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Old 02-13-2019, 11:31 AM   #1
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12v thru Cat5 Cable -Harebrained idea?

I have a disconnected Cat5 cable (previously used to power the now disconnected Sunexplorer solar monitor) that runs from the power side of my Avenue to the other side where I'd like to install a USB charger outlet.


I really don't want to "do it right" and try run new wires across the van to the opposite side because the difficulty just wouldn't be worth it in my opinion. Would the 8 wires within the old Cat5 (ethernet) cable provide the 2.4A required to power the USB outlet?


If so, how would I wire it since the 8 wires are individually insulated? 4 for positive & 4 for negative? All 8 positive and find a separate ground?


If this is the most stupid post you've ever seen, you can tell me. I'll only cry a little bit.
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Old 02-13-2019, 11:40 AM   #2
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I dont see anything stopping you from using the CAT5 wire to get 12v there for a USB charger. Id just pick a couple of pair for +12 and a couple of pair for ground. Id fuse it at 5A the start of the cable just in case something goes wrong someday.
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Old 02-13-2019, 12:48 PM   #3
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Quote:
Originally Posted by rowiebowie View Post
I have a disconnected Cat5 cable (previously used to power the now disconnected Sunexplorer solar monitor) that runs from the power side of my Avenue to the other side where I'd like to install a USB charger outlet.


I really don't want to "do it right" and try run new wires across the van to the opposite side because the difficulty just wouldn't be worth it in my opinion. Would the 8 wires within the old Cat5 (ethernet) cable provide the 2.4A required to power the USB outlet?


If so, how would I wire it since the 8 wires are individually insulated? 4 for positive & 4 for negative? All 8 positive and find a separate ground?


If this is the most stupid post you've ever seen, you can tell me. I'll only cry a little bit.
.

Cat5 cable varies in the gauge of the wires used to make it. On my desk right now I happen to have pieces that are 23, 24, and 26 gauge.


According to most sources, 26 gauge can safely carry 0.36 amps per pair. 23 gauge can carry .72 amps per pair. These figures have to be derated due to the number of pairs in the jacket, if you use all four you have to reduce the power on each one by something like 33% (I don't have the table handy).


So, 2.4 amps would be over the limit, unless you have unusually heavy gauge Cat5 and use all the pairs.


A fact to consider is that running the wires in parallel does create the risk that if there is a loose connection or one wire breaks, the remaining wires will be overloaded and could overheat.


https://www.powerstream.com/Wire_Size.htm
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Old 02-13-2019, 01:03 PM   #4
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I used to run comms through cat 5 (actually cat 3) using 30V. and long distances.
So, yes, you can do it.
I'd probabley start with making sure none of the existing wires are shorted or grounded accidentally. (Use a VOM meter and compare each lead to all the others.) Since it's a short distance you could rig a clip tester with a bulb on one end and a battery on the other.
Then, just to provide more copper, I'd use 4 and 4.
Cat 5 is twisted pairs so interference is lessened.
Write everything down or take a photo just in case are you need to remember what you did.
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Old 02-13-2019, 02:27 PM   #5
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Quote:
2.4 amps would be over the limit, unless you have unusually heavy gauge Cat5 and use all the pairs.
Youd be unlikely to draw 2.4 amps on these lines since your USB charger is regulating the 12-13v down to 5v. Your current drain is likely to be in the 1a range.
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Old 02-13-2019, 04:40 PM   #6
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Harebrained idea; YES!

cat5, 6 7 etc are data cables

at most they can carry 90w under PoE standards
ie 2A at 48 V
that does not mean 8a at 12 V as the current capacity is more limited that the voltage
power losses are also I^2 * R

run proper flexible DC cables if you need power delivered
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Old 02-13-2019, 06:43 PM   #7
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Originally Posted by waninae39 View Post
Harebrained idea; YES!

