Mixed Lights to Same Power Source Query

[Redford73]

I know the Topic Heading is probably confusing!

 

I am using LED strip lights for my depot building and will either wire up to the 16V output on a standard Hornby controller (probably with resisters) or to a 9V battery.

 

But I have a signal box near the depot which I wanted to use a spare Hornby Skalelight bulb I have on.  All the other Skalelights are at the other end of the layout linked up to the Skalelight socket unit. and powered separately.

 

Rather than link the stray light up to the others with long length of wire can I link up the skalelight bulb to the same power source as the LEDs? 

 

I will be using a single switch to activate the lights for the depot and the signal box so would prefer they are all wired in series.

 

The short way of asking this question is can I mix LEDs and standard bulbs and link to the same power source? 

[kevinlms]

I know the Topic Heading is probably confusing!

 

I am using LED strip lights for my depot building and will either wire up to the 16V output on a standard Hornby controller (probably with resisters) or to a 9V battery.

 

But I have a signal box near the depot which I wanted to use a spare Hornby Skalelight bulb I have on.  All the other Skalelights are at the other end of the layout linked up to the Skalelight socket unit. and powered separately.

 

Rather than link the stray light up to the others with long length of wire can I link up the skalelight bulb to the same power source as the LEDs? 

 

I will be using a single switch to activate the lights for the depot and the signal box so would prefer they are all wired in series.

 

The short way of asking this question is can I mix LEDs and standard bulbs and link to the same power source? 

I'm not familiar with the types you mention, but in general, certainly not in series, as the brightness levels will probably be all over the place.

But you can still do them in parallel, using the one switch. Make you that the LED's have a suitable resister in series.

Experiment & see what happens.

[Crosland]

The LED strips are usually designed for 12V and include suitable resistors. On 9V they will either not light or be dimmer  than usual (maybe a benefit for a more realistic model). On 16V they will be brighter and potentially short lived. You need to work out the current drawn by the length of strip you use and select an appropriate resistor to drop the extra 4V.

 

Check that the bulb is rated for 16V! 

[smokebox]

Is the 16volts ac? Coz LEDs don't like ac.

[chaz]

Many LEDs, especially high output ones, are not much affected by a voltage reduction. You may well find that your LED strips are perfectly happy and give sufficient light on 9V. increasing the voltage to 16V is risky. It's not voltage that damages LEDs - it's the resulting current increase. Unless you know the value of the resistor(s) incorporated in the strip lights and the way the LEDs are wired it's going to be difficult to do the maths. My advice would be to stick to a PSU with the correct output.

 

As to whether you can connect a bulb to the same source - providing you wire it in parallel and don't ask the PSU to supply more current than it can cope with (an overload) there should be no problem.

[chaz]

Is the 16volts ac? Coz LEDs don't like ac.

 

Whilst technically you are right - LEDs are safer on DC, in practice providing the current is limited to a sensible level (say 50% of Imax) the diode aspect of an LED will block the reverse bias component of the AC.

[Redford73]

Thanks for responses.

 

My real query was about mixing not so much how to power the LEDs.  I have used the LEDs on another layout and on the 12V accessories output of a controller which was a little bright but the resisters supplied with the strips worked ok though actually made them a little too dim.  I was going to try the 9V possibly without resisters as this might get the lights to  the right level of brightness. 

 

I will look at doing the Skalelight bulb in parallel. 

[chaz]

Thanks for responses.

 

My real query was about mixing not so much how to power the LEDs.  I have used the LEDs on another layout and on the 12V accessories output of a controller which was a little bright but the resisters supplied with the strips worked ok though actually made them a little too dim.  I was going to try the 9V possibly without resisters as this might get the lights to  the right level of brightness. 

 

I will look at doing the Skalelight bulb in parallel. 

 

OK - you can certainly wire LEDs and bulbs to the same PSU providing you wire them in parallel with the resistors in the LED wiring,  not that for the lamp and providing the current draw does not exceed the max' specified for the PSU. LEDs and lamps are both passive devices and will not affect each other.

 

Hope that helps.

 

Chaz

[Redford73]

For those interested I managed to do it bar a few problems.

 

I have wired up three sets of 18 LED strips which will be in the depot building and a single Hornby Skalelight for a nearby signal box.  Here's what happened;

 

Connected all the wires to small terminal blocks - positive/red wires to one negative/black to the other.  Return black wire then went from terminal block to Gaugemaster 'D' controller 12V DC accessory output terminal.  Red wire from terminal block to on/off switch, red wire from on/off switch to 'D' Controller. I added red and black wire from the Skalelight to the same terminal blocks.   

 

Result the Skalelight worked the LEDs didn't?  After checking the switch and trying without the Skalelight same result.  I then changed the wires attached to the 'D' controller so they were in the opposite terminal output on the 12V output and the LEDs worked?

 

I am probably being totally stupid here but should it not matter which way round the wires are (at the controller end of the circuit) and given the initial set up was with all wires corresponding in colour/polarity should that not have worked?

 

I will add resisters as per above posts the lights were pretty bright even on the 12V output but at this stage I was just testing to check the wiring was ok.    

[chaz]

Yes, the polarity does matter. LED - light emitting diode - diodes only conduct in one direction. Sorry, should have mentioned it before.

 

Chaz

[Crosland]

I am probably being totally stupid here but should it not matter which way round the wires are (at the controller end of the circuit)

Yes, it does matter.

 

and given the initial set up was with all wires corresponding in colour/polarity should that not have worked?

 

Assuming conventional colour scheme, the Red wire should go to the +ve output of the controller. You didn't say which way round you connected at the controller.

[kevinlms]

 

I am probably being totally stupid here but should it not matter which way round the wires are (at the controller end of the circuit) and given the initial set up was with all wires corresponding in colour/polarity should that not have worked?

 

I will add resisters as per above posts the lights were pretty bright even on the 12V output but at this stage I was just testing to check the wiring was ok.    

As you have discovered, lamps don't matter which way they are connected to a power supply, but LED's do. That is the lesson, not the colour of the wires.

 

Put the resistor(s) in as soon as possible. Luckily you haven't blown the LED's. Some will advocate that resistors might not need to be used, but its good practice to do so.

[Gordon H]

Some will advocate that resistors might not need to be used, but its good practice to do so.

 

More to the point, it is bad practice NOT to do so.

That is to say, a current limiting device of some kind is always required in the circuit, simplest of which is a resistor.

[chaz]

More to the point, it is bad practice NOT to do so.

That is to say, a current limiting device of some kind is always required in the circuit, simplest of which is a resistor.

 

You are quite right to say that current limiting is essential with LEDs. Being semi-conductors they have no effective internal resistance to limit the current and an excessive flow will destroy them (usually instantly) - however the OP talks of LED striplights. These might well have resistors built in - certainly if they are rated 12V I think we can take that for granted. Flashing LEDs are similarly rated at 12V - they have an internal IC which includes the necessary resistor.

 

Hope that's helpful?

 

Chaz

[Redford73]

Thanks.  Yes, don't worry I am not using the lights until I have installed the resistors and literally just tested them.  Should have realised the LEDs needed correct polarity - I think I was just lucky on my other layout and had connected them correctly and didn't realise it mattered!