 EE help, Voltage Drop over copper |
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| bd1308 |
 May 2 2005, 10:08 PM
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#1
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Sir Post-a-lot  Group: Members Posts: 8,020 Joined: 24-January 05 From: Louisville,KY Member No.: 3,501  |
okay, i have a question. I'm trying to do Power-Over-Ethernet using the (unused) blue pair of ethernet wires. 5VDC......i run the wire (~70 or so feet) and plug it in, and not enough voltage to boot my wireless router....seems that i need under 1.4VDC....how the hell can i add 5VDC to 1.4VDC. I tried getting one of those adjustable AC adaptors and hooking them in series and parallel... in series neither worked...got like 1VDC, and in parallel, well....i tested it later (after it was working) and found the voltage to be around 14-15VDC.....what the hell?
AC adaptor->modified 10/100->~70 foot run to attic->blue pair seperated from RJ45 Jack->in-to router. |
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| Loser_Cruiser |
May 2 2005, 10:47 PM
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#2
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Member Group: Members Posts: 407 Joined: 4-April 05 From: Bellingham, WA Member No.: 3,873 Region Association: Pacific Northwest |
If you truly need a power over CAT 5 cable, it would appear your power source is not large enough to source your load. V= RI, as you increase your resistance of the cable by increasing the length of wire, the voltage will drops with a constant current. It gets worst as you max out the current capability of the wire gauge. Therefore as you increase length of wire you are increasing resistance in the wire and need to increase current (Larger Power supply in Amps, 5V 1amp, or 2 amps 3amps). 5Vdc=1.8Amps X 3 Ohms (70 ft of wire). It looks like a 5Vdc @ 2 amps would work for that application.
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Posts in this topic
bd1308 EE help May 2 2005, 10:08 PM
914GT First of all, your adapter needs to be able to sup... May 2 2005, 10:19 PM jkeyzer Ohms law will tell you the voltage drop to expect ... May 2 2005, 10:20 PM lapuwali I was just about to type in almost exactly what jk... May 2 2005, 10:30 PM bondo What you need is a power supply with remote sensin... May 2 2005, 11:20 PM bd1308 the AC adaptor is OEM.....5VDC....regulator would ... May 2 2005, 11:33 PM bd1308 ethernet does have 2 unused pairs....cool stuff. h... May 2 2005, 11:36 PM bondo May 2 2005, 11:44 PM bd1308 okay....just thought of something....why couldn... May 2 2005, 11:52 PM lapuwali May 3 2005, 09:09 AM jkeyzer Make sure the 9V adapter is capable of supplying t... May 3 2005, 09:19 AM Dr. Roger won't the EMF surrounding these power wires to... May 3 2005, 09:36 AM jkeyzer Well regulated DC will not have a significant effe... May 3 2005, 10:12 AM davep DC can cause problems also if the current draw is ... May 3 2005, 10:21 AM Tom Perso Couldn't you just double up the wires? Ethern... May 3 2005, 10:29 AM bd1308 jkeyzer: AC power wouldnt work...the bleedthrough ... May 3 2005, 10:42 AM bondo ... May 3 2005, 05:26 PM bd1308 yeah...i'm just not so sure about this whole b... May 3 2005, 06:34 PM 914GT Lynksys makes a power over ethernet adapter kit. I... May 3 2005, 07:45 PM
bondo May 3 2005, 07:51 PM |
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