What sort of store sells 3V DC adaptors?
July 30, 2012 8:15 AM   Subscribe

I need to buy a three volt DC adaptor with a barrel shaped connector. (Picture the normal 12V DC adaptor, but with a smaller connector on the end that plugs into the device.) And I need to get it this afternoon, in between running some other errands. Where should I look? What sort of store carries this sort of thing?

I don't think I've ever seen odd-sized power supplies sold separate from the device that they power — but then, I've never really looked for 'em either. The device I need this for is something I bought online, so I can't just go back to the store where I got it.

I'm in Austin, TX if it matters.
posted by nebulawindphone to Shopping (24 answers total)
 
Radio Shack, who carry less and less components as time goes on, is worth a shot for something this ubiquitous. Give them a call before showing up and they should be able to tell you if they carry loose adapters at all.

Also, Fry's would almost certainly have it, but I don't know how near to one you are.
posted by griphus at 8:19 AM on July 30, 2012


Radio Shack carries a wide range of adapters, or at least they used to.
posted by brianogilvie at 8:20 AM on July 30, 2012


Fry's has a ton of that kind of stuff.
posted by Burhanistan at 8:21 AM on July 30, 2012


I was going to suggest Fry's also. What you need is an universal ac to dc adapter that comes with a variety of DC plugs (and goes as low as 3 volts)
posted by bluefrog at 8:23 AM on July 30, 2012


Here is something from RS. A bit overpriced, but convenient if you're in a hurry.
posted by bluefrog at 8:28 AM on July 30, 2012


Radio Shack, Best Buy, or your local AAA or other travel agency office will likely have these.
posted by valkyryn at 8:35 AM on July 30, 2012


Also, you didn't note it, but sure you get the correct amperage and connector width as well. Both of these things vary.
posted by griphus at 8:42 AM on July 30, 2012


I was just about to ask that as a followup question, actually. How do I work out what amperage I need? It doesn't seem to say on the device itself, and I can't find any info online. (Under "power requirements" the manufacturer's brochure just says DC 3.0 V when using the AC power adaptor and doesn't tell you how many ants it draws.)
posted by nebulawindphone at 8:47 AM on July 30, 2012


(Ants? Amps. Please do not infest my recorder with ants. I do not think that will help.)
posted by nebulawindphone at 8:47 AM on July 30, 2012 [2 favorites]


According to this it's a 3V, 1A, center positive. I can't vouch for the veracity, obviously.
posted by griphus at 8:56 AM on July 30, 2012


Ah, never mind. I dug up the actual manual and it's in there. One amp. Mkay.

But I'm still curious, in a teach-me-to-fish sort of way. Would there have been any way I could have calculated this or made a reasonable guess? (Based on the type of device it is, maybe? Or the number and type of batteries that it takes? Or...?) Or is this something that is unguessable and absolutely has to be specified?

(Electricity fascinates me, but it also makes me feel like a total moron.)
posted by nebulawindphone at 8:57 AM on July 30, 2012


Watts = Amps x Volts, so Amps=Volts/Watts
posted by bluefrog at 9:07 AM on July 30, 2012


Aren't modern DC adapters generally current-limited devices? That is to say, they will only deliver as much amperage as they are asked for, regardless of the load? I know older transformer-based adapters had to be correctly matched to keep them from blowing out whatever they were attached to but I think with modern switchmode adapters the amperage rating is more of a capacity than a fixed output. So you can just err on the safe side and try to get an adapter that seems a bit more powerful than you'd really need.

Someone please correct me if I'm wrong.
posted by Scientist at 9:09 AM on July 30, 2012


There's a semi-standard diagram convention on devices that use barrel connectors for power, something like:

3V 1A - -C *- +

where the very bad ASCII-art is supposed to be a representation of the tip/ring in the connector. If it's not on the device, check the manual.

What you need to know to replace one of these is:
  1. Voltage — if it needs 3V, 4.5 V or 6V, that's what you have to give it. Not below, not above. You can't tell how well regulated your device is internally, so stick with exactly how it's rated.
  2. Power/Current — sometimes the rating is given as current (in your case, 1A), sometimes as power (3W). As bluefrog said, there's a simple relationship between these in DC. As long as your adaptor provides at least enough current as the rating, you should be good. You can be a bit over in current, and you'll be fine (so 1.5-2A is okay). Going too large means you're paying for what you don't need.
  3. Polarity — the tip/centre can be positive or negative. Centre negative (+ -C *- -) is rarer, but happens. This matters, and is sometimes switchable for those multi-adaptors you can buy.
  4. Connector size — the great thing about barrel connectors is that there are so many standards to choose from. Don't try to fudge the wrong size.
And yes, there are also AC power adaptors which provide low-voltage AC; beware of these in the surplus store. These are rare for devices that can also run off batteries.
posted by scruss at 9:23 AM on July 30, 2012 [1 favorite]


Fry's definitely carries an AC->DC adapter with multiple tips that goes down to 3v and is rated for 1200 MA. I bought two last week for my Sony HR-MP5 effects units.

