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Author Topic: Router Power Requirements  (Read 509 times)

risk_reversal

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Router Power Requirements
« on: June 25, 2019, 11:08:47 AM »

I have a question regarding the power requirements of routers.

I have a TP-Link W9970 running FTTC 40/10 service. It works great.

I donít use the wifi on this unit as it has been reports as rubbish, so it is turned off. Am using a Netgear unit for wifi.

The W9970 has a USB port (2.0 spec, I understand) such that a USB 3/4G dongle can be used for fail-back. I am currently using such a dongle (Huawei E367 3G).

The PSU to the W9970 is rated as Output 12V 1A.

So to my question. How much power does my W9970ís functions use, assuming I had wifi on. By that I mean, how much power, Amps, does say the modem side use of the 1A available.

The reason I ask this is because the E367 (which I have tested) uses .05/.7A at idle and about .25A (with peak of .28A) during use and this therefore much reduces what is available to power the rest of the routerís functions.

I did run across this page which says that one can either use a more powerful PSU say 2A for the router or a powered USB hub as resultant power shortages without these measures can affect both the router and the speed of the dongle when in operation.

https://www.ofmodemsandmen.com/power.html

The reason that this got me thinking is that I was considering upgrading the E367 to a 4G dongle but ran across several articles stating that some 4G dongles were power hogs when in use with some having power requirements of 800mA (0.8A) and clearly > USB2.0 specs of 0.5A.

I have tested the E367 for a short while by pulling out the phone cable to the router and it seems to work ok with DN 5-6meg and Up 1.5-2 meg

This post is more of an interest topic rather than a problem if you see what I mean.

Has anyone researched this topic at all.
« Last Edit: June 25, 2019, 11:13:32 AM by risk_reversal »
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IanG

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Re: Router Power Requirements
« Reply #1 on: June 25, 2019, 04:06:26 PM »

I too have noticed that modem/routers take considerably less current than the rated current of the power supply, even allowing for 500 mA from USB sockets. This might simply be because power supplies come in standard sizes, and a 600 mA max modem will come with the next supply size up of 1A.

Measuring the maximum current is not straightforward. It would have to include all operating conditions including start-up and re-flashing, and sample fast enough to detect transients.

The linked page, which recommends fitting a higher current power supply, seems unduly alarmist, and is specific only in a vague soft of way. The 500 mW transmit power mentioned is illegal in the EU, where the maximum is 100 mW eirp.
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sevenlayermuddle

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Re: Router Power Requirements
« Reply #2 on: June 25, 2019, 07:14:45 PM »

There may be some confusion here, between power and current, you really canít discuss them as if they are equivalents.

A 12 Volt supply, capable of supplying 1 Amps, equates to 12x1=12 Watts. 

A 5V USB device consuming (say) 0.8 Amps is consuming 5x0.8 = 4 Watts, which is only a third of that 12 Watt PSUís capability.

You canít guarantee that internal voltage conversions within the router are 100% efficient, thatís down to the designers and in any case there are limits to efficiency, so there may be more Ďwastageí.   But the designers  have a strong incentive to make internal voltage conversions as efficient as possible as inefficient equates to heat, and devices that run hot cause all manner of problems, that are expensive (for the manufacturers) to overcome.

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IanG

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Re: Router Power Requirements
« Reply #3 on: June 25, 2019, 07:52:13 PM »

Indeed, I should have been clearer.

From what I remember, the efficiency of 2.4 GHz transmitters is about 40%. So to transmit 100 mW of RF power, the output stage might consume 250 mW, the remaining 150 mW being dissipated as heat. There is also the conversion from the input 12V to the lower voltage of the RF power stage, which might be 3.3. Taking the conversion efficiency as 80%, power from the +12V input is then 312 mW, or  12/0.312 = 26 mA.

26 mA is not a lot, and as the transmit stage emits packets sporadically, the average over a second is likely a lot less.

Adjust the numbers for your own calculation.
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risk_reversal

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Re: Router Power Requirements
« Reply #4 on: June 25, 2019, 10:50:42 PM »

May I ask if any of you use a USB mobile dongle as fail-back in your routers (I'm sure that you do) and during times when your main internet has gone down (rareish these days I agree) has the dongle performed well that you have noticed.

Also have you measured the power requirements / wattage of your mobile dongle
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sevenlayermuddle

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Re: Router Power Requirements
« Reply #5 on: June 25, 2019, 11:20:01 PM »

One way to get a gut-feeling as to power consumption, is to feel how hot a thing is.

For example, I have a 15W soldering iron.   The tip covers just a small area but is hot enough to scald my hand.  If I were to grasp it when hot, Iíd probably be googling for ways to treat major burns.  So I am aware that 15W, in palm sensory terms, is quite a lot of power.

Contrast with an energy-saving LED bulb, rated at 3W. With its larger surface area and lower power, if I grasp it immediately after use it might be a little uncomfortable.  But probably not so much as to require a trip to A&E, or even to require reaching for the savlon.

A more quantifiable method is to plug in the equipment via a plug-in wattmeter at the 230v mains socket.   Connect/disconnect the various ancillary items, and record the before/after difference. :)
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Weaver

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Re: Router Power Requirements
« Reply #6 on: June 27, 2019, 11:07:10 PM »

@risk_reversal I do. I use a USB 3G NIC as a failover device in my Firebrick router, and the router switches over to 3G when all the DSL links go down.

I have 3G not 4G because I only have a rubbish USB NIC (a Huawei something-or-other, I forget the model). I need to ask my ISP for some help getting a better one set up so as to enable 4G.

I only very belatedly noticed this thread because I have been very ill recently. So I have just this minute approximately posted a duplicate thread to yours.
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risk_reversal

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Re: Router Power Requirements
« Reply #7 on: July 01, 2019, 11:56:41 AM »

I only very belatedly noticed this thread because I have been very ill recently.

Sorry to hear that...

So I have just this minute approximately posted a duplicate thread to yours.

Great minds think alike...!!!

@risk_reversal I do. I use a USB 3G NIC as a failover device in my Firebrick router, and the router switches over to 3G when all the DSL links go down.

I have 3G not 4G because I only have a rubbish USB NIC (a Huawei something-or-other, I forget the model). I need to ask my ISP for some help getting a better one set up so as to enable 4G.

Well as I mentioned above I have a 3G Huawei E367 dongle which is old. It is detected and works fine with the W9970 that I have.

I was looking to get the 4G Huawei E3276 as it has the rotating usb plug but on doing some research found the above page as well as forum posts stating that this model uses a steady 800mA which is well above USB2 specs. With a 1A psu this would also lead to trouble.

The info posted by another member in your other post was informative.

Not sure if I want to get a powered USB hub and try to use the 4G E3276 for fail-back as it would not be used often.
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