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DCC-AC-DC Rectifier
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[quote]QUOTE: <i>Originally posted by claycts</i> <br /><br />Im a little dense on this one. <br />1. DCC is AC voltage in the rails <br />2. HO power is DC from the rails 0-12v about <br />3. There is a AC/DC rectifier IN the decoder to allow the DC motor to run on AC power? <br />I would like to get this into my itty,bitty brain before I start doing the ConEdison things on my MESSterpece. <br />Thank you <br />George P. <br />"no train work till AFTER the car show"[xx(] <br />[/quote] <br /> <br />Well, time for an electornics engineer to see red, not at your post George, but at some of the horrific misinformation given in repsonse to it. <br /> <br />1.. DCC is AC power on the rails. The DC component of a DCC signal is, or should be very close to, ZERO. But it is not AC like you get from Con Edision, it is a high freqnewcy square wave AC which is modified by the DATA which is being sent ot the decoders. <br /> <br />2.. DC power (what you refer to as HO power) is somewhere between 0 and about 15 or maybe even 18 volts depending on your power pack. <br /> <br />3.. Yes, their is a rectifier on the decoder board. And YES, if does supply the power for the motor! But not directly. Here is how a decoder works: <br /> <br />The AC signal from the track is passed through a rectifier, a small amount of signal is 'sniffed' off the big signal and is sent to the decoder to be decoded. The bulk of this power is then filtered and becomes pretty good clean DC. <br /> <br />Another part of the decoder is called the 'H' bridge. You dont need to know why, but it is because when the circuti is drawn out it looks like an 'H'! This 'H' bridge is used to control the power flow to the motor to control its speed. But varying a DC voltgae, like you do in a DC power pack, is horribly inefficient and produces a lot of waste heat. SOmething we cannot deal with in the loco. So the itty-bitty little microprocessor on the decoder produces what is known as a PWM, Pulse Width Modulated, signal which turns the 'H' bridge on an off to control the AVERAGE output to the motor. This is very efficient, because the control circuitry is ON or OFF - both states dissipatihng virtually no power and resulting in pretty close to zero heat output. <br /> <br />The motor, by virtue of its mechanical inertia effectively integrates this signal and thus it has the same effect as DC. <br /> <br />But this is also the 'growl' or 'whine' you hear in some older and cheaper DCC decoders. If the PWM signal is within the audible frequency range the motor windings can act like a loudspeaker and you can 'hear' the PWM. <br /> <br />ERRORS SPOTTED ELSEWHERE: <br /> <br />The rectifier diodes on the average decoder board that I have seen are quire capable of handling between 1 and 3 Amps. When it is kmoving the average N or HO loco only consumes a few hundred milliamps. But the average decoder is capable of handling anywhere from 1.5 to 2 Amps to handle the loco when it stalls. The limitation on the current that is avilable to the motor is a fiunction of the 'H' bridge more than the rectifier. <br /> <br />Whether we like it or not, the signal on the rails in DCC is AC. It is not sine wave, and in fact it is not square wave either! <br /> <br />If you want to power lamps from DCC powered tracks, you dont need the rectifier, just use a resistor to limit the voltage to something reasonable. <br /> <br />If you need to use LED's then use the bridge. You can either use 4 individual 1N4001 or similar diodes, or you can buy small bridges in an integrated package that would be more conventient due to the reduced amount of soldering. Ask your friendly local supplier for something rated 50PIV or greater at about 1 AMP. <br /> <br />I hope this helps clarify some things. <br />John <br /> <br /> <br /> <br />
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