DC Adapter question

The 7.5 VDC may (and may not, but we don't know) be important, so you'd best stick with something very close to that.

The 1500mA is a minimum. Which means that the unit you describe below as 1700mA is just fine. The only catch with the current is that if it says some specific voltage at a specific current, as the actual current drawn goes down the actual voltage delivered will go up. Hence you don't want to use something able to supply twice the required current simply because it will be so under loaded that the voltage will be significantly higher than what it would be with a full load.

However, as noted, the voltage doesn't always make any real difference either! Lots of units are powered with "switching" power supplies, and the voltage chosen is merely a convenient one. "Convenient" may be the best deal they can get on purchasing bulk orders, or may be related to a size that is commonly available.

One example that has been discussed in detail in this newsgroup is the power supply for Linksys WRT54G routers. They come with a 12 VDC 1A supply. The unit will work off a supply of less than 5 volts to more than 20 volts though. The actual power used stays about the same, so as the voltage goes down the current goes up. Using a 6 VDC supply it would be a good idea to have one rated at 2 Amps. An 18 VDC supply would probably do fine if rated at 750 mA.

As Jeff Liebermann originally pointed out, with the WRT54G the upper voltage is probably limited by when the capacitors blow up (literally).

The 1700 mA unit is perfect.

The 1000 mA unit would almost certainly work. The question merely how long before it failed. Not if, just how long. At that difference in rated current, it might fail within minutes. It might take months. You'll have the 1700 mA one stuffed in a box on a shelf, just in case, long after the device it powers has been tossed into the trash.

Reply to
Floyd L. Davidson
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Reply to
Peter Pan

Hi, I just moved from the UK to the US. I brought my Wireless access point/router with me, but I need to get a new DC adapter for it so that it works on the 110V supply here.

It says on my UK adapter that the output is: 7.5V DC 1500mA 11.25VA

Every universal adapter I find that has 7.5 as an option, seems to have a current rating of either below, or above the 1500mA I need. They are usually either about 1000mA, or 1700mA etc.

Does anyone know if this is a required rating, or if it will automatically only take the current required, as long as it's set to 7.5V ?

For example, if I get the one with only 1000mA rating, will it not work? If I get the 1700mA one, will it be too much and blow the wireless access point?

Thanks for any help, Daniel

Reply to
Ann-Marie

Thanks for the replies. Next problem, the only place I've found that supplies universal adapters with any kind of current above about 500mA seems to be some canadian place called mainelectronics, but their ordering/shipping seems a bit crappy. Other than E-bay, any ideas on other US places that I could get more of a range of universal adapters? I've already tried places like radioshack, but they're all low current.

Thanks again Daniel.

Reply to
Ann-Marie

the AP will take what it needs, so the rating should be at least equal to what you had before.

Was the UK supply only rated 220-240V on the input and not multi-voltage ?

Getting a spare for the equivalent AP (or a whole AP) off ebay would be another approach.

and don't use channels >11 :-)

Phil

Reply to
Phil Thompson

Get the higher one, it will only draw the current it needs. Check that it's the regulated and not unregulated type and check the polarity is correct.

Reply to
Kenny

A power supply current rating is the maximum available current. Any equipment connected to it will draw no more current that the equipment rating. Your wireless access point/router will draw no more current than the rating of the wireless access point/router (which should be printed on the unit.)

I suggest you check the Wireless access point/router label for the DC power consumption. The rating of the 220 VAC adapter you have has a rating that seems to me to be very high, much higher than the two 120 VAC adapters used by the two wireless access point/router units I own (12 VDC @ 300 MA and 12 VDC @ 500 MA.) Your adapter supplies up to 11.5 Watts, as compared to 3.6 Watts and 6 Watts for the two I have.

One thing to consider is the flood of very inexpensive wireless access point/router units in stores like CompUSA and Office Depot. If you are willing to wait for a mail-in-rebate, the price can be as low as $8 US for a

802.11g Motorola wireless access point/router (my $8 US Motorola is Model WR850G.) This price is less than half the price of a 7.5 VDC @ 1500 mA adapter; RadioShack, for example, charges $39.95 US for a 3 to 12 VDC @ 1000 mA multi-voltage adapter, and $34.95 for a 40 Watt 120 ACV to 220 VAC transformer with US type AC plug and UK/European AC socket.)

Phil Weldon

Reply to
Phil Weldon

Sorry, I left out the POINT of checking the power requirement level on the wireless access point/router. You need only get an AC adapter with the correct voltage and sufficient current rating to meed the requirements on the label, and not the current rating on your 220 VAC adapter. A lower current adapter will be much easier to find, and much cheaper.

Phil Weldon

Reply to
Phil Weldon

Another solution is to get a 110V to 240V AC transformer, then you can use your existing adapter.

Reply to
Kenny

This place has them.

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William Lee

Reply to
Will-Lee-Cue

You could just get a 117VAC to 220VAC stepup transformer. You probably have other devices that run off 220VAC.

