Common return using two different types of controllers?

[Sol]

Yes ,the Gaugemaster site does indicate that their power supply M1 has two separate outputs & the UDS controller requires 2 separate inputs making it suitable for common return.

[kevinlms]

7 hours ago, Sol said:

Without seeing the circuit of the Gaugemaster unit, one can only assume then that it was one secondary coil of the mains transformer serving both controllers circuitry.

 

Common return wiring can only be used with separate windings of transformers and have a understanding of electrical interconnections . I have used common return wiring for 50 plus years with both DC & DCC with no problems - granted my career path in telephone exchanges may have helped.

Agreed.

 

However I can see a potential (sorry!) problem.

 

Looking at the Model D, it has 2 controlled 12 Volt DC outputs, which it states as suitable for common return, so must have two transformer windings.

But it also has a 12 Volt DC uncontrolled output (states for lighting etc). As well as a 16 Volt AC output (states for accessories, such as point motors, including with a CDU). 

The latter (the AC) states NOT suitable for common return, so it can't be a separate winding. No mention about the 12 Volt uncontrolled, but I suspect that it uses the same power source as the 16 Volts AC. In that case not suitable for common return either.

 

I think that must be where the warnings for NOT using common return comes from. How many modellers would not fully understand these limitations, on what appears to be an 'All in One' controller/power supply?

 

That would lead to some modellers, hooking up two trains and the AC (possibly with a CDU) and connecting points using the same common return. This will give them trouble, without doubt.

[Clive Mortimore]

Going back to the OP, the advise is not to use common return when more than ONE transformer is to be used. With common return if one controller is not in use but still connected to the layout the transformer will change the the low voltage to the high voltage, so if unplugged you have mains voltage coming out of the plug waiting for you to pick it up.

 

As a nurse I worked on a plastic surgery ward, and at times we would look after the minor burns patients when the burns unit was full. I cared for a lot of people who had been electrocuted, apart from looking after them as if they had had a heart attack, they needed the burn where the electricity found an earth dressed two or three times a day. Many times we could not find the burn where it entered the body.

 

Use common return, because you won't have me cleaning and redressing the burn on your backside , as I have retired now.

[Crosland]

13 minutes ago, Clive Mortimore said:

Going back to the OP, the advise is not to use common return when more than ONE transformer is to be used. With common return if one controller is not in use but still connected to the layout the transformer will change the the low voltage to the high voltage, so if unplugged you have mains voltage coming out of the plug waiting for you to pick it up.

 

Transformers need AC to work. So, if, and only if, the powered controller is putting out AC (or pulsed DC which is just AC with a DC component) onto the track AND that waveform can get back through the electronics of the other controller to the transformer is there any problem. A simple bridge rectifier at the input to the controllers will block any back feed to the transformer.

 

Moreover, the point about common return is there is only one common connection (the return). There is no connection between the "supply" sides of the two transformers and no way to complete the circuit as described.

 

Any setup with smooth DC on the tracks is perfectly safe with multiple transformers.

 

[34theletterbetweenB&D]

We forever get this argument about common return with cab control, and it is so simple.

 

If you have the knowledge of the underlying principles, necessary technique and the skill to apply it, this is a simple, economical and completely reliable method, as a great number of successful layouts prove. It is no trouble at all to have a cab control layout running DC and DCC simultaneously on common return, I do this near daily and nothing has ever been damaged as a result. The electron knows where it has to go.

 

I started using common return as a schoolkid, but I had at that point already passed my physics O level, and here I am some fifty years later completely unharmed, from this and many other 'interesting things' that may be done by slinging the electron about.

 

If you don't know how, you cannot do it, so leave well alone. But don't suggest 'cannot be done'. That's your ignorance speaking and makes you look silly, to be frank.

[kevinlms]

11 hours ago, Sol said:

Even old modellers like the late Rev Edward Neal used common return  and cab control on his West Midland Lines back in the 1940-50's.

A modern version  http://www.rail.felgall.com/cc.htm

Probably back then, the Split Potential system was also used, which often involved relatively high current transformers. Quite likely hand made and possibly dangerously so.

