I would like to power this sign from a 120v supply.

It used to be powered from 3 AA batteries in series (4.5vdc)




There is a 10 ohm 5% resistor (brown, black, black, gold) on the positive lead.


I have this transformer for the power supply but I realized it wasn't going to supply DC to the leds. Is there a reasonable way to make this transformer work or a recommendation for an alternative power supply?

 

Looking at your transformer it says 24Vac/ 25Vac (possibly a 24-0-24 centre tapped one,) so ideally all your 9 Leds need to be wired in Series with a resistor, and use two 1N4001/5 type Diodes to make a Full Wave bridge rectifier.




If the leds are about 2.5V each or higher, i would split the leds 5 on one half, 4 on the other, and use two resistors say 100 to 150 ohms, choose resistors to give equal brightness.

 

Otherwise, go to just about any junk shop or OpShop and get an old regulated 5V plug pack. That will do it but if you are worried about it not being 4.5Volts, just add one series 1N400x diode in line, with the stripe end (cathode) to the resistor in the LED +Ve line, and the non stripe end (anode) to the power supply +5V line. The diode will drop about 0.7V to keep the supply within the old battery range.

 

Sorry if my transformer nameplate was illegible in the first post but it's actually 120V AC input and 2.25V+2.25V AC 300mA output.

 

View attachment 128633
Sorry if my transformer nameplate was illegible in the first post but it's actually 120V AC input and 2.25V+2.25V AC 300mA output.

Right that's approx 4.5V with load so you can put leds in parallel with series resistors in each led,say 100 to 150 ohms,, with a four diode bridge rectifier.

 

Right that's approx 4.5V with load so you can put leds in parallel with series resistors in each led,say 100 to 150 ohms,, with a four diode bridge rectifier.


View attachment 128634

Where would the taps on the transformer connect in that diagram?

 

Where would the taps on the transformer connect in that diagram?

Use the Reds only, this will give you 4.5VAC like this....

 

By your questions I assume you are an electronics novice so I'd recommend you do not proceed with using this transformer as it entails wiring mains voltages.
Try instead using an old 5V power supply as I mentioned earlier.


Or get someone who knows what they are doing to wire the transformer. You can easily kill yourself (or someone else) playing with mains power!
If you go ahead with this, please be careful connecting the transformer up.
The black wires go to the mains.
The green wire will not be used.
The red wires go to the AC inputs of a bridge rectifier.

 

By your questions I assume you are an electronics novice so I'd recommend you do not proceed with using this transformer as it entails wiring mains voltages.
Try instead using an old 5V power supply as I mentioned earlier.
View attachment 128640

Or get someone who knows what they are doing to wire the transformer. You can easily kill yourself (or someone else) playing with mains power!
If you go ahead with this, please be careful connecting the transformer up.
The black wires go to the mains.
The green wire will not be used.
The red wires go to the AC inputs of a bridge rectifier.

View attachment 128639

Thank you for the replies, while I am an electronics novice I promise I'm familiar with conventional electricity and I will be able to test the device in a shop prior to installing.

Just to clarify, I will build the rectifier bridge sketched above. Should I use IN7004 diodes as previously specified? Also there are not any resistors in the diagram, should I remove the existing 10 Ohm resistor that was used when batteries were the power source?

 

Your leds are all wired in Parallel without a series resistor, chances are the 4.5vdc will make them light up but brighter, with the original 10ohms, when they were on the batteries they relied on the battery internal resistance to also drop the current, yes use any diodes 1N4001/7 try it...

 

The diode on the 5VDC power pack is largely unnecessary given most new 1.5 volt alkaline batteries will run at 1.6 - 1.8 volts (~ 4.8 - 5.4 VDC for a three cell pack) for some time before dropping down to their nominal 1.5 volt rating.