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  #1  
Old 06-03-2009, 05:44 PM
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Default Milliamp Question

OK - here's a question for all you electronically savvy people.

I have a Yamaha drum machine that I love. Model # RX8. Have had it for close to 20 years.

Recently, the power adapter died. Has a short in it or something. It is a 15v, 500ma output adapter. I need a replacement as I want to use this machine in a master class in two weeks.

The only thing I can find as a replacement is RadioShack adapter. However, it is a 15v, 1000ma output adapter. So it has twice with millamps.

Would the extra 500ma damage my drum machine or does it not really matter? I didn't buy the RadioShack adapter (yet) because no one in there seemed to be able to answer how the milliamps matter.

Help! Thanks
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  #2  
Old 06-03-2009, 06:03 PM
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Default Re: Milliamp Question

That's potentially quite a lot of current extra. I'm not an electronics guru by any stretch of the imagination, but I would suggest not using the Radio Shack model. I'll see if I can dig anything up.

http://cgi.ebay.com.my/AC-Adapter-SC...mZ220351867252

?
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  #3  
Old 06-03-2009, 06:27 PM
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Default Re: Milliamp Question

From what I have been taught and told, and what seems to make sense to me, is that getting the proper voltage is what matters...you will only draw as many amps as the drum machine needs.
ie, if you have a 40W bulb, it will be drawing .33A (Power/Voltage=Amperage); if you have a 60W bulb, it will be drawing .5A; but no matter what bulb you use, it will still be 120V.

Nonetheless, when I left my adaptor for my digital set 1500 miles away, I went to Walmart and found a multiadapter (10 or so tips interchangable plug tips with switchable voltage/amperage ratings) for about $20. See if you can't find one of those that will work.
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  #4  
Old 06-03-2009, 06:32 PM
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Default Re: Milliamp Question

Thanks to both of you guys.

Yeah....double ampage (is that a word?) **seeems** bad but I also do remember reading or learning that again, it'll only draw as much millamps as it needs. So in that case...extra is fine.

I'll give it a shot. Worst case scenario is that I fry a 20 yr old machine that I see on eBay for $40-$50. I probably need to upgrade to something made in this century anyways....
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Old 06-03-2009, 06:48 PM
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Default Re: Milliamp Question

Well only drawing what it needs makes perfect sense.
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Old 06-04-2009, 12:16 AM
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Default Re: Milliamp Question

Take it from a licensed electrician, the advise given you is correct. It will only draw what it requires. This TX will probably last longer than the original, because of less heat buildup.
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Old 06-04-2009, 02:59 AM
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Default Re: Milliamp Question

Thanks again guys. Big help!
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  #8  
Old 06-04-2009, 03:17 AM
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Default Re: Milliamp Question

I can tell you this about going the other way. I bought a Casio Keyboard at a yard sale for my grandaughter but it didn't have a power supply. I had an old one that was the right voltage, but the amperage was about 20% of what it required. After about an hour, it killed the keyboard. That was the verdict from the repair shop.
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Old 06-04-2009, 06:52 PM
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Default Re: Milliamp Question

I'm surprised that it killed the keyboard, I would have thought that the power supply would have failed first, because it was forced to deliver more current than it was designed for. Did the power supply get ruined as well? If so then perhaps at the moment of failure there was a surge that fried the keyboard.
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  #10  
Old 06-16-2009, 09:12 AM
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Default Re: Milliamp Question

Yeah I don't see how an underpowered adapter could kill the keyboard. The keyboard not functioning with only 20% of the required power makes sense though.
Maybe the adapter got too hot, some insulation melted and it short circuited? I can imagine that doing SOME damage to the keyboard...
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  #11  
Old 06-16-2009, 12:07 PM
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Default Re: Milliamp Question

Quote:
Originally Posted by donv View Post
I can tell you this about going the other way. I bought a Casio Keyboard at a yard sale for my grandaughter but it didn't have a power supply. I had an old one that was the right voltage, but the amperage was about 20% of what it required. After about an hour, it killed the keyboard. That was the verdict from the repair shop.
This is exactly true. I've built a couple of computers in my time and the power supplies you use tend to be more about power in Watts than current, same principle. You could fit a 1.5kw power supply to your bog standard beige box that you're using now (to give you an idea, most stock PCs that are not designed for performance or a small form factor come with 250-300w power supplies) and it would actually work better due to it being designed for performance+better cooling etc. However if you fit a power supply that is too low a current and you exceed that current then you actually do risk blowing components so yeah this is absolutely true.