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It would also be helpful if you would disclose the maker and model number of your wireless access point and router. The problem is that the sticker label is NOT what the unit draws. The voltage is probably correct, but the current drain of the router may be considerably less than the current rating on the transformer. It would be easy enough to measure the current drain of the router with an amps-guesser and size the power supply accordingly.

I don't like the universal adapters (the ones with a switch from zero volts to more than enough to blow up anything if you goof). I've confiscated those from customers before they blow up their laptops and electonic devices. Actually, the usual problem is not the voltage but the polarity of the connector. Getting it backwards is all too easy. About 3-4 times per year, someone drifts into my shop with a blown something and a universal replacement adapter. Not recommended unless you glue the switch and plug adapter in place.

More current is always a safer bet. If it says 1500ma on the adapter, then 1500ma or larger will do just fine.

1000ma might work if the access point draws less power. The typical access point (no router or switch section) burns about 8 watts. At 7.5VDC that's about 1000ma. However, without measuring the current drain, this is pure speculation on my part.

Another problem is that if it actually does work at 1000ma, it might be running at near its maximum rating. That's a problem because the limit is set by iron core saturation which results in gross inefficiency, heating, and a small fire if left alone. This is another reason why underrated power supplies are a bad idea.

No. Only excessive voltage or reverse polarity can do any damage. The access point will draw only whatever it decides to draw in current. Having excess current capability will have no effect on how much the access point draws.

Reminder... Since you're now in the colonies, kindly reset your firmware to US regulations and standards. If it's not possible, see if there is a replacement flash firmware from the unspecified manufactory web pile.

Reply to
Jeff Liebermann

Hi, It's a D-link DSL-604+, it has built in modem, router, switch, WAP, so I guess thats why it takes quite a lot of power.

I looked in the manual, and it says the power consumption is 12W max, which, I worked out to be 1.6A at 7.5V - would that be right?

If I get this 1700mA adapter, and run it at 7.5V, is there a risk of fire or anything? or is that only if I got a lower rated one.

Reply to
Ann-Marie

True. The DLink DSL-604+ is not sold in the US. It does DMT ADSL so it will probably work with most US DSL ISP's. Check with your local DSL ISP to be sure.

That will save me the effort of looking up the specs. Yep, 1.6A is correct. 12 watts / 7.5V = 1.6A

Nope. The rated current is where it will run forever without overheating difficulties. Only the lower current drain adapters will cause problems. However, just to be sure, check if the power adapter gets unusually warm when you first plug it in.

Reply to
Jeff Liebermann

Almost, but not quite. If a DC supply is significantly under loaded, the voltage will rise. How much depends greatly on the design chosen.

For that reason it is probably not a good idea to use a supply rated significantly higher than the original supply was rated for... *if* the voltage actually makes any difference at all.

(But if, as is true with many wifi units, the onboard supply is actually a switching power supply, which is basically insensitive to input voltage, it simply won't make any difference at all.)

Bad idea. The supply has to be able to provide current at

*peak* usage. Trying to measure that can be very difficult, if not impossible for most people. With a wireless radio, for example, the peaks happen when the unit is transmitting and may be for very short bursts. If you simply measure the current while the unit is idle, what you measure is a totally misleading value.

Ah, you got that one pegged.

Reply to
Floyd L. Davidson

Transformers are recipical devices so a US adaptor (240 to 110) can supply

240 from 110 by reversing the connections just make sure you have a transformer and not a ballast reduction. In this case likely won't hurt anything it just won't work.
Reply to
Not Me

A supply could be rated at 1000A and work no differntly than one rated at 1700mA. It is the *voltage* rating that one must be cautious about. Now, if there was a way you could measure the actual current drawn by the unit, i would expect that it would draw less than 1500mA - perhaps as low or lower than 1000mA. If that were true, then you could use the less expensive supply. However, in your case, it is wiser to use a supply rated at or more than 1500mA.

Reply to
Robert Baer

That would depend on the regulation, but regardless... I've never seen a regulated wall wort.

Reply to
Floyd L. Davidson

The 1 volt is generally true, but...

Many electronics devices (two that I know positively fit this description are the Linksys WRT54G(S) series of wireless routers and the USR Courier series of modems) use a switching power supply internally. They aren't particular about the voltage fed to them. A WRT54G router will work well on any voltage from about 4 V to at least 20 V. A USR Courier will work at least with supplies from 9 V to 24 V.

Doesn't necessarily help. With above two examples, a higher voltage will cause less current to flow. Ohm's Law suggest that if the voltage goes up the current necessarily goes up. But these devices are not simple resistors, and don't act like resistors. Other devices do though...

The problem is that while what you've said is often right, sometimes it isn't. There's no substitute for an experienced eye when it comes to making judgement calls like selection of non-approved replacement parts. And it's always a crap shoot.

And monster PC's! :-)

Reply to
Floyd L. Davidson

BWAHAHAHAHAHAAHAHAHAHAHAHAAH! You f****ng moron.

There's your contradiction, you fuckwitted cunt.

Reply to
Infected puffer fish snot

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