cat5, 6 7 etc are data cables

at most they can carry 90w under PoE standards
ie 2A at 48 V
that does not mean 8a at 12 V as the current capacity is more limited that the voltage
power losses are also I^2 * R

run proper flexible DC cables if you need power delivered
The OP doesn't want to go through all the effort of fishing a new wire pair to that location. This chart indicates that with 28 gauge and the worst insulation, you could put 2.1A through EACH wire (.7 degraded from 3A because they are bundled.) Since you are using, let's say, four wires for +12 and another four for ground there is plenty of capacity to handle the amp or so the adapter will require.
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Old 02-13-2019, 07:30 PM   #8
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Thanks for the replies. I don't have to have a USB in that location, however, it would be nice. I'm mainly looking to use the old Cat5 for something useful, rather than leave to old dead Sunexplorer monitor in place or just use a cover plate for the opening.

Some additional information I failed to include that would have been helpful is the outer sheath says the wiring is 26AWG. I estimate the wire length to be no more than 12-15 ft. since it is directly across the aisle and wire appears to run underneath. I'm estimating the length to run a few feet down, over, and up and I've seen no excess wiring rolled up anywhere.
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Old 02-14-2019, 12:16 AM   #9
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Quote:
Originally Posted by rowiebowie View Post
Thanks for the replies. I don't have to have a USB in that location, however, it would be nice. I'm mainly looking to use the old Cat5 for something useful, rather than leave to old dead Sunexplorer monitor in place or just use a cover plate for the opening.

Some additional information I failed to include that would have been helpful is the outer sheath says the wiring is 26AWG. I estimate the wire length to be no more than 12-15 ft. since it is directly across the aisle and wire appears to run underneath. I'm estimating the length to run a few feet down, over, and up and I've seen no excess wiring rolled up anywhere.
.
26 would certainly be no problem!

I used it for the control panel for our hybrid inverter. You could also use it for a battery monitor.
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Old 02-14-2019, 09:45 AM   #10
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Originally Posted by daleyocum View Post
26 would certainly be no problem!

I used it for the control panel for our hybrid inverter. You could also use it for a battery monitor.
Good idea about the monitor, as that was what is was powering already. I may go ahead and install the USB and definitely use a small fuse as per your suggestion. I may even start with a 2A fuse just to be very conservative.

Thanks to all who replied.
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Old 02-14-2019, 12:05 PM   #11
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Quote:
Originally Posted by rowiebowie View Post
I really don't want to "do it right" and try run new wires across the van to the opposite side because the difficulty just wouldn't be worth it in my opinion. Would the 8 wires within the old Cat5 (ethernet) cable provide the 2.4A required to power the USB outlet?
ANSI TIA/EIA 568 says Cat 5e wiring is no larger than 22 AWG, normally 24 AWG, but allows for 26 AWG for short runs. It has a +60C temperature rating.

The ANSI LV 2018 standard for RV low voltage wiring, section 4-2, states: "Conductors shall have a minimum insulation rating of 90C (195F)." Also, section 4-3 lists the minimum acceptable conductor size for DC power delivery as AWG 20.

While it will likely work, recommend considering installing it correctly with the proper overcurrent protection. Agree with:
Quote:
Originally Posted by Mollysdad View Post
Write everything down or take a photo just in case are you need to remember what you did.
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Old 02-14-2019, 01:14 PM   #12
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Thanks.

Now for a correction (can't find the face palm emoji). I guess I'd ealier over-thought this, and then posted in a hurry last night.

I was using a spare Cat5 ethernet cable I had cut for the specs rather than the actual one for the solar controller. Soooo.

The corrected specs are the Cat5 in the Avenue is 24AWG, but 4 strand rather than the 8 strand I previously reported. Gauge is up (good), but number of wires is down (bad).
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Old 02-14-2019, 03:15 PM   #13
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Originally Posted by rowiebowie View Post
Thanks.

Now for a correction (can't find the face palm emoji). I guess I'd ealier over-thought this, and then posted in a hurry last night.

I was using a spare Cat5 ethernet cable I had cut for the specs rather than the actual one for the solar controller. Soooo.

