Connecting 12v lights in serial

[cozzie4d]

Hi all,

I'm working on recreating my legoland/town city of dreams, with multiple trains and lots of lights.

Now I was wondering, is it possible to connect 12v light bricks in serial. Aka, do I have to run wires from each light to the side input of the transformer, or can I connect them to each other. If so, that would save a ton of wire and headaches.

Any input is appreciated.

[Andy Glascott]

Yeah, you can run them in a chain no problem. That said, I’ve only ever connected 2 or 3 in sequence so I don’t know how many you can connect that way in total. Before you put them on your layout just connect them in sequence and see how many you can do. 

You can either plug the connectors into the back or side of each other, or, to save connectors, you can fit 2 wires into one connector, just strip a little more of the grey plastic off and twist the copper wire together before putting it back into the metal plug. 

[JopieK]

When you use the original (double/two wire) cables they are in fact parallel and not in series. That is b.t.w. also how it is done in a house (at least the power sockets). 12V is actually quite high for such a small lamps (these days they would have obviously used white LEDs).

[Toastie]

7 hours ago, cozzie4d said:

12v light bricks in serial

You could ;) but what you want to do is "chaining" them in "parallel" 

For example only, like this:

In principle, you can chain a lot of 12V light bricks that way - it all depends on the 12V P-supply's capability (= how many amperes it can deliver). And of course on the 12V cables (i.e. their resistance, but they are doing quite well in this regard). Just try it out! 

Best and good luck,
Thorsten

[cozzie4d]

Thanks all.

@Toastie your picture looks more like serial to me, because you're connect 1 light to the transformer, and the other pass through one to the next.

[Toastie]

1 hour ago, cozzie4d said:

and the other pass through one to the next

Well, each lamp is directly (i.e. via the LEGO cable connection) connected to the transformer; this is usually called they are "connected in parallel". A serial connection would be when transformer output_1 would go to lamp_1_in, lamp_1_out would go to lamp_2_in and so forth and finally lamp_n_out would go to transformer output_2. See for example here: https://www.allaboutcircuits.com/textbook/direct-current/chpt-5/what-are-series-and-parallel-circuits/. You can replace the resistors used in these example with 12V Lego lamps and the battery used with 12V LEGO transformer. 

All the best,
Thorsten

 

Edited July 12, 2024 by Toastie

[cozzie4d]

Ah yes, gotcha. So the only difference compared to 1 cable per light brick, is that the further down the line, more bricks share a single cable, but still in parallel. I guess it then comes down to “how well” the cables can handle this (resistance?)

[Toastie]

Essentially yes!

2 hours ago, cozzie4d said:

I guess it then comes down to “how well” the cables can handle this (resistance?)

Sort of, yes:

The cables attached to each other in parallel, provided they have "good" contact pins (i.e., they are not significantly corroded, "Kontakt 60" spray is a good choice for cleaning them in addition to wiping them several times after spraying them), do represent one "wire pair" to which all the lamps are attached.

The current flowing in this "wire pair" is what they need to handle. When adding one lamp, the current flowing through that lamp adds to the total current flowing in the entire wire pair (I), provided by the power supply.

This additional current flowing through that added lamp is determined by its resistance R. The total resistance of all lamps decreases with each lamp added according to: 1/R(total) = 1/R(lamp 1) + 1/R(lamp 2) + ... 1/R(lamp n). The current flowing in such a circuit is I = U/R, where U is the voltage of the supply, in this case 12V. The units are Volt (V) for U, Amperes (A) for I, and Ohm for R.

Example: Let us assume, the resistance of a lamp is 100 Ohm (which it is not, just for the sake of clarity). At U = 12V, the current flowing through that one lamp is I = U/R = 12V/100 Ohm = 0.12 A. Putting two lamps in parallel leads to = 1/R = 1/100 Ohm + 1/100 Ohm = 0.02 1/Ohm and this to R = 50 Ohm. So the current doubles: I = 12V/50 Ohm = 0.24 A. For three lamps you get R=33.3 Ohm and I = 0.36 A - so each lamp adds 0.12 A to the total current flowing.

There is of course a limit (that I don't know, but could do some rough calculations) to having lamps in parallel on one power supply: a) how much current can the supply deliver and b) how much current can 12V LEGO cables handle before they get "warm".  And these are all "ideal case" numbers, the reality may look a bit different, but in this case not that much.

Best,
Thorsten

[FGMatt]

39 minutes ago, Toastie said:

Essentially yes!

Sort of, yes:

The cables attached to each other in parallel, provided they have "good" contact pins (i.e., they are not significantly corroded, "Kontakt 60" spray is a good choice for cleaning them in addition to wiping them several times after spraying them), do represent one "wire pair" to which all the lamps are attached.

The current flowing in this "wire pair" is what they need to handle. When adding one lamp, the current flowing through that lamp adds to the total current flowing in the entire wire pair (I), provided by the power supply.

This additional current flowing through that added lamp is determined by its resistance R. The total resistance of all lamps decreases with each lamp added according to: 1/R(total) = 1/R(lamp 1) + 1/R(lamp 2) + ... 1/R(lamp n). The current flowing in such a circuit is I = U/R, where U is the voltage of the supply, in this case 12V. The units are Volt (V) for U, Amperes (A) for I, and Ohm for R.

