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Avoiding train lava when using multiple powerpacks


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I just had a thought after seeing some more dramatic images of molten trains on facebook;


I use KATO Unitrack.


Several of my trains (mostly, but not exclusively TOMIX ones such as Shinkansens) have electric couplers and pickups in each car, and are quite long. Is there a risk of overloading or short circuiting the trains when moving from one block to another with TNOS or with two different Power Packs (e.g. with the KATO double crossover, or with just one isolated block to another)?


Only talking about analogue operation with PWM.


Would really like to avoid finding out the hard way that I shouldn't have done something and having destroyed several of my trains or turning them into lava.

All of them are equipped with lights by the way.


I was also thinking of using 2 different Power Packs on the two diverging ends of one KATO #6 switch. Not a reversing loop; really two different Power Packs attached to each of the diverging ends, without using any insulators otherwise, so that the single track can be powered by a different Power Pack depending on the orientation of the switch. Would that cause any issues?



Edited by Yavianice
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Martijn Meerts

Way back when I was doing analogue Dutch / German H0 scale, I had several loops all running on their own power pack. The loops were connected to each other by turnouts to make it possible for a train to move to any loop. The trains in this case weren't lighted or had current conducting couplers, but some of the trains were pretty long, so you did get a single loco / powered car bridging 2 power packs. This never caused any issues as long as the power packs output the same current, and were set to the same direction.


Not sure how TNOS works with regards to blocks and power packs and such, but with DCC you can have as many boosters (power packs) as you want, and there's no issue with trains going from 1 booster section to another. Of course, with DCC, boosters are generally controlled by the central station, so output is always equal on the entire layout.


If you have some old cars you're not planning on using, you could always test things. As long as they have power pickup of any sort, just take off the shell, add a light / LED strip or something else using power, and then hardwire the power pickups of multiple cars together.

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TNOS has the current and next block powered at the same level, until it reaches the final sensor, in which case both the final and previous block are powered down at the same rate. So it does seem consistent. I reached out to TOMIX with a few more related questions, and will report back when (and mostly IF) they send me an answer.

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Martijn Meerts

What's the short circuit detection like in a TNOS system? If it's well detected and cuts off power immediately, it would be very much possible to just experiment with it. Especially if you're monitoring the situation, and do a test setup with a couple of short blocks, so that should a short circuit occur and the TNOS doesn't detect it, it's easy enough to remove the train from the track manually.


Of course, it's not fail proof, most (probably all) DCC systems do have short circuit detection, but there have been instances where a short wasn't detected, and it did melt a train. This most often seems to happen on turnouts, so it might be something to do with the power to the frog in that case.

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I know with plain Jane MRC dual throttles the power coupled Shinkansens have no issues going thru a double crossover between two the two power packs. As martijn notes if similar amp throttles it shouldn’t be a problem. We use to even do it between a higher amp throttle mrc and a Kato power pack and all we got with regular motor cars was a little boost in speed when fed by both when the motor car was crossing the xover.

im kind of guessing that if there were a particular issue with the TNOS system, Tomix throttles, and power couplers Tomix would warn of it.



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The TNOS instructions are clear that blocks and sensors within them should be arranged so that when the train reaches a sensor, it is totally out of the previous block, and that when reaching the sensor causes the train to decelerate, it should have enough room to come to a total stop without reaching the next block. I think that covers it.


Rich K.

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