Car inverter to charge my network router

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Old 10-11-20, 05:19 PM
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Car inverter to charge my network router

Hi all,

I live in Atlantic Canada, and unfortunately, due to severe weather conditions and a very poor grid, power outages are not uncommon. Those outages can last between a few hours to a few days, depending on the location.

I have a network router with a backup battery included in the router itself, however, the battery does not last longer than 4h. I have 3 of those batteries, which means after 12 hours I am done.

I am thinking that a car power inverter would be the easiest solution to resolve my issue, as I do not want a power generator.

My router is in the basement, and it is powered via AC:


In order to reach the battery of my car in the garage, I need an extension cord of 75ft:
  • What gauge is it recommended for the extension cord?
  • Is it a problem to use an extension cord with an inverter?
  • I know that a pure sine wave inverter is recommended, considering that I could possibly use it to power both my router and my laptop, which wattage should I consider for the inverter?
  • I'd rather prefer to use the cigarette lighter port (15A fuse) rather than connecting to the battery, do you see any problem in terms of amperage? My alternator generates 100A - 14V
  • How long (approx.) do you think I can power the two devices before I need to run the engine? Like, half an hour? One hour? Of course, I do not want to drain the battery of my car. My scope is to be able to re-charge both the router and laptop batteries so that I can continue to work for another 4 hours. Please see the picture below for the specs of the router backup battery.


If I am missing something, any suggestion is very welcome!

Thank you,
Alex
 
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Old 10-11-20, 05:58 PM
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First- unless your internet is through a satellite dish, a widespread outage that takes down power over a wide area is ALSO likely to take out the grid that powers your internet company's equipment.

You may want to think about a generator and cellphone based internet, because cellphone companies generally have automatic generators,
I DID find that anything with electronics worked better when the power to them was run through a computer UPS which has the circuitry to clean up "dirty" sine waves from a generator. Example, during the Halloween ice storm, my oil furnace wouldn't run directly from the generator, once I passed the power through a computer UPS, it kicked on without any problem.

When the east coast got hit with the 2011 Halloween ice storm, and Hurricane Sandy, I relied on a generator to run the house, and got internet through the cellphones. The trick was using "USB tethering" which let the cellphones charge from a laptop over a USB cable while the phones provided internet over the USB. The laptop would charge up and stay running for hours, so if/when I had to service the generator or it ran out of fuel in the middle of the night, the laptops could just run off their batteries until the generator was going again.
 

Last edited by Hal_S; 10-11-20 at 06:24 PM.
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Old 10-12-20, 04:15 AM
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Hi Hal,
Thank you for your feedback.
I do not need a generator, I live in the city, and during the last 10 years, the longest outage lasted 3 days, I managed without a generator. So in my case, it would be a waste of space and money.
All I need is what I asked for in my message below.

I hope you or anybody else in this forum can answer my questions.
I believe I provided all the possible details, and if I missed something, I will be happy to provide more.

Thank you!
Alex
 
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Old 10-12-20, 04:43 AM
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If you are limiting yourself to a 15amp cigarette lighter in the car then that makes your choice of inverter much easier. Maxed out you will only get 180 watts out of the cigarette lighter. So, if your consumption will be anywhere close to that I would look for the most efficient inverter you can find, probably a pure sine wave.

Because of the long run from your car it would be best to have the inverter in your car and convert to 120 VAC right at the beginning. Then use extension cords to carry the power to your router. Because your cigarette lighter socket can provide so little power you don't really need to be worried about the extension cord. Even a cheap one will be able to handle what your inverter can produce.

You asked how long your car battery will last. To know that you need to add the power consumption of your router and computer. Then add in the conversion/efficiency loss of the inverter and that will tell you how many watts you are using. Then you need to look at your car's batter and find it's capacity. And, when recharging the car's battery keep in mind that the alternator cannot generate the 100amps you mentioned at idle. The engine would have to be at high rpm to get that much power so plan on getting closer to 15-20 amps of charging power at idle.
 
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Old 10-12-20, 05:28 PM
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Hi Pilot Dane

Thank you very much for your response.

First, let's see if I am correct regarding the wattage consumption of my router, as it is not written specifically on its label. On the power supply (image in my initial post) I read, Input 100-120V - 1.5A.
Does it mean that my router consumes 180W max?
If this is correct, then through the cigarette lighter I could only power my router.
The same applies to my laptop, 100-120V - 1.3A = 156W
So, the two together would draw approx. 336W

My car battery has a capacity of 70 Amp Hours, does it mean that if I connect the inverter directly to the battery I could have a max. load of 840W? If that is the case, then I would need a more powerful inverter, like, 1000W?

