Electric RR and PTC Resettable Fuses

The best resettable fuse I know is the PSX-1AC. I don't have experience with the PTC fuses, but do know that they do not interrupt the current completely. There is still some leakage current. Also I think there is some reset time...they have to cool down. I don't think the interactive operation of the train layout is the ideal place to use them.

Hi CJACK

Thanks for the reply. I was thinking of install them in the engine as not to damage the Electric Rail Road electronics and the engine in the event of derailment or short.

Yes. Probably would not hurt, but they do have to heat up and only protect in case of a short in the engine. I think a TVS would be good in the engine. Electronics is harmed by voltage spikes more than shorts inside the engine.

Thanks CJACK.

The PTC with an ERR install is totally different than using the PSX-AC for circuit protection of the track power, and they serve two different purposes.

When I install the ERR Cruise Commander Lite, I use a 1.1A hold PTC in series with the motor to protect the board in case of a motor stall.  It doesn't affect the normal operation, but if you stall, it will keep the excessive current from toasting the output FET motor drivers.

I also use a PTC when I run track power between an engine and the tender to protect the wiring in case of a derailment.  I put it in series with the connection between the two.  If the engine or tender derail and a roller lands on an outside rail, sometimes it'll cook the wire before the breaker trips.  This also works well for passenger cars between the pickups.

I've roasted a wire with rollers on outside rails, how fast is that PTC, faster than a wire covering getting hot? Just wondering, no experience with them.

Yes, it does a nice job protecting the wire.  Rated properly, it'll open far faster than a wire will get hot enough to melt insulation.  For passenger cars, all of my installations have LED's, so I use a much lower rated one at around 250ma trip.  No reason to need more, that's way more than all the lighting draws.

I've done a lot of work with PTC fuses. In general, they are not fast, but I would say they are comparable to a "slo-blo" automotive fuse. There are a lot of types and a lot of curves, I generally use the Littelfuse ones. Detailed curves and specs on their web site. Curves vary with voltage rating.

In my opinion they are fine for protecting conductors, or something like a solenoid or transformer or motor where I2T is what counts. I usually size them pretty small, there is a lot of space between the trip point and the hold point, and you can run them at or a little above the hold point without trouble.

Now, what you get with "no-name" products is a different topic completely, but most of my ebay purchases have included traceable manufacturers markings.

FWIW, I use a .5A hold, 1A trip PTC fuse in series with the feed to my Fastrack uncouplers, to protect against "stuck buttons." This gives me pretty much full current for about 5 seconds, tapering to a very low value about 1 second after that. Uncoupler draws about 1.8A, if I recall correctly.

I buy all my PTC products from Digikey from brand name manufacturers.

While reading here I was thinking it might be nice to have a list of PTC's and their recommended sizes for different uses around our layouts and in our trains. I would be happy to make/maintain a list and maybe even post it to one of the saved document threads like there are for TMCC, DCS, etc. 

So far we have:

1.1A hold, ??? trip for ERR Cruise Commander Lite (GRJ)

??? hold, 250mA trip for passenger car LED lighting (GRJ)

0.5A hold, 1A trip for Fastrack Uncoupler tracks drawing about 1.8A (other brands may have similar requirements?) (PLCPROF)

Anyone have others/more to add? And do I have it correct here? Did I miss any so far? Is this a dumb idea?

Actually it's a great idea for a sticky of lists of commonly asked questions on TVS, PTCs and maybe some other devices used on layouts.

Thanks one all for the suggestions and comments.

John for a AC/DC Commander kits which are marked DC 7.0 which PTC would you install?

I haven't used the PTC with those, the drivers are pretty robust and will take a lot of abuse.

cjack posted:

Actually it's a great idea for a sticky of lists of commonly asked questions on TVS, PTCs and maybe some other devices used on layouts.

I have some good part numbers from previous threads on TVS and I can add those too. If anyone else has anything to add please do. And thanks for any more info anyone else can add.

 My email is in my profile, might be better for suggestions so we don't hijack this thread.

Dear John

Thanks for the clarification. It was nice to meet you and thanks again for all yor help.

Dear rtr

Go ahead and post them here.

Thanks, Kris.  Your posts always get me to thinking more about these things.

Doesn't look like there is much to add or much further interest though? Here's an update with the TVS info I have. I tried to give proper credit for each item. If I picked the PTC part numbers I would probably get them wrong so any help with selecting the correct PTC part numbers would be much appreciated.

The updated list so far:

PTC resettable Fuse - 1.1A hold, ??? trip for ERR Cruise Commander Lite (GRJ)

PTC resettable Fuse - ??? hold, 250mA trip for passenger car LED lighting (GRJ)

PTC resettable Fuse - 0.5A hold, 1A trip for Fastrack Uncoupler tracks drawing about 1.8A (other brands may have similar requirements?) (PLCPROF)

TVS Conventional - Digi-Key Part Number 1.5KE36CALFCT-ND - 1.5KE36CA - 36 volt, bi-directional - Sized for a PWZW when the whistle button is depressed. This peaks over 33 volts if the compensation winding is considered. (Part number recommended by many, explanation by Dale H)  (Digi-Key part numbers from GRJ) 

TVS Command Control - Digi-Key Part Number 1.5KE33CALFCT-ND - 1.5KE33CA - 33 volt, bi-directional - Sized for the modern 18 volt bricks. The 18 volts peaks a bit over 25 volts. (HiRailers Unlimited & Independent HiRailers Group, explanation by Dale H) (Digi-Key part numbers derived from GRJ's above for 33 volt version)

For the TVS I believe the 1.5KE36CA is most recommended here on the forum and also the most widely used as it seems it would be suitable for either the modern bricks or the transformers with whistle buttons.  

All corrections and/or additions welcome.

RTR12,

  Making a listing of these for all to access is a great Idea!  Kudos to you, sir......

And thanks to all for your great input from the rest of us.... a big help, indeed !

Jesse    TCA

Gentlemen

I am always in favor of advancing our hobby.  I also am in favor of a health and respectful debate of the issues as well.

Thanks rtr12 what until you see my next two questions.

Corrections below.

rtr12 posted:

PTC resettable Fuse - 1.1A hold, ??? trip for ERR Cruise Commander Lite (GRJ)

I checked what I ended up with, and I'll make a correction.  I am using 750ma hold, 1.5A trip models, Digikey: MF-R075-0-99-ND.  These go in one of the motor leads, I'm trying to protect the drivers from a stalled motor.  I only use these for the Cruise Commander Lite.

PTC resettable Fuse - ??? hold, 250mA trip for passenger car LED lighting (GRJ)

I never really worried about the hold specification, as long as the trip is around 250ma, the hold takes care of itself for LED passenger car lighting applications.  I'm actually using this Digikey part: 490-4808-1-ND

 ... snip ...

All corrections and/or additions welcome.