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Author Topic: Running power to radios  (Read 1115 times)
KK4DPN
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« on: September 29, 2014, 06:40:42 PM »

I'm looking to improve the way I power my radios. Currently I have a CB and a 2m VHF radio. I run them off of a spare 12v outlet which is on a 15a circuit. This has been more than enough to power the radios but I'd like to go a step further and wire directly to the battery.

What is the best way to do this? I've checked out the Rigrunners but they seem massively overpriced for what they are. Ideally I'd like to have one set of heavy gauge wires running into the interior of the car directly from the battery and then have the wires from the radios connect to that wire in some way for their power. Both of the radios currently have fused power wires.

What is the best way of doing this without breaking the bank?
« Last Edit: September 29, 2014, 06:43:49 PM by KK4DPN » Logged
M6GOM
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« Reply #1 on: Yesterday at 05:30:24 AM »

The car audio guys are your friends.

I use one of these each for the ground and the live. You feed it with a 4 gauge cable from the battery and then just wire the radios into it. $9.99 with free shipping.



http://www.ebay.com/itm/Sound-Quest-PDBD-G21-Dual-Power-4-Gauge-to-8-Gauge-Ground-Distribution-Block-/161367893499

Search on Ebay for Power Distribution Block.

You of course need to put a fuse in the main feed wire to the block but again the car audio boys come to your aide. I use one of these and they come with fuses up to 80A.

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KK4DPN
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« Reply #2 on: Yesterday at 07:11:14 AM »

Thanks for the response, that looks exactly like what I'm looking for.

So fuse both the positive and negative wires just beyond the battery, connect them to this splitter, and then connect the fused power wires for the radios? Does that sound about right?
« Last Edit: Yesterday at 07:25:36 AM by KK4DPN » Logged
KD0REQ
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Posts: 950




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« Reply #3 on: Yesterday at 10:46:45 AM »

might want to search www.w8ji.com mobile stuff for thoughts on fusing the negative lead.  his take is that if the negative fuse blows, ground buss on everything mobile since Ford went neg-ground in the late 60s, and another surge comes along from whatever source, it will take a path through everything solid-state in the radio.

this is reputed to be not good at all, even in the tube days.
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G8YMW
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« Reply #4 on: Yesterday at 11:12:56 AM »

Now comes the problem.
Which is right?
Fuse both power lines?
Fuse only the positive?
 Huh Huh Huh

My own thoughts. I cannot see how the perceived problem is going to happen if the negative fuse blows, where is the surge going to get into the radio, after all its an open circuit.

I am prepared to be proven wrong
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73 details Tony
Sent by WW2 Royal Navy signal lamp
WD5GWY
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« Reply #5 on: Yesterday at 11:18:54 AM »

Now comes the problem.
Which is right?
Fuse both power lines?
Fuse only the positive?
 Huh Huh Huh

My own thoughts. I cannot see how the perceived problem is going to happen if the negative fuse blows, where is the surge going to get into the radio, after all its an open circuit.

I am prepared to be proven wrong
[/quote
The current can still flow thru the coax shield connected to the radio.
James WD5GWY
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KK4DPN
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« Reply #6 on: Yesterday at 11:44:28 AM »

Now comes the problem.
Which is right?
Fuse both power lines?
Fuse only the positive?
 Huh Huh Huh

My own thoughts. I cannot see how the perceived problem is going to happen if the negative fuse blows, where is the surge going to get into the radio, after all its an open circuit.

I am prepared to be proven wrong
That's my line of thought as well. My Alinco mobile has fuses on both sides and it came that way from the factory.

From reading around it does make sense to leave the ground side unfused, but I seem to always see installations where both sides are fused so I assumed it was a correct practice.

So should I instead run fused, heavy gauge wire to the positive side of the battery to my distribution block and then run a ground lead straight from the chassis without a fuse to the distribution block? Would that be better? What should I do with the fuse that is on the negative side of my radio's power cable? Remove it?

