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Voltage, Current, Distance Question

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Confuzzled

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Not really sure where to post this. It's not really a radio, but it is a wireless device.

I need to power a device ~50' away from any AC. It came with a 5V, 2A wall wart. I have 22AWG wire run the distance, but it doesn't seem to be making the trip. Device gets power enough to light the 'power on' LED, but not enough to operate.

What do I need to do to get 5V and at least 1.5A at the device? Higher current PS? Larger wire? Higher voltage PS with a 5V regulator at the device?

At one time I had a vague familiarity with Ohm's Law, but that was decades ago.
 

WouffHong

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Voltage loss

:roll:
Not really sure where to post this. It's not really a radio, but it is a wireless device.

I need to power a device ~50' away from any AC. It came with a 5V, 2A wall wart. I have 22AWG wire run the distance, but it doesn't seem to be making the trip. Device gets power enough to light the 'power on' LED, but not enough to operate.

What do I need to do to get 5V and at least 1.5A at the device? Higher current PS? Larger wire? Higher voltage PS with a 5V regulator at the device?

At one time I had a vague familiarity with Ohm's Law, but that was decades ago.
E=IR ;-)

The wire size is too small.
If you are using 4-strand Telephone wire (not recommended),you could parallell the red and green and the yellow and black into doubled wires. Be very careful that you get the polarities correct! ;-) :roll:

However it would be MUCH better to buy some 16-18-gauge cable and if outside, a weather resistant version.

Da Wouff
 

Thayne

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The simplest way would be to get get the 120VAC out there, but I realize that brings code or safety issues into play. Even if you used 14 gauge wire don't forget 50' is actually 100' as far as resistance is concerned, and your load may not like it if the 5V drops lower when it needs an amp or 2--
 

RBFunk

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IF and only IF this is a temporary thing your best bet is to bring the 120 AC to the unit using an extension cord. In addition to electrical code problems you also want to make sure that nobody will trip over it.

The other possibility involves opening up the wall wart and replacing the small diameter wire with a wire large enough to allow a smaller voltage drop but now you are back to having a large wire that someone could trip over.
 

Confuzzled

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Well, it's 40' straight up, so I'm not worried about a tripping hazard.

I thought about doubling up the conductors, but I'm not sure that'll be enough either. I might try it and see what happens. I could get some 18G bell wire.

For now, I have an extension cord up the mast, but I don't want to leave that for two reasons:

*Connection is not weatherproof, although I could probably fix that.
*Possible AC hum induced into antenna cables. (TV and cell phone, not radio)
 

Confuzzled

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I thought about using the wall wart or a hardwired 5v PS in a weatherproof box, but I'm just not wild about having 110VAC up there if I don't have to.

I'm considering pushing either 12 or 24VDC up to a 7805 (5v regulator) or similar.
 

OCO

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Send low voltage A/C up the cable and convert to DC where you need it. Long DC runs always are problematic (Tesla showed Edison this solution a few years ago)..
 

rescue161

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Send low voltage A/C up the cable and convert to DC where you need it. Long DC runs always are problematic (Tesla showed Edison this solution a few years ago)..
Agreed! 5VAC up the mast to a full-wave bridge rectifier. Done. You can even make one out of the transformer that you are already using. Just remove the bridge and then reinsert it at the device.
 

Confuzzled

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Problem there is, all the wall warts I have are ultrasonically welded which make them a real pain to get open. Dug through some old stuff and found a couple of FW bridges, so I may try to fabricate something.
 

OCO

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Problem there is, all the wall warts I have are ultrasonically welded which make them a real pain to get open. Dug through some old stuff and found a couple of FW bridges, so I may try to fabricate something.
A jewler's saw or a hobby razor saw used on the seam is how i've been opening bad wall warts for about 40 years..:D
 

kruser

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A jewler's saw or a hobby razor saw used on the seam is how i've been opening bad wall warts for about 40 years..:D
I've used brute force for years with good results!
I squeeze them very tight in a large vise and then knock them at the seams with a ball peen hammer. The glue (chemical weld) usually pops right apart and I'm in.
I only squeeze one half and I always try and determine the half that is the inside part of the housing.

You do need to be careful doing this with supplies like Dell uses for their laptops as well as other supplies that pack everything very tightly inside.
I've never cracked a board yet though but maybe I've just been lucky. Most supplies I find have a fair amount of air space inside.
 

Confuzzled

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The 7905 Voltage Regulator shows a rating of 1 Amp, but I'm not sure if that's for the supply or the load. I have a 10VAC source already in use and available, but it's rated for about 8 amps. The load device though shouldn't ever draw more than about 800 milliamps.
 

rescue161

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The 7905 Voltage Regulator shows a rating of 1 Amp, but I'm not sure if that's for the supply or the load. I have a 10VAC source already in use and available, but it's rated for about 8 amps. The load device though shouldn't ever draw more than about 800 milliamps.
It may be a typo, but the 7905 will produce negative 5 Volts. You want a 7805 for +5VDC. You also need a bridge to change AC to DC before the regulator.
 

jim202

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Not really sure where to post this. It's not really a radio, but it is a wireless device.

I need to power a device ~50' away from any AC. It came with a 5V, 2A wall wart. I have 22AWG wire run the distance, but it doesn't seem to be making the trip. Device gets power enough to light the 'power on' LED, but not enough to operate.

What do I need to do to get 5V and at least 1.5A at the device? Higher current PS? Larger wire? Higher voltage PS with a 5V regulator at the device?

At one time I had a vague familiarity with Ohm's Law, but that was decades ago.

Maybe it's time that you told us just what kind of a device your trying to supply power to up the tower. There may be other ways to skin the cat, but we need to know what kind of a cat you ran up the tower. My gut feeling here is that your trying to use some sort of antenna pre amp.
 

Confuzzled

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My gut feeling here is that your trying to use some sort of antenna pre amp.
Nope. Just a small camera. But it is a wireless camera, so it's sort of radio.

Possible side advantage of having the 7805 up there is that it just might help keep frost off the dome depending on how much heat it generates.

(Yeah, 7805 is what I got along with a bridge and a couple of caps.)
 
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jackj

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Just a couple of pieces of info.

A series voltage regulator like the 7805 works by throwing away the excess voltage. You can figure out the amount of heat it throws off using P = I x V. P = power in watts, I is the current through the device and V is the voltage drop across the device. Using your figures; you need 5 vdc which means you will be throwing away 5 vdc (assuming no voltage drop in the wire). So 5 volts times 1.5 amps equals 7.5 watts. You'll need a pretty healthy heat sink.

A 7805 is only rated for 1 amp so it won't handle the current in the above example, it's protection circuitry will decrease the output voltage to keep the current within the device's limit. The current the load draws equals the current into the device, it isn't a transformer.

There are series regulators available that will handle higher current.
 

ipfd320

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First off the poster didnt even state if it was ac or dc voltage he is using this here changes things out alot..if its 5 dc i would take the 22awg and go with 18 check voltage at the end of the line if its still low go to step 2 a vatiable voltage transformer wall pack sold at radio shack and set it to 6.0 volts again take reading at end of line....if your in the range of 5-5.3 your good....good luck
 
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