converting AC to DC

How much current do they draw?  If they're not current hogs, I'd just use a bridge rectifier, capacitor, and a three terminal regulator to generate the correct voltage.  If you use an LM317T, you can "tune" the DC voltage to the voltage that makes them work their best.

You can use the previously mentioned LM317 and get the 4.5 volts directly as well.   If you use the LM317T, you can pull about 100ma without a heatsink, additional current will probably require some sort of heatsink.

Another method is an LM2596 DC-DC regulator module.  These go for 99 cents on eBay with free shipping but will take a couple weeks to come from Asia; search eBay for "LM2596 module".  They can deliver 1000 mA or more of current so should be able to drive quite a few signs.

You add a bridge rectifier in front of it to convert AC to DC, adjust the voltage to 4.5VDC or whatever (you need a meter), and you're off to the races.  These modules use switching regulator technology which effectively eliminates heat issues which can be an issue with linear regulators (such as the LM7805 or LM317) when dropping large voltages as you would if going from 14VAC to 4.5VDC.  But as the guys say, if only driving a small load, a linear regulator can be expedient.

If experimenting before final installation, I add screw-terminal connectors for quicker connect/dis-connect.  You can use 4 diodes instead of a bridge if that's what you have handy.  These are illustrated in the upper module in the photo.

Thank you all for your very helpful advice.  (this forum is sure a great place for getting quick answers).  I like Stan's LM 2596 approach. Stan, am I correct that in your accompanying photo the  upper module is a LM 2596 but just with screw-terminals connected on both ends?  Could I power three Miller signs with one module. If so would I wire them in series or parallel?

Bob

Stan has added the screw terminals and diodes to rectify the AC to DC.  You would wire miller signs in parallel using these modules.

LM2596 Module

Why not just buy this?

Well thanks Dave - I didn't know there was such a device.  This sounds like the most elegant solution. Where would be the best place to buy one?

Bob

From Miller Engineering, it's their solution to powering their signs.

Once again thank you John for being so helpful. What a great resource to this forum you are.

Bob

Don't forget these:

AC to DC LM317 Converter

Sort of what gunrunnerjohn was talking about earlier, only ready made. The price has even come down since I got some last year. Maybe I'll get some more?

Definitely can't go wrong using a Miller power supply for a Miller sign!  Note that the Miller module is conveniently pre-set to 4.5VDC output whilst the eBay adjustable LM2596 modules requires a voltmeter to set the output voltage.  It wasn't clear initially that you were using Miller signs or what specific voltage and current capability you needed.

As for the LM2596 module, I see you can now get one that includes the bridge rectifier but it runs about $6 shipped (from Asia) - search eBay for "LM2596 AC module".  So these would be AC or DC input, and adjustable DC output.  I'm sure the price will eventually come down.  And for those that like the convenience of screw-terminals, I figure a version will also appear soon enough.

Seems awful steep for a rectifier!  I can buy the module without that one extra part for $1, so they're getting $5 for a 50 cent bridge rectifier.  I wish I could sell them for that.

Once again I dropped into a forum and learned tons..

I just purchased from ebay a few of the ac-dc to dc boards for some lights on the layout. Now I am sure I ordered the correct ones for my application.

You guys are the best.

Thanks to all

Bob, I know you got a better solution, but to answer your question, Rectifiers are just diodes oriented to produce DC from AC.  The rectifier can also be made via 4 diodes, as seen on some of the products above.

Using diodes to drop voltage is a crude way to do it, but it would be best to rectify AC first than use diodes to drop DC voltage.  You would need less diodes as polarity is already set.  This is how a QSI bottom board does it.  Rectifies AC to DC than uses 4 large diodes to get a lower DC value for the motor.  G