# Electrical question - power suppliesWatch

#1
I have a set of speakers with a broken power supply.
I also have a broken laptop with a working power supply.

Broken speaker power supply:
18 v
3.5 amps

Working Laptop power supply:
18.5 v
3.5 amps

Do you think they are rated close enough that I could cut off the ends of each power supply and swap them?

If so, how do I tell which wires are which, as in the polarity of the inner/outer parts of the plug?
The laptop supply is straightforward as it has this on it:

The speaker supply has no such info tho, is it safe to assume it would be the same?

Cheers.
0
7 years ago
#2
Most speakers require an AC-AC power supply while laptops use an AC-DC one, so it probably won't work. I'd check, in any case... (do you have a multimeter or something?).
0
#3
Good point.

I just looked at both power supplies and they both mention "AC Adapter" so I assume they are both AC.
I don't have a multimeter no, I should probably get one! There's been so many times when I've really needed one haha.
0
7 years ago
#4
It should work as long as they're both AC-DC, the power supplies probably vary in voltage by more than 0.5V anyway.
0
#5
Exactly, plus I'd think the devices themselves have a tolerance either direction of the quoted voltage rating.
I'm gonna buy a multimeter before I do anything, I didn't realise they were so cheap on eBay!
0
7 years ago
#6
ebay ftw! just make sure you solder and insulate them properly, don't want any fires!
0
7 years ago
#7
A multimeter won't really help you tell if the supply is AC or DC. The cheapest way to tell would be to have a 2 lead bi-colour LED and suitable resister. This should then show one of the two colours solidly for DC or something in the middle if it's AC (and if you waved it around fairly quickly you would see both colours)

There should be a symbol on the PSU that indicates the output that shows if it's AC or DC output probably next to where it states 18V 3.5A

The symbol on DC supplies is:

The symbol on AC supplies looks like ~

If the speaker PSU is DC then there's a good chance it's also got a positive tip (+ve is in the centre connector). Although having no indicator on the speakers indicating polarity could suggest it's AC at which point there's not much you can do easily.
0
#8
Well I gave it a go and it works.
I now have a laptop power supply that branches off to 2 tips, one for the laptop and one for the speakers, both of which work.
Although I haven't tried both at once, im guessing it would just fail to power either device rather than blow up or something.

Thanks for the info everyone.
0
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