The corrected specs are the Cat5 in the Avenue is 24AWG, but 4 strand rather than the 8 strand I previously reported. Gauge is up (good), but number of wires is down (bad).
.

.
With four conductors it's not actually Cat5, more something like a telephone-style cable. That's fine and I wouldn't hesitate if it were my trailer putting an amp or two through it if you used two conductors for + and two for ground.
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Old 02-15-2019, 12:16 AM   #14
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100 % Worst Case spec.

How do any of us leave the house for fear we will exceed a specification of some sort??

I am looking at a PoE (power over Ethernet) power injector for powering a 2 amp 600 miliwatt broad band bridge that is 100 feet up on a tower using Catagory 5 cable.

The the injector is rated at 2.8 amps and is certified in the US and Canada for critical communications.

And we are sweating a USB charger circuit spec. at 2.4 amps in-rush current to charge a cell phone or tablet?

Remember that is 2 pair of a 4 pair twisted pair shielded fire rated cable.

Good grief, 100% worst case engineering is one thing bug just trying to reuse a cable to charge a cell phone is a bit paranoid.

Murphy Laws is quietly laughing.

Safe travels (With 5 lb fire extinguishers by you bed)
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Old 02-15-2019, 12:25 AM   #15
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How do any of us leave the house for fear we will exceed a specification of some sort??

I am looking at a PoE (power over Ethernet) power injector for powering a 2 amp 600 miliwatt broad band bridge that is 100 feet up on a tower using Catagory 5 cable.

The the injector is rated at 2.8 amps and is certified in the US and Canada for critical communications.

And we are sweating a USB charger circuit spec. at 2.4 amps in-rush current to charge a cell phone or tablet?

Remember that is 2 pair of a 4 pair twisted pair shielded fire rated cable.

Good grief, 100% worst case engineering is one thing bug just trying to reuse a cable to charge a cell phone is a bit paranoid.

Murphy Laws is quietly laughing.

Safe travels (With 5 lb fire extinguishers by you bed)

Murphy and I kinda have a thing and spend way too much time hanging out together. But I think in this case, you're saying "go for it".

And the fire extingisher is in the entry well. Not at arms length, but only 6 ft. away.

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Old 02-15-2019, 08:49 AM   #16
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rowiebowie,
Amen!
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Old 02-15-2019, 09:30 AM   #17
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Originally Posted by Jekerrville View Post
How do any of us leave the house for fear we will exceed a specification of some sort?? Good grief, 100% worst case engineering is one thing bug just trying to reuse a cable to charge a cell phone is a bit paranoid. Murphy Laws is quietly laughing.
Fear of doing what Airstream certifies they meet as the MINIMUM required when they deliver a trailer or Class B to you? Yes, I would have some concern if I found that Airstream delivered my trailer without meeting the specifications they claim.

I have no idea where you got the idea that ANSI LV 2018 is 100% worse case engineering. That is factually incorrect.

Recommending that everyone follow accepted minimum safety practice is always a good idea.

73/gus
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Old 02-20-2019, 11:37 AM   #18
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Check out the power over Ethernet (cat5) specs:
https://en.m.wikipedia.org/wiki/Powe...ds_development
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Old 02-20-2019, 12:47 PM   #19
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I'd use it with a 1A fuse without a single worry

Usb 5v 2.1 amp isn't the same current you'll see at the 12V feed, a cheap 70% efficiency converter would pull .76A , so stick a 1A fuse on the cat5 cable and move on


I happen to have NASA EEE-INST-002 on my desk, table 4A, 26gauge wire, bundled, in a vacuum (no cooling), 1.4 amps.
That's for 200C Teflon insulated, cat 5 is 60C pvc, so cut it by 75% is .35A, times 4 pairs is back to 1.4 A, which is 50% more than you need

Like I said, stick a 1A fuse on it and sleep worry free.
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Old 02-20-2019, 03:18 PM   #20
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I see no problem. In fact you could run only +12 thru the cable and tie ground to the chassis. I would get a 12 to 5 volt converter (ebay about $5) and drop the voltage at the end.
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