Using a higher rated DC transformer

You could even use one rated for 25 or more amps (should you be able to find one) as long as you do not exceed 12VDC on the voltage. Your RS rep knows whereof he speaks.

snipped-for-privacy@yahoogroups.com

Matthew,

This time (surprisingly!), the Radio Shack guy is correct. As long as the transformer is rated for the same voltage and *at least as much* current, you'll be fine. The connected device will draw only the current it requires, regardless of the capacity of the source.

Regards, Eric

Hi guys! Thank you very much for your reply! On another newsgroup, a gentleman mentioned that if the higher rated wall transformer is UNregulated, then it may put out higher voltage but if it IS regulated, I should have no problems. So with that in mind, 2 questions.

1) Is this accurate? 2) The power supply I intend to use reads: 12VDC 2.5A MAX

Does the word "MAX" there imply that devices drawing a lower current can indeed make use of this transformer. Does that word imply it is "regulated"?

Again, thank you!

Yes, that's accurate to some extent. It really depends on the equipment it is meant to power. If the device uses an unregulated 12VDC wall transformer then it will have an internal regulator. If the internal regulator is rated for the higher swings (maybe 18V) of the unregulated wall transformer you're OK.

Unfortunately, it's the missing wall transformer that you need to examine to determine whether it was regulated or unregulated. The only alternative is to open up the device and trace the power leads to see what regulator it uses.

MAX means MAX. IOW, all it means is that it cannot supply more than 2.5A.

How heavy is the new 12VDC/2.5A transformer? If very light it is most likely a reugulated switched-mode power supply. If relatively heavy, it's probabvly a magnetic transformer type and may be either regulated or unregulated. Regulated 12VDC @ 2.5A is somewhat rare but not unheard of.

What is the device? Maybe someone who also has it can tell you whether it needs 12VDC regulated or unregulated.

snipped-for-privacy@yahoogroups.com

The device is a LinkSys BEFCMU10 Cable Modem.

Actually, I was so desperate to get it working, I bought another identicle cable modem and I'm using ITS transformer temporarily until I can get one that will work. Then I will return the new one to the store. So, I do infact have THE right transformer at this time. What markings should I look for?

It weighs 5.6 ounces and is 2" x 3.5" x 1.25" in dimension.

Thank you!

My guess (and it is just that - a semi-educated GUESS) is that it's a switched mode power suppy (SMPS) which are almost all regulated. I've a

15VDC/1.0A regulated SMPS which weighs about 4 oz. while all of my 12V magnetic transformer style power supplies weigh 12 oz or more. But the heavier transformer type could still be regulated.

The only way to be certain is to contact Linksys Support and ask them, telling them you lost the original power supply.

Otherwise, if you have a friend with a voltmeter, you can measure it. Or, assuming you are going to buy the replacement at RS, ask your friendly RS rep to measure the one from Linksys. If regulated it will measure 12V while, if unregulated, it will measure more, up to 17-18V.

One final clue is that California, Europe, East Asia and other regions now have efficiency standards for wall transformers that can only met by SMPS types so my guess is that Linksys will be using them - I know that D-Link (which I use) does so.

snipped-for-privacy@yahoogroups.com

One added caution. The measurement needs to be made with a cheap multimeter rather than a more sophisticated True RMS Voltmeter. The latter will show the equivalent DC voltage which will be close to 12V even for the unregulated supply.

snipped-for-privacy@yahoogroups.com

Good thing I'm cheap, eh? I have one available. Again I would like to say thank you to everyone for your helpful comments! I really appreciate your taking the time!

Matthew

A final point - using a regulated 12VDC supply will likely work even if the device expects an unregulated supply. In the latter case, the internal regulator will output an even lower voltage and as long as there's adequate headroom (i.e. the regulator needs a couple of volts to do its thing), it will be OK.

snipped-for-privacy@yahoogroups.com