Can we make an adsl modem work with battery.

[mneary]

A 9V 500mA input is an indication (to me) that it's being regulated to 5V with something like a 7805. Supplying 12V to that regulator would make it run pretty hot (75% more dissipation). Probably won't damage it, but there could be intermittent thermal cutouts.

 

[3v0]

Given that it is battery powered and you want to go from 12V to 5V you may want to look into a switching regulator.

 

[Hero999]

A switching regulator is a good idea but thay would involve modifing the box and I don't think he wants to do that.

Have you measured the actual voltage from your adaptor?

 

[Nigel Goodwin]

It all really depends on the actual requirements of the modem, as Hero999 says a good start is to measure the output of the existing power supply (AC or DC, and regulated or not).

I use a Belkin ADSL modem/router at work, and the power supply died on it, it said on the supply 12V and x amps (can't remember the current), and on the back of the router it said 12V near the socket, and indicated the polarity of the pins (so obviously DC).

So I simply got a regulated wallwart from the shop, of sufficient current, and set it to 12V - and it's been working fine for ages now. I've got no doubt that simply replacing the wallwart with a 12V battery would work perfectly as well.

 

[mvs sarma]

as the OP is seeking a 9V DC at 0.5A, he could well try out 7809 with a heat-sink, from a 12V/7AH battery and supply it, taking care of polarity.He should not have an issue at all. Charging arrangement, he may have to make.
Having seen all this I would rather suggest that he may power it from an adopter with the UPS he may have.

 

[Hero999]

The problem with that, is that it won't last very long, as soon as the battery voltage drops below 11V it will stop regulating working properly.

 

[mvs sarma]

The problem with that, is that it won't last very long, as soon as the battery voltage drops below 11V it will stop regulating working properly.

I still don't get the great advantage of using DC for an ADSL modem in case OP is using a Desktop. In case of Laptop, of course, he could power it from mains. May be it is a case Of wall wart failure and he might be searching for alternatives. He could well attend to it. generally there would be a thermal fuse embedded in the winding. it can be accessed and replaced.

 

[shareebacha]

Well why i want this is because i m using a laptop, and power for adsl modem is coming from mains, but i live in pakistan, and i m out of electricity for about 5 to 6 hours a day. Now if i m downloading something from rapidshare and my electricity goes, the download stops and all the efforts go to vain, and i have to start downloading again.

Now the ups solution will work, but it will be an expensive solution.

All i want is my modem to work with a battery when my light goes, before i turn on my generator. So my download dont stops.

Hope you can understand my dilemma fully now

 

[mvs sarma]

Well why i want this is because i m using a laptop, and power for adsl modem is coming from mains, but i live in pakistan, and i m out of electricity for about 5 to 6 hours a day. Now if i m downloading something from rapidshare and my electricity goes, the download stops and all the efforts go to vain, and i have to start downloading again.

Now the ups solution will work, but it will be an expensive solution.

All i want is my modem to work with a battery when my light goes, before i turn on my generator. So my download dont stops.

Hope you can understand my dilemma fully now

Try to use a motor cycle type battery with a regulator 7809 with a heat sink.
You may have to arrange for charging the battery

 

[Diver300]

The problem with that, is that it won't last very long, as soon as the battery voltage drops below 11V it will stop regulating working properly.

If he is using a 12 V, 7AH lead acid battery, and pulling 0.5 A, It should last about 14 hours. It won't drop down to 11 V until the battery is almost flat. Lead acid batteries have a fairly flat discharge curve and the voltage stays high nearly to the end.

http://www.ibt-power.com/Lead_acid_tech/Discharge_1.jpg

It does depend on what battery type is used. Eight alkaline batteries would start at 12V and would drop below 11V quite quickly.

 

[yaskhan]

hi there,

i am from pakistan too and am facing the same problem of power failure / power loading shedding (one hour on and one hour off).

I have the same modem 9V and 0.5A from PTCL.

What i am planning to do is ro replace my emergency light battery with a 9V battery ( the emergency light's battery is currently of 6V). I have to also change the tubes of emergency lights to 9V. Its got the charger built in so i am supposing that it will charge the 9V battery as well. Its simple to takke out two wires from the battery and plug it in the modem. The only thing which i cant understand is that

Should i have to get a battery whoz initial current is 0.5A?

Also please inform if 9V 4.5AH battery is good enough for one hour back up if fully charged or should i go for a higher AH battery.

I am also a noob so am am stuckup with the 0.5A thingy??

The battery which i already have in my emergency light states

6V 4.5AH Maintainance free lead acid battey.
Standby use 6.75- 6.90 V
Cycle use 7.20 - 7.50 V
Initial current: less than 1.35A

so i suppose that the replacement battery should be like this

9V 4.5AH or higher Maintainance free lead acid battey.
Standby use 9.75- 9.90 V (dont know what it is)
Cycle use 10.20 - 10.50 V ( dont know what the hell is this too)
Initial current: less than or equal to 0.5A ?? (is it so)

Also i guess i have to search for the tubes which i will replace in the emergency light with 9V and 0.5A current. (Confused about this too)

I am also using a laptop which gives me a good backup of 2 hours with an hour of charging.

I also want to do uninterupted work and without installing ups as i do not have a budget for that.

Please advice what to do??

 

[audioguru]

Nobody makes a 9V lead-acid battery. They use 2V cells so three cells are in a 6V battery and six cells are in a 12V battery.

You need a 12V battery and a 12V battery charger. Then make a 9V regulator that is powered from the 12V battery.

