Dumping the extra amperes

[zmint]

Respected members,
My ADSL+ modem is rated at 10V 550 mA input, but the power adopter I am trying to replace with, is rated at 10V 750 mA output, as result the unit is overheating. It is working fine as I am surfing now, but the overheating will reduce its life, I reckon.

Please help me with, dumping the extra 200 mA in some sort of electronic component.
I don't want to temper with the the components inside the adopter, but fix something with the output already being received.

Thanks

 

[rmn_tech]

The Modem will only use the current it needs even if your psu was capable of providing 5A the modem would take only the 550mA it needs it is running hot probably because it is designed that way it is not because your psu can supply more current.

 

[audioguru]

The battery in your car uses 770A or more to turn the starter motor when it is cold in winter. But the clock in the car does not use all 770A, it uses only as much current as it needs which is only about 0.001A. You don't need to "dump" the extra 699.9A because it is simply not needed.

Maybe your 10V/750mA adapter is cheap so its voltage is not regulated and has a higher output voltage when its load is less than 750mA. then the extra voltage caused the modem to over-heat.
We cannot recommend adding a resistor to the output of the adapter to "dump" 200mA because we don't know how much current the modem uses.

 

[KeepItSimpleStupid]

Make sure your replacing the adapter with the correct one. I know Westel uses an AC voltage rather than DC.

Adapters can be regulated or unregulated.

I am SUPPOSING (because I don't have any more info) that the adapter and the requirements could be different. e.g. You could be using a 10 V AC adapter and it wants a 10 V DC adapter as an example.

The ~ usually represents AC whereas a dotted line parallel to a solid one means DC.

What is the model of the modem? Can you link to a datasheet?

 

[carbonzit]

I think you're needlessly questioning whether it's an AC or DC adapter, since the O.P. says "It is working fine as I am surfing now". The only problem seems to be the (perceived) overheating.

So, O.P., just how warm would you say the adapter is getting? Too hot to touch? Smoking? or just uncomfortably warm?

 

[KeepItSimpleStupid]

I believe the perceived overheating has to be related as to how it operated before. Regulated DC, Unregulated DC and AC need to be checked. DC applied to an AC system will allow the adapter to work. 10 VAC would give 7.07 V and a DC adapter would supply 10 V. If we assume a 1 amp power requirement for a router, it would have to dissipate 3 W more. The 7 VDC is a good value for a 5 V regulator.

So, what I am showing is that a 10 VDC adapter will work. There may be 2 diode drops to deal with, so that 10 VDC may become 9V which could be dropped to 5V by the router.

So, a DC adapter of the same value of an AC adapter will cause a higher heat dissipation.

 

[zmint]

Thanks everyone for helping

Maybe your 10V/750mA adapter is cheap so its voltage is not regulated and has a higher output voltage when its load is less than 750mA. then the extra voltage caused the modem to over-heat.

I think it is not cheap. I opened it to have a have look at the circuit. It had 2 different IC's, Zenor diods, A small light transformer & many more components which likely indicated that the output is regulated.

@KeepItSimpleStupid
It is a DC Adopter.

@carbonzit "just how warm would you say the adapter is getting? Too hot to touch? Smoking? or just uncomfortably warm? "
The adopter gets uncomfortably warm, but it's the Modem itself I am worried about not the adopter.
The Modem gets "a little higher degree of uncomfortably warm."

The only option I am left with is what rmn_tech said "it is running hot probably because it is designed that way"
Poor designing though !

Thanks once again.

 

[KeepItSimpleStupid]

Now, was the original adapter DC?

 

[MrAl]

Respected members,
My ADSL+ modem is rated at 10V 550 mA input, but the power adopter I am trying to replace with, is rated at 10V 750 mA output, as result the unit is overheating. It is working fine as I am surfing now, but the overheating will reduce its life, I reckon.

Please help me with, dumping the extra 200 mA in some sort of electronic component.
I don't want to temper with the the components inside the adopter, but fix something with the output already being received.

Thanks

Hi there,


As you probably already noted, not all wall warts are created equal. A wall wart rated at 10v 500ma from manufacturer ABC may not be the same as a wall wart rated 10v 500ma from manufacturer XYZ. The reason is sometimes the manufacturer makes a custom order from a company that makes wall warts, and they fully test their products with the wall wart they ordered. So if company ABC makes a wall wart and tests it with their product and it works fine they eventually ship. But if someone substitutes the wall wart made by company XYZ it may either under power it or over power it even though it has the same 'ratings'. Note that i quoted 'ratings' to bring to attention the fact that all ratings are not the same either.

With all this said, it's best to get the exact same wall wart from the company who specified it.

In your case where you want to use another wall wart that has a higher ampere rating yes your unit could be overheating most likely because that new wall wart can supply power at a higher voltage than the old wall wart, and that means more heat.

One thing you can do rather than parallel a resistor is to put a resistor in series, which would help to drop some of the extra voltage during use. Alternately, a diode or two in series to drop some of the voltage. You might have to experiment a little as to what value resistor or how many diodes you need.
For example, a 1 ohm 1/2 watt resistor would drop 0.5 volts, while a 2 ohms 1 watt resistor would drop 1v. A single diode will drop about 0.7v, and two diodes about 1.4v, and three diodes about 2.1v. If you try diodes, the type 1N4004 would work fine.

To test, you'd have to make sure the wall wart works ok during times of low mains line voltage unless you dont get that condition too much in your area, and then you just have to test it with the lowest line voltage you commonly see in your area. If you loose connection now and then you would have to lower the resistance or remove one diode and test again. Not hard to do but does require a little experimenting.

 

[zmint]

Now, was the original adapter DC?

Yes the original adapter is DC and from the same manufacturer too.

A diode or two in series to drop some of the voltage. You might have to experiment a little as to how many diodes you need. If you try diodes, the type 1N4004 would work fine.

Will definitely try this one. A bunch of 1N4007 are at disposal, hope they can also do the trick ?

To test, you'd have to make sure the wall wart works ok during times of low mains line voltage

The expensive UPS sitting around, will take care of that.

Not hard to do but does require a little experimenting.

This is the most interesting part.

 

[KeepItSimpleStupid]

Thanks for answering my question. The original and the replacement being DC is good. If you have a voltmeter check the output voltage under load if possible.

Otherwise, besides poor connections or a failed component, I have no other ideas. Something in the modem could have caused the adapter to fail. I bought a modem off of ebay for a quick replacement. I really should have the other one set up for non-bridge mode so that the DSL vendor can test with me. My network is so wierd, I need to be able to simplify quickly. One modem, one computer, mo bridge mode.

 

[MrAl]

[requires a little experimenting]

This is the most interesting part.

Hi again,

Oh, so you are like most of us here who like to do a little experimenting now and then.
That's definitely good

I happen to be experimenting with something myself too, a highly stable crystal oscillator.

 

[52613 sfw356645eh5ah6j75]

maybe as they say above, maybe something in the modem shortcircuited and that burned the original adaptor.
u should check how much current it draws with the multimeter. Look if it's below of what it says in the label in its back

 

[carbonzit]

Can't you read? It's right up there in the very first post:

My ADSL+ modem is rated at 10V 550 mA input