Example: Let us assume, the resistance of a lamp is 100 Ohm (which it is not, just for the sake of clarity). At U = 12V, the current flowing through that one lamp is I = U/R = 12V/100 Ohm = 0.12 A. Putting two lamps in parallel leads to = 1/R = 1/100 Ohm + 1/100 Ohm = 0.02 1/Ohm and this to R = 50 Ohm. So the current doubles: I = 12V/50 Ohm = 0.24 A. For three lamps you get R=33.3 Ohm and I = 0.36 A - so each lamp adds 0.12 A to the total current flowing.

There is of course a limit (that I don't know, but could do some rough calculations) to having lamps in parallel on one power supply: a) how much current can the supply deliver and b) how much current can 12V LEGO cables handle before they get "warm".  And these are all "ideal case" numbers, the reality may look a bit different, but in this case not that much.

Best,
Thorsten

As a practical point, and given the age of 12V cables, it's probably worth using your "best" cables closer to the power supply, as they'll carry the greatest current. 

[cozzie4d]

Wow, thorough and scientific explanation, thanks :)

I'll give it a go and see when it becomes an issue, I guess cables getting warm. I'm currently using 1 transformer for everything, might go for a 2nd one to spread things a bit. Also useful for more control on 2 separated tracks.

[Toastie]

1 hour ago, FGMatt said:

as they'll carry the greatest current

Well, sort of - in an ideal case, the current is the same in all cables. The problem with "older" or better, less conductive cables, is that they a) act as series resistors in the common line (reducing the voltage and thus current further down) and b) power dissipation in these is higher than in better conducting cables, as the generated electrical power is proportional to the resistance: P = I^2 R.

Best,
Thorsten

[FGMatt]

5 hours ago, Toastie said:

Well, sort of - in an ideal case, the current is the same in all cables. The problem with "older" or better, less conductive cables, is that they a) act as series resistors in the common line (reducing the voltage and thus current further down) and b) power dissipation in these is higher than in better conducting cables, as the generated electrical power is proportional to the resistance: P = I^2 R.

Best,
Thorsten

With the physical set-up, the current will split equally across each light; eg in a 5 light parallel circuit drawing 0.5A in total, each part of the circuit will draw 0.1A. With the cabling as it is, that means that the cable closest to the power supply will have to carry 0.5A, the next cable will carry 0.4A, and so on.

Edited July 17, 2024 by FGMatt

[Toastie]

2 hours ago, FGMatt said:

With the cabling as it is

Yes, you are absolutely right - I simply thought "textbook" - in most examples, there is one wire split into branches with different resistances. Sorry for the confusion, and thank you for clearing that up!

All the best,
Thorsten

[FGMatt]

2 hours ago, Toastie said:

Yes, you are absolutely right - I simply thought "textbook" - in most examples, there is one wire split into branches with different resistances. Sorry for the confusion, and thank you for clearing that up!

All the best,
Thorsten

No worries!

One extra thing I'd add is that you could also connect it as a ring if you wanted a large number of lights (ie connect lamp 4 to the power supply too).

You'd need to do it very carefully though to avoid short circuiting, I'd suggest checking it with a multimeter before plugging it in.

[cozzie4d]

Quick update; I connected a bunch of them to each other and then to the transformer. All working as expected.

One thing I did notice though, when I use any of the remote accessoires (press the buttons), the lights flicker. Any idea what might cause this, perhaps pulling too much power from the transformer?

[Toastie]

2 hours ago, cozzie4d said:

I connected a bunch of them

Define bunch ... any chance of assessing the current flowing through the switch/supplied from the power source? 

Flicker as in going on and off on a regular basis, like blinking, or do they "erratically" flicker?

Best
Thorsten

[cozzie4d]

Hi. They go a bit darker and then lighter again, but only when I press a button on the remote accessoires (connected to the transformer).

When I don't touch anything the lights shine normally I think.

A bunch would be 6 or 7 going back to 1 connection in the transformer.

[Toastie]

51 minutes ago, cozzie4d said:

but only when I press a button on the remote accessoires (connected to the transformer)

And that button/these buttons does/do something else, like throwing a switch point, right?

If so, that is totally normal as the invoked "action" needs some current to work, voltage may then temporally drop, once the action is over, voltage is back to normal. It would happen upon operating a motor or such.

I initially thought you switch the lamps, but it sounds as if you are having the lamps hooked up directly to the transformer, and something else is turned on/off, correct?

Best
Thorsten

[cozzie4d]

Hey. Correct, the buttons are indeed for switches, signals and crossing. I basically have 3 sets of connected lights; the 3 cables lead into the far left/ last remote accessoires’s side input 

[cozzie4d]

So, now that I have everything connected, some findings:

• when pressing the electronic crossing buttons, the barriers come down very slow (need to keep the button pressed)
  • when I disconnect the 3 sets of connected lights to the far left accessoire remote, the barriers open normal (I believe, for 40 year old lego :))
• currently I have 1 transformer with
  • 3 electronic switches
  • 1 electrical railroad crossing (7866)
  • 2 signal posts (7860)
  • 3 sets of serial connected lights (each about 4 to 6 lights
• and another transformer, just with 1 set of 4 serial connected lights

I'm starting to get the feeling that I need to spread the load a bit, OR use a different transformer (could also be non-lego) for my lights.

