Some advice please: 

what is the relationship between a wall wart power supply and a component in terms of volts and amps?

Do the V and A need to be an exact match to the component?

or as long as the wall wart has more V and more A than that required by the component are you good to go??

or does V need to match and as long as the wall wart supplies a max W higher than the component requires you are good to go???

or the other way around?

and, as an example, if I have a 12v 1.8a wall wart, what range of specs on the component would be ok?

Thank you.

A very quick reply, I've been unable to login since moving and getting a fixed IP address, yet resetting to the same password worked!

Anyway, and others may like to provide more detail...

In general, you want the SAME voltage and at least the current specified on your component, with caveats and gotchas.


It'd be better if you told us what the component requires, rather than what wall warts you have.

The gotcha is that a linear power supply (i.e. conventional old transformer, rectifying diodes, smoothing capacitors) will specify so many volts at so many amps.
BUT. If it is under-loaded, let's say it says 12V at 4A, it expects to deliver 4A at 12V, and if you only draw 1A from it, the voltage will soar to greater than 12V.
The transformer windings have a certain resistance, so if lightly loaded the voltage drop across them will be less than calculated for 4A, and so you will get a higher voltage out - even more, if completely unloaded. (I'm assuming it's just a conventional linear supply, and not regulated internally, here.)

Those kinds of wall warts are noticeably quite heavier than their switch mode power supply (SMPS) counterparts, so you can tell them apart.
SMPS ARE regulated, so it matters not a jot if you want to draw less, say 900mA or 0.9A from your 1.8A capable supply. It will stay at 12V.
However, you mustn't ask for more than 1.8A from it. It will possibly have over-current protection and shut down, but it won't be adequate.

So tell us what the component you want to power specifies in V & A requirements.

If your wall wart feels quite light, it's likely an SMPS type, and will keep at 12V for anything under 1.8A.
(However, wall warts (is that an Americanism?) can also include chargers, which might have different built in circuits to monitor a battery.)


I hope that helps a little! ;=})

Ross

I remembered this pic from HiFi Humour and had to trawl back to p,3 to find this cartoon.





Ask anything again, understood or not;- ;=})

And from p.2 of the same, this from Owen Young back then:





Cheers!!

Feb 14, 2024 20:47:47 GMT 12 RdM said:

I remembered this pic from HiFi Humour and had to trawl back to p,3 to find this cartoon.





Ask anything again, understood or not;- ;=})

Ha! A while ago, in a clean out, I got rid of a number of AC adapters as I thought I’d never use them again. This still left me with a box full of various AC and DC supplies.

Recently I got an old Project turntable out for comparison purposes or eventual sale. Of course, I then couldn’t find the specified 18v AC power supply and reckon that was one of the ones I discarded. I bought one from Jaycar but took it back as it had a bad hum.

Then I realised the speed of an AC motor depends only on the frequency so tried a 12V one and that works perfectly with more than enough torque to drive it.

so, check me on this, but I think you are saying:

if it is a conventional old transformer (heavier) best to match both V and amps.
but
if it is an SMPS transformer (lighter) then if the V matches, anything lower than the Amp rating is fine.

So a SMPS with 12V 1.8A will be fine for a component that wants 12V 500mA

Feb 15, 2024 17:34:22 GMT 12 paulsaints said:

so, check me on this, but I think you are saying:

if it is an conventional old transformer (heavier) best to match both V and amps.
but
if it is an SMPS transformer (lighter) then if the V matches, anything lower than the Amp rating is fine.

So a SMPS with 12V 1.8A will be fine for a component that wants 12V 500mA

Indeed, exactly. Thanks!