Driving with several transformers, Herbert's Railway-Site

MÄRKLIN H0 conventional driving and electromechanical automatisation

A5: Driving with several transformers -
Danger from incorrect connection

ATTENTION: Safety relevant topic !!!

Driving with only one transformer soon shows its limits.

A second track, a second train, a second transformer are needed.

If a connecting track is created between the two lines and the transformers are incorrectly connected, dangerous voltages can occur.

We don't want the syrian hamster suddenly lying dead on the track ...

What do you need to know?

The two circuits must - of course - be separated. Otherwise both trains will run with both transformers. That is not the point.

How do you make separation points in the track?

A piece of paper (picture right), cardboard, and insulating tape between the contact tabs of the center conductor of the track to be separated is sufficient for the M track.

Märklin offered ready-made cardboard pieces under the number 5022 (picture left).

And there were dividing tracks (picture right), 90 mm straight tracks, where the central conductor was interrupted. They were delivered with signals that were set by hand-lever directly at the signal. See Märklin no. 7339, 7539 and 7400.

The K-Track has the 7522 insulating piece (picture left).

Alternatively, you can bend or shorten the copper tabs so that they can no longer touch each other, or you can also use paper between the tabs (picture right).

There are small insulating caps on the C track system under the number 74030 (picture left). Alternatively, you can also work with paper (picture) or adhesive tape, but it is a lot of fiddling.

Now the lines are separated (at all points where the central conductor crosses from one line to the other), each line has its own current feeder section and is connected to its own transformer.

The brown connecting cables are connected via the rails ...

That’s logical, isn't it? We only separated the middle conductor!

Here it comes:

The two power plugs of the transformers are plugged into two sockets. You can plug them in either way, two options each.

If they are "wrongly" plugged in, you can measure up to 60V between the center conductors of the two lines (worst case if the power supply is just at the upper tolerance (conditions in Germany) and the switchover is activated on both transformers).

When both transformers are fully turned up, the voltage can be approx. 45V. For "toys", 24V is permitted.

Oh, that's way too much.

What are we doing about it?

Connect transformers “in phase”!

Preparation:

1^st Connect the plugs of the two transformers to a power strip with a switch (switched off).

2^nd Connect the BROWN „0“ connections of both transformers.

3^rd Connect a measuring device for AC voltage, a multimeter or similar, to the YELLOW „L“ connections of the two transformers. Set the measuring range so that the possible 45V AC voltage can be displayed.

Alternatively, an lightbulb can be connected if it can handle 45V.

4^th Keep your fingers away from the conductive points, switch the power strip "on".

If zero volts or a very low voltage is now displayed or the lightbulb remains dark, the two power plugs are correctly inserted.

To check that the result is correct:

1^st Switch off.

2^nd Turn ONE of the two plugs over.

3^rd Switch on again.

The correct position of the two plugs is when zero volts is displayed or the light bulb remains dark!

So that it stays that way for all time, mark the position of the plug and the power strip (which is now reserved for the model railway).

Up to here, Märklin has also explained (german):
Link to “Sicherheits-Vorgabe”

What Märklin does not mention in that document:

A transformer "translates" one AC voltage into another.
(For technical background see
"White - blue - orange - transformers between good and evil")

The modern Märklin transformer takes 230V (in Germany) and outputs e.g. about 16V at the light connection.

The "translation" also works backwards:

If you apply 16V between the brown „0“ connection and the light output „L“, you have 230V on the mains plug (I've just tried it, it's really true basically! I measured 191V!).

Märklin has recognised the necessity of the warning and has added a sticker to newer transformers 6647, 66470, 66471:

Attention safety hazard!

Do not connect the transformers in parallel, otherwise
mains voltage at the disconnected plug!

When operating several transformers,
observe the operating instructions.

Here is the comment of a member of my Facebook group, master electrician Dieter Hammerl:

And never connect the traction current red connection or light current yellow connection in parallel. This also causes the voltage to be too high and, when the plug is pulled out of the socket by a transformer, 230 V is generated at the poles of the plug.

In the first instance, you can get an electric shock in your hand or on the part of your body with which you touch the poles, and in the worst case you get a current entry and a current exit (two burns).

But if we look at it from the second perspective, the result of this contact can be dangerous. If your layout is in the basement and the board is a bit damp or your track body at the M-track touches an earthed part (can happen in every moba room), then you earth your measure connection and now the consequences of the touch are no longer harmless, but can end fatally.

End of quote.

To my article about the transformers someone commented: "It's a toy...".

Dieter Hammerl: “sure, if you follow all the rules 100%, it is harmless and a toy, whereas you can also get seriously injured with toys.”

When can this happen unintentionally?

If you have connected several transformers to your system, but only one transformer is plugged in and...

· a locomotive bridges a separation point with its current collector shoe or

· there is a circuit fault.

Therefore:

ALL transformers to a common socket strip,
plugs in the correct position and
always switch them all on and off together.

The Prototype Märklin-H0-Knowledge Layout-Building Modelstock

state: 21.06.2023 17:56

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