectional TVS, which is useless for an AC circuit and which your transformer will probably destroy immediately.  The "C" in the part number is essential, to get a bidirectional TVS.  So "1.5DE43CA".

Ya know, I knew that. ;)  Crucial typo, that was.

Thanks for the clarification.