AC Adapter Amp Output?

Chip Fossa · Post by **Chip Fossa** » 27 Dec 2011 9:18 am

My brother-in-law gave me an almost brand new Motorola SB5100 Surfboard modem he hasn't used in years, but it came without the ac adapter.

The SB5100 is exactly the one Comcast rents out of which I also have. [$7.00/mnth].

So I want to get my B-I-L's one going and give Comcast back their's.

The rating on CC's adapter is 12V @ 750mA.

I found an adapter in my stuff that has the same polarity, is 12V, but is 1A. Will this 1A baby blow the modem?

On some stuff I've been reading, it appears it's hard to predict the size of the current going through for various reasons. And of course, some blow-ups can happen.

It's also not easy locating an exact 12V750mA replica.

Thanks all. Would love to get rid of that $7/mnth rental fee.

Wiz Feinberg · Post by **Wiz Feinberg** » 27 Dec 2011 9:47 am

Chip;
A power adapter converts voltages higher or lower and supplies up to so many amps, or milliamps. It does not push current; it is pulled out by the devices that are drawing power from them, as needed.

So, the adapter you have is rated at 1000 milliamps (1 amp), but the modem only draws 750 ma. While that is close to the maximum, it might work for you. I would keep the modem dusted off and in open air, to keep it from overheating and drawing more power than the adapter can supply.

If the modem draws more power than the adapter can handle, the fuse inside the adapter will blow.

Ideally, you would want an adapter capable of supplying double the amperage of the device it is powering. See if you can get a 1.5 amp/12v adapter, with the same polarity.

Chip Fossa · Post by **Chip Fossa** » 27 Dec 2011 12:37 pm

Thanks Wiz.

That's just the info I was trying to find. Once again Wizardo to the rescue.

I thought I did see a 1.5A adapter in the 'stuff', but didn't check the volts or polarity.

As long as it's the adapter that might blow and not the modem, heck, that's OK. I'll just keep it aerated and dust free.

Mucho Appreciado, again, Wiz

Ron Page · Post by **Ron Page** » 30 Jan 2012 9:42 am

Since the 12V @ 750mA specs came from your adapter and not your modem, it's likely that the modem draws significantly less than the 750mA. You've probably got plenty of capacity with the 1000 mA.