RR_Mel Too many variables. Is the power supply well filtered? If you had the LEDs in series with capacitors if the capacitors became charged the LED would not offer enough load for the LEDs to work. Need more accurate description of how you have it wired. Are the capacitors really Farad or mfd? Try charging the capacitors with the power supply then connect them to the LEDs. Mel
The power supply is nothing more than an MRC train transformer.
When applied to this circuit the voltage went up, probably due to feedback from the circuit that I was testing.
In normal operation on the railroad, the circuit will live in a more highly controled environment, 10.2 volts of well regulated dc.
I guess the FWR (Full Wave Rectifier) was usurping enough voltage that little got across to the circuit in question. I will take input readings from my transformer, and will put a meter across the output of the rectifyer.
RAOR
The Route of the Broadway Lion The Largest Subway Layout in North Dakota.
Here there be cats. LIONS with CAMERAS
BroadwayLionHim puts five volts bench power on the circuit, lights come on as condencers charge, but wait what is this: without touching the input voltage the bench volt meter is now reading 8, no wait, 9 volts! This cannot be good for my condencers, but the voltage must be coming from the condensers, for I have not changed the bench power. Hmmmm....
Hmmmm....
I don't think I understood this.
you have a DC bench supply with a meter and a knob that allows you to adjust the bench supply voltage which you can see using the meter. You set the bench supply to 5V with nothing connected to it. But when you connect it to the super-caps and LEDs, did you say you observed a voltage greated than 5V on the bench supply meter ??
BroadwayLionLION got some 12v LED strips, one for each car. At 12 v these are very bright, at 5 volts, they are still OK
i'm also surprised that LEDs could operate over a such a wide voltage range, 5-12V. I don't understand why an LED that can operate at 5V doesn't burn out at over twice the voltage. There must at least be a resistor in series with the LEDs.
BroadwayLionWell lets add the rectifier so that we can be sure to have the correct polarity onboard our train. HEY, now nothing works.
HEY, now nothing works.
As Randy said, there's a voltage drop across the 2 conducting diodes of the bridge, 1.4V = 2 * 0.7. This would reduce the bench supply voltage from 5V to 3.6V which may be below the minimum operating voltage of the LEDs.
This can easily be tested measuring the voltage at the bridge rectifier output. It should be 1.4V less than the input. The bench supply voltage can be raised until the voltage at the bridge rectifier output is 5V or until the LEDs begin to light.
greg - Philadelphia & Reading / Reading
You didn;t accidently get a 7905 -5 regulator, did you? That one goes ground, input, output from left to right. A 7805 +5 regulator should be input, ground, output.
I'm thinking you may have strange results until the track voltage gets high enough - the regulator needs about 2V more than the expected output, plus you have 2 diode drops through the bridge that keeps the polarity straight, so you won't get 5V out until you are feeding the circuit with almost 9 volts. If your power supplies do pulse power, you can put a smaller cap, maybe 50uF, across the DC terminals of the bridge, which will charge to the pulse peak even if the throttle is at a lower setting.
Ptherwise, the rest of the design should work. You might want to put a diode and 100 ohm resistor in series with the super cap to block inrush current. The diode and resistor go in parallel, with the diode oriented such that when the regulator side is more positive, the current has to flow through the resistor. When the input voltage drops and the caps have to supply power, it goes out via the diode. Like the old DIY version of keep alive from Marcus Ammann. Whose site is missing one of the header tags and will not display at all in IE, just ends up downloading the HTML code.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
The LION and his circuit: to keep passenger lighting ON while the train stops (Non DCC version)
LION got some 12v LED strips, one for each car. At 12 v these are very bright, at 5 volts, they are still OK, which is good, since LION thinks he wants to work with a 5 volt circuit.
LION got some 2.5 Volt, 4.7 Farad condensers. Him put two together in series like a battery giving him a 5 volt, 2.3r Farad device.
Him puts five volts bench power on the circuit, lights come on as condencers charge, but wait what is this: without touching the input voltage the bench volt meter is now reading 8, no wait, 9 volts! This cannot be good for my condencers, but the voltage must be coming from the condensers, for I have not changed the bench power.
Well lets add the rectifier so that we can be sure to have the correct polarity onboard our train.
HEY, now nothing works. (Test -full wave- rectifier on bench... checks Ok)
LION got 5v regulator. Him not add it to circuit yet as the circuit is not happy yet.
But how ought I to wire this regulator. The center pin is Common, ergo negative in my circuit. But which side is raw voltage and which side is output voltage. From pictures LION sees, if regulator is lying flat with heat sink to the rear, it seems as if the right pin is raw, and the left pin is regulated.
Would the addition of this regulator fix things, or only complicate things. |LION turned off the lights and the soldering iron and came back down to the office to contemplate matters.
Do any electronic knobs here have suggestions for LION. Him trade you a nice peice of wildebeest for a good answer.
ROAR