 

But I don't think that is very good solution in this day and age, so I won't go into more details. Transformers are cheap these days

[Clive Mortimore]

I must have it very wrong.

 

 

At least I know I am safe, and can fault find very very easily.....not that I have to.

 

 

A bit more dramatic as one train crosses from one mainline over to the other side of the station. Watch for the movement in the steam depot as well. DC Cab control no common return.

[Junctionmad]

The issue with common return is that the potential exists for confusion where power supplies turn out to be commoned together often without the knowledge of the user 

 

furthermore the preponderance of SMPS abc the fact that some/many have earth bonding means issues can arise , linear transformer based supplies are virtually banned now anyway 

 

nobody is suggesting “ it can’t be done “ nor that it’s inherently somehow unsafe, but there are good electrical /electronics reasons why separate ground returns are a good idea, especially as more and more electronics are deployed on model railways 

 

in the general scheme of things for the average layout the advantage of slightly less wire is today a dubious benefit. 

 

Dave 

 

 

Edited July 24, 2019 by Junctionmad

[Titan]

I have no choice but to use common return, as I run OLE electrics and diesel independently on the same tracks.  I did get a very weird fault due to accidentally having connected two OLE sections on the Down and Up together which did not show up until a particular move was attempted...

[AndyID]

Meanwhile, returning to the OP's question which was:

 

On 14/07/2019 at 23:43, Demondrille Junction said:

Hi all. I've a basic question with regards to common return track/controller wiring.  Do the controllers have to be the same type or brand? 

From searches in the past I know that each controller must connect to separate transformers but I've not been able to find any mention of the subject relating to controller compatibility.  Maybe it doesn't matter, but I don't know.

 

My situation is I have a GM UDS panel controller which has two track outputs with switchable inertia/brake and a newly acquired Morley Vector Zero Two.  Thanks to Mikesndbs thread I knew about the different waveforms of the two controllers and I'm worried if one might damage the other through a common return. Any thoughts?

 

 

Do the controllers have to be the same type or brand?    No, they do not.

 

I know that each controller must connect to separate transformers but I've not been able to find any mention of the subject relating to controller compatibility.  Maybe it doesn't matter, but I don't know?     A compatibility issue is highly unlikely but if there was it wouldn't make any difference whether you used common return or not.

 

My situation is I have a GM UDS panel controller which has two track outputs with switchable inertia/brake and a newly acquired Morley Vector Zero Two.  Thanks to Mikesndbs thread I knew about the different waveforms of the two controllers and I'm worried if one might damage the other through a common return. Any thoughts?      Again, any sort of interaction that might result in actual damage is highly unlikely (good controller designs include protection against that sort of thing) and it's not going to make any difference whether you use common return or not.

 

 

 

 

 

[Clive Mortimore]

Theory and practice are not always the same. I am sorry I repeated what the designer of the Gaugemaster controllers advised when I worked for them...he like me must have been barking up the wrong tree because the experts have written we are wrong.

Odd thing is it works.

And fun to drive trains on.

 

[AndyID]

Hi Clive,

 

Nobody is saying you are wrong.  Your method works perfectly well. So does common return. Please stop suggesting that it does not. Whether people prefer to use it or not is a matter of personal preference.

 

I don't happen to care for DCC much but I try not to go around bashing people over the head and telling them they are making a big mistake if they want use it.

 

BTW, times seem to have changed. There's a tutorial on the Gaugemaster website on how to use common return. I put it to you that your former colleague at Gaugemaster had a gigantic bee in his bunnet

 

Cheers!

Andy

 

 

 

 

[Clive Mortimore]

18 hours ago, AndyID said:

 

That's odd because Gaugemaster says the UDS is suitable for cab control and common return.

 

http://www.gaugemaster.com/instructions/uds.pdf

And what does this say?

 

http://www.gaugemaster.com/instructions/GMTFK12.pdf

[Nearholmer]

The wording and diagram in the item that Clive highlights seem at odds with one another to me.

