Wiring Question

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daugherh

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#1
Hello All,

Let me start by saying thanks in advanced for your advice. I have researched this through many of the threads here on the RR Forums but wanted to throw out my scenario for any custom stuff I may need to know.

I currently have a Motorola CDM1250 in my vehicle that is installed using the OEM wiring harness, etc. It was professionally installed by the local M shop and has worked flawlessly. I'm preparing to remove the CDM and add two XPR 4550s (one VHF and one UHF). My question is this:

Will the power cable that is powering the CDM from the battery be large enough in size to feed a power distro block in the car's interior that I plan to hook both of the XPRs to? The CDM has ignition sense and I figure I can just tap that ignition sense line (fused currently at 2 amps) and use that to ign sense both of the XPRs.

I'm not sure of the wire gauge of the CDM's power cable but I want to say it's 12 awg. Looking at the specs of the XPR 4550 I see that both the UHF and VHF is rated for a max of 14.5 Amps draw on high power transmit. I will most likely never transmit with both at the same time.

Is using a power distro worth the effort and just run each radio's power lead to it (maybe 3 feet max) or since it's just two radios should I just run each to the battery like I currently have?

And for those that say just run both to the battery, will the CDM's power cable work with the XPR or do I need to pull two XPR leads?

Thanks again and I hope this makes since as it's been a long day.

Cheers to all.
 
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#2
Just use the existing cable. You already eliminated the one case that would prevent that - transmitting on both at the same time. So, the current draw at any one time won't be more than you would have had with the CDM provided it's a similar power level.

Yes - the ignition sense should be fine, too.
 

SteveC0625

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#3
Two small thoughts on this.

First, verify that the existing power cable is 12 awg. Any smaller and you'd want to replace it anyway. Also check the entire length of it and make sure it's in good condition with no cracking, rubbing, etc. FWIW, those of us who upfit cars and trucks regularly would strongly urge that this is the time to run much heavier wire to your distribution point.

Second, the ignition sense fusing is generally recommended to be 2 or 3 amps for each radio, even though it actually draws a fraction of that. If you're planning to run two radios off the existing ignition sense wire, you may want to fuse at 3 amps if you use a single fuse at the source. Also, verify the condition of the wire.

Since you are going to create a distribution point, I suggest you consider one of the small fuse blocks that use ato/atc fuses. They're inexpensive and readily available at auto parts stores everywhere. If you can, get one that comes with a cover. And if you decide to add something else later, you've got a connection and fusing ready to go.
 
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#4
Even though your existing wiring may be adequate now, I would recommend going bigger on the wire size and put a high current fuse or circuit breaker right at the battery in addition to a distribution block with individual fuses or breakers for each device in the cab.

You can usually use the existing wire to pull new wire through the firewall and original path to save time. Its nice to have less voltage drop and to accommodate additional equipment in the future.
prcguy
 

daugherh

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#5
Voyager, Steve and prcguy,

I appreciate all of your inputs and will take them all into consideration. I'm going to have to wait until the funds are right to order the radios but definitely like Steve and PRC's advise and the option to have expandability.

What size wire would you recommend pulling to the distro point? I'm thinking 8 or 10 with a 50-75ish main (higher??) and then branching off each device at a proper lower rating fuse.

Also, if it helps I'm doing this in a 2002 Ford Escape XLT. I've got the one with the sunroof so the M shop installed my 1/4 wave UHF on the back part of the roof. I'm going to probably use a hood lip mount for the VHF unless I put another NMO mount on the roof somewhere. Not to change the subject of the topic to antennas, but it's still wiring in a way. Any suggestions as to other points for a second antenna on this vehicle? And can I run the NMO's coax with the high level power feed through the firewall or does it need to be separated?

Thanks again.
 

SteveC0625

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#6
Voyager, Steve and prcguy,

I appreciate all of your inputs and will take them all into consideration. I'm going to have to wait until the funds are right to order the radios but definitely like Steve and PRC's advise and the option to have expandability.

What size wire would you recommend pulling to the distro point? I'm thinking 8 or 10 with a 50-75ish main (higher??) and then branching off each device at a proper lower rating fuse.
#8 wire fused at 50 amps at the battery end should be more than adequate for your needs. #10 would be fine at the same fusing if your run is 10' or less. Here's a good wire chart for you:


Don't forget to pull the same size ground wire to your distribution location. Ground it to the frame at a factory grounding point under the hood near the battery and set up a lug or grounding strip at the other end. I like the lug because I can fashion up a good one with hardware from my parts box without a trip to the store or waiting for an order to arrive. But either is good.

If you're really interested in learning about wiring up cars for multiple radios, lights and sirens, etc. check out elightbars.org which is where the pros at upfitting hang out. There's tons of info in existing threads about this and more.
 

daugherh

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#7
Don't forget to pull the same size ground wire to your distribution location. Ground it to the frame at a factory grounding point under the hood near the battery and set up a lug or grounding strip at the other end. I like the lug because I can fashion up a good one with hardware from my parts box without a trip to the store or waiting for an order to arrive. But either is good.
Thanks again Steve

Just out of curiosity...I know what a ground strip is but what are you calling a "lug"?

Thanks.
 

SteveC0625

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#8
Thanks again Steve

Just out of curiosity...I know what a ground strip is but what are you calling a "lug"?

Thanks.
It's a single bolt, usually 1/4-20 or larger it can be fastened most anywhere. The ground wires are all connected using crimp-on terminals. As long as it is inside and corrosion is not an issue, it's great. Like I said, I can grab the bits and pieces out of my parts bins and create it in a jiffy.

You can purchase commercially made lugs for both hot and ground, but since you'd want to fuse everything at the distribution point, a hot lug there isn't very useful compared to a nice fuse block. This is what I mean: http://www.amazon.com/Positive-Insulated-Battery-Power-Junction/dp/B005I5I5GI
 
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