Can we make an adsl modem work with battery.

[shareebacha]

I have an adsl modem and i have was just wondering if i can use a battery to make it work. The power rating of my modem is 9V DC and 0.5 A.

Now the question:
1) Do I have to connect a battery providing current exactly 9V, 0.5A?
2) Or can i put any supply as long the output is 4.5W? (I read somewhere on the net that power = Volt x Ampere)
3) And what factor determines how long a battery will last. Like a battery working in camera will drain much faster than it is in any other device.

I am a total noob so please an explanatory answer would be quite good.

 

[mvs sarma]

Generally the modems use dual polarity power supplies. So the AC (low voltage) input is easy to convert. If you feed DC input, the -ve voltage is to be generated internally -- as it is not possible, you may have to mod the psu over there to incorporate DC-DC inverting converter for the load current it needs. Instead of all these things, better supply the modem from an UPS.

 

[shareebacha]

Though it went over my head. But still thanx for the asnwer.

 

[mvs sarma]

Though it went over my head. But still thanx for the asnwer.

need any clarity?

 

[shareebacha]

yeah! clarity will certainly be helpful!

I hope i m not annoying u

 

[mvs sarma]

The tentative schematic is self explanatory and suggest how to use DC input to get -ve voltage unless we use a DC-DC conveter with -ve output ?

 

[shareebacha]

Thanks Sarma!
Seems its not my cup of tea..
But still thanx once again.

 

[3v0]

Generally the modems use dual polarity power supplies. So the AC (low voltage) input is easy to convert. If you feed DC input, the -ve voltage is to be generated internally -- as it is not possible, you may have to mod the psu over there to incorporate DC-DC inverting converter for the load current it needs. Instead of all these things, better supply the modem from an UPS.

The OP said

The power rating of my modem is 9V DC and 0.5 A.

Why are you talking about dual polarity ?

 

[mvs sarma]

The OP said

Why are you talking about dual polarity ?

Yes. I should have seen the 1st para, that i missed. generally we use a step down transformer as input.
I really missed it. Thanks 3v0.

The moderated reply could be.
" As the spec indicates 9V at0.5 amps, the O P may have to supply 9V or close to that. "
Now the cup of tea is not that bitter , I hope, Shareebacha.

 

[whiz115]

as far as i know a adsl modem can work just fine from batteries... because i have done it with a wireless one. The only drawback is the power dessipation which might exhaust the batteries faster than you would want.

i'm speaking for devices that use a simple transformer to power up.

 

[shareebacha]

oh great.
SO that means i can use a 9v battery to operate my modem.
wat about the ampere stuff ??? i mean the modem rating is 0.5a?? so anything that i might have to check before buying a 9v battery ??

 

[3iMaJ]

Batteries have what are called mAh (milliamp-hour), which is how many milliamps the battery can supply for an hour. A decent 9v battery can source 1200 mA for an hour.

So, assuming that your modem doesn't require more than 9v (which it may) you can run it for about 2 hours on a 9v battery.

 

[shareebacha]

oh thanx!!
will try it. Hope it doesnt damages my modem

 

[audioguru]

The voltage of a little 9V alkaline battery will be 9V for only a few seconds at 500mA. Then it will be 7V in 10 minutes and will be dead in a little over half an hour. The modem might stop working in less than 10 minutes.
You need a HUGE 9V battery.

 

[Hero999]

It's possible to make a small inverter with an h-bridge to convert DC to AC squarewave.

 

[shareebacha]

so how much ampere battery should i get to be able to make the modem run atleast an hour.


@hero999
why do i have to convert dc to ac ??

 

[Hero999]

Based on the assumption that most modems are rated for DC not AC.

If your modem is rated for DC, you could probably just stick a 12V sealled lead battery on the input and it'll probably be fine, since the output from the adaptor will probably be as high as 14V with no load connected.

 

[shareebacha]

Well on the adapter it is written that the output is 9V.


And if i do connect a higher voltage battery(for eg 12v) will it harm my modem?

 

[audioguru]

The modem is designed to use a 9V power supply. A 12V power supply or battery might cause it to fry. a 12V battery can have its output regulated down to exactly 9V.

 

[Hero999]

The modem is designed to use a 9V power supply. A 12V power supply or battery might cause it to fry.

It's possible but I very much doubt it, the adaptor probably isn't regulated and pumps out well over 12V when it isn't fully loaded.

Somehow, I can't see them using 10V capacitors, and transistor circuit that'll burn out if powered from 12V.