Kato S power pack melts down, Kokis everywhere

[Sheffie]

I think I would have preferred it if the unit had just caught fire.

 

What happened was, I had finished running my Kato EF510-500 and the 15 assorted Kokis and containers that it regularly pulls. I reversed the power on the mainline power controller and flicked the switch on the control panel to turn the train off the mainline and into the goods yard. I was distracted by a four-year-old and a wife who was having a loud facetime conversation with her mother about the inadvisability of getting a manicure given the current public health situation. So the first clue I had that anything was amiss was the freight train coming to a sudden halt. I quickly realized what had happened: the locomotive had reached the insulated uni-joiners separating the goods yard from the mainline loop, and had got into an impossible situation since the mainline power supply was in reverse and the goods branch supply was still in forwards, where it had been ever since the train left the yard. 

 

So.

 

I flipped the directional switch on my old 'S' class power pack from forwards to stop.

 

From stop to reverse.

 

Without touching the speed setting.

 

Some unique aspect of these circumstances was enough to cause the 'S' class power pack to fail. When I say "fail", I mean that, instead of supplying a voltage at a user-controlled point between 0 and 12V (nominal, slightly more since this is a Japanese unit plugged into an American house), it started putting out MAXIMUM POWER. My freight train, having essentially zero inertia compared to its prototype, rapidly achieved maximum speed. Upon hearing this, and seeing this, I reacted by cranking the throttle down to zero. Unfortunately, I was not yet aware of the failure of the supply, and by the time I'd realized that the train really was not slowing down at all, several wagons had left the track, and, indeed, the table.

 

In the end, the damage was really very slight. Two of the newer-spec Koki 104's fell to the hardwood floor, scattering their containers in the process, but appear not to have sustained any damage, beyond one handrail becoming unseated. A further two Koki 104's and a Koki 250000 collected on the outside of the R249 curve behind my engine shed, without losing any containers. All brake wheels are accounted for.

 

My most solid locomotive stayed on the tracks, despite the adjacent wagon leaving the table.. Truly, the EF510 is the honey badger of freight locos.

 

As to the power supply... meh. There was an acrid stink noticeable shortly after the accident, and the unit remains in a purely digital state. It will supply +/- 100% power and nothing else. Having opened it up and looked inside, I don't think I will be able to fix it. Certainly the potentiometer that is the basis of the control is fully functional, within the limits of my ability to test it. I wasn't able to work out exactly how the circuit works, but it seems to be using a large transistor as (perhaps) an amplifier. I presume that the transistor is burned out in such a way that current now simply flows through it without regulation.

 

This is, essentially, the excuse I need to by a third 'SX' controller designed for the American market. I've bagged up the old one, but I'm not sure I will ever come back to it.

 

What's your take-away? It's a data point to be aware of when weighing up whether those fancy gold plated commemorative 'S' supplies are a good buy.

Edited March 21, 2020 by Sheffie

[Kiha66]

It sounds like you burned out the transistors on the throttle.  Its unfortunate, but it can happen.  Transistors abused in this way usually fail in the open state.  Unfortunately reverse voltage protection usually adds quite a bit to the cost of the throttle, so its pretty rare to see it on basic DC power packs.

 

The same thing happens if you short the motor side of a DCC decoder to track power.  I've certainly accidentally done that myself more than once!

[brill27mcb]

Sorry to hear about this. A very unusual failure!

 

The S throttle is nothing more than the most basic DC power supply: the AC transformer reduces the commercial voltage and feeds it to a bridge rectifier that creates full-wave, unfiltered DC, in this case a nominal 15 V DC. The voltage of that is then regulated by the potentiometer and the amplifying transistor from 0 to 15 V DC. It's a very basic electronic design with no sophisticated pulses, spikes, square-waves of such things. That's why I like it.

 

The Kato S power pack with the English writing is in fact made for the export market. It's the same inside the blue box as the version with the Japanese writing, but comes with a differently-lettered metal plate on top and a different wall transformer for proper voltage reduction in 120 V AC (and maybe 220 V AC) markets.

 

The newer Kato SX has a lot more complication, as does any pack with "constant lighting" or pulse-width modulation (PWM). With the growing sophistication of electronics inside model locomotives, these can cause unexpected problems. I discovered, by accicent, the following: I was running an ordinary Kato/Lemke tram/trailer pair, and while it was running I added a newer Hornby/Arnold DC Duewag-prototype tram on the same track. Normally, with the limited power capabilities of an N transformer, I would expect the Kato tram to slow down slightly when the second tram was added. Instead, it sped up dramatically! I don't understand it, but I could rock the Hornby/Arnold tram off and on one of the two rails and the Kato tram would go back to normal speed, then speed up, and so on. I can't explain why this happens, but that's when I decided to switch from PWM and constant lighting (Tomix) to the "plain vanilla" Kato S. I now have too many trams and trains that are made with complicated circuit boards, DCC provisions, factory-installed DCC, and/or coreless motors with which a power pack with sophisticated features might interact badly and possibly damage. So I have gone back to basics (except with our club layout and my Tomix TNOS setups). By the way, there is an issue with some "pulse" power packs frying DCC circuitry in N scale locomotives, if the pulses they produce exceed 18 or 25 volts. The old Troller and the MRC 1300-series power packs are specifically mentioned.

 

With your failure, I am also surprised that the red circuit breaker button didn't pop open.

 

That said, I wouldn't buy the gold Kato S power pack, either. But maybe, because it is so "collectible," people will not actually use it. (After all, wouldn't want fingerprints to deface that gold finish! Better to keep it in a sealed display case, maybe behind a velvet pull curtain.  🙂 )

 

Rich K.