Lionel Train Electronic assistance...

[JJ Harris]

To Whom it May Concern... searching the internet for help and ran across your website... lots and lots of useful and helpful information... THANKS for making it available, however I have a "problem" and cannot locate a positive answer from your information and thought maybe you could point me in the right direction.

LIONEL... I have installed some alternating flashing LED Ditch Lights... they work GREAT with locomotive sitting still, regardless of track voltage.

Here is what I have done... from the track I pickup the AC voltage, rectify with a bridge, send the DC voltage to a 7805 regulator... the output of the 7805 DC- is sent to a purchased flasher board. The 7805 has .1 uf ceramic capacitors on input and output leads to ground... the DC+ output of the 7805 has 68 ohm resistor connected LED cathode... the flasher board is connected to the other side of the LED... the flashing is via DC- being switched.

EVERYTHING WORKS GREAT when locomotive is sitting still, regardless of the track voltage, BUT when the locomotive starts to move these LEDs operation become erratic, regardless of track voltage. I ALSO installed a 10 uf electrolytic across the LED connection, after problems cropped up, which helped, but still erratic.

Suspect back EMF from the dual motors???

I would appreciate you pointing me to one of your articles or somewhere else that may have a simple answer.

Exciting circuit... looks great... just erratic is all.

THANK YOU so much for any reference materials or assistance, Jay

 

[cowboybob]

Welcome, JJ Harris!

Can you supply us with a schematic, or at least a block diagram (as detailed as possible) of your circuit?

...from the track I pickup the AC voltage,...

Also some voltages, before and after the bridge and the flasher ciruit, with and without the train running, would be a help. I am assuming that you are varying the track voltage over a 0VAC to some higher VAC, as one would with a train set.

It does sound as though the train's motors are drawing down the voltage levels below the operating voltage of either the flasher circuit and/or the LEDs. The intermittent functioning might be related to the intermittent connection of the train to the tracks, not unheard of with train sets (had a really cool Lionel when I was 8!!).

There is also a minimum voltage below which the 7805 cannot maintain 5VDC.

I am curious why you're switching the DC- line.

 

[audioguru]

The AC voltage is rectified with a bridge, then NO BIG MAIN FILTER CAPACITOR so the input to the 5V regulator is jumping up and down at 120Hz.

 

[JJ Harris]

I will prepare a sketch of the circuit and measure some points of interest and post ASAP... THANKS, JJ

 

[4pyros]

You need to add a big cap after the rectifier.

You can look here;

https://electronics.stackexchange.com/questions/73863/cap-value-for-full-wave-rectifier-circuit

 

[JJ Harris]

THANKS... I suspected a capacitor is what I needed, but just how BIG??? Of course space is a concern... here is what I am working with... again, with any amount of track AC Voltage, the circuit works perfectly as long as the locomotive is sitting still... motors not running, but when the motors start, the operation become "erratic" and the flashing LEDs are not in sync, both are lit sometimes or just either one and then it will start flashing in sync then erratic, never turning completely off. PLEASE REVIEW and suggest what capacitor I should use... currently you will note some .1uf I installed as smoothing capacitors. THANK YOU, JJ

 

[MikeMl]

The brushes in the train motors are arcing, and the inductance of the motor winding(s) causes a spike between the tracks. I would try two things: First, put a 1000uF 25V electrolytic capacitor across the output of the bridge, in parallel with the 0.1uF at the input of the 7805. Second, if the cap doesn't fix it, add a 100 Ohm resistor between the + side of the bridge and the + side of the 1000uF capacitor.

 

[4pyros]

.1uf I installed as smoothing capacitors.

The .1uf is not a smoothing cap, its to keep the regulator stable and should be as close to the regulator as possible to do its job.

I suspected a capacitor is what I needed, but just how BIG???

Without doing all the math you start at 100uf and work up from there until the flasher circuit work and then add a little more.

 

[JJ Harris]

THANKS everyone for some suggestions and ideas... will review them all and starting with the easiest suggestion first, I will continue till the problem is solved. I will advise the "fix" and do sincerely appreciate the ALL the input, suggestions and ideas. Sincerely, JJ

 

[JJ Harris]

PROBLEM RESOLVED... THANKS to everyone who made suggestions... simple fix, just added a 1000uf @ 35VDC electrolytic capacitor behind the bridge rectifier and before the regulator... all is well... works perfectly... attached is a revised sketch that may be helpful to anyone else experiencing a similar problem... THANKS AGAIN, JJ

 

[4pyros]

Did you step up the capacitance or did you go strait to 1000uf?

 

[JJ Harris]

Hi... went straight to the 1000uf... I live in rural Florida with no place locally or nearby to get parts on impulse except Radio Shack... that is only 35V size they had in stock... the 50V selection, slightly better, were too large physically for the space I had. JJ

 

[crutschow]

What is the maximum AC voltage?

 

[JJ Harris]

My transformer maximum output is 23VAC... THANKS, JJ

 

[Mike odom]

also, your 68 ohm resistor feeds the LED anode, not cathode, as you stated in post #1.

 

[JJ Harris]

OOPS... JJ

 

[crutschow]

My transformer maximum output is 23VAC... THANKS, JJ

It that's RMS then the peak voltage from the rectifier output is about 31Vdc, which is acceptably below the 35Vdc rating of your capacitor for reasonable reliability.