A 4.5AH battery will power the 0.5A modem for about 9 hours but then the battery might be ruined from discharging too low.
if the battery is used to power the modem for only 4 hours then recharged, it will last much longer. Recharging after it is discharged to half will take about 5 hours.

 

[crutschow]

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

A good NiMH AA battery has a 2AH or more rating and can deliver high currents. Eight batteries in series will give you 9.6V nominal, which the modem should tolerate. This should run your modem at 0.5A for at least a couple hours, and probably will run over 3 hours, depending upon the low voltage dropout point of the modem.

 

[dknguyen]

Physics, does not let you make a 9V lead acid battery. A single lead-acid cell produces ~2. THis is physics. You can't make a 4.5 cell battery. No way around it.

But you can certainly take a 12V battery and efficiently generate 9V from it.

A battery rated for 1000mA-h (or 1A-H) is theoretically able to supply 1000mA (or 1A) for 1 hour. If you draw current from it twice as fast then it will last half as long, and if you draw current from it half as fast then it will last twice as long. It works proportionally like this (in theory).

Time = (Amp-Hours)/(Amp Draw)
Time = (milliAmp-Hours)/(milliAmp Draw)

In reality, if you draw the current twice as fast the battery will last LESS than half as long. And this effect gets worse and worse as you draw more and more current.

In reality, if you draw the current half as fast, the battery will last MORE than twice as long. And this effect gets better and better as you draw less and less current.

So theoretically, a 4.5AH battery can supply 0.5A for about 9 hours.

 

[pxjain]

Hi

I am trying to solve a similar issue and needs advice of experts here.

The Chinese modem supplied by the broadband provider BSNL (India) has issues with its AC adapter. If you leave it on for couple of hours it gets very hot and if you leave it on for couple of days, it will burn.

The AC adapter outputs 9V AC and rated at 1 Amps. I replaced the Chinese modem with D-link 502t, recommended by the local supplier. The D-link modem also came with 9V AC and rated at 1A. I suspect the Chinese modem is a copy of the D-link as the web administration is exact the same. However the D-link adapter didn't last for more than couple of weeks.

I think the voltage fluctuates quite frequently and hence cause these adapter to burn. I am looking for a solution to power up my modem, which requires 9V AC 1Amp and can work under voltage ranging between 170V to 240V.

I couldn't find any 9V AC to AC adapter that are regulated. Is there any thing like AC to AC regulated power adapter?

I was thinking of buying a 230V AC to 9V 3.2Amps AC adapter. Will it work with the modem that requires 9V 1Amp AC as input?

The reason I want to go with a higher Amp is so that it does not get hot. Am I thinking right?

Please advice.

Thanks in advance

 

[audioguru]

I think the problem is that your mains voltage is not regulated like it is in modern countries.
The mains voltage at my home in Canada is within 1V from 120VAC.

My electric utility company warned that they might reduce the voltage with brownouts if people do not stop wasting electricity by lighting trillions of Christmas tree lights. They replaced many those incandescent lights with LED lights for free and gave away many compact fluorescent light bulbs. Now the peak power used is less.

 

[pxjain]

I think the problem is that your mains voltage is not regulated like it is in modern countries.

That is right, I never have to worry about the adapters here in the UK and when my dad first told me about his issues, I couldn't believe it, until I experienced it myself when I visited him last time.

That's why I am looking for some answers here.

1) If I connect an unregulated adapter that outputs 9V 3.2A AC to this modem which required 9V 1A AC, what voltage will the adapter provide 9V or 9*3.2/1=28.8V or some where in between?
2) If it will not provide 9V, can I connect this modem with a 9V regulated DC adapter?
3) If the modem can't be connected to a DC source, can I buy some components to turn the 9V 3.2A AC to a regulated 9V AC?
4) What happens when the input voltage drop from 230V (this sis the input voltage the adapter requires) to say 180V, will it change the output voltage?

Please someone can answer my questions.

I don't want to buy this adapter and then port it to India, only to find that it turns the modem in smoke.

Many Thanks

 

[audioguru]

The 230V to 9V adapter is a simple transformer that has a voltage ratio of 230/9= 25.56 times.
If your mains voltage drops to 180VAC then the output of the adapter will be only 7VAC and the modem might not work.
If your mains voltage increases to 280VAC then the output of the adapter will be 11VAC and the modem circuit might smoke and burn.

The mains voltage is supposed to be regulated at 230VAC, not the adapter.

Ask somebody in India what they do about the horrible flucuating mains voltage there.

 

[pxjain]

Thanks a lot for clarification. Even if I regulate the input voltage for the adapter to 230V, what happens to the output voltage with respect to the current.

The adapter is rated at 3.2 Amp. If I connect it to the modem requiring 1Amp, will the voltage be still 9V or it will shoot up to 9*3.2/1 = 28.8V. In other words, how do i regulate the output voltage of the adapter to 9V AC.

Ask somebody in India what they do about the horrible flucuating mains voltage there.

Most of the people I spoke to say they only use the modem when they browse and then switch them off. I would like the modem to be on all the time so that the VOIP adapter remains connected to the internet and I can call my parents. But for this to work, I will need the modem to be up and running all the time.

 

[ericgibbs]

The reason some of these modems require 9Vac as an input, is because of the RS232 voltage level requirement.
The modem internal diodes half wave rectify the 9Vac to give ~ +9Vdc and ~-9Vdc.

A way to solve your problem would be to make a regulated +9Vdc 0V -9Vdc and internally wire this into the modem, by passing the installed diodes.