Will 2 X 1 AMP supplies cause damage?

[Longpockets]

Hello All,

Question -

Will a loco be damaged if it receives 2 X 1 Amp supplies of power from two power supplies at the same time.

Explanation as to why -

After in excess of 12 months I have finally laid some track, on boards, as SWMBO will not let me dig up the garden. Never tackled G Scale before, so still a newbie at this. It is about 24 ft long (3 x 8ft. boards) end to end with three separate tracks at the mid point. 1 st. is a passing loop, 2 nd. in the center is a full run end to end & 3 is another passing loop, with two points inserted to allow a full curcuit of track (future extension) to run into it. Each track is isolated from the others and I have power to each passing loop by means of two seperate 1 Amp power supplies. I have bridged power from each passing loop to the central track with a switch to one of the bridge wires from each passing loop. This should allow power to reach one of the loops and the central track, depending on how the switches are set, and should also allow the curcuit to be operated idependantly from the other two tracks i.e run a loco end to end and a loco on the curcuit at the same time. However it also means if the switches are set wrongly the central track will receive power from both supplies at the same time. Finally, at last, the question this is about. Will a loco be damaged if it receives 2 X 1 Amp supplies of power from two power supplies at the same time.

I think I am likely to get a one word answer to this. If it is yes could you please advise how I should wire the track to acheive what I need.

I know this probably seems a long winded way of setting this up, especially using two 1 Amp supplies, but I have obtained the track and the power supplies over a period of time as I could afford it.

Your thanks for your help/advice in advance.

Regards

Tony

 

[stevelewis]

A loco will probably wont be damaged by receiving 2 x 1 amp power supplies as LGB etc locos run OK on 10 amp supplies.

BUT more importantly there is a personal risk to yourself in what you propose, if the 2 power supply units are connected electrically at the output (low voltage side) ar have the potential to be connected by switching, and one is unplugged then power from the 'live'unit may be fed back into the unplugged unit and into its transformer, this could result in potential high voltage being sent to the exposed plug, with the risk of serious electric shock

Many recent power units such as a Gaugemaster Model D I have for my small scale layout carry a warning on them telling users not to connect 2 units together due to the risk of shock!!

 

[ntpntpntp]

I think you should use a double pole double throw (DPDT) switch to connect the centre track to one or other of the controllers. That way you can't connect both controllers to the track at the same time. This is a simple example of what's called "cab control" in model railway electrical wiring, where each section of track can be switched to one of multiple controllers as a train progresses round the layout.

 

[Neil Robinson]

Steve, I think your warning is very apt and relevant for digital operation, but I don't think that there is such a grave danger with analogue as the dc output from one controller would not be stepped up by the transformer in a second unplugged controller.
There is still risk of about 50V dc from the combined output of two dc controllers if they are interconnected inappropriately.

 

[stockers]

Steve is dead right - no pun - but!!!

Just use one controller and some switches to direct the power to the track you want.

 

[stevelewis]

Neil Robinson - 14/11/2009 6:47 PM

Steve, I think your warning is very apt and relevant for digital operation, but I don't think that there is such a grave danger with analogue as the dc output from one controller would not be stepped up by the transformer in a second unplugged controller.
There is still risk of about 50V dc from the combined output of two dc controllers if they are interconnected inappropriately.

I beg to differ.
If there was little risk why would the manufacturers go to the trouble of actusally placing a WARNING on their products??
I quote from the Gaugemaster unit:

CAUTION SAFETY RISK

Do not connect the outputs from seperate units in parallel as FULL HOUSEHOLD current will be present at a plug pulled out from its socket!
There then follows a diagram illustrating the risk.

 

[dutchelm]

Gaugemaster put this warning on Transformers as it is possible to backfeed & produce mains voltage on the plug. This cannot happen once the current has gone through the rectifier as that is effectively a one way path.

The problem with using 2 controllers is that if the outputs are different you can self destruct the controllers!

 

[spike]

If the two controllers do get connected in parallel they must be at the same exact voltage.
Any difference in voltage , can be as little as 50>75mV and the one with the higher voltage will supply all the current.

 

[korm kormsen]

i would be afraid to try this.
if one transformer gives "forward" and the other "backward" one or both of the transformers plus the motor in the loco might produce some nice smoke.

 

[Neil Robinson]

spike - 14/11/2009 9:47 PM

If the two controllers do get connected in parallel they must be at the same exact voltage.
Any difference in voltage , can be as little as 50>75mV and the one with the higher voltage will supply all the current.

However most of the time the train would be powered by one controller, so one controller supplying all of the current during a changeover from one section to another won't be any different to normal operation.

korm kormsen - 14/11/2009 10:47 PM

i would be afraid to try this.
if one transformer gives "forward" and the other "backward" one or both of the transformers plus the motor in the loco might produce some nice smoke.

With the controllers connected in opposition they would tend to cancel each other out giving little voltage to power the motor. There is a risk the current from the controllers would exceed their rating, but this risk is always present in, for example, certain derailments or dropping any piece of metal across the rails and the controller's inbuilt protection should be capable of tripping before any damage is caused,

I have found two references to two LGB analogue controllers being recommended for this sort of application in my copy of LGB's technical manual, one on page 109, the other on page 147.

 

[Longpockets]

ntpntpntp - 14/11/2009 6:44 PM

I think you should use a double pole double throw (DPDT) switch to connect the centre track to one or other of the controllers.

Many thanks for the advice. A quick visit to Maplins today for DPDT switch, a rubber switch cover to waterproof it, a IP65 junction box to mount it on and some connectors together with a couple of hours outside this afternoon and it is done. I also checked out Neil Robinson's references to LGB book to see what it was about and all is fine. No worries or problems now.

Thanks again to you all particularly to you and Neil for the good advice.

Regards

Tony