24 volt golf car batteries to run a wireless router

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zotdoc
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24 volt golf car batteries to run a wireless router

Post by zotdoc »

I would like to set up a wireless router in a field to take signals from a laptop (500 feet away) to an ethernet I/O board that will shoot a fireworks show. I have a 3 - 8 volt golf cart batteries in series that will shoot the firework igniters. With my setup, the wireless router will work best out in the field near the batteries. Would it be better to use a commercially purchased dc/ac inverter and then plug in the wall wart that comes with the router, or could I roll my own 24 volt to 9 volt dc/dc converter and skip the inverter and wall wart? Personally, I'd like to make my own (for the fun of it) but I need to know if the output of such a home brew device would hurt the wireless router due to some factor I don't know about that makes it significantly different than the output of the wall wart?
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haklesup
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Post by haklesup »

A properly designed dc/dc converter would definately have less ripple than the wall wart (especially one powered by an inverter). The converter could also have a more compliant current limit designed in. Both of these would make it better than a wall wart.

As for using ethernet for fireworks I suppose thats ok as long as the commands you transmit are sufficiently complex that nothing but you can activate the output (not noise, not hackers, not a lost packet).

I suggest you try one 8V battery all by itself (maybe with a fuse). I'm sure that router further regulates the 9V to 5V and 3.3V at least before making use of it. More than likely, it will power up at 8V maybe as low as 6.5V and possibly as high as 12V (my LinkSys router uses a 12V wall wart). Check the specs in the manual, it might even tell.
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dacflyer
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Post by dacflyer »

i have used batterys many times in place of wal-warts..just as long as the batterys are the same voltage as the output of the walwart..

also pay attention to some wal-warts, because some are AC output

but typically most are unfiltered DC..and the insides of the device does the real filtering and such.

also the device is going to use what ever current it needs..i say this because some people fear feeding too much current into a device..you cannot do that ,but do use a fuze for safety and pay attention to polarity..
check it test it before plugging it into the device..and note the polarity on the unit itself..

never trust the polarity markings on cords, unless you know for sure.

good luck...
SETEC_Astronomy
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Post by SETEC_Astronomy »

dacflyer wrote:also the device is going to use what ever current it needs..i say this because some people fear feeding too much current into a device..you cannot do that
ah hem, that would be me. I always have the fear that there is to much current available and feel the need to step it down. You guys could settle this in my head though. To be clear. As long as the current is at the right voltage you will not harm your circuit by having large currents available? But there are times when it's safer to limit the current available because accidentally shorting a wire or part with a lot of current behind it is more violent and dangerous than when there isn't. Right?
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haklesup
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Post by haklesup »

A properly functioning curcuit will use only as much current as it needs at the supply voltage provided. As long as your source supply can provide a little more than the maximum your circuit needs, everything will be good. Go ahead and use an unfused car battery (well over 600A short circuit current possible) and it will be fine.

However if you did so you would be taking a big risk.

Current limits really show their stuff when something goes wrong. If a component fails or gets externally shorted the current limit will limit the total damage that can occur. Consider the car battery, it can punch a 1/4" hole in #16 steel in milliseconds. Put a 1A fuse in line and all you get is a small spark and maybe a toasted resistor or diode rather than a fire.

Current limiting can be acomplished by circuit design, fusing or simply by selecting components like the transformer (wall wart) to be unable to supply much more power than you need. Not only does this intrinsic current limit protect your circuit somewhat, it also cost you less than a higher current power source.

Very high current shorts like the car battery tend to reopen quickly and dramatically (among a shower of molten metal) but more typical supply currents like a few amps, can stay shorted indefinately and cause considerable heat if not limited to a safe value or shutdown by a fuse or circuitbreaker.

The Linksys and Belkin routers I have all take DC wall warts but if yours were AC, the battery idea might or might not work.
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projectguy
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Post by projectguy »

Recently I have also been researching using a DC-DC converter to power a laptop off of a 24 volt system. I find it hard to believe there is not an off the self device that would do just this. A typing Dell requires 19 volts at 10amps which is a high current draw. I checked into using a Buck Regulator to convert 24 to 19 volts on the National Semiconductor site. Using a LM5642 High Voltage Buck Convertor 19 volts is possible. The National Semiconductor site is very helpful in designing power circuits. On the internet I also research who might also be making such a device and found http://www.zahninc.com/sd1a.html who can make a 19 volt buc converter at 10 amps cost is rather high at over $100.00 with a metal case but it is possible.

Makes the 12 Volt AC inverter and extension cord and wallwart a better deal but it so bulky.
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dacflyer
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Post by dacflyer »

SETEC_Astronomy wrote:
dacflyer wrote:also the device is going to use what ever current it needs..i say this because some people fear feeding too much current into a device..you cannot do that
ah hem, that would be me. I always have the fear that there is to much current available and feel the need to step it down. You guys could settle this in my head though. To be clear. As long as the current is at the right voltage you will not harm your circuit by having large currents available? But there are times when it's safer to limit the current available because accidentally shorting a wire or part with a lot of current behind it is more violent and dangerous than when there isn't. Right?
thats why i suggested using fuzes {:>)
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haklesup
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Post by haklesup »

Aftermarket Notebook PC adapters are usually very compact and often quite powerful. While that 19V, 10A solution will cost a bundle http://www.targus.com/us/product_detail ... ku=APA05US there are lower power units that do quite well.

I have the 120W version of the above and its smaller than my cell phone and the input is 11-16VDC/11A and the output is 3-24VDC/6A. not variable but a bunch of choices depending on the adapter tip.
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