How to deliver variable AC 5 - 18 volts ???

Goeytex

Senior Member
Some motors (inductive loads) will not operate well (or at all) with phase angle control. Phase angle control ( typical dimmer circuit) is generally. but not always, used for control of resistive loads (Lamps, heaters, furnaces, etc.) Phase angle firing also generates a large amount of electrical noise as well as annoying acoustical noise when used for motor control.
 

fernando_g

Senior Member
I remember reading somewhere in this thread that the motors were universal motors, which is another way to say series wound motors.

If that is the case, they will work with AC or any polarity DC.

And controlling variable DC with a Picaxe is far easier and more accurate.....and the trains will run smoother too.
 

joe paul

Senior Member
Hi Fernando G and Folks,

For backward compatibility, because a DC off-set is used to trigger bell, horn, whistle, it needs to be variable AC on the rails. There are electronics on-board that might not do well with PWM DC, also. I have tested older locos with Picaxe PWM DC, and they run o.k., but there may be issues with heating and mechanical reversing units which are solenoids that are energized all the time the motor is running. The idea is to imitate an old transformer's variable AC wave form as closely as possible, but I have found my own work-around for now. Thanks, everyone, for the help, ideas and suggestions!

Take care, Joe.
 

nekomatic

Member
I'm coming in a bit late here but what's the maximum current requirement - could an audio power amplifier do the job if fed with a suitable input signal? An amplifier specified for 40 W into 8 ohms should be able to deliver 18 V AC at a couple of amps. You can get suitable modules new on eBay fairly cheap or you could just find and use an old hi-fi amp as is. You'd need to provide a suitable input signal, there are lots of ways you could do this but one way would be to generate a DC voltage from PICAXE DAC, smoothed with a capacitor, gate this on/off with a PWM signal and transistor or MOSFET, and pass the resulting square wave to an RC low-pass filter.
 

joe paul

Senior Member
Hi Folks,

It was this:


Crude, but simple, diode string, but you need hefty diodes. Output to the track would vary depending on which relay the Picaxe energizes, one at a time. (I posted the above on page 3 of this thread.)

For the DC off-set, something like this, but a relay instead of the push button:





Take care, Joe.
 
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