 

The wording talks, very correctly, about the risk of "back energisation" from transformers connected in parallel, whereas the diagram appears to show not simply transformers but packaged transformer/controllers; it certainly doesn't show things that I would recognise as transformers from any symbology that I've come across in 40+ years of electrical engineering.

 

If Gaugemaster mean that the outputs of their controllers shouldn't be connected in parallel, they might be better saying so in plainer language.

 

Plainer even than the words in the leaflet highlighted by AndyID, which say: "The outputs of two or more control circuits must not be connected in such a way that both wires may accidentally be connected together, i.e. through switches or points, e.t.c.", which leave doubts in my mind about whether connecting controller outputs in parallel causes a safety risk to people, or simply might cause damage to the kit.

 

Is anyone from Gaugemaster reading this thread?

 

PS: Although model railway packaged transformer/controller sets are (certainly used to be) sometimes spoken of  as "transformers", most of them, certainly all of those used for 12V dc model railways, are not simply transformers.

 

 

Edited July 24, 2019 by Nearholmer

[34theletterbetweenB&D]

1 hour ago, Clive Mortimore said:

... I am sorry I repeated what the designer of the Gaugemaster controllers advised when I worked for them...he like me must have been barking up the wrong tree because the experts have written we are wrong...

Commercially he had an interest in saying so, especially with the lifetime guarantee offered with the product. In his shoes I would do the same: one less way for a customer to do damage requiring repair.

 

Exactly the same approach of most consumer electronics manufacturers, typically putting 'no user serviceable parts inside' on the labelling on the outside of the case. It is complete bovine droppings, but probably discourages most.

 

But not me, and all the others with the relevant knowledge. It doesn't apply to us...

[Grovenor]

Quote

 

  49 minutes ago, Clive Mortimore said:

And what does this say?

 

http://www.gaugemaster.com/instructions/GMTFK12.pdf

 

 

Basically it says "don't be stupid" As everyone has been saying above common return requires a separate transformer or a separate secondary winding for each controller. There is no suggestion that transformers should have the secondaries paralleled. Even if both transformers were connected to the same plug to eliminate the hazard illustrated any small mismatch in the transformer outputs would create circulating currents wasting power and possibly overheating.  Hence don't connect transformers in parallel. Many transformers made with two independent secondaries were manufactured to close tolerancies so that the secondaries could be parallelled to double the current rating, is such cases the instructions make it clear.

But for common return this is not an issue as the requirement is to keep them separate.

Both sets of Gaugemaster instructions are correct for the respective items. And both of those items will happily work together using common return track wiring if connected correctly.

Like any electrical issue learn before doing and try to avoid scaremongering about easily mitigated hazards when the technique has been in successful use for 70 years or more.

Rgds

 

Edited July 24, 2019 by Grovenor

[AndyID]

28 minutes ago, Clive Mortimore said:

And what does this say?

 

http://www.gaugemaster.com/instructions/GMTFK12.pdf

 

Hi Clive,

 

It says never to connect the secondaries of two transformers in parallel which is absolutely correct. That is a major no-no. Unfortunately the diagram is wrong as it appears to show two controllers with their outputs connected to each other.

 

Obviously two controllers with connected outputs isn't going to be useful but it's not a safety issue. It's also has nothing to do with common return. (If it was a safety issue with common return it would be just as much of a safety issue with non-common return wiring.

 

Cheers!
Andy

[Nearholmer]

Andy and 34C

 

Are you confident that there can never be a risk of back-livening by parallel connecting the outputs of controllers if they are switch-mode power supplies, as opposed to more traditional arrangements? I have to confess that I get confused on this point.

 

Kevin

Edited July 24, 2019 by Nearholmer

[AndyID]

16 minutes ago, 34theletterbetweenB&D said:

 one less way for a customer to do damage requiring repair.

 

 

Except that it doesn't make any difference whether the controllers were being used with common return or not. It's just as easy to back drive one controller into another on a layout that's not wired for common return. Hence my comment about bees and bunnets.

[Grovenor]

16 minutes ago, Nearholmer said:

The wording and diagram in the item that Clive highlights seem at odds with one another to me.

