Model railway power supply

[RandomGrinch]

With youngsters about - Please do make sure that what ever PSU's you buy, are sourced from reputable suppliers, so they provide adequate isolation from the mains.

Reputable source, I agree with.

I would go further and suggest that the power supplies have a wound transformer at 50Hz to ensure there is assured isolation from the mains supply.

Isolation would be desirable, but as long as the PSU is from a reputable source, the risk from a SMPSU is extremely low.
From a very early age, children are using phones and iPads etc that will be plugged in and charging from SMPSU.
The LED Christmas lights will also likely have them.

After all, there are some on here that suggest children could go up into an enclosed space and lay loft insulation!

 

[Harry Bloomfield]

After all, there are some on here that suggest children could go up into an enclosed space and lay loft insulation!

Only since employment opportunities decreased for cleaning chimneys

 

[FiremanT]

A lifetime ago, I had a set with a mail coach, which opened a scoop as it passed the collection point hook, to collect the 'mail-bags', further along, it would fire the collected bag back out, into a collection bin.

Yes, that’s what I had , inherited from my older brother. Also a working helicopter that flew off a flat bed, and probably the coal truck mentioned by another, it went over a bridge, and a door opened in the base, dropping the load.

 

[FiremanT]

With youngsters about - Please do make sure that what ever PSU's you buy, are sourced from reputable suppliers, so they provide adequate isolation from the mains.

I would go further and suggest that the power supplies have a wound transformer at 50Hz to ensure there is assured isolation from the mains supply.

Not sure if I am answering your point, but the actual PSU’s will not be accessible to the kids. The idea is to wire everything under the baseboard, with the only items for the kids to touch (apart from the train itself) being the illuminated rocker switches, and a couple of light switches used where it is not feasible to avoid.

 

[bernardgreen]

the actual PSU’s will not be accessible to the kids

The track I assume will be accessible to the children, A failure of the isolation barrier in a PSU could result in the track becoming Live ( 230 V )

 

[RandomGrinch]

The track I assume will be accessible to the children, A failure of the isolation barrier in a PSU could result in the track becoming Live ( 230 V )

Again,

This isn't about control for the locomotive, this is a supply for the buildings in the diorama.

The OP has bought a trainset that will include an appropriate controller.

Also, as before, it would be very unusual for a train controller NOT to be supplied by a SMPSU these days, the risks are minimal.

Examples from Hornby here:

Hornby 12v DC Control

Our complete range of transformers, clips, switches, transformers and powered accessories opens up this magical miniature world.

uk.hornby.com

 

[FiremanT]

The track I assume will be accessible to the children, A failure of the isolation barrier in a PSU could result in the track becoming Live ( 230 V )

I see. Yes they would, of course. Has this failure occurred in practice?

I would not be using the PSU for the track, that would be a Hornby Controller, but presumably the same risk is present.

The PSU’s will be used for illumination of trackside furniture LED’s, in place of batteries. The idea being that the kids can turn on and iff the decorations, without having to handle the items to find the on/off switch.

What would actually happen to 3.5v / 4.5v / 12v LED’s if they were suddenly introduced to 230v? Bearing in mind the thin wire used to connect

 

[RandomGrinch]

...and just as a quick example of DCC control, here is an Airfix dockside crane that I modified - all controlled by a wireless DCC controller.

 

[bernardgreen]

There are two critical components in the isolation barrier in an SMPS ( Switched Mode Power Supply ) between mains voltage and ELV ( Extra Low Voltage ).

(1)
An opto isolator, most often this a dual in line package with adequate ( 3mm ) separation between mains voltage and ELV ( Extra Low Voltage ). If this device does fail then the ELV will no longer be regulated but the isolation barrier is unlikely to be compromised,

(2)
A small, high frequency transformer, one winding is connected to the incoming mains via the switching system, the other winding is connected to the ELV output. In many SMPS units the insulation ( plastic tape ) between the windings is as thin as possible in order to reduce the size of the transformer and hence the size of the unit.

In small SMPS units the transformer is almost always a layer wound device.

 

[FiremanT]

There are two critical components in the isolation barrier in an SMPS ( Switched Mode Power Supply ) between mains voltage and ELV ( Extra Low Voltage ).

(1)
An opto isolator, most often this a dual in line package with adequate ( 3mm ) separation between mains voltage and ELV ( Extra Low Voltage ). If this device does fail then the ELV will no longer be regulated but the isolation barrier is unlikely to be compromised,

(2)
A small, high frequency transformer, one winding is connected to the incoming mains via the switching system, the other winding is connected to the ELV output. In many SMPS units the insulation ( plastic tape ) between the windings is as thin as possible in order to reduce the size of the transformer and hence the size of the unit.

In small SMPS units the transformer is almost always a layer wound device.


View attachment 318013

Thanks, but it does not answer my questions?

 

[RandomGrinch]

There are two critical components in the isolation barrier in an SMPS ( Switched Mode Power Supply ) between mains voltage and ELV ( Extra Low Voltage ).

Yes, true.
I would also mention the class X/class Y caps.

However, as earlier, if these supplies are from a reputable source, what is the actual level of risk?

Thanks, but it does not answer my questions?

I hoped keeping this out of the Electric forum would avoid some of this!
There will be no problem using a SMPSU for lighting your buildings.

 

[bernardgreen]

However, as earlier, if these supplies are from a reputable source, what is the actual level of risk?

It is very low if the "reputable source" uses a good design and has adequate quality control procedures in place.

I was asked to check an SMPS feeding a small 12 V drill as the user could feel a "weak vibration" from the metal case of the drill. The ELV hovers about 120 Vac above ground/Neutral when measured with a high impedance meter, The voltage between ELV+ and ELV- terminals is 12 volts DC.

 

[RandomGrinch]

I was asked to check an SMPS feeding a small 12 V drill as the user could feel a "weak vibration" from the metal case of the drill. The ELV hovers about 120 Vac above ground/Neutral when measured with a high impedance meter, The voltage between ELV+ and ELV- terminals is 12 volts DC.

Yes, it also happens with aluminium bodied Macbooks. The tingle is from the 100uA (ish) that the cap is allowed to pass across the transformer.
And yet, they are still safe to use.

 

[Harry Bloomfield]

Yes, it also happens with aluminium bodied Macbooks. The tingle is from the 100uA (ish) that the cap is allowed to pass across the transformer.
And yet, they are still safe to use.

You can get a similar leakage, from the antenna socket, of many TV's - voltage, but miniscule current behind it.

 

[bernardgreen]

allowed to pass across the transformer.
And yet, they are still safe to use.

Until the transformer inter winding insulation breaks down. Happens very very seldom but the possibility should not be ignored.