Some questions about making my own version of Tomix's CL

[HantuBlauLOL]

Hi guys..

 

I've bought a LED strip, it's schematic is like this:

 

 

It lits normally when I use a standard smooth DC power pack (tomix's N1), but when I use a CL one it acts weird.

 

It lits when the motor still not running (CL function on), but when the motor starts running it turns off slowly as the motor speed increases.

 

Any fix for this?

Edited August 29, 2015 by HantuBlauLOL

[kvp]

I'm pretty sure that a 12V DC led strip should not work with the different polarity DC that is used to run the trains. Also, your circuit diagram is missing the current limiter resistors, any diode bridges and other components. Third the circuit above is designed for constant voltage operation with a current limited power source, so unless you run your trains at a fixed 12V (or with 3.3V white leds x4 a minimum of 13.2V), it should not work.

 

I might be able to help you if you post a photo of your circuit (preferably connected) and tell us how you connected it to your train. Any other information on the product would also be good.

 

ps: Normally a led strip that goes into a model train should have a diode bridge between the inputs and the leds themselves, normally with a filter capacitor. Installing one without these components would burn out the leds when the train is moved in reverse. Also leds mounted in series have a high turn on voltage, normally usable with fixed voltage DCC only. (the diode bridge+filter capacitor pair is still required)

[HantuBlauLOL]

I haven't installed the rectifier yet, but I had another LED circuit (parallel) that works even without rectifier and cap.

 

Also how much ohms is needed for the current limiting resistor?

Edited August 5, 2015 by HantuBlauLOL

[HantuBlauLOL]

How about if I mod the circuit to become like this

 

 

But I'm still not sure about the resistor value, can you suggest one?

[HantuBlauLOL]

-sorry-

Edited August 5, 2015 by HantuBlauLOL

[mrp]

Are you sure that strip is meant for 12V?  What is the manufacturer / part number?

 

Usually 12V strips have three LEDs in series so that the total of the forward voltage drops is less than the supply voltage.  The forward voltage drop for a white LED is typically about 3.2V, so 3 in series is about 9.6V.

 

Say you want to limit the current at 10mA, the calculation is:

R = (12 - 9.6) / 0.01 = 2.4 / 0.01 = 240 ohms

 

But 4 times 3.2V is 12.8V, which is already higher than your supply voltage.

 

Also, the capacitor should be across the supply voltage - generally after a diode bridge.

 

Something like this:

 

 

RC is optional - just limiting the charge current into the capacitor - maybe about 10 ohms.

 

RL is the current limiting resistor for the LED strip.  I usually use 1K or 2K so that the LEDs aren’t too bright.  But when the total of the LED forward voltage drop is more than the supply voltage then a current limiting resistor doesn’t make much sense to me.

 

 

[HantuBlauLOL]

It was actually for 220V, with some 390 ohms resistor per meter, but I removed the resistors to become usable with 12V. I thought the circuit on first post is already suitable for 12V without the need for resistor. So what I need now? I also can make them all 8 parallel like in some post above, but I'm not sure how much ohms needed to make it works.

[mrp]

​The best configuration for 12V is to have 3 sets of LEDs in series and a current limiting resistor for each set of 3.  Wiring LEDs in parallel is not a great idea because unless the forward voltage drops are prefectly matched you won’t get consistent brightness levels.  I can’t think of any easy way to reconfigure the strip you have so that the LEDs are in groups of 3.  Sorry to say but it’ll probably be easier to just start again with a section of 12V strip.

[kvp]

220V led strips don't work with 12V traction power. The general idea is to use a rectifier, a filter capacitor in parallel (without a current limiting resistor) to be CL compatible, then led + resistor pairs in parallel with the resistor set for 12-18 V operation and the right brightness. (the design voltage maximum must be higher than the maximal voltage of the controller so it won't burn out and the turn on minimum must be lower than the minimal voltage of the controller so it lights up and stays that way)

 

Reasons:

-the diode bridge is needed so the circuit works regardless of direction

-the capacitor is needed for the CL circuit to work (size is determined by the number * current of the leds)

-and there should be no current limit into the filter capacitor as the CL pulse can't work if there is one

-the leds need a current limiting capacitor each (unless they are balanced, but most cheap ones are not)

-and they all have to be connected in parallel to be able to light up at an as low voltage as possible (usually 0.7*2+3.3 = 4.9 ~ 5V)

-also the diode bridge helps keeping the filter capacitor charged when the motor is running, so the motor can't drain it when the CL pulse is off

 

Edited August 6, 2015 by kvp

[HantuBlauLOL]

Yeah.. This one was intended for experiments anyway.