The vehicle in question is a Ford, if that makes any difference.
« Last Edit: Yesterday at 12:21:28 PM by KK4DPN » Logged
K0BG
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« Reply #7 on: Yesterday at 12:24:24 PM »

Whether you leave the fuse or remove it when grounding the negative lead to that chassis depends on the vehicle, and where you attach it. Very late model vehicles have ELD (Electronic Load Detection) within the negative lead. Either as part of the negative connector, or around the lead itself. In these cases, there is only one connection to each battery post, and only one negative battery connection to the chassis, albeit partly grounded through the drive train itself. If the connection is at the same spot (usually a bolt of screw), and the connection fails, there is a chance that starter current could flow through the chassis of the transceiver. Or, an LDT (Load Dump Transient) could occur as well. Rare to say the least, but the fuse should prevent damage—maybe.

Unfortunately, most of the connections from the negative lead to the internal circuit boards consists partly of circuit traces. Almost no circuit trace will handle anywhere near the instantaneous current capabilities of a 30 amp fuse. It doesn't hurt anything if it remains, no matter the wiring scheme, so the discussion is moot.
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KK4DPN
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« Reply #8 on: Yesterday at 12:39:17 PM »

I'm still confused and somewhat frustrated. It seems like everything I've seen so far has been 50/50 on whether to run the ground wire to the chassis with no fuse, or run it directly to the battery with a fuse. And then some people say to install a dedicated chassis ground while others say to use an existing chassis ground near the battery.

I just want to know what the best/safest way is of running this for my vehicle. It's a 2005 Mercury Montego. I don't want to just pick an option and wind up frying one of my radios with starter current.
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K5LXP
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« Reply #9 on: Yesterday at 02:52:09 PM »

I don't want to just pick an option and wind up frying one of my radios with starter current.

Then don't run the negative lead to the battery.  Run it to a point near where the battery is connected to the chassis.  Done.  Running the negative lead directly to the battery causes more problems than it cures.  I know that some radio and vehicle manufacturers recommend the practice but I specifically reject it. 

I don't run the positive lead to the battery terminal either.  Most every vehicle made for years has a high current tap or terminal on the power distribution box that is both convenient and safe from corrosion.


Mark K5LXP
Albuquerque, NM
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M6GOM
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« Reply #10 on: Today at 07:51:58 AM »

Leave the fuse in place on the radio power cable, run the main negative wire from the distribution block unfused to where the main wire from the battery bolts to the body/chassis which is also usually a jump point as well. That way it is virtually the same as a direct connection to the battery negative post but without the downsides of a fault on the main battery to body/chassis negative cable.

This is how I've done mine. In the following picture there's the wide braid which bonds the hood to the main body. You can see the black negative cable from another bolt and directly below it slightly to the left is the battery negative jump point you can see sticking out and the main battery negative to body cable connects to that point. I used serrated washers to cut through the paint rather than sanding and removing the zinc rustproofing so that along with the contact provided by the bolt ensures a good connection. DC continuity between the negative wire I put in and the battery jump point is zero ohms which is what you want.

I could of course just slacken the battery jump point and use a suitable sized ring or spade crimp/solder connector and may do in the future.



« Last Edit: Today at 07:58:35 AM by M6GOM » Logged
N8YQX
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« Reply #11 on: Today at 10:24:02 AM »

I understand the theory behind fusing both negative and positive power feeds. With that being said, I don't know of any OEM that fuses both positive and negative for their modules. This leads me to believe that this is a very low risk issue.

Personally, I only fuse positive on my mobile installs, and I have yet to lose any equipment.
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73,
N8YQX
K3GM
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« Reply #12 on: Today at 11:58:20 AM »

...I don't run the positive lead to the battery terminal either.  Most every vehicle made for years has a high current tap or terminal on the power distribution box that is both convenient and safe from corrosion.....

I was going to say this as well.  There are typically two heavy gauge wires molded into the B+ connector that connects to the battery post.  One runs down to the starter, while the other runs to a very large fuse, sometimes aptly named "Mega" fuse usually mounted on the firewall under a protective cover.  Think of this as the Mains breaker coming into your house.  You could pick voltage off either leg of the service entrance, but it's probably not a good idea.  Same think here.  So this is where I pick B+ off of.  Here is what one looks like on a General Motors, GMT900 platform.


« Last Edit: Today at 12:04:00 PM by K3GM » Logged
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