What I am trying to determine, is the biggest load I can 'safely' connect to my car, using either the lighter or the car battery terminals. Of course, considering that the alternator can generate 100A max.

Thank you for helping me

Alex
 
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Old 10-12-20, 05:58 PM
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Your router power supply can supply 12vdc and up to 5amps.
In order to supply 5A it needs 1.5A or 180 watts of AC.
However..... routers draw very little power.
Actually you'd be better off using the 12v directly from your car to your router.
No conversion = no losses.

Some typical router current needed
 
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Old 10-12-20, 06:01 PM
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Back to high school physics equations.
V=O x A or Volts equals Ohms times Amps.
W=O x A x A or Watts equals Ohms times Amps squared.
Since V=OA you can substitute O x A to get
W=V x A or Watts equals Volts times Amps

The router's power supply input requires 1.5 A at 120V or 180 watts.
The router's power supply output provides 5 amps at 12V or 60 watts.
The "wall wart" inverter that powers your router wastes 2/3 of the power it gets as heat.
Any cigarette lighter inverter you find will likely have similar efficiency at turning the car's
12v DC into 120v AC as the wall wart does at turning that 120v AC back into 12v DC.
You are pursing a solution that is likely to waste 89% (1/3 x 1/3) of the usable power as heat.

While there are "camping power stations" (basically a big battery pack) they take around 4 hours to store 74Wh, so the 60 watt router and laptop will drain most camping power stations faster than you can recharge them.

Sorry to be blunt, but I only see 2 options
A) purchase a small camping generator.
B) charge the laptop in the car, with the laptop charging a cellphone over a USB cable, while you tether your cellphone data over the USB cable.
 

Last edited by Hal_S; 10-12-20 at 06:24 PM.
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Old 10-12-20, 06:05 PM
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If you have something like a Kill-O-Watt you can plug your devices in and see their actual draw. But for the purpose of sizing an inverter using the 2.8 amps from your power supplies labels is probably a good place to start and will include some buffer room.

"What I am trying to determine, is the biggest load I can 'safely' connect to my car..."
I think the better question is how long can you power your devices. You can place a huge draw on your car's battery for very short periods. When starting it can be putting out several hundred amps, but it can only do it for seconds.
 
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Old 10-12-20, 06:40 PM
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Originally Posted by Metallo
the two together would draw approx. 336W
Unfortunately, no. Not when you factor in transformer losses.

The power inverter needs to SUPPLY 336W in output at 120V
Assuming the inverter has the same 33% efficiency (180W input to provide 60W output) for 12vDC to 120vAC then the you'd need to draw a constant 3 x 336W = ~1000W at 12 volts, which is 84 amps

Originally Posted by Metallo
My car battery has a capacity of 70 Amp Hours
Ok, and running the laptop and router via an inverter from 12v to 120, then wall wart from 120 to 12v will require around 84 Amp Hours. The laptop and router will drain the car battery in under 50 minutes.
(we haven't even discussed losses from the extension cord FROM the car to the router.)
 
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Old 10-13-20, 04:29 PM
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Thank you all for your valid comments.

I have asked my ISP about the max wattage consumption of their router, however, I do not think it consumes more than 20W, which is more or less what any other wi-fi router consumes (max.).
I can try and buy a 1000W inverter and see how that works. It should easily charge both devices.
If not, I can do one per time, but 1000W should be more than enough for my use.
I prefer to buy a pure sine wave as quality matters, especially with electronics.
Also, it is recommended to use an inverter and not direct DC to DC as many people say that routers may have issues to manage 14V of the car battery, it could work but the long term may be an issue.

Should I need to charge any other device that is more demanding in terms of consumption, I can still connect the inverter directly to the car battery terminals, that should allow me a bit more.

Alex
 
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Old 10-13-20, 07:31 PM
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A 1000 watt inverter is completely overboard there. Go with something more in line with what you need.

Stay with a 400w max pure sine wave..... not modified sine wave.
Expect to pay roughly $85-100 for the unit.

Don't be fooled by 1000w knockoffs for $39.
Get it from where you can return it if not happy.
I've always used TrippLite products. A trusted name in electronics.
This unit on amazon looks to be good. Inverter
 
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Old 10-14-20, 04:01 PM
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Hi PJMax,

Yes, I was in fact thinking of 400W or 600W pure sine max.
Common sense does not suggest I would need 1000W to power a laptop and a router.
There are inverters and inverters, good ones are 90% efficient, so I will go for a small one and I should be good to go.

