OK to power USB speakers with Apple iPod charger?

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Developer55

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I’d like use an Apple iPod charger, model A1205, putting out 5 watts (5 volts x 1 amp) to power a pair of USB-powered AcoustiX Convertible Speakers (power output: 3 watts RMS—1.5 watts per channel—with an impedance of 10 ohms), to use with a portable CD player.

I have tried this setup and it has worked OK, with a good sound level output from the speakers.
However, I wonder if doing this is unsafe, because the Apple charger puts out more watts (5 W) than the rating of the speakers (3 W), and if it could result in an electrical hazard.

I suppose that the 3-watt output rating of the speakers could be derived from any of three permutations of voltage and amperage:

3 V x 1 ampere
1 V x 3 amperes
or
(square root of 3) V x (square root of 3) amperes

In each of these three scenarios, could the 3-watt speakers (1.5 W + 1.5 W) safely handle the 5-watt output of the Apple charger?

Maybe the speakers might pull only as many watts as needed. On the other hand, the 3 volts the speakers consume together would be less than the 5 volts the charger is pushing out, and perhaps the speakers would not be able to safely dissipate the excess voltage.

Many thanks for any feedback on this question.
 
The 3W rating on the speakers relates to music power, not to the electrical power being drawn off the power supply.

Your speakers should have a power rating for USB power. If they draw more power than the charger, you might damage the charger. But you can't damage the speakers with more powerful adapter.
 
The 3W rating on the speakers relates to music power, not to the electrical power being drawn off the power supply.

Your speakers should have a power rating for USB power. If they draw more power than the charger, you might damage the charger. But you can't damage the speakers with more powerful adapter.
 

Developer55

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The manufacturer's specifications say that both speakers together have a "power output: 3 watts RMS."
 

photonboy

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Hey,
Power devices don't PUSH the power onto a device. The device draws the power based on its resistance.

What you need to ensure is that:
a) the VOLTAGE of the power source is correct (5V), and
b) the AMPERAGE (or Wattage if rated at same Voltage) is higher on the power source side.

If that's true, which it sounds like, then you're okay.

*What can happen is you damage the power source if you draw too much; that's usually right away (i.e. plug it in then smell something burning). Or if it had some sort of protection circuitry the power might just be limited and cause noise quality issues. Other protection circuitry may prevent the device even turning on.

**Don't confuse RMS, VA, and Wattage terminology either. It's probably best to look at the amperage since we're dealing with the same voltage.
 

Developer55

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That's useful info.
 

Developer55

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Yes, I think so. The voltage output for a USB 1 or USB 2 port is 5 V, also the voltage output of the Apple charger, and I presume that the amperage used by the speakers would depend on their power need (and it would also vary depending upon the speaker volume control setting). And, as you say, any strain would be on the power supply if the power need of the speakers exceeded the power supply's specifications.
 

Developer55

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Thank you PHOTONBOY and ALABALCHO for your feedback. According to a website, "Ken Shirriff's Blog," in the Apple iPhone charger, "The input AC first passes through a fusible resistor (striped), which will break the circuit if there is a catastrophic overload." I would presume that the iPod charger has a similar type of protection. The Apple iPod charger is UL Listed (among its test lab compliances), and the UL product safety standard would include requirements for a protective device such as an overcurrent or thermal protective device to open the circuit in case of overload.

On the other hand (in an analogous situation involving other Apple devices), according to a forum post on the http://apple.stackexchange.com website: ". . . when you connect an iPad to an iPhone charger, it will try to get a full 2.1A, but won’t be able to as the charger is only capable of supplying 1A. This results in a considerably slower charging time as the iPad is effectively draining the battery as fast as it can be recharged." (In this example, the iPad apparently is "on" while being recharged.) Apparently, although the charger has a protective device that can break the circuit in case of excessive overload, an overload less than "excessive" is manageable by limiting the amperage used, although I presume that the excessive (over 1A) amperage draw is shed by conversion into extra heat, which somehow must be “manageable.”
 

Developer55

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Good idea. Do you mean use a multimeter to measure the amperage draw of the speakers to see if it exceeds the rated amperage output of the power supply? Where do you insert the multimeter leads? Wouldn't that be difficult since the USB plug needs to be fully pushed into the power supply USB socket, thereby providing no easy access to bare metal?

Yes, overheating certainly would be a warning of overload, and maybe also a little whiff of ozone.
 

nukemaster

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Most USB speakers are designed to work within the USB standard 500ma limit(2.5 watts).

Having a larger power supply is rarely an issue unless the load is VERY small then some types/designs of power supplies will not regulate well(this is not much of an issue for most uses.).

It is unlikely that any quality switching power supply would do much more than just shut down or current limit(cut out or lower the voltage to the point that the connected device stops working).

If it makes you feel any better, I have used free(little promotional units with a built in Li-Ion battery) usb chargers to power some HP usb speakers in a power out without issues.

Many of these little units use a fairly high efficiency class D amplifier(PWM) as well. This will reduce average power draw since less power is wasted like it would be in a normal Class AB amplifier.
 

Developer55

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Using a battery-powered USB charger to power my USB speakers is an excellent idea. I have an old LifeLine PowerBank (2800 mAh) designed for recharging cellphones, portable gaming devices, and MP3 players. I'll give that a try.
 
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