Question about transformers and current conversion

[russellc]

Hey all,

Don't usually ask for help, but this time I'm really stumped. I have the Logitech Z5500 5.1 speakers which I bought in Canada, so they are rated for 110 V. However, I moved to to Hong Kong recently where the voltage rating is 220 V. I bought a transformer a few days ago that is for converting 110 V to 220 V current, but I'm wary about trying it at all because now I'm reading that it needs a transformer rated for 500 W, but the one I bought is only for 300 W. However, is it possible to simply make do with the 300 W transformer for now until I decide to buy a 500 W transformer? Or is it gonna break my speakers permanently? I will not be cranking it up full blast all day long. If anything, I will just be middle-to-low volume watching movies and playing games once in awhile, so as far as I understand, I would only be using a fraction of the rated power.

The problem still stands, however, that I do not want to my speakers to break for whatever reason because I wanted to be cheap and not buy another transformer. However, it would be great if I could use the one I bought on impulse for the time being if it means it might be a little more quiet than usual (and as long as it doesn't explode!).

Thanks for the help!

[Mordkanin]

converting 110 V to 220 V current

That's a nonsensical and silly statement to an electrical engineer.

Annnnnyway:

Watts are a unit of power. P=VI (voltage * current). This is constant in a transformer, as you're just shifting current and voltage linearly, keeping power the same.

Your 300W transformer will overheat if placed under load, possibly limit current, and thereby drop voltage. (Over 300W, depending on the design, it may or may not saturate, resulting in a current limit/voltage drop, but either way, it will overheat) You will not likely damage your speakers, but there is a risk of your transformer catastrophically overheating and bursting into flames under load.

[xTdub]

If the transformer cannot supply enough power, the worst that will happen is your speakers won't turn on, but not having enough power will not break them in any way.

[Tomoko]

If you bought a transformer to step up from 110 to 220 that's the wrong kind, you would use that to plug in foreign 220v devices into a North American 110v socket. You need one that steps down from 220 to 110 volts for your speakers. Don't worry about watts. This guide might be helpful in explaining what you want: Travel Voltage Converters

[Mordkanin]

If you bought a transformer to step up from 110 to 220 that's the wrong kind, you would use that to plug in foreign devices into a North American socket. You need one that steps down from 220 to 110 volts for your speakers. Don't even worry about watts. This guide might be helpful in explaining what you want: Travel Voltage Converters

They're the same thing. A transformer has no concept of 'direction'. Primaries and secondaries in simple transformers are only labeled as such for convenience's sake and can be swapped at will.

[russellc]

That's a nonsensical and silly statement to an electrical engineer.

Annnnnyway:

Watts are a unit of power. P=VI (voltage * current). This is constant in a transformer, as you're just shifting current and voltage linearly, keeping power the same.

Your 300W transformer will overheat if placed under load, possibly limit current, and thereby drop voltage. (Over 300W, depending on the design, it may or may not saturate, resulting in a current limit/voltage drop, but either way, it will overheat) You will not likely damage your speakers, but there is a risk of your transformer catastrophically overheating and bursting into flames under load.

Could you please then explain the proper way for me to put it so I can learn? Not everyone is an almighty electrical engineer such as you.

In any case, thanks for the help. So I suppose then, that if I do not turn it up full blast for the time being and not creating a load for the transformer, it should be okay?

[Tomoko]

They're the same thing. A transformer has no concept of 'direction'. Primaries and secondaries in simple transformers are only labeled as such for convenience's sake and can be swapped at will.

Yes, you can do that with a transformer if it's not one of those travel deals where you'd have to take it apart to do that. I'm not sure which kind he got so I thought I'd point that out. Of course I guess it wouldn't matter since he wouldn't be able to plug the wrong type into the outlet anyway, unless it was a universal one like this.

[Mordkanin]

Could you please then explain the proper way for me to put it so I can learn? Not everyone is an almighty electrical engineer such as you.

In any case, thanks for the help. So I suppose then, that if I do not turn it up full blast for the time being and not creating a load for the transformer, it should be okay?

Maybe.

Like I said, your failure mode would be overheating. Generally, transformers are rated to a particular temperature rise in still air.

Current and voltage separate things. That's what I was talking about. In this case, you care about power: watts. There's a relation between current and voltage that keeps power constant. P=VI.

Don't even worry about watts

AHHHHH!!!!! After the primary/secondary rating, the power rating (Watts on consumer devices, VA for industry/EEs) of a transformer is the only other thing most people doing simple voltage conversions like this would care about, and is the one thing that would make a transformer overheat and fail! A 1VA transformer, for instance, would burst into flames almost instantly if you tried to use it for a 500W application.

Edited January 26, 2011 by MioTheGreat

[russellc]

Maybe.

Like I said, your failure mode would be overheating. Generally, transformers are rated to a particular temperature rise in still air.

Current and voltage separate things. That's what I was talking about. In this case, you care about power: watts. There's a relation between current and voltage that keeps power constant. P=VI.

AHHHHH!!!!! After the primary/secondary rating, the power rating (Watts on consumer devices, VA for industry/EEs) of a transformer is the only other thing most people doing simple voltage conversions like this would care about, and is the one thing that would make a transformer overheat and fail! A 1VA transformer, for instance, would burst into flames almost instantly if you tried to use it for a 500W application.

Thanks for the info. The transformer I got can be switched for both directions, so that's not a problem. I guess for the time being I'll use the 300 W transformer and make sure to just turn it off when I'm not using it, in addition to keeping an eye on it when using it. I'll see how that works out and get a 500 W transformer if necessary :D

[Tomoko]

A 1VA transformer, for instance, would burst into flames almost instantly if you tried to use it for a 500W application.

500W speakers?

I must be way behind. Mine just require 40. :laugh:

[Mordkanin]

I work with fairly large (many kilowatts) power supplies, so my sense of small power scales is a little skewed.

These 500W speakers will likely never breach 300W except for very short bursts. In this application, the transformer should do fine.

(Oh. Depending on design, if there are HUGE surges exceeding 300W, you could experience some sound distortion due to saturation of the transformer and cuts in input voltage)

Regardless, the education about what could go wrong is useful, and I can't in good conscience say "do it! do it!" without the explanation.

[russellc]

I work with fairly large (many kilowatts) power supplies, so my sense of small power scales is a little skewed.

These 500W speakers will likely never breach 300W except for very short bursts. In this application, the transformer should do fine.

(Oh. Depending on design, if there are HUGE surges exceeding 300W, you could experience some sound distortion due to saturation of the transformer and cuts in input voltage)

Regardless, the education about what could go wrong is useful, and I can't in good conscience say "do it! do it!" without the explanation.

Great to have the knowledge from someone with experience. Information on the internet about this is conflicting and not very useful.

However, having the knowledge before trying it is definitely my intent (with what could go wrong and right) since I do not want my house to burn down. I'm fairly certain most fires are caused by electrical issues. With that in mind, transformers most definitely don't seem like the best thing to tread lightly with!

Thank you very much for the wealth of information as I have been putting this off for a couple months now because I have not found dependable info, until now :)