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I am confused about how much power the Z-4000 is capable of providing, as well as the circuit breaker protection.

The following occurs in two separate Z-4000 transformers - with each handle hooked up to a separate terminal strip that in turn feeds groups of O-scale buildings. When each handle is cranked up to produce ~ 11-12 volts and 4-5 amps, the building lights that the handle is powering pulse - normal brightness to less bright with a frequency of 1-2 seconds each - annoying behavior to say the least. If I lower the handle to about 10 volts and 3-4 amps, the lights will stay steady (but some flashing signs need 12 volts, thus I need to figure out what's going on). Note: accessory terminals are not being used.

I was under the impression that each throttle of a Z-4000 had a 10-amp circuit breaker, and therefore each handle could go up to 10 amps. However, based on this pulsing, I am thinking the entire transformer is rated at 10 amps - because as I approach 9-10 amps (total amps from both sides of the transformer) the unit is reaching capacity and this pulsing is some sort of maxed out behavior.

Or, what could be causing this?

Note: I have short length (3 ft) 16 gauge wire from transformer terminals to terminal strip - and building wires (around 22 gauge) that vary in length from 1 to 4 feet connected to terminal strip.



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 You're not exceeding the power. What you are experiencing is the transformer oscillating about it's set point. This instability varies with the load and setting. If the accessories output is appropriate for what you need it may be more stable. I've had the same issue with the CW80. It's most noticeable with lamp that vary brightness with a small voltage variation.

It's a common design goal to prevent oscillating but not always easy to accomplish.

It's remotely possible that there is some adjustment on the inside circuit board to reduce the feedback loop gain of the regulator. I doubt it, but one can hope. I think also that a lamp load which takes a finite time to warm up and increase it's resistance can lead to instability also because it then reduces the current slightly which cools off the lamp and causes the current to increase get the picture. It might also help if you put some outboard resistance in series with the bulbs to decrease the effect and allow you to operate at a different (higher) voltage.

Thanks for the replies.

Chuck, how would I install outboard resistance? I don't know what this is?

John, I recently tried calling MTH service on another matter and was on hold for 20 minutes...gave up. They don't answer e-mails either. Very poor service.

Bobby, I doubt there's any wires crossed...since its happening on 4 different circuits.

Well that's just a thought if you had some various values of resistors to try in your parts box. The resistor value would be on the order of one ohm at say 10 watts if you are drawing 4 or 5 amps. The resistor would be in series with the lamp load. Like transformer A terminal to the resistor, the other end of the resistor to the lamp, the other end (common terminal) of the lamp to the U terminal.

What accessory voltages are available and did you try them?

Arthur P. Bloom posted:

Since lamps are basically resistors, adding more resistance to the supply legs will do nothing helpful.

Your best solution is to use a plain old transformer, one that doe not have wonky bits inside.  I use a few ZW's for all my fixed A-C supplies, and a telephone company D-C supply for relays and signalling.


My thought was just to change the operating voltage to one that is stable and still have the desired illumination.

However, a different non-electronically controlled transformer will of course work, but that wasn't the question.

Last edited by cjack

Well, it's Deja vu time and I am just seeing the latest replies to this thread that I had started 4 years ago!

FWIW: I had solved the problem by adding more transformers and distributing the load to each, however I am in the same situation yet again. I suppose its my own fault, as I continue to add buildings with lights here and there around the layout thinking that one or two won't exceed limits, silly and hopeful me (think of the father in A Christmas Story where he has myriad Christmas lights plugged in the wall outlet). The amperage output per Z-4000 "handle" or side is between 5-6 amps, and given that I have two Z-4000s just for accessories/buildings that totals about 11-12 amps per transformer, which isn't good apparently. I guess I should've bought a couple of ZWs a while back when I had the chance, but at that time was broke. I will likely need to add yet another transformer just for accessory lighting! It is getting monotonous but building a fantasy world knows no bounds.

Last edited by Paul Kallus

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