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Author Topic: Power Cable Help  (Read 7268 times)
AC8DQ
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« on: March 21, 2011, 07:52:37 PM »

I am new to mobile installs and I am hoping to avoiding burning down my vehicle.

I am planning to install an ICOM 7000 in my 2002 Toyota Highlander.  My current plan is to mount the radio in the back to minimize the antenna lines.  I figure I will need roughly 12' of power cable to get front the dash are to the back.

Here is what I have worked out so far:
10 gauge 1' cable from battery to Power Pole fuse holder (40 amp) and then about 6' of power cable through the firewall to a RigRunner 4005h.

Then from the RigRunner back to the radio I figured I'd splice the current power cable into an extension (10 gauge) with Power Pole connectors.

Can you think of anything I'm missing?  Is the 10 gauge back to radio overkill or would 12 gauge suffice?

I was also thinking about adding a PWRguard from West Mountain as well.  Any thoughts on this?

Thanks for looking!

Bill
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K1CJS
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« Reply #1 on: March 22, 2011, 04:44:51 AM »

Ten gauge would be the MINIMUM to run from the battery back to the rig runner.  As a matter of fact, I'd consider eight gauge to minimize voltage drop, and I would run it right back to the radio.  Also, get some of those heavy--and I mean HEAVY--duty fuses from a stereo supply shop.  They know that the regular fuses are woefully inadequate to really handle the high current draw of the high power stereo systems without dropping voltage.  Ham radio systems can draw just as much sometimes.

If you do that, you may not need the PWRguard at all.

Other than that, sounds like you've got things planned OK.
« Last Edit: March 22, 2011, 04:47:08 AM by K1CJS » Logged
K0BG
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« Reply #2 on: March 22, 2011, 07:14:38 AM »

Personally, I wouldn't do it the way you suggest.

The Rig Runner is not waterproof, and shouldn't be mounted under the hood. The wire between the Rig Runner, and the battery should be fused close to the battery end. There is an unused teat on the main power cable entrance. It is a little hard to see, as it is usually pushed in. The grommet is actually in two sections, so fishing a wire through isn't all that easy. Just don't use any metallic tools to do the job. That wire should be at lease size 10, and I'd use 8 if it were me.

The radio's power cable is 10 JWG, which is roughly 11 AWG, and is 3 meters long, and I wouldn't extend it.

The idea of getting the radio close to the antenna doesn't have much merit. RG8X is plenty good enough for the application, and the loss difference between a 5 foot piece, and a 15 foot piece is all but immeasurable. Don't forget to choke the common mode, or you'll have problems with the ABS.

If you need more information, visit my web site.

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AC8DQ
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« Reply #3 on: March 22, 2011, 08:22:55 AM »

Thank you both for your replies.  I will step it up to 8 gauge for sure.

I had planned on mounting the RigRunner inside the car, under the dash in the passenger footwell.  Thanks for the heads up on the unused grommet.  I will search for that tonight.

There is a good mounting location for the radio up front that I originally considered.  The center console has an open area beneath it that is sort of wasted.  I will measure it up and see if everything will fit there.

I saw a good set of MAXI fuse holders from Stinger.  I will stop by my local car audio shop to see if they carry them.

Alan, thank you very much for your website.  It is an amazing resource.  I have been pouring over it, but as you can see  I still need more help!

Thanks again,

Bill
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K0BG
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« Reply #4 on: March 22, 2011, 01:18:34 PM »

Just make sure you have adequate ventilation around the radio. In some vehicles, the area you're considering gets rather warm in the winter time.
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W3LK
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« Reply #5 on: March 22, 2011, 01:53:22 PM »

I made the mistake of putting RigRunners in a disaster communications vehicle to handle both radios and the emergency lighting. Vehicle vibration kept generating intermittent connections. Finally trashed them and went to terminal barrier strips.
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W8JX
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« Reply #6 on: March 22, 2011, 07:58:55 PM »

Thank you both for your replies.  I will step it up to 8 gauge for sure.

8 is over kill here and the difference in voltage drop between 8 and 10 ga is .1 volts (.3 vs.4) so there is no need for it here.
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W5LZ
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« Reply #7 on: March 22, 2011, 08:35:29 PM »

I've had a radio in almost every vehicle I've ever owned.  In most cases, I would run the largest cable I could find for the power line, welding cable works very nicely.  Making the end of the cable a power distribution point wasn't difficult, also wasn't very 'pretty', but it worked just dandy, almost like moving the battery to the radio.  Didn't have to worry about adding anything later, that welding cable would handle it just fine.
The last one I did handled two 2 meter radios, and HF radio, and a screwdriver antenna's power draws with ease.  Using those 'Anderson Power Poles' was also a very nice touch (and a distribution block).  Wish they'd been around 20 years ago!
That would be an over-kill for your use now.  But what about later??
 Paul
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W8JX
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« Reply #8 on: March 22, 2011, 09:08:06 PM »

There is no plus to using more cable size than you need and actually more negative to it in that a oversize cable is far more difficult to route and hide than a smaller one. Also in a worse case scenario short circuit from insulation cut and 12 ga wire will burn off and fail while a 10ga might too but 8 or larger will likely not and start a fire. Also consider that many cars only use 8ga wire on alternator outputs feeding back to cars main buss and biggest I have ever seen was 6ga with a high output alternator. When is last time you saw 10 ga or bigger on a factory 100 watt radio power cable?
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K0BG
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« Reply #9 on: March 23, 2011, 07:57:08 AM »

John, the main reason for using larger cable it to minimize voltage drop, as you mentioned, but your calculations are off.

