Run a router off batteries

mrcool

mrcool

EGO Addict
Joined
Nov 14, 2008
Messages
1,283
I have a Belkin router that I'd like to run off batteries - basically in a back pack.

I know you can run pretty much everything off a power inverter in a car. However, I'd like to lug around something a little lighter than a car battery.

I've done a little research, but I pretty much known nothing about electricity. Here's what the AC adapter for the router says:

Input: 120VAC 60Hz 14W
Output: 4.5VDC 1.5A

Thanks much.
 
For this you will need a little bit of Electronics Engineering knowledge.

To provide 4.5vdc at 1.5A for a long period of time, you will need a source voltage of at least 12vdc. I would suggest 2x6v lantern batteries connected in series for this.

You will need to purchase a voltage regulator IC, a few resistors, and a few capacitors.

avr01.jpg


With a Vin of ~12vdc, I would suggest using a 500MF electrolytic capacitor for C1, and a 0.5MF cap for C2. This will allow for a more stable power supply. As we all know, computer electronics LOVE good, clean power!

The above shown IC (LM7805) is only rated for 1 Ampere (amp) at 5vdc. There are others out there that are rated above 1 Ampere, but they get ridiculously expensive.

A way around this is to use good-ol-Ohm's Law.

P=IxE and E=IxR

P=Power in Watts
I=Inductance in Amperes
R=Resistance in Ohms
E=Energy in Volts

So Vout power availability of 5Watts is less than the needed 7.5Watts for the router. Since voltage is our only variable, a different Voltage Regulator will be needed.

A voltage output (I saved the math for ya) of 7.5vdc at 1 Ampere will suit you just fine for this application.

The LM7809 has an output of 9vdc at 1 ampere. This will give you 9 watts of available power. You can then use resistors to reduce the available voltage down to ~5vdc and still have the needed wattage.

Total build cost ~$15USD

Total Package size (not incl. batt.) ~2"x1"x4"

Guess @ Runtime: 6-8 hours.

There are many other options including a battery charging system and power level monitoring. I can include these if you like, but that crosses my degree-for-free line. ;)

If you're really interested in doing this, I'd be more than happy to help you out. I have to warn you, however, that it's MUCH cheaper to learn a bit about electron physics and try it for yourself.

I hope this has helped you and let me know if you need anything else!

Best of luck!
 
Wow. Thanks much!

I'll do some googling and head scratching and hopefully come out with something that works. Hehe
 
you might be able to already purchase a power supply that you can plug into your sig lighter that you can do minimal changes to.
 
actually you should be able to run that off of 3 AA batteries wired into a plug for it but the life would be extremely short like a few mins. but what Angellas has outlined in his schematic would defiantly do the job and would prolly get it going for a full days use as long as it's off when not in use. but it could get costly over the weeks for batteries if you don't use rechargeable ones.

what are you trying to accomplish with this anyways.
 
Last edited:
blizbiggy said:
you might be able to already purchase a power supply that you can plug into your sig lighter that you can do minimal changes to.
Click to expand...

kinda that would take care of the side with the 2 6v batters because i believe a car runs with a 12v battery but what the schematic was showing was taking the 12v dc from the batteries down to 4.5v dc for the router.
 
If you don't want to go carrying lantern batteries, look into a nickel-cadmium (NiCad) or nickel-metal-hydride (NiMH) battery pack. They're substantially lighter and rechargeable, at the expense of cost. However, for a mobile application, they're the way to go. You could even use a trickle charger powered by your car to keep them in top shape. Assuming you're not planning to use this continuously for hours at a time, you should only need a 9.6V pack or so.

Actually, come to think of it, there's an easier solution: Cordless tool battery packs! Often you can simply solder onto the connectors or else put on a crimp terminal, and there's your power source; they even come with a charger too. Somewhat expensive here too, but a brand like Ryobi (which I use) isn't too bad; get a 12V pack or so. 18V would work, but a part like the 7805 will overheat and will require a heat sink if you push it-trust me on this! I've run them off 18V from 9Vs in series, and all the excess voltage is lost as heat, which can burn you after only a few minutes.

The 7812/7809+resistors solution would work, but at a severe loss of power, because that's highly inefficient. For what you're doing, I would think that a clean 5V supply would do just fine.

I'm not an EE, I'm a mechanical engineer, but I'd like to add something to that schematic, Angellas: a 1N5817 Schottky diode between the +Vcc input and the ground line. If you accidentally hook up the power backwards, it won't trash your router. This is a case of a $.10 (max!) part saving a lot of money. I think that a 1N914 diode from RadioShack (something like $2 for 10) would do the job too.

