Power requirements for Mafen signals

[alain10025]

Dear all,

 

I recently got some Mafen N-scale signals for my layout ( https://shop.model-fab.com/en/sncf/725-04-8436579380199.html ). I find them really nice and detailed. I am wondering however if there are specific requirements in terms of current. It is written on the box 21V max but there is no mention of any amperage. 

 

I am planning on building a little circuit with 6-pin switches to activate these signals and I cannot find any specifications that would allow me to chose my power supply. 

 

I was able to find that the LEDs of these signals (which seem to be SMD 0603) have a low amperage requirement but the Mafen signals come with electrical resistances so I am guessing higher amperage may be ok... 

 

Have you ever used these signals on your layout ? Would you have any recommendation for wiring them ?

 

Thank you !

 

 

Edited August 5 by alain10025
didn't say "hi" !

[cteno4]

Most all 0603 LEDs I’ve seen and used have been standard 20mA, but I always run them a bit lower (usually a lot lower). The ones you linked to are rated for 20mA.

 

jeff

[alain10025]

9 hours ago, cteno4 said:

Most all 0603 LEDs I’ve seen and used have been standard 20mA, but I always run them a bit lower (usually a lot lower). The ones you linked to are rated for 20mA.

 

jeff

Thank you for your reply ! Would you have any advice for how to wire these LEDs ? It is my first time planning such wiring and I am thinking of some kind of board with 6-pin switches but this is all blurry to me... May I ask what kind of power supply you used ? Thank you !

[cteno4]

For led lighting I generally use 5v power supply as I don’t usually run LEDs in series, just each on their own. This way it’s not wasting more power jsut heating up resistors more. 

 

With each led you need a resistor in line with it to reduce the current to what you want for the LED. In general most leds we use are 20mA LEDs, so best to run them at like 15-16mA to not be running them full out and last longer.

 

to calculate the resistor needed you use this little equation   V = I * R   Or solving for the desired resistance value  R = V / I

 

Where

 

V is the voltage from from your supply to the voltage the led uses. Most led are 3-3.5v so to be conservative a bit V would be 5v - 3v = 2v power drop needed.

 

I is the amperage you want to run the led at. In this case they are 20mA max so conservative run them at 15mA

 

so R = 2 / 0.015 or R = 133ohm

closes bigger resistor value in 1/4w resistors is a 150ohm

 

make sense?

 

im not sure about what you are talking about a board with a 6 pin switch. You mean a rotary 6 position switch? How do you want to control the LEDs for the signal. I assume each position on the rotary switch would light up a different combination of the 4 LEDs?

 

you could do a little board that just took the wires from each led of the signal with a resistor in line and the rotary switch supplied the power in different permutation at each terminal of the rotary switch. Would be a bunch of little jump wires from the switch terminals. But the issue with this is only a small permutation of all the light combinations can be done like each one on alone or two on together and two on individually. To get all the combinations then you need some sort of an isolator chip. A small nano arduino board does this great as it can power each led on different I/o circuits so you could do any permutation of lit LEDs at a time. But then you need to have a way to tell the arduino what combination you want, so it’s not simple. Multi channel dcc decoders can also do the same thing as an arduino but again you have to develop an interface or program to set the desired combo on the decoder.

 

jeff

 

[alain10025]

Jeff, first of all, thank you very much for your detailed reply ! 

 

The reason I am puzzled about the power supply for the Mafen signals is because there already is a resistor built-in and the only specification is the max voltage (typically 21V DC). I am quite new to electrical (or should I say electronical here) wiring but I understand the V = R * I relation you indicate. I guess I was wrong to expect a specification in amp as the power supply will impose the voltage and the intensity will be a consequence of the resistor on the signal.

 

I take note of your comment with respect to the amp recommendation (15 mA instead of 20 mA max) and I understand this will actually translate into a reduced voltage (around 15.5 V since the max voltage is 21 V).

 

With respect to the 6-pin switch, I am talking about this kind of switch. My idea would be to have a simplified command for the signal (one position of the switch to turn on the red LED, and the other one for the red LED for instance). 

 

So, basically, in terms of wiring, I was considering a DC power supply, connected to the aforementioned switch and the signal. Do you see what I mean ?

 

I am really new to this kind of thing, so far, my only experience with LED is the connection of Kato LED lights... which is pretty straight forward :)

 

I cannot find much details on basic wiring for Mafen signals but I see a couple of posts here and there talking a bout "Qdecoders"... I guess this is basically a "xxl" switch that already embeds the different combination of lightings for the signals that may feature a large number of LEDs but I am not really sure.

 

Thank you !

 

Alain

 

 

[Kingmeow]

Your power supply current should be greater than or equal to the total current that all your LEDs draw, when on.  You will not blow out any LEDs (with resistor) by using a power supply with "too much" current.  Your device(s), in this case LEDs, will draw whatever current it needs and is rated at.

 

For example, you can use a 1A or even a 10A power supply to power a single LED if thy forward voltage calculation noted by Jeff above is followed and you add the appropriate dropping resistor.

[cteno4]

Hi Alan,

 

Yes as kingmeow says you don’t need to worry at all about your power supply amperage, the resistor limits the current on the down side no matter how many amps your power side could provide! One of those neat tricks of physics/electronics.

 

Even for signals, LEDs are quite intense pin points of light so always being conservative won’t really effect brightness that much and save you from burning a led out.

 

Sorry your switch link didn’t work, but I now think I get your 6 pin switch being like a 6 pin dip switch maybe? Then each led on a signal would have its single switch. That works great. Just route the positive of the power thru the switches with a resistor on each of the other switch pins and the resistor soldered to positive terminal of each led. All the negative leads of the LEDs can go to a common ground (negative) of the power supply.

 

yes there are fancy multi I/o dcc decoders out there to control stuff like signals like this that is then run by layout control software, but that gets int a lot more heavy automation and programming usually.

 

jeff

[alain10025]

Kingmeow and Jeff, thank you ! I am having a much clearer picture of what I need to do.

 

Jeff, with respect to the 6-pin switch, yes, I was thinking about as solution similar to the one you link to, I believe it can be an easy way to control my signals.

 

Alain

[cteno4]

Yep they would be very simple just have to pop the switches to the pattern you want. The dip switches are pretty tiny, usually with switches are 2.54mm on center so you really need to flip them with a little stick. A piece of down sharpened down on one end and flatted a bit works well. They are meant to be setting switches and not used much once set. Not sure of their life span for throws as though, but I expect many thousands.

 

When I was a kid there was a chap in our neighborhood with a massive ho layout that had traditional signaling system with the rotary switches like in prototype controls. But they operated by huge bank of relays to throw switches and signals, it was an amazing job of engineering.

 

jeff

[alain10025]

I finally decided to order a few on/off switches (of this type), I intend to use one for each set of colors on the signals. Thank you again for your advice !

 

Alain

[cteno4]

Alain,

 

there are much smaller (and cheaper) mini toggle switches (and prewired mini toggle switches) that may help make your control panel smaller also on ebay and aliexpress. They take a week or two to get to you and same stuff Amazon is selling (and at times the same sellers).

 

jeff

[alain10025]

Very nice, thank you Jeff !