Thank you!
Alex
 
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Old 10-15-20, 05:21 AM
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One thing I've done is use a computer UPS. I then get a large gell cell battery like is used in solar power applications and use that instead of the small internal battery of the UPS. I cut the UPS's battery wires and extend them so they can be connected to the larger external battery. When the power is on the UPS charges the battery and when the power goes out you can have 10+ times as much run time as a standard UPS.
 
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Old 10-15-20, 06:05 AM
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For routers and most network equipment, and laptop modified sine wave is just fine. Switch mode power supplies don't really care how clean the AC input frequency is because they get converted to DC at the first stage anyway.
Some computers (especially servers) with active PFC power supply does require pure sine wave though. Active PFC tries to correct power factor and causes overload to the inverter.

So, if there are big price difference between pure sine wave and modified sine wave inverter, I'd go for modified sine wave. If there aren't much price difference, go with pure sine wave.


If you can get a used on-line UPS cheap, that might work better for you. On-line UPS has pure sine wave and you could modify or use external battery connector for a larger battery. One downside is that they have a loud fan that runs all the time. This is because on-line UPS converts AC to DC then back to AC all the time. This results in cleanest power all the time. Also, there is no transition delay when power goes out or comes back on.
 
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Old 10-15-20, 10:19 AM
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Lambition,

I have always been reluctant to go for UPS because, in the end, we are still talking about batteries with limited time before they are drained.
When a power outage occurs in my area, it can be three hours as well as 3 days, if the latter, I need something to recharge.
Which is the reason why the power inverter is my preference for what I need, computers, printer, router etc.
When you turn the engine of your car on, you know that your battery recharges, since the garage is attached to my home it is practical for me to do, cheaper than buying a generator which, besides, would need its space to be stored.
I think everybody adopts the best solution for its own needs and situation. An inverter is very easy to set-up and ready to be used at any time. I do not want to have the frustration to work on my computer not knowing if my UPS will last longer than the outage itself.

Thank you!
Alex
 
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Old 10-15-20, 12:02 PM
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I think you are under the misunderstanding that your car is a good generator. It's nowhere close. As I mentioned before, your car's alternator will not put out 100 amps at idle. That means you will have to put a brick on the gas pedal to hold your car at high rpm for long periods just to charge the battery. Or, you'll have to start it up and let it idle for a even longer time... just to charge the battery. That's a very huge engine to run for the very small amount of power you'll get out of it. And because of the battery's small tidal capacity you'll have to recharge it very frequently. Discharge it too deeply and you will damage the battery and maybe not be able to start the car.
 
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Old 10-15-20, 02:10 PM
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The best solution for your stated facts is to get a camping generator.
 
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Old 10-15-20, 05:20 PM
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Hi All,

Thank you for your advice, but I am still convinced that in order to power a network router and a laptop, I do not need to spend unnecessary money either on a camping generator or a UPS.
Do I need to keep my car engine running at idle speed for 8 hours a day? I am fine with that, it will get me going. A good quality inverter connected directly to the battery, no accessories on, only the inverter.
I am pretty sure it will work just fine.

Alex
 
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Old 10-15-20, 06:36 PM
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Originally Posted by Pilot Dane
your car's alternator will not put out 100 amps at idle. That means you will have to put a brick on the gas pedal to hold your car at high rpm for long periods just to charge the battery
Originally Posted by Metallo
Do I need to keep my car engine running at idle speed for 8 hours a day?
.
Um, no.
Your plan has major inefficiencies over several segments:
A) a car alternator pushing out 12V DC power,
B) an inverter turning 12 volt DC power into 120 volt AC power,
C) power from the 120v AC power over the length of the extension cord,
D) the wall wart loss of turning 120 volt AC power into 12 vote DC power

Just purchase a camping stove.
 
  #20  
Old 10-16-20, 07:30 AM
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If you need a power back-up for extended period of time, some sort of a generator is the only way to go. For computer uses, inverter generators are the best way to go because regular generator's outputs are pretty unstable (especially smaller portable ones). Also yhey don't play well with UPSs if you have any.

When you turn the engine of your car on, you know that your battery recharges, since the garage is attached to my home it is practical for me to do, cheaper than buying a generator which, besides, would need its space to be stored.
As an emergency back-up inverter connected to car will work, but In a long run, generator will be cheaper. As others have said already, car alternator is not very efficient. Idling for hours is also not good for your car engine.
 
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