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Author Topic: How do I add additional power in automobile?  (Read 3381 times)

Posts: 3

« on: April 07, 2001, 07:18:24 AM »

I've been running my HF rig in my car for a couple of months, and it's been working perfectly. I've run 8AWG power cables directly from my battery terminals and through the firewall. Both the positive and the negative leads are fused at the battery. These power leads are directly connected to my rig, which sits on my passenger seat.

This power setup worked great when I only needed a single power source for my rig. Now, I'd like to add some additional equipment, such as a digital signal processor and a SWR meter with a backlight. Both of these use very little power, but they need a 12V power source.

What's the best way to connect these additional power leads? I'd like to have the flexibility to connect and disconnect these systems at any time, and add additional power at a later date for additional equipment. This also should be something asthetically pleasing, if not easy to hide under the seat or behind the dash.

I want to do this right, but I don't have the background to understand the proper connectivity requirements (or safety considerations) for automobile use. Can anyone help?

73, James/AG4DX

Posts: 984

« Reply #1 on: April 09, 2001, 12:31:20 AM »

In either CQ or QST magazine ( I can't remember which ) there is an ad for a 12V distribution box. You can either buy one or build one to take the 12V from the car battery and divide the output to two to three jacks for use as you see fit. A simple box with the jacks for the output on the front and an input 12V jack in the back should do the job for you. Just be sure you are using a wire of sufficient size for the power load and fused accordingly. Fusing each power output jack would be wise as well.

Posts: 21764

« Reply #2 on: April 09, 2001, 03:46:13 PM »

I'd recommend not re-inventing the wheel on this.  The RV/camping/trailering industry has already created numerous high-quality, low-cost 12Vdc power tap products for mobile applications, and it's best to stick with those.  They are tried & proven, flame-resistant, polarized and goof-proof, and readily available at RV/trailer supply stores.

There is a product called a power-tap which simply crimps on to your existing #8 gauge main power wiring and provides lower-current taps for accessory equipment.  You'll find them all over the place in trailers, and frequently under automotive dashboards as well.  They cost very little and are very secure, require no special tooling or soldering, and are what the whole automotive industry uses.

For making connection to the accessories, there are 2-post polarized M-F connectors which are molded onto wires and also readily available.  Just fit them to the power taps and your accessories for simple plug & play solutions that are safe and polarized.  If the accessories are not fused internally, I'd always recommend they be fused individually, in the power lines to the accessories themselves -- since a pair of big, fat 30A fuses (or whatever you have in line already at the battery) are going to take quite a while to blow if you have a small short circuit in the #22 gauge wire that goes to your SWR meter lamp!  (In this case, the small gauge wire is likely to burn up before the fuses.)

73 & safe mobiling!

Steve WB2WIK/6


Posts: 1

« Reply #3 on: April 15, 2001, 08:57:22 AM »

I also have run heavy wire from the battery to the interior of my van, fused at the battery.  At that point there are a couple of options.
I have a friend who used terminal strips to make his connections.  He mounted a piece of plywood to the body and then the terminal strip to that.
I use Workman polarized connectors on all my equipment. These are almost the same as the connectors that Motorola uses on the M120 mobile radios. They are available at a lot of CB shops, they use them for hooking up large current load items. Also available at hamfests and ham stores. They can be found in varying wire gages, I have both 14 and 10 gage that I keep in the OS Kit. Positive potential side is insulated to keep short circuits from happening and polarized to keep from hooking them up backwards. Works for me.

Posts: 44


« Reply #4 on: April 17, 2001, 09:55:04 PM »

You might try having a look at a distribution block that is used in car audio application. Street Wires (Esoteric Audio), Monster Cable, Rockford Fosgate, and Lightning Audio all make asteically pleasing distribution blocks. Streetwires makes theirs for use with barrel fuses. All of these use set screw inputs and outputs. Check out Crutchfield at

Hope this helps,
Nick Mullins
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