Another interesting fact is that if you exceed the rated electricity for your plug sockets (in the UK it's 13A in other places it might be different) then the whole thing will set on fire! That's what fuses are for, although i'm sure you knew that already! That's another example of only drawing the current it needs right there. your plug sockets are rated for 13A but that's a huge amount of current that very few devices would ever need, how would they work if this wasn't true?

In short TS if you got bored, don't worry about the current output being too high, in fact make sure your power supply can give you a HIGHER current then you'll need!
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Old 06-16-2009, 12:33 PM
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Default Re: Milliamp Question

Quote:
Originally Posted by eddiehimself View Post
This is exactly true. I've built a couple of computers in my time and the power supplies you use tend to be more about power in Watts than current, same principle. You could fit a 1.5kw power supply to your bog standard beige box that you're using now (to give you an idea, most stock PCs that are not designed for performance or a small form factor come with 250-300w power supplies) and it would actually work better due to it being designed for performance+better cooling etc. However if you fit a power supply that is too low a current and you exceed that current then you actually do risk blowing components so yeah this is absolutely true.

Another interesting fact is that if you exceed the rated electricity for your plug sockets (in the UK it's 13A in other places it might be different) then the whole thing will set on fire! That's what fuses are for, although i'm sure you knew that already! That's another example of only drawing the current it needs right there. your plug sockets are rated for 13A but that's a huge amount of current that very few devices would ever need, how would they work if this wasn't true?

In short TS if you got bored, don't worry about the current output being too high, in fact make sure your power supply can give you a HIGHER current then you'll need!
My PC used to crash and reset itself due to an insufficiently powerful PSU, but as far as I can tell the PC components weren't damaged. However I replaced the PSU after it happened maybe about 5 times with a 550W PSU :) I have a power-thirsty graphics card for when I make 3D models (or play games).
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  #13  
Old 06-16-2009, 12:41 PM
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Default Re: Milliamp Question

Quote:
Originally Posted by Big_Philly View Post
My PC used to crash and reset itself due to an insufficiently powerful PSU, but as far as I can tell the PC components weren't damaged. However I replaced the PSU after it happened maybe about 5 times with a 550W PSU :) I have a power-thirsty graphics card for when I make 3D models (or play games).
some PCs do have safety systems built in like this. The PSU in this one i think is like 720w or something. It was actually cheaper than the 650w one which was nice.
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Old 06-17-2009, 05:22 AM
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Default Re: Milliamp Question

A lesson here is to unplug the wall wart when you're not using it. It draws current even when the power is off, wasting electricity and shortening the life of the transformer.
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  #15  
Old 06-17-2009, 01:49 PM
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Default Re: Milliamp Question

Quote:
Originally Posted by eddiehimself View Post
some PCs do have safety systems built in like this. The PSU in this one i think is like 720w or something. It was actually cheaper than the 650w one which was nice.
The PSU that made my PC crash could deliver 400W max, preferrably not too long. 550W is all I need :)
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  #16  
Old 06-24-2009, 11:38 AM
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Default Re: Milliamp Question

Yes the transformers work on demand.

Quote:
Originally Posted by donv View Post
I can tell you this about going the other way. I bought a Casio Keyboard at a yard sale for my grandaughter but it didn't have a power supply. I had an old one that was the right voltage, but the amperage was about 20% of what it required. After about an hour, it killed the keyboard. That was the verdict from the repair shop.
As far as the keyboard failure. Some devices use DC transformers, some use a reduced
AC voltage. It would be easy to miss one little letter when trying to find a replacement.
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  #17  
Old 06-24-2009, 03:41 PM
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Default Re: Milliamp Question

Quote:
Originally Posted by Moktie View Post
As far as the keyboard failure. Some devices use DC transformers, some use a reduced
AC voltage. It would be easy to miss one little letter when trying to find a replacement.
Honestly, i think he would have noticed if it had been running on AC power. It's pretty easy to spot.
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  #18  
Old 06-24-2009, 04:53 PM
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Default Re: Milliamp Question

Beware of polarity! There should be a graphic like this on your machine and every AC adapter. Make sure this matches. The wrong polarity can damage polarized capacitors.
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Last edited by genericdrummingusername; 06-24-2009 at 04:54 PM. Reason: That was a big picture.
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  #19  
Old 06-24-2009, 05:18 PM
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Default Re: Milliamp Question

Quote:
Originally Posted by genericdrummingusername View Post
Beware of polarity! There should be a graphic like this on your machine and every AC adapter. Make sure this matches. The wrong polarity can damage polarized capacitors.
Many devices have diodes built in to avoid such damage. It also means that if it runs on batteries it will die pretty abruptly when the battery dies down.
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