Menards 4.5 volt power adaptor

You have to test the output under its intended load to get accurate readings from unregulated power supplies like this.

We are not talking amps here. Amps change under load. voltage remains constant. 4.5 volts output should not be 8.9v, thats double the voltage.

Pat

Amperage is half(actually a third) of the equation. Until you try it, it appears you will never believe it.

This is totally normal for non-regulated wall wart type linear supplies.

What are the complete specifications on the label of the power supply?

Label reads: Output 4.5 volts DC 1000 mA. With my meter, I'm getting 8.9 volts from each jack. double the voltage. This adaptor is mislabeled. Like a train transformer that outputs

18 volts and you double it to 36 volts, you will have damage. I have a 4.5 V adaptor from radio shack and it reads 4.8V.

Pat

OK - it's not mislabeled - that output is with a 1 amp load - quite a bit for a cheap wall wart.  The cheaper the power supply, generally, the higher the open circuit voltage over the rated figures. It's completely normal.

Do that same test with a 1/2 to 1 amp load(use ~6 volt light bulbs for a "safe" test). You will see the voltage drop to within 10% of 4.5 volts.

I believe this has been brought up and discussed here many times before. ADCX Rob has it, this is an un-regulated power supply. Try what Rob says to test it and see for yourself. Regulated power supplies are more accurate and read much closer to specs with load or no load. Un-regulated power supplies can be all over the place with no load.

Now this in knowledge I can use

Thanks Rob for the info. I guess the magic word is unregulated.

Pat

To test the power supply, put a 5 ohm power resistor across the output and measure the voltage again.  It will be down near 4.5 volts.  The voltage will depend on the load, and you have now simple way to determine what the load is.  You could start by using a 5 ohm resistor and hook up your load with the 5 ohm resistor.  If the voltage is too low, increase the size of the resistor until your load with the resistor results in a 4.5 volt output.

The power dissipated in the resistor is V^2/R, so make sure the resistor can dissipate the power.  V should be around 5 volts with the resistor connected, and so V^2/R is about 5 watts.  The resistor is going to get hot.

My problem with this unit is the "L" shaped plug that requires a large hole through the train board to use it. A straight plug would require a small hole to pass it through.

I don't like those 90 degree connectors either. I cut the wires on my 4-connector adapters so I could keep the holes in the table small, , just passing the wire though, and hid the connector area behind the building with a very small bush/tree, and re-spliced the wires back below the table. A bit more work but saved a 5/8 - 3/4 hole having to be bored through the table.

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