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Latest project - adding LED's to the Williams EZ Street police car!

I wired the five LED's (two headlights, one flashing light for the siren, and two taillights) in series and the circuit was fine when tested before installation in the vehicle.  When I connected the positive lead to the pickup roller and grounded the negative lead (installed them in the vehicle) they ceased to function properly.  The strobe light does not flash regularly and the headlights and tail lights flicker.  I am running them off of a DC power source for the flashing LED.

Should I have wired them parallel with resistors or do I need a small constant voltage power source in the vehicle?  Any help would be appreciated.

I am sure someone will ask me for more information, as I am sure I have left something out of this post !



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There may be 2 issues here.   First if the strobe has an internal flashing circuit in the LED, it needs to be wired with its own dropping resistor in parallel to the others.   Otherwise the internal flashing circuit is trying to cycle all the LEDs in the series.  Second if the total voltage drop of the 5 LEDs exceeds the supply voltage, they won't light. For example white LEDs have a drop of 3-3.5 volts and red LEDs are 1.8-2.1 volts.  So for 2 white and 3 red LEDs, your total voltage drop is around 12.4 volts if they are all in series.   If the supply voltage is less than that they won't light.  You may need to separate the strobe into one circuit, and the headlights in another, and the tail lights in a 3rd circuit.   Each will need a different dropping resistor which can be calculated here.  You will need the DC supply voltage to make the calculation either from the documentation or measuring it with a multimeter.

I am not clear why it worked in the test setup but not in the installation.   If there is an external flash circuit, again, it needs to be only supplying the strobe LED.

You state you are running them off a DC power source, but if you are connecting them to pickup rollers and ground, you are using AC.  It needs to be rectified to DC, or the LEDs will have a short life.  Since AC track power is variable, you should also use a voltage regulator circuit.   I know this got complicated in a hurry . . .


The track is being powered with a DC supply, not AC.  Superstreets vehicles will run on either.

I wondered about the variable power to the pickup rollers ... ?

But, I thought it may have something to do with running them in series.  They do light when given appropriate voltage from the source.  If the flasher is the 3rd light in the sequence, would it still being trying to control the entire series, or just the lights that come after it in sequence?


Anything in the series string will be affected by the flasher in the string.  You MUST supply pure DC to a flashing LED, and it needs to be alone in the circuit.  Also, "DC" on the rails isn't sufficient.  Another point, with DC on the rails, what happens when you reverse polarity to run the other direction?  You reverse the polarity to the LED's and they all stop working.

OK.  If the vehicle can run on AC or DC, there is at least a diode or rectifier in the car converting to DC for the motor.   Depending on whether there are other components this could drop the supply voltage in the car.   That would explain the circuit working externally but not in the car's circuit.

If you are using a flasher LED, it will flash all other LEDs in series with it, no matter where it is in the series circuit.  It will need to be in its own circuit with a current limiting resistor.

Without knowing what circuit components are in the car, one option is to create 3 circuits as I described in my first post and run them off track power (center roller and frame/ground).   This will bypass the circuit in the car.   Use the LED calculator to get the value of the current limiting resistor for each circuit.  Enter the maximum DC voltage that will be applied to the track.  This assumes that there will be no reversing switch that changes the polarity.  The downside is that they may not light at lower voltages.

Constant lighting will require a voltage regulator.   Electronics Gurus Gunrunner John and Stan may weigh in on this.   Also Lee Willis is the expert on all things 'Streets.   I suggest doing a forum search on his posts.   


@dennish posted:

...Latest project - adding LED's to the Williams EZ Street police car!

... I am running them off of a DC power source for the flashing LED.

So we're all on the same page, you have this:


Can you tell us what flashing LED you have? 

You say the circuit tested "fine" on the bench.  By circuit you mean the 5 LEDs connected in-series?  And the head/tail lights maintained constant brightness even when the strobe LED blinked?

Do you have a photo of the guts of the car?  I'm curious available space to add more "stuff."  With a motor, gear transmission, and probably a diode or bridge rectifier to allow AC operation, there may not be much room for adding a voltage regulator, capacitor, or whatever.

As for the variable voltage, I'd think you'd want to be able to adjust speed and maintain constant brightness or something close to constant brightness.  If this is what you want, have you experimented to find what range of DC voltage you see operating the car at?  This range of voltage will dictate the type of circuit needed.


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stan2004 - Yes, that is the correct EZ Street vehicle.  The LED is a standard 3mm Red Color Diffuse Flashing LED from LED Switch.  The five light circuit did function properly when bench tested with a constant DC power source.

Bob - I think you are on to the cause of my problem.  I am planning on rewiring them in parallel as you stated.  I am hoping that solves the problem.

GRJ - I am leaving the rectifier alone and do not plan on running them in reverse, so that should not be an issue.  I chose the DC power as I seem to remember Lee Willis advocating that for finer control over the Streets vehicles.  Didn't you develop a small constant voltage board sometime in the last several years?  I seem to remember reading about it.  Would that be a suitable way for constant voltage to the LED's?


If going bare-bones, I suggest at least investing in a diode to isolate the LED circuit (and its capacitor) from the motor.  Otherwise the capacitor is going to "waste" its stored energy driving the motor during voltage drop-outs.  Apparently the motor's existing momentum is good enough to ride-thru the intermittent hiccups in power.

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