The smallest included tip seems to fit my M10 recorder.

If you still have the packaging for your M10, check it first. My M10 came with an external 3V power supply.

Alternately, consider getting a set of Sanyo Eneloop batteries and a charger. I can easily get 12 hours of recording time out of a pair with the M10. Considering how long it will run on batteries, I doubt it will ever come close to drawing a full amp. The Sony designers probably just tossed in an existing power brick that provided sufficient power.
posted by b1tr0t at 9:27 AM on July 30, 2012


Here are the symbols scruss is trying to draw.

Also, a follow-up question for scruss (that the OP might find useful): the spec sheet says the power consumption is 0.27W, which wouldn't work in the W=A*V equation, as it yields 11A. How does that work out?
posted by griphus at 9:35 AM on July 30, 2012


The wattage rating given in the specs is probably an estimate of real-world power consumption over time, but the power supply needs to be able to provide enough current for short spikes of high demand.
posted by contraption at 9:58 AM on July 30, 2012


Scientist - you are not completely wrong, though cheap adapters which deliver higher voltages under lower load still exist. The key word here is regulated. An unregulated adapter might be built such that it's 5v at 1A but you'll get a higher voltage under less load.

It's also more common for electronics to have on-board regulation to deal with imprecise input. The question becomes HOW imprecise.
posted by phearlez at 10:14 AM on July 30, 2012


Actually, griphus, bluefrog has the second equation wrong: P = I×E, so I = P/E = 0.27/3 = 0.09A. This is a tiny amount, so basically almost anything would work. We love devices with no moving parts!
posted by scruss at 10:32 AM on July 30, 2012


Radio Shack. And bring the device with you, to make sure the tip fits in.
posted by Marky at 11:10 AM on July 30, 2012


It's also more common for electronics to have on-board regulation to deal with imprecise input. The question becomes HOW imprecise.
It may be common, but it isn't something your should rely on when dealing with expensive audio gear. Roland/Boss are somewhat infamous for putting their regulators into their expensive power bricks, rather than the synths and pedals. A great way to fry your vintage Roland SH-101 is to plug in an off-brand 9v adapter.

On the other hand, I've seen teardowns of consumer Sony power adapters that show Sony scraping by with the absolute cheapest possible design. The M10 comes from Sony's Pro Audio group, though, so all bets are off.
posted by b1tr0t at 11:22 AM on July 30, 2012


Right. So to make sure I'm getting all this:

I went and bought an adjustable adapter with regulated output. It's got a 3V setting, and it promises you can use it up to 2500 mA on any voltage setting.

It sounds like this might be overkill in the sense that I could have gotten away with something way dinkier. But if I'm understanding correctly, it won't fry my gear or catch on fire or anything really upsetting like that. Yes?

If you still have the packaging for your M10, check it first. My M10 came with an external 3V power supply.

Yeah, mine did too, but it's stashed in a box somewhere and I'm leaving for the field tomorrow. :)

posted by nebulawindphone at 1:34 PM on July 30, 2012


It sounds like this might be overkill in the sense that I could have gotten away with something way dinkier. But if I'm understanding correctly, it won't fry my gear or catch on fire or anything really upsetting like that. Yes?
Correct. 2.5 A is way overkill, but it won't hurt anything. And if you got one with multiple tip-adapters, you can probably use it with just about anything short of a laptop.

Just be sure that you have it setup for tip-positive, as marked on your M10, before plugging it in.
  • Voltage should match exactly (5%-10% variation may be OK, but exact is better)
  • Polarity should match exactly (don't get this wrong, many components can die if they receive the opposite voltage from what they expect)
  • The device should draw less Amps than the supply can provide (1000 mA = 1A)

posted by b1tr0t at 1:52 PM on July 30, 2012 [2 favorites]


Beautiful. Thank you!
posted by nebulawindphone at 3:16 PM on July 30, 2012


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