Question: Transformer Output vs. Accessory Power Needs

[Anonymous]

Can anybody give me any guidance on balancing transformer power outputs against accessory power requirements? I'm struggling to figure out how to determine what will work, or better yet, why what I have does not work.

I have a K-Line 120F Fixed Voltage Transformer dedicated to run lamps in 18 buildings, plus several operating accessories (MTH firehouse, carwash, fueling station). Everything works fine for a short while (5-30 minutes), then the transformer circuit breaker cuts power and it won't work again until it cools off. Same thing happens when I remove the operating accessories and just try to light the buildings.

It seems to me this must indicate excessive load. I could try trial and error to see how many buildings it could power, but this is not a very gratifying solution. So -- how can I determine what this or any other transformer can handle in terms of powering accessories?

I've tried calculating the total wattage of the accesories, in this case, 18 buildings * 2.5 watts each per bulb = 45 watts. The transformer is nominally rated at 120 watts, but I can no longer find any specs on it given K-Line's bankruptcy and the disappearance of website and tech support. Still, it seems I'm using only a fraction of its output. So why does the circuit breaker keep popping?

Many thanks in advance for any guidance y'all might be able to provide.

Bob W.
Houston, TX

[jefelectric]

Your lamp calculation look pretty good. Only things I can think of is a high resistance short circuit in the wiring somewhere or the circuit breaker is defective. Not familiar with the K-line transformer, but some of the older Lionel transformers will develope problems with the ciruit breakers tripping prematurely as they age. If you have a way to measure the current, you can determine the cause.

[Anonymous]

Some of the MTH buildings I have have more than one bulb. After the transformer heats up it looses a bit of efficency and thus the load increases and it trips the breaker. If you cut the voltage to 12 volts you will pull less amperage and prolong lightbulb life. Also the breaker on the K-line transformer is very sensitive to solenoid activated accessories. Mine will not drive 3 lionel oil rigs because it interprets the inrush current to the solenoid as an overload.
I run these types of accessories on fixed voltage transformers with appropriate fuses.
Another thing you can do is convert your building lighting to LEDs which use considerably less power.
The K-Line transformer is excellent for running trains but not so good at driving accessories for the reason explained.

Dale hz

[4kitties]

I'm with Dale hz, I bet it's heat buildup. I purchased a dedicated Lionel KW for my layout lighting and low-power accessories. Like you, I thought that a unit of this size would have more power than I would ever need. I set it up to use one of the variable outputs to run my lamps at about 12 volts. A meter reading showed the current draw to be about 5 amps, which works out to 60 watts more or less (part of the load is electronics.) All went well for about an hour, and then the breaker started cycling. I pulled the cover off and found it to be quite warm inside - too wam to keep my fingers on the transformer core. Obviously the heat was being conducted and radiated to the breaker. With the cover off the cycling problem immediately went away but since it's not safe to leave the unit open, I'm exploring ways to install a very small, computer-type cooling fan to help remove the excess heat. I think K-Line rivets their cases together though, so it wouldn't be easy for you to do the same with your transformer. Plus, any such modification would void your warranty if it is still in effect - not that our K-Line warranties are any good at the moment.

The best answer would be a ventilated, variable-output power supply with large power reserves, made just for the purpose. I don't expect any of the O gauge manufacturers to offer such a unit, but I bet there are electronics companies that do. Do any forum readers know of such a unit?

Good luck Bob,

Joel

[martinden]

Joel --

The circuit breaker on your KW is defective. It should carry 5 amps indefinitely -- for hours -- without tripping. Forget the fan and get a new circuit breaker. (BTW, early KWs had an adjustable CB, with a screw on it; if yours is one of them, just adjust it.)

[Anonymous]

Joel and martinden, thanks for the comments.

I've since switched out the K-Line 120F Power Chief for the K-Line 120 watt variable output transformer, and while there's no CB problems, I've noticed the unit gets very warm, as yours does, Joel. Does anybody know if this is just a fact of life with K-Line transformers, or have I somehow miscalculated the power needs versus the transformer output? (18 buildings * 2 bulbs each * 2 watts is only 72 watts versus the nominal output of 120).

Thanks,

Bob

[Anonymous]

Bob

Most any transformer gets warm when plugged in.You do not state the voltage you are running for the buildings. I dont know the amperage of the bulbs but 150 ma wouldnt be unreasonable. At 18 volts this would be 2.7 watts per bulb. 36 bulbs would be about 90 watts. You also mentioned other accessories you are running,some of them have lights. If you run at 12 volts you pull less perhaps 1.5 watts per bulb. A transformer should not be run at more than 80% of its rating. 80% of 120 is about 96 watts. This should not be exceeded on a continouous basis.

I use 6, 12 volt 300 watt transformers to drive my layout lighting. I run 12 circuits with 10 amp fuses,2 per transformer. 20 amps at 12 volts is 240 watts,that is the most I can pull per transformer which is 80% of its rating. If that is exceeded the fuses will blow.

Dale Hz

[lionelsoni]

A transformer draws two components of current from the power line.

One is due to the load current. It is in phase with and proportional to the load current, but smaller by the turns ratio of the transformer.

The other is the "magnetizing" current, which lags the voltage by 90 degrees. It is proportional to the magnetic flux in the transformer core, up to the point where the core "saturates". Then it takes increasingly more current to maintain the flux that the voltage waveform demands. All transformer designs are compromises between size and saturation. Small transformers, like toy-train transformers, tend to be designed to go farther into saturation than big ones, since the cost of the power wasted by the magnetizing current in pushing through the winding resistance is not important and the small transformer can (usually) get rid of a greater proportion of heat.

Because the magnetizing current increases greatly with increased line voltage, it may be that your line voltage is unusually high. It is also possible that the transformer designer just screwed up by making the transformer too small.

[waltrapp]

Thank you for this topic and thank those that contributed!

This past Christmas I used an "N" scale transfomer to power some lights that I coverted from battery power to transformer power. Worked great, for about 20 minutes. Then they would go out.

I didn't realize that a transformer "lost power" the longer that it is used. I guess that's what happened to me.

I'll be more aware, and careful, this coming Christmas that's for sure!

Thaks - walt

[Anonymous]

Bob Nelson aka lionelsonli -- thanks for the education on transformer operation. I've wondered for some time how they manage to work, and you've cleared up a number of things.

Bob W.
Houston, TX
Go Owls