I won't proclaim that I'm absolutely right on this; I'm speaking from 7 years of robotics experience and just passing on what has been very successful for me. My robots currently run on custom Sanyo NiMH packs capable of 7.2V@4000mAh (roughly $60/pack paid for by sponsorship), and I buy a lot of surplus/clearance battery packs of various chemistries for experimentation. I've easily built a dozen of those 7805 circuits in the past for 5V logic circuits, some including more power-efficient regulators (LM2940 comes to mind, same package/pinout, better efficiency) and MOSFET reverse-voltage protection. I don't have a ton of specific information on my website (http://jedrobotics.tripod.com) because I don't want people ripping off my custom schematics, but I'm more than happy to give advice and whatnot.
 
jeod66 said:
I'm not an EE, I'm a mechanical engineer, but I'd like to add something to that schematic, Angellas: a 1N5817 Schottky diode between the +Vcc input and the ground line. If you accidentally hook up the power backwards, it won't trash your router. This is a case of a $.10 (max!) part saving a lot of money. I think that a 1N914 diode from RadioShack (something like $2 for 10) would do the job too.
Click to expand...

You are 100% correct, and I support your post fully.

I left out a TON of things that could be and probably should be in this particular application. I was just looking to set him off in the right direction. It would not be very hard to add in some checks and balances to the system including fans for cooling and rectifiers for cross-prevention / AC arresting.

Thinking of pre-built packages kinda makes me cringe. Unless, of course, it came with a FULL schematic. I have a thing for starting from scratch.

Thinking from an 'I want to do this' standpoint, your idea of using NiCD batteries would suit him just fine. However, smaller batteries and an in-system charger / power level monitor would be best. Esp. if this will be used over and over.

There are literally millions of options. I could show you some, but.....give a man a fish VS. teach a man to fish... ;) Well, you catch my drift.

Robotics Experience: Raytheon / E-Systems Robotics team, 1997-2001 gg, robotics engineers!
 
Last edited:
Angellas said:
I left out a TON of things that could be and probably should be in this particular application. I was just looking to set him off in the right direction. It would not be very hard to add in some checks and balances to the system including fans for cooling and rectifiers for cross-prevention / AC arresting.

Thinking of pre-built packages kinda makes me cringe. Unless, of course, it came with a FULL schematic. I have a thing for starting from scratch.

There are literally millions of options. I could show you some, but.....give a man a fish VS. teach a man to fish... ;) Well, you catch my drift.
Click to expand...

I couldn't agree with you more. I like to build things on my own too, and the reverse-protection just stood right out to me as a "must-fix" to prevent catastrophic failure. Great posts, and since I saw it on the ShoutBox, congrats on that award too! You're in business now with all this information, mrcool. ;)
 
That would be an excellent choice for someone that has a few parts laying around. You will not, however, be able to eliminate resistors for this application. This will eliminate the need to use resistors to create a voltage drop on the Vout side of the Vreg only.

Here's a simple schematic to provide 5vdc on the Vout side of that Vreg.

vvr01.jpg




I have to warn you, however, that this IC is just as inefficient as the 7805. The only benefit of using a variable reg (in this case) is to adjust the needed voltage to compensate for start-up draw.

In this schematic, a varistor is used but a static resistor may be used in it's place if needed.

Another issue.....If you use a variable Vreg and don't have a meter to test the voltage, you WILL blow your router into tiny little pieces. The above schematic will net you proper voltage (5vdc on your 4.5vdc input) just don't deviate from the design.

A better option for battery use is the PT5100. It's a low-loss Vreg and I have used them more than once for battery powered devices. The company is now owned by Texas Instruments so I am unsure of the new part number. I'm sure Radio Shack's cross-reference guide will get you what you need. They are, however, close to $15USD a piece last I bought them.

Here's an example schematic:

avr02.jpg


As far as your connector goes, I usually grab a wall-wort (sure, we'll say that's the technical term...) power supply out of my drawer and cut the end off. The best way is to take your device into the store and take a few out of the package. Any sensible Radio Shack will allow you to do this and MAY have a few in the back for you to test. If it fits, most likely it will work just fine. BE SURE to get the polarity correct, especially with the above designs. If you happen to get it backwards, there are no 'oops' checks at all.

Normally, I'd draw you up a lovely schematic to work from. Unfortunately, a recent Raid 0 crash has lost my AutoCad. I'll get it installed and show you what I mean over the next few days.

Just to clarify, these are NOT my designs. These are designs of others that I have used before as a base. I usually don't post schematics of my personal designs. Most people don't either. When I get ACD re-installed, I guess I'll be nice and design something for you. ;)

You're also going to need to look at board etching kits. You can't just solder it all together and pray nothing shorts. Radio Shack (I'm just referencing them because it seems that's where you'll buy from?) has project cases to put the board in, PCBoards, and kits to etch the board with.

I hope this has helped a little. It's really hard to explain years of schooling and training when you don't know the experience level of the student. :) I'll continue to try to help and I hope you're adventurous enough to try this. Most any Elect. savvy tech started by 'trying' things out! Best of luck to you and feel free to ask if you have any more questions!
 
You must log in or register to reply here.

Latest posts

Back
Top