Problems extending the wire of a DC power adapter

Reply

  #1  
Old 11-18-13, 09:57 PM
Member
Thread Starter
Join Date: Aug 2013
Location: Pakistan
Posts: 38
Problems extending the wire of a DC power adapter

I have a wireless router in the basement. It has a USB port for attaching external storage. The problem is that there is no power receptacle nearby so I had to extend the routers and the external hard drive's power adapter's cable by about 30 feet. Both the wireless router and the external hard drive's power adapters are rated at 12V 2 amps. The router is working fine, but I am having problems with the hard drive.

I was aware that extending DC cables can result in voltage drop, so I was careful to make sure that there was minimal or no voltage drop due to the extension. After installation, I measured voltage at the other end and it was 12 volts. But when I connect the external hard drive, the led lights up, and the hard drive whirs repeatedly as if it is starting up, but it never really starts up. Initially I thought there was a problem with the drive, but after connecting it to a normal 12V 2 amp power adapter it worked just fine.

Now I am not sure what the issue is. I have 12V at the end of the extended power adapter, why is the hard drive not working? Am I losing some current due to the extended power cable? Do I need to get a 12V 3amp power adapter to get this to work? Looking for some ideas.
 
Sponsored Links
  #2  
Old 11-19-13, 05:10 AM
Group Moderator
Join Date: Mar 2003
Location: NC, USA
Posts: 17,129
Did you measure the voltage at the end of your extension with a load applied? You really won't see the voltage drop show up until a load is applied.

If running low voltage DC for any length I like to go quite large on the conductors. A cheap source could be outdoor low voltage wiring. It's relatively inexpensive and it's conductors are much larger than what you'd find on a 2 amp wall wort power supply. Another option is to use an extension cord to get close to your router & hard drive and plug your wall wort into the end of it.
 
  #3  
Old 11-19-13, 06:37 AM
ray2047's Avatar
Group Moderator
Join Date: Mar 2006
Location: USA
Posts: 32,662
The obvious solution is run a 120 volt receptacle to the location of the equipment. A lot simpler and maybe cheaper than what you are trying to do. Why aren't you doing that? Are there no lights in the area where the router located?
 
  #4  
Old 11-20-13, 12:43 AM
Member
Thread Starter
Join Date: Aug 2013
Location: Pakistan
Posts: 38
I thought about putting a power receptacle near the equipment, but I decided against it, because frankly, it would look ugly. I have a DSL modem and one router in the basement this is connected to one access point on the ground floor, and then there is the external hard drive. That makes a total of 4 power adapters. I wanted to keep it neat and clean with minimal mess so I routed all the cables to a central location through a duct and had power supplied from a single location.

Both the router and access point use a 12V 2 amp power supply and they have been running fine with 30ft extended cables. I have used 24 AWG single core copper wire for both. For the external hard drive I used slightly thicker cable I guess its 18 AWG, but it is stranded. The power consumption of the hard drive is 10W according to specifications.

I haven't checked the voltage drop when connected on load, so I guess I will do that first. If there is a voltage drop, can it be solved by getting a 12V power supply that can output more amps or would I need a higher voltage power supply with the same ampere rating?
 
  #5  
Old 11-20-13, 03:16 AM
ray2047's Avatar
Group Moderator
Join Date: Mar 2006
Location: USA
Posts: 32,662
I thought about putting a power receptacle near the equipment, but I decided against it, because frankly, it would look ugly.
The receptacle could be in a cabinet or piece of furniture.

If there is a voltage drop, can it be solved by getting a 12V power supply that can output more amps or would I need a higher voltage power supply with the same ampere rating?
Neither. As stated earlier it is wire size that primarily causes the drop.
 

Last edited by ray2047; 11-20-13 at 06:36 AM.
  #6  
Old 11-20-13, 04:10 AM
Member
Thread Starter
Join Date: Aug 2013
Location: Pakistan
Posts: 38
Thanks for your help. I'll start by checking the voltage drop first and then try substituting it with thicker wire.

According to the link below, 16AWG should work I think. It can handle 5 Amps up to 15 feet so I suppose it should be able to handle 2 amps over 30 feet. what do you say?

Amps and Wire Gauge - 12V Circuit
 
  #7  
Old 11-20-13, 04:28 AM
chandler's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Dec 2005
Location: USA
Posts: 39,968
What kind of "duct" are you running all this cabling? We can't see your set up, but surely there is a way to install a receptacle nearer the router. DC voltages drop dramatically with length, no matter what size wire you use, due to the nature of the transformer's ability to produce the voltage needed at the end.

Edit: OK, I see you are in Pakistan. Electrical systems vary from country to country, so our advice is based on North American standards. Yours may not comply, so be aware of that.
 
  #8  
Old 11-20-13, 05:01 AM
Member
Thread Starter
Join Date: Aug 2013
Location: Pakistan
Posts: 38
It's a 16x16mm PVC duct used to route wiring. There are a couple of CAT 5 cables in the duct, and I was hesitating putting a high voltage AC cable in there. Just trying to play safe.

Installing a receptacle near the router is PLAN B, I could always go that route if the DC wiring does not work out.
 
  #9  
Old 11-20-13, 06:15 AM
chandler's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Dec 2005
Location: USA
Posts: 39,968
OK, it's a conduit or raceway. I was thinking of an air conditioner "duct". Yeah, you can't mix line voltage and low voltage in the same conduit. The others on the forum may help more, but it may be possible to run your line voltage in a 1" conduit inside the 6x6 raceway. Wait on verification of that, but it seems a way out.
 
  #10  
Old 11-20-13, 06:34 AM
ray2047's Avatar
Group Moderator
Join Date: Mar 2006
Location: USA
Posts: 32,662
Didn't notice you weren't U.S. I was struggling to figure out why the router wasn't six feet or less from a receptacle. That is midway between the code required twelve foot maximum spacing for receptacles here. If you use cable rated for the highest voltage rated cable in the conduit you could use the same conduit for high and low voltage. Example if you use 600 volt cable for a 220 volt supply you could use that same type of cable for your 12 volt supply.
 
  #11  
Old 11-20-13, 09:11 AM
Member
Thread Starter
Join Date: Aug 2013
Location: Pakistan
Posts: 38
Ok. So I removed the wire from the conduit and it was about 6 feet longer than it needed to be, so I just cut off the extra length, reconnected the power supply and the external hard drive booted up just fine. So i guess that did the trick.

I couldn't check the voltage when plugged in because there seemed to be no way to insert the multimeter probes into the power connector at the other end and get a reading out of it, so I did a DC ampere test instead. When the hard drive is powered on the amps go up to a max of 2.3 and then quickly settle down to about 0.6. I guess those figures are acceptable for a 12V 2amp power supply. Thanks to everyone for their help. I appreciate it.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes
'