DC for Twin Coil Machines

Model Railroader General Discussion (Model Railroader)
1

In Andy Spereando’s book, he mentions that DC can also be used to power Switch Machines. Any recommendations on Voltage/Amperage?

Thanks!
GF

2

GF: short answer: DON’T

The problem with using DC to power twin coil machines is the inductive spike when you release the controller. It can burn out the contacts in the switch machine controller.

AC is cycling +0-0+0-0 so the current shuts off without arcing. This is why AC voltage rating on most switches is ten times the DC rating for a given current.

You can get wall transformers from Wal-mart, Radio Shack, DigiKey, etc that put out 12 to 18 VAC, perfect for those old twin coils.

Nigel

3

AC is easier and cheaper to use with twin coil machines.

DC requires a large number of diodes to prevent damage to the controllers.

Nigel

4

GF
Around 20-25 volts AC with a 3 or 4 Amp. output capacity will throw most twin-coil machines, with the ability to throw two machines wired together to operate a crossover [ two switches together ].
I have used miniature sprung-to-off toggle switches available from Radiospares in UK. Not sure of the US source but probably Radio Shack,
whatever, use the highest quality you can afford,
they will last longer, and are easier to operate without burning-out the coils due to welded contacts. Mine survived 6 years use on a portable
show layout that went on display every other weekend spring to fall, with no switch failures and only 2 machine coil burnouts, both due to operator error.[ leaning on the control panel!]
Dave Elbourne, Rugby, England.UK.

5

Thanks guys. I think I’ll stick with AC.

My concern was slowing a train down when throwing the switches, but the way I designed my layout it has two distinct “halves” which would lend themselves to one particular cab each. There is heavy switching on each half, so powering the turnouts on either half with its own cab power would be preferential-- the cab controlling the mainline train would not be drawing AC power while the switching train would be slow/stopped when throwing switches anyway. Hope that makes sense. Thanks again.
GF