For example, 15 feet of #10 at 22 amps (nominal 100 watt transceiver), is .678 volts. For #8 it's .426, and #6 it's .268. There are two reasons for minimizing it. First, radios like the Icom IC-7000 will shut down when the voltage drops to ≈11.6. If the engine isn't running, the drop is enough to cause the radio to shut down.

The major one is IMD. It is very tough to design any nominal 12 volt transmitter, yet maintain the FCC mandated IMD rating. In fact, an Icom IC-7000 will just achieve the rating at 13.8 volts. Drop it to 12 volts, and the IMD increases by about 6 dB. Some older models are far worse in this respect.

Lastly, if you select the correct type of wire, it is not difficult to string even #2. From what I've personally seen, some folks could even run #18, and make it look good.
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K5LXP
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« Reply #10 on: March 23, 2011, 10:27:11 AM »

>  in a worse case scenario short circuit from insulation cut and 12 ga wire
> will burn off and fail while a 10ga might too but 8 or larger will likely not
> and start a fire.

I think that's the job of a fuse, not the wiring.


Mark K5LXP
Albuquerque, NM
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W8JX
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« Reply #11 on: March 23, 2011, 10:29:34 AM »

Well it is doubtful that you would need to actually run 15 feet to power radio in a car (which would be 30 feet total circuit length) Next last 100 watt rig I checked (a TS570) drew 17.2 amp at 100 watts out not 22 amps. So lets crunch some numbers 15 foot run 10 ga at 17 amps (more realistic here) is .51 volts for 10 ga and .82 for 12 ga. a 12 foot run would be .41 and .66. Also consider that while this number consider return leg, you should also ground radio to chassis of car (I do thru a jumper to seat mount bolt) which cuts return resistance way down and therefore reduces circuit losses. If we use a factor of say 40% (not 50 to say no return circuit loss)  find that 15 feet with 10 is .3 and 12 is .5 volts and for 12 feet it is .24 and .4 volts. Also consider that a car electric system will usually average around 14 to 14.2 when car is running and can get to 15 volts when it is cold out so even a .8 drop is not a issue. If you are really hung up on size, two 12ga in parallel are equal to a single 8ga but easier to run and two 10ga are equal to a single 6ga. And lastly remember that house current rating for wire sizes in conduits and bundles do not apply to single routed wires which have much higher safe load rating.  
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W8JX
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« Reply #12 on: March 23, 2011, 10:31:47 AM »

I think that's the job of a fuse, not the wiring.


Providing fuse is in a place near power source t do this but this is rarely the case. THis is why alternator output leads have fusible links that will burn off and fail in a short circuit.
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K1CJS
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« Reply #13 on: March 23, 2011, 03:51:27 PM »

If the run was to the back of the vehicle, 10 gauge is marginal.  The Icom may not like the possibility of voltage drop as indicated by K0BG.  For a run to the under dash area, 10 gauge may be OK, but I still would not use it.

If you've ever seen the power runs made by stereo shops to power those god-awful earthquake machines that they put in cars, you would find eight gauge cable is the MINIMUM they use just for that reason--voltage drop.  And there is some very good eight--and even six--gauge cable made for running in tight places.  It is even more flexible than regular automotive twelve of fourteen gauge cable, and it's better protected too.

Some Wally Worlds carry specially packaged power wiring and connections for the do-it-yourselfer earthquake machine nuts!  Those wiring packages give you more cable than you'll possibly need, but they're ideal for ham installations too.
« Last Edit: March 23, 2011, 03:55:56 PM by K1CJS » Logged
K0BG
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« Reply #14 on: March 23, 2011, 03:55:30 PM »

John, you need to come up to speed here, and I don't mean that as a putdown.

I used 15 feet because the original post was a trunk mounted unit; hence the 15 feet. In my personal case, it is actually closer to 20 feet. I drive a Honda Ridgeline. The gear is in the trunk under the bed floor, and the cable (#2) is routed down to the left unibody-frame channel, and out near the trunk where there is another 2 feet of cable.

In case you have missed the latest rules.... Fusible links are no longer used. The main reason is, they cause vehicle fires! Any vehicle sold in America, since 2002, has a fuse in the alternator line. Ones made after 2006, have a fuse in the starter line.

Any made-for-mobile, 100 watt output HF radio will be about 50% efficient when operating on a nominal 13.8 vdc. You also have to include the necessary cooling fan draw, and some nominal circuitry lose. Icom says the peak current draw of their IC-7000 is 22 amp. This is the same rating Kenwood uses. Yaesu says 21 amps. The actually current draw, of my personal IC-7000, on dead carrier, with the cooling fan on full speed, is just shy of 23 amps, at 14.0 volts! Or, about 320 watts!

You speak of alternator output voltages of 15 volts when cold. The BCI (Battery Council International) says the maximum should be no more than 14.5. In my Honda Ridgeline, the max, even in sub-zero situations, is no more than 14.4.

You also speak of running a pair of wires, rather than one large one. Well, if one wants to save money, as if two is better than one, that doesn't compute in this case. If for no other reason than the thickness of the insulation.

Then you mention household current ratings vs. conduit etc. In a household wiring scenario, even in conduit, the NEC specifies 90° C. In a mobile scenario, the wiring has to be specified, under fed law, as 105° C. And in case we forget, all vehicle wiring, almost without exception, is bundled! In fact, even closer than that allowed under NEC rules in conduit. So your "safe load rating" doesn't apply.

Lastly, before you give Mark, K5LXP, a hard time about what he knows about vehicle electrical systems, you'd best visit his web site.
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