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Electronics Wizzards - Power Supply Question

post #1 of 9
Thread Starter 
I sold a paradigm x-30 subwoofer control unit on ebay but did not have the power supply (wall wart). In the ad, I directed the buyer to buy the power supply from Paradigm. To make a long story short. The buyer was having problems getting through to them, got impatient, and went ahead and bought a power supply 'with similar specs' from a different source. The non-paradigm power supply allows the x-30 to power up, but then immediately shuts down.

The spec for the Paradigm Power supply:

(INPUT: AC 120V 60HZ 4W OUTPUT: AC 24V 100mA)

The spec for the other power supply:

(INPUT: AC 120V 60HZ 10W OUTPUT: AC 24V 450MA)

So, here is the question, could hooking the x-30 up to this other power supply have ruined it? He says that that can't happen, I am not so sure. He also implied that he may have used other power supplies to try to get it to work! I do not know what specs those may have had.

He is threatening to ask for a refund ... should I give it to him? The unit worked fine when it went into storage. Your sage counsel appreciated!
Edited by RayGuy - 11/3/13 at 9:42am
post #2 of 9
Quote:
Originally Posted by RayGuy View Post

I sold a paradigm x-30 subwoofer control unit on ebay but did not have the power supply (wall wart). In the ad, I directed the buyer to buy the power supply from Paradigm. To make a long story short. The buyer was having problems getting through to them, got impatient, and went ahead and bought a power supply 'with similar specs' from a different source. The non-paradigm power supply allows the x-30 to power up, but then immediately shuts down.

The spec for the Paradigm Power supply:

(INPUT: AC 120V 60HZ 4W OUTPUT: AC 24V 100mA)

The spec for the other power supply:

(INPUT: AC 120V 60HZ 10W OUTPUT: AC 24V 450MA)

Wall wart power supply specs range from approximations to wildly inaccurate. Powering up and then shutting down is a sign of too much voltage, which may be made more likely by the far higher current rating of the second power supply.
Quote:
So, here is the question, could hooking the x-30 up to this other power supply have ruined it?

Possible.
Quote:
He says that that can't happen,

He's optimistic in a self-serving way.
Quote:
I am not so sure. He also implied that he may have used other power supplies to try to get it to work! I do not know what specs those may have had.

Well made equipment tends to protect itself from mismatches like this, which may be why it shuts down right away.

If you can, engage a technically-minded experienced electronic tech third party.
Quote:
He is threatening to ask for a refund ... should I give it to him? The unit worked fine when it went into storage. Your sage counsel appreciated!

For the money possibly involved, I'd give the refund and chalk it up to experience. If you sell stuff, sell stuff that you see working well right before you ship it out.
post #3 of 9
Thread Starter 
Quote:
Originally Posted by arnyk View Post




If you can, engage a technically-minded experienced electronic tech third party.
.

Thanks for the info! As to engaging a third party? Who would that be? How would I get them involved? Not quite sure what you mean by this? Please elaborate.
post #4 of 9
A decent quality wall wart with the specs he is posting should not damage the unit.

Current is a function of the device being powered so ideally, using a 450mA supply with the proper voltage will not be any different than a 100mA supply if the device doesn't draw more than 100mA. In other words, the power supply is a voltage device and provides 24 volts and the unit draws as mush current as it needs. So a higher rated power supply at the same voltage should not be a problem. However, when wall warts are underloaded they can provide higher than listed voltage.

Most likely, in my opinion, using the "incorrect" power supply would not damage the unit even if it is providing slightly higher than designed voltage. However, I would not refund the money unless he has tried the proper power supply.



Those specs on the Paradigm model are interesting though. It says it provides 100mA at 24 Volts which would be 2.4 Watts but it says it's rated for 4 Watts. On the model the buyer has described, it's 450mA at 24 Volts which is 10.8 Watts...very close to the stated power rating.

(I'm assuming all values are provided in RMS, which is typical unless specified otherwise)
Edited by hockeyrcks9901 - 11/4/13 at 7:39am
post #5 of 9
Thread Starter 
Just a quick follow-up. Turns out it was much ado about nothing. The x-30 survived the mismatched power suppy with flying colors! The buyer was finally able to get the original equipment power supply and all is now well.

Thanks to all who responded. Greatly appreciated!
post #6 of 9
Quote:
Originally Posted by hockeyrcks9901 View Post

A decent quality wall wart with the specs he is posting should not damage the unit.

Current is a function of the device being powered so ideally, using a 450mA supply with the proper voltage will not be any different than a 100mA supply if the device doesn't draw more than 100mA. In other words, the power supply is a voltage device and provides 24 volts and the unit draws as mush current as it needs. So a higher rated power supply at the same voltage should not be a problem. However, when wall warts are underloaded they can provide higher than listed voltage.

Most likely, in my opinion, using the "incorrect" power supply would not damage the unit even if it is providing slightly higher than designed voltage. However, I would not refund the money unless he has tried the proper power supply.



Those specs on the Paradigm model are interesting though. It says it provides 100mA at 24 Volts which would be 2.4 Watts but it says it's rated for 4 Watts. On the model the buyer has described, it's 450mA at 24 Volts which is 10.8 Watts...very close to the stated power rating.

(I'm assuming all values are provided in RMS, which is typical unless specified otherwise)

The problem can come in because these wall warts often are not regulated voltage. So, while in theory you're correct that higher current shouldn't matter, it can in these non-regulated cases.

If you check the voltage from the wall wart when not loaded, you'd likely find it's higher than 24V. But, the system design is such that the load of the connected device and the current capability of the wall wart will cause that voltage to sag down to the appropriate level. If you connect a wall wart with considerably more current capability, as was done in this case, the load doesn't cause as much voltage sag thus the X-30 was probably shutting down due to high input voltage.
post #7 of 9
That's why I said a quality wall wart...

Anyways, it looks like it all worked out.
post #8 of 9
Quote:
Originally Posted by whoaru99 View Post

The problem can come in because these wall warts often are not regulated voltage.
Most devices do the regulation, and for that matter a fair amount of additional filtering, internally. Some do it in the wall wart, which of course means if you use an unregulated poorly filtered wall wart you'll have a problem.
post #9 of 9
FWIW, since I happen to have a couple X-30s and the wall warts laying around gathering dust, figured I'd experiment..

According to the trusty Fluke 87, OCV of the Paradigm wall wart was 27.1V. When connected to the X-30 the wall wart voltage sagged to 23.7V.
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