 

-I just haven't installed the bridge, I definitely will, because its not a directional light.

-probably the total current needed for LEDs is about 0.16A. How much farad is needed?

-

-current limiting resistor, you mean?

 

Also another question, what is the resistance of N scale motors? Especially for Tomix motors.

 

I want to add an extra resistor with the same resistance as the motor to balance the light intensity between motor and trailer cars.

 

 

I don't have an avometer..

Edited August 6, 2015 by HantuBlauLOL

[kvp]

 

-probably the total current needed for LEDs is about 0.16A. How much farad is needed?

If i remember correctly, then for Tomix CL this is around 3-4 uF for factory made lighting circuits. Home made ones with high current leds usually use more power and a larger capacitor is needed.

 

-current limiting resistor, you mean?

 

You set the current of each led with a single resistor, that is connected serially with the led. A led without a current limiter is a short with a voltage drop. (for a very short time, since they burn out) The resistor needed for each led is determined by the voltage and allowed current of the led and is different for each type and brand. They are the small rectangles above the leds on my drawing. Please consult your local electronics engineer about the value that is needed for your leds.

 

Also another question, what is the resistance of N scale motors? Especially for Tomix motors.

I want to add an extra resistor with the same resistance as the motor to balance the light intensity between motor and trailer cars.

You have to connect the lighting parallel to the motors, not serially. This means the motor is out of the loop for every lighting circuit, be it in a motor or trailer car. Failing to do so would change the light intensity depending on the load across the motor. (so after the high current and high intensity during starting the lights would just fade out when the motor picks up speed)

 

 

I don't have an avometer..

Any other brand of multimeter would be fine, but you don't need one. First because the values for each part must be calculated before assembling anything, second because the lighting circuit must be independent of the currently existing circuits on board the train and 3rd, because you don't really seem to understand electronics. Buying off the shelf lighting kits or asking a local engineer would be easier and much better.

[inobu]

The CL is sending out a 20kHz 12 volt square wave. It uses Pulse Width Modulation to control speed. The average voltage level illuminates the lights but does not drive the motors.

 

kvp is addressing the key points. The cap has to buffer the 20kHz PWM which maybe the magic number for the 3-4uF cap

 

The PWM has to be regulated in order to drive the LED. The problem is in the forward voltage of the LED.

 

The specifications of the LED's forward voltage needs to be aligned with the supplied voltage (CL). Chances are the voltage requirements of the LED strip exceeds the average voltage output of the CL at "train idle".

 

Inobu

[HantuBlauLOL]

Got it, I'll search for 1-5uf elcos next time I go to shop.

 

Actually I've managed to make it works, I used the full parallel scheme with just one resistor after the bridge, also a 47uf cap before the resistor attached in parallel. It works good, but the 47uf is just too big for some trains.

 

Some months ago I used a 3 in series LED strip like mrp mentioned above, and I use a full bridge rectifier diode also 220uf cap. I wired those in parallel to the motor, but strangely the lighting on the motor car is not as bright as on the lighting on the trailer car. That's why I asked about motor resistance, I thought it would affect it in parallel config too. This one was blue LEDs, because the white one is not available on the shop yet. So I decided to do some experiment with it.

 

Inobu san, I think it could be fixed with a higher capacitor value as it smoothens the PWM signal for the light only.

[HantuBlauLOL]

Hi guys, I wanted to make a CL compatible directional light, but the space is very small. I'm thinking about this, would it work?

 

 

I don't want to start another thread just for asking this..

[kvp]

The capacitor should be on the other (power source) side of the current limiting resistor. Normally you would add diodes to prevent the discharging of the cap by the motor, but that can be left out and it would still work if the cap is slightly larger.

[HantuBlauLOL]

So.. I need 2 resistors?

 

How much farad is required? The space is so little..

[kvp]

You only need one for both leds. Without the diodes the required capacitance depends on the motor, so you should experiment with it. Just make sure it's a polarityless type.