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Author Topic: Separate ground and negative-cable battery sensor  (Read 8508 times)
AC4RD
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Posts: 1235




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« on: October 04, 2012, 12:53:13 PM »

I'm getting closer to putting a radio in my new car; I've always just run 8ga wire straight (fused, of course) from the battery terminals to the radio.   I've heard a lot of talk about the new battery sensors and wondered if I should mount the negative terminal of the radio on the car's inner fender, where the negative cable from the battery goes to ground--thinking I'd avoid the sensor that way.

But now I find this, specific to my manufacturer, on the web.  It seems to suggest to me that straight to the battery terminal, and not to a separate ground anywhere else, IS the correct course (pasted material below.)   Comments or advice, y'all?   TIA!
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emphasizes the caution not to install an additional ground cable to the battery on any vehicles equipped with a battery sensor. Installing an additional ground cable to a battery (-) terminal may cause the battery sensor to incorrectly recognize the battery state (charged/discharged) and temperature information. Advise customers not to install an additional battery ground cable. Emphasize the fact that a vehicle repair caused by the additional battery ground will not be covered under warranty.

The battery sensor, which is embedded on the battery (-) terminal transmits battery voltage and temperature information to the ECM. The ECM controls alternator voltage output necessary for the various vehicle electric units by duty cycle based on signals received from the battery sensor. Also, on some vehicles with the ISG (Idle Stop & G0) function, the idle stop and auto start are determined by the battery state of charge (SOC) and state of health (SOH) information received from the battery sensor.

If an additional ground cable is installed on the battery (-) terminal, the battery sensor may incorrectly register that the battery is in a discharged state, despite a normal battery condition. This may cause the battery sensor to transmit incorrect information to the ECM, alternator voltage output and ISG control, resulting in improper operation of various systems and
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WX7G
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« Reply #1 on: October 04, 2012, 02:39:51 PM »

The auto manufacturer is saying to NOT connect an additional cable to at battery negative terminal. The transceiver negative cable can connect at the end of the battery negative cable.
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W9MMS
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« Reply #2 on: October 04, 2012, 07:01:21 PM »

Running two fused cable directly from the Battery is what I would recommend.
It prevents a bunch of problems, among them is " Ground Loop"
Visit ...... http://www.k0bg.com/

  http://www.k0bg.com/loops.html

Concerning wire size from battery to the Radio, I would go with at least 4 swg wire to prevent voltage drop.


(((73))) Milverton.
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AC4RD
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« Reply #3 on: October 05, 2012, 04:07:16 AM »

The auto manufacturer is saying to NOT connect an additional cable to at battery negative terminal. The transceiver negative cable can connect at the end of the battery negative cable.

I was thinking it warned against providing another path to ground (ground cable) OTHER than the existing path through the sensor.  (As in, go to the terminal rather than provide another path to ground via the frame.)  And as I think about it, there's not much way to do that, since the sensor is apparently embedded in the negative terminal connector.  (The negative cable in this car goes from the battery terminal with an apparent sensor to an inner-fender grounding lug, not much longer than a foot in length.  Anything other than the terminal itself goes through the sensor, I think.)  Thanks for the clarification! 
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K1CJS
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« Reply #4 on: October 05, 2012, 09:50:56 AM »

It can also mean that the sensor will detect any draw down from a terminal connected device as a battery low voltage, and ramp up the charging of the battery.  The result could be battery overcharging and possible damage. 

The best idea is to either contact the vehicle manufacturer or connect the radio cables south of the sensor instead of 'between' the battery and the sensor--which is what connecting directly to the battery terminal is going to do.  If there is a pigtail attached to the negative terminal to a ground on the vehicle frame, that would be a good place to connect to--as some people have indicated on other threads.
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WX7G
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« Reply #5 on: October 05, 2012, 10:00:44 AM »

Running two fused cable directly from the Battery is what I would recommend.
It prevents a bunch of problems, among them is " Ground Loop"
Visit ...... http://www.k0bg.com/

  http://www.k0bg.com/loops.html

Concerning wire size from battery to the Radio, I would go with at least 4 swg wire to prevent voltage drop.


(((73))) Milverton.

Your recommendation goes against what the automobile manufacturer says. Running an additional cable directly from the battery negative terminal defeats the current sensor.
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K0BG
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« Reply #6 on: October 05, 2012, 12:11:59 PM »

You need to reread the caveat in the wiring article, David. If the vehicle is equipped with a BMS and/or VQS, then the provided jumps point are to be used. As more and more vehicles incorporate idle engine shut off, the need to use the jump points will become almost universal. We're not quite there yet.

And note I said jump points. Depending on the model, where the Hall device is located, and where the battery is located, you don't use the chassis at all! Only Ford has updated their two way radio wiring guide, so when you're not sure, you should contact your dealer's service manager.
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AC4RD
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Posts: 1235




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« Reply #7 on: October 06, 2012, 08:51:45 AM »

then the provided jumps point are to be used. As more and more vehicles incorporate idle engine shut off, the need to use the jump points will become almost universal.
And note I said jump points.... Only Ford has updated their two way radio wiring guide, so when you're not sure, you should contact your dealer's service manager.

Thank you to everybody who has offered input!  It's been very helpful.   I've asked the service manager twice with no response, and the owner's manual doesn't say a single stinking word about it--apart from a generic warning never to install third-party accessories or gear of any kind.  :-/  However, I noticed that the negative battery terminal (which DOES incorporate the sensor, apparently) also has an unused terminal on it, with the sensor in between the battery and the extra terminal.  I'm guessing that was put there for some accessory use, so I'll give that a shot. 

I've got a rear-hatch mount ready to install, and I think I'll start off this week playing with 20w and the local 6m repeaters, or maybe 15m with a Hustler antenna, and see how that goes.  I'm not at all pleased with the hatch mount, though, so I suppose semi-soon I'll either get a trailer hitch installed, or suck it up and have a ball mount installed on a quarterpanel.   We'll see.  Again, thanks to all for the input!  73!
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K1CJS
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« Reply #8 on: October 06, 2012, 10:28:40 AM »

....However, I noticed that the negative battery terminal (which DOES incorporate the sensor, apparently) also has an unused terminal on it, with the sensor in between the battery and the extra terminal.  I'm guessing that was put there for some accessory use, so I'll give that a shot. 

That is the point where any 'direct to battery' connection should be done.
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