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Author Topic: VW Jetta mobile installation  (Read 5896 times)
N8DV
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« on: September 07, 2010, 11:20:36 AM »

Hi all, I was wondering if anyone has a VW Jetta and successfully found an easy way to penetrate the firewall of the vehicle to hookup to the battery. There are two 12 volt, 20 amp power plugs in the vehicle. I don't think voltage drop would be an issue here, I rarely use more 50 watts to transmit on vhf. I have even thought about getting a gel-cell battery and hooking the radio up to the battery. My last resort will be to got to the dealer and see what they can do for me but I wanted to see if the assembled multitude has any constructive suggestions for this installation. The mobile antenna will not be an installation issue, just hooking up the radio. 73
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K0BG
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« Reply #1 on: September 07, 2010, 11:26:03 AM »

It isn't the 20 amps per se, it's the voltage drop! Most accessory outlets are wired with #14 or #16, and that just isn't large enough to keep the drop below .5 volts.

If all else fails, bring the wire over to the inner fender area, and down to the kicker panel, on which ever side is most convenient.
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N8DV
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« Reply #2 on: September 07, 2010, 01:05:12 PM »

Thanks Alan. I forgot about the gauge of the power plug wire! These German cars just don't leave too many gaps to put wires through.
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N8DV
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« Reply #3 on: September 08, 2010, 01:46:55 PM »

I temporarily hooked up the vhf radio using 10 gauge wire to a 20 amp plug and plugged it into the power plug. The radio switched on on gave a reading of 14.1/14.2 volts. In my old vehicle, it was 14.2/14.3  Now this was measured by the radio a Yaesu FT2800M. I think this voltage drop is insignificant when operating the radio. Am I wrong?
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K5LXP
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« Reply #4 on: September 10, 2010, 06:54:40 AM »

> I think this voltage drop is insignificant when operating the radio.

Depends on how much current you were drawing.

2/10ths of a volt at say, 500mA during receive is .4 ohms, which at 12A or so on transmit would drop almost 5V, which of course is unacceptable.

If the .2V drop you're seeing is at a 12A draw your drop is 17 miilliohms, which sounds hard to believe for a vehicle power spigot plus the drop for the radio power cord.  So knowing the current is important to decide what drop is acceptable and what isn't.


Mark K5LXP
Albuquerque, NM
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AB5GU
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« Reply #5 on: September 12, 2010, 10:39:28 AM »

Did you notice the 10 watt max power limit in the owners manual. If you keep the power within the 10 watt limit, the existing wiring is fine.
Marty AB%gu
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KD4LLA
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« Reply #6 on: September 15, 2010, 09:10:13 AM »

"I temporarily hooked up the vhf radio using 10 gauge wire to a 20 amp plug and plugged it into the power plug. The radio switched on on gave a reading of 14.1/14.2 volts. In my old vehicle, it was 14.2/14.3  Now this was measured by the radio a Yaesu FT2800M. I think this voltage drop is insignificant when operating the radio. Am I wrong?"

My FT2800M will shut off if I use high or mid power while using the supposed "high amp" power receptacle in my Dodge Caravan.  Plus I have never seen a voltage reading over 13.7 on the radio's display.  I know it's a problem, I would just rather work around it.

Mike
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K0BG
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« Reply #7 on: September 15, 2010, 10:04:22 AM »

You're wrong.

The voltage should be measured when you are transmitting, not receiving. The rule of thumb is to have less than a .5 volt drop. Considering that the accessory jack is no doubt wired with nothing larger than #14,  (or #16 as is the case most of the time), the drop will be more than .5 volts under transmit.

You might think about another issue too. A vehicle electrical fire is the most costly repair you can imagine. It can easily total out a brand new $40,000 vehicle! Do you really want to take the risk? While there are some disagreements about where to connect the ground (battery or battery chassis ground point), the fact remains, a direct hookup if the way to go. If you doubt that, download the manufacturer's data about radio installations.
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WX7G
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« Reply #8 on: September 16, 2010, 05:37:38 AM »

Is the Jetta 12 volt outlet fused? If so it is protected. If the radio operates satisfactorily when plugged into this source is there a problem?
« Last Edit: September 16, 2010, 05:40:39 AM by DAVE CUTHBERT » Logged
K0BG
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« Reply #9 on: September 16, 2010, 03:56:01 PM »

There are several parts of this issue. While I might agree in some cases, that if it isn't broke, don't fix it, there are others which just don't, or can't, pass muster. Drawing heavy power from an accessory socket is one of those.

With the exception of a couple of Toyota products (bed mounted DC power), and most Ford Heavy Duty trucks with bed power hook ups, the accessory socket (aka cigarette lighter sockets) really aren't meant to draw heavy loads from. Oh, they have fuses, so it's okay! No, it really isn't.

The Jetta's accessory socket is wired with #16. You can verify this by looking at the Repair Manual at your local dealer. It is fused with an ATO 10 amp fuse in earlier models, and an ATO 7.5 amp fuse in newer models. This fact alone should tell you something.

And of course, there's the spring-loaded center contact....

What the real problem (what Mark and I are saying), is voltage drop. Whether or not this causes IMD problems is perhaps moot, but what isn't is the fact it falls on deaf ears most of the time. What's more, the factory specifically states, that two way radio gear needs to be connected directly to the battery. That too is in the Repair Manual. 

I can't speak for anyone here, but I just won't go out on a limb, by suggesting anything that could have major repercussions in the future.
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K7RBW
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« Reply #10 on: September 17, 2010, 07:33:51 PM »

YMMV, of course, but I've had the cigarette "lighter" (a.k.a. Aux. power connectors) melt without the fuse blowing. The plastic mountings around the metal connectors don't seem to hold up too well if the metal gets hot.

Good luck!

--bob
K7RBW
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N3IMU
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« Reply #11 on: September 22, 2010, 08:19:04 AM »

Do yourself a big favor: go to a car audio shop and ask them to install a power line from the battery. They do this sort of thing all the time, in all types of cars. They'll most likely feed it through an existing grommet in your firewall. It may look impossible to you, but audio shops are accustomed to dealing with cramped installations of high-powered, voltage-sensitive aftermarket electronics. If that won't work, they might drill a new hole and grommet it. In any case, the power cable will be professionally installed. Some things just aren't worth doing yourself.

Whatever you do, don't take it to the dealership for this. I've dealt with the service departments in several VW dealerships for my '01 Beetle, and have been thoroughly unimpressed with their skills. Asking them to do anything beyond standard maintenance on your Jetta is a recipe for disaster - and a massive ripoff, as they overcharge for everything.
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K7BWH
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« Reply #12 on: December 03, 2010, 10:24:54 PM »

How did you finally resolve your installation? I managed to run wires from battery through firewall in my 2004 Jetta 1.8T, and could write something up if you really needed.

Barry WA7KVC
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AD5X
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« Reply #13 on: December 04, 2010, 04:36:02 AM »

I had a Y2K Bug for about six years.  Right over the drivers knees was an accessory opening that had a heavy stud that was used for powering a high power audio system if installed.  I bet VW has this in other cars as well.  That stud was fused (in the fuse block) for 30 amps.  I ran my IC-706MKIIG from this stud for several years.  Worked great - measured voltage drop under 100 watt CW key-down was 0.2V at the stud.

Phil - AD5X
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