Do you feel it should keep working fine with 3 +1 + 2 = 6 remotes attached plus a whole bunch of lights?
Curious if someone has experience with this.

In theory I could also have some bad connection somewhere, that interferes, but in that case I wouldn't expect the lights to work and the remote accessoires also to work.

[Toastie]

That is a nice layout!

32 minutes ago, cozzie4d said:

I'm starting to get the feeling that I need to spread the load a bit, OR use a different transformer (could also be non-lego) for my lights.

I would for sure take this route. The lights seem to be a permanent and quite demanding load for the LEGO transformer, otherwise the barriers of the crossing would not change their behavior. If you are not a purist, you should just get any cheap but powerful 12V DC thingy; even modern/semi-old/old computer power supplies (not laptop stuff, desktop supplies) usually have a good amperage 12V power line. There are so many other 12V DC solutions available. When these are all incandescent LEGO lamps, 12V AC will also work fine - no need for rectification. 230/12 AC transformers come in really cheap, just make sure you have good amperage, maybe 5 or even 10 A. These were used for old outdoor Christmas lighting quite often - yes I am old, and yes, I have assembled a good amount of old stuff. These devices hardly break even after +30 years of usage.

If you tend to be purist, just get another 12V LEGO transformer for the lights. These are also comparably cheap even on BL ...

And then use your current 12V LEGO transformer for the delicate instrumentation you have going!

All the best
Thorsten

[Andy Glascott]

My layout has 2 transformers controlling it, one with 8 accessory switches connected, the other with 5. Both have lights connected to the end of the switch panel, the lights do flicker occasionally, most of my switches are approaching 40 years old and there are at least 2 varieties of signal switches in there. Loose connections do happen, over time the pins on the switches (like all the Lego pins) get compressed and need to be spread out again, so either could be the cause of flickering lights. 

If you look closely at a pin you'll see it has 4 segments, there needs to be a small gap between them and over time they get pushed together, particularly if your control panel flexes when you move it. I use a small penknife blade to gently push them apart - I find the width of the blade is enough widening. Gently push the sharp side of the blade into the pin from the round end, the blade will push the prongs of the pin apart just enough. 

It may also be worth using a voltage meter to check the output of your transformers, both to the track and to the accessories - I recently discovered one of my spare transformers only puts about 50% power to the track but full power to the accessories. Don't be alarmed if the reading shows a volt or two above 12 as well, all of mine were putting out 14v at full power.

[XG BC]

these old iron core transformers can put out more voltage than expected, especially since they were wound for 220V/110V nominal depending on region, and not for 230V/120V nominal like it is now. They dont have any voltage regulation on them, just the transformer going into a rectifier, going into a capacitor to smooth out the voltage a bit. Modern switch mode power supplies can control the voltage themselves, and are much smaller and more efficient since you are running the transformer at a much higher frequency than 50/60Hz. Regarding the connectors: you can get these from electronics stores aswell, they are just 2.6mm connectors. id preferably even replace the cables, if you have issues, maybe even with a ticker gauge, depending on how long your cables are and how much load you have. You can see what happens when your connectors if they have too much current on them by looking at nvidias melting power connector.

[FGMatt]

10 hours ago, XG BC said:

these old iron core transformers can put out more voltage than expected, especially since they were wound for 220V/110V nominal depending on region, and not for 230V/120V nominal like it is now. They dont have any voltage regulation on them, just the transformer going into a rectifier, going into a capacitor to smooth out the voltage a bit. Modern switch mode power supplies can control the voltage themselves, and are much smaller and more efficient since you are running the transformer at a much higher frequency than 50/60Hz. Regarding the connectors: you can get these from electronics stores aswell, they are just 2.6mm connectors. id preferably even replace the cables, if you have issues, maybe even with a ticker gauge, depending on how long your cables are and how much load you have. You can see what happens when your connectors if they have too much current on them by looking at nvidias melting power connector.

Most voltages haven’t actually changed; eg the UK “changed” from 240V to 230V by relabelling it. In practice the voltage is allowed to be from slightly under 220V to slightly over 250V, so 240-ish is fine. 

[Toastie]

26 minutes ago, FGMatt said:

so 240-ish is fine

I also believe so. BTW, the larger the amperage of a transformer is, the closer they are producing their labeled voltage. I have a 9VAC, 300mA transformer here, which spits out 14 VAC without load (and breaks down to 9V when loaded) - but my 12VAC/10A transformer puts out 12VAC independent of load ... it's the physics behind the Maxwell equations 

Furthermore, the incandescent lamps TLG was using in their 4.5/9/12V lineup can really tolerate some “overvoltage”. The lifetime of the lamps goes considerably up, when running below nominal voltage. So 12V +2V (- makes it even better) is really not that big of a deal.

All the best
Thorsten