Multi output transformers, blocks, and new trains

[jimhaleyscomet]

Now I understand.  Thank you!

Jim H

[lionelsoni]

Hard on the transformer from the heating of the fault current, hard on a modern train from the voltage spikes, hard on any train from the fault current flowing through the locomotive or car wiring from pickup to pickup and from the arcing.

[jimhaleyscomet]

So is running a multiblock transformer hard on the train, on the transformer, or both?

Just curious. 

Jim H

[lionelsoni]

The difference between connecting different transformer outputs together and connecting together blocks controlled by rheostats from a single transformer output is that, when the train passes over or stops over the gap, it is merely shorting out the rheostat, which is just a passive resistor and completely unharmed by this.  The same is true when you use diodes for voltage dropping.  They are also passive and not harmed by shorting them out.

When you tie two outputs from the same transformer together, a fault current will flow.  It doesn't flow in the transformer common or ground at all.  Since most postwar transformers have their single circuit breaker in series with the common, the fault current can never trip the breaker.  This can damage even the ruggedest postwar transformer.  I have some type-Z transformers that attest to it.  They are burned in a distinct section in the middle of the secondary winding, the part between the roller positions of the two outputs that must have been shorted together--probably the very last time the transformers were used!

Another consideration is that, even if the short circuit across the gap is brief, it probably will produce a voltage spike when the magnetic field that it produces collapses, as with any short circuit on the output of an inductive source like a transformer.  Voltage spikes have been known to damage modern locomotives.

[chuck]

Waveform isn't an issue.  You are bridging two "seperate" power supplies.  There is no nominal circuit or any type of circuit protection while whatever is bridging the circuits is bridging the circuits other than the device doing the bridging.  So long as nothing goes wrong while this is happening, this is only a minor issue.  When something does go wrong it becoems a bigger issue/problem.  The current is going to try and get to common however it can and go through whatever it needs to do so.  Using differnt taps on a classic ZW doesn't change this, it's just as dubious.  PW trains were like Panzer tanks when it came to this type of abuse so it wasn't as much of an issue.  Modern switching power supplies and electronic circuit boards are less forgiving.

[jimhaleyscomet]

Bob wrote:

lionelsoni --> Joined on 12-27-2001 Austin, TX Posts 2,882	Re: My Christmas Layout and New Train
	I guess I'll make my standard warning here against running between blocks powered by different transformer outputs.  At least the transformers are separate, so that the circuit breakers are effective.

I can see how different transformers (especially modern ones) might have different wave forms.  Here is my question.  How is using a rheostat different from using a multitap transformer (like the old ZW) if each of the ZW's outputs have a separate circuit breaker and surge protector?  Either way doesn't the engine see the same voltage drop across the block connection?  I have a rheostat on order but was just wondering.

Jim H