 

The wording talks, very correctly, about the risk of "back energisation" from transformers connected in parallel, whereas the diagram appears to show not simply transformers but transformer/controllers; it certainly doesn't show things that I would recognise as transformers from any symbology that I've come across in 40+ years of electrical engineering.

That instruction is specifically about the transformers and the wording is fine, but agreed the diagram is not the best. I suspect they used a stock symboloriginally produced for other instruction sheets.

16 minutes ago, Nearholmer said:

 

If Gaugemaster mean that the outputs of their controllers shouldn't be connected in parallel, they might be better saying so in plainer language.

 

Plainer even than the words in the leaflet highlighted by AndyID, which say: "The outputs of two or more control circuits must not be connected in such a way that both wires may accidentally be connected together, i.e. through switches or points, e.t.c.", which leave doubts in my mind about whether connecting controller outputs in parallel causes a safety risk to people, or simply might cause damage to the kit.

If you parallel the outputs of two controllers, with both wires the problem comes when you reverse the direction on one of them. With proper design the cutouts will operate to protect them. But it is difficult to fully protect if they are set to low speeds for some time they may overheat and cause damage. This will not be  a direct safety risk to people unless it caused a fire. NB This has nothing to do with common return and is equally likely with non-common return wiring if a loco was accidentally driven half over a section break with the controller connected to the recieving section reversed, then you left it cooking while you went for a brew.

16 minutes ago, Nearholmer said:

 

 

Is anyone from Gaugemaster reading this thread?

 

 

 

[AndyID]

16 minutes ago, Nearholmer said:

Andy and 34C

 

Are you confident that there can never be a risk of back-livening by parallel connecting the outputs of controllers if they are switch-mode power supplies, as opposed to more traditional arrangements? I have to confess that I get confused on this point.

 

Kevin

 

Hi Kevin,

 

Switch-mode or not, PSUs have (or bluddy well better have) isolating transformers and rectifiers. The order/frequency/voltage might differ, but they all have them. That makes it virtually impossible for them to transform in reverse.

 

And, even if there was a risk, common return or not won't make any difference.

 

Cheers!

Andy

 

 

 

Edited July 24, 2019 by AndyID
typo

[Nearholmer]

Hmmm ....... I have this nagging doubt in the back of my mind that I've read that some domestic computer PSUs don't provide isolation, and I know that some people have uplifted computer PSUs to create model railway PSUs.

 

As you say, though, not really a common-return question.

 

K

[AndyID]

6 minutes ago, Nearholmer said:

Hmmm ....... I have this nagging doubt in the back of my mind that I've read that some domestic computer PSUs don't provide isolation, and I know that some people have uplifted computer PSUs to create model railway PSUs.

 

As you say, though, not really a common-return question.

 

K

 

Hi Kevin,

 

They have to but switch modes operate in reverse order. The mains input is first rectified and smoothed into high voltage DC. That gets "chopped" into high frequency, high voltage AC. That is then passed through a small transformer to produce the desired voltage which is rectified and smoothed to produce the desired low voltage DC.

 

Some computer PSU bricks have their 0 volt output tied to mains ground. That would create a problem if someone tried to use them with common return, but they are still "isolated" from line and neutral.

 

Cheer!

Andy

[kevinlms]

1 hour ago, Clive Mortimore said:

And what does this say?

 

http://www.gaugemaster.com/instructions/GMTFK12.pdf

I assume you are referring to this statement.

 

CAUTION: It is very important that the outputs of two or more transformers are not connected together in parallel. i.e. both wires. If this is done, there is a risk of electric shock from a plug not inserted into a socket.

 

The statement has nothing to do with common return, its about putting the outputs of separate transformers in parallel. That is highly dangerous & illegal and certainly is not specific to Gaugemaster.

 

Have a careful look at the diagram to the right of the warning. Remember, the diagram shows a TRANSFORMER and NOT a controller.

[Sol]

Clive, using two wires per section & not common return, have you thought what is the result when a loco straddles two sections controlled by two different controllers? The outputs are joined - commoned on two wires.