AC/DC Circuit Design Help?

You may want to look into a multi-voltage output power supply like this.

Just plug it in, and multiple voltage outputs are available.

Larry

This ac/dc adjustable buck converter would likely do what you described

Larry...

Well aware of these adjustable wall warts.  But I was trying to avoid a separate external connection for this accessory after modification.  Would prefer to have it powered with the same 2-wire AC accessory connection to the Fahnestock clips.

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Andy B....

Looks like a good possibility!!!  Thanks for the tip!

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Appreciate the help.

KD

What PW accessories would this fan and ac/dc fit into?

How about just using a small ac motor, i found mine seaching low rpm ac motor, lots of dc but there is an ac version, trade off is reduced rpms, not sure what your blowing but if 3 to 18 rpm is available 

dkdkrd posted:

I'd like to add a device to an existing Lionel PW accessory.  

This supplement would have a small micro-motor, like the small can motors in R/C drones, the fan smoke unit in our larger locomotives, etc..   In fact, this device will be simply creating a small airflow (no heater/smoke), using a small plastic impeller pressed on the motor shaft end.

Ideally, I'd like to have the motor (DC) powered by a circuit connected to the existing two Fahnestock clips of the accessory.  That would dictate the AC input.  Looking at the variety of micro-motors, however, their power needs seem to range from about 0.6V to 6.0V DC, depending on the motor size.  Since they'd only be pushing air, I don't believe the load would be much above the free load.

I've always been intrigued with the small in-line circuit that Evans Design has with their LED's, offering AC/DC conversion as well as the reduced voltage for powering the LED.  But, that circuit is apparently incapable of powering, say, a 1.5v micromotor (so I found out empirically!  ).

Possible circuit design?  Alterations required to accommodate various micro-motor DC requirements?

Any/all help appreciated! 

KD

Are you trying to turn a search light beacon with a small fan ?   J

andy b posted:

This ac/dc adjustable buck converter would likely do what you described

Note the minimum DC output for this module is 3.3V which may not be low enough for OP's application - he mentions a 1.5V DC micro motor for example.  Also, the AC input range is limited to 20V maximum.  This is fine for 14-16V AC Accessory voltage from a train transformer.  BUT, if choosing just one AC-to-DC converter module to "stock" your parts bin, I'd choose one with a higher AC range.  That is, one might want a module like this in a piece of rolling stock where AC track voltage from some transformers might exceed 20V AC.  I can't see the parts used on the module but the limitation is usually the IC regulator chip's voltage handling capability.

If you don't mind a bit of soldering (which you might be doing anyway to connect your motor), for less than $2

A 10 cent bridge rectifier (unfortunately you have to buy 10) performs the AC-to-DC conversion.  The LM2596 type DC-to-DC regulator does the adjustable voltage regulation down to 1.5V.  If you do get one of these LM2596 modules get one with a 220uF capacitor particularly on the input side.  Many LM2596 modules on eBay have only a 100uF on the input side.  You can see the 100 of 220 on the capacitor in the photo.  I think either will work fine in your specific application but for the same cost I'd get a 220uF version when doing AC-to-DC conversion.

It might be a challenge to find a low-cost off-the-shelf regulator that goes down to 0.5V DC.  Note that you can attach one of your 9 spare bridge rectifiers to the OUTPUT of the module.  This will drop the output voltage by another 1.5V or so.  So if you adjust the module to 2.0V DC, the motor will actually see only 0.5V DC.  You'll lose precise voltage load regulation but if just driving a DC motor, it will be adequate.

To be sure, there are many more options.  Yes/no soldering, with/without screw-terminal connectors, bigger/smaller, wider/narrower voltage ranges, etc. 

stan2004 posted:

andy b posted:

This ac/dc adjustable buck converter would likely do what you described

It might be a challenge to find a low-cost off-the-shelf regulator that goes down to 0.5V DC.  Note that you can attach one of your 9 spare bridge rectifiers to the OUTPUT of the module.  This will drop the output voltage by another 1.5V or so.  So if you adjust the module to 2.0V DC, the motor will actually see only 0.5V DC.  You'll lose precise voltage load regulation but if just driving a DC motor, it will be adequate.

To be sure, there are many more options.  Yes/no soldering, with/without screw-terminal connectors, bigger/smaller, wider/narrower voltage ranges, etc. 

Another option would be to set the buck converter to 1.5 - 2V output, then add a combination of regular and/or Schottke diodes in series to drop the voltage to where you want it around 0.5V.  For example, setting the output to 1.7V and then adding two regular diodes (which typically drop 0.6V each) in series would provide your motor with 0.5V.