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Author Topic: Connection to battery  (Read 1162 times)
KV9U
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Posts: 166




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« on: May 13, 2008, 08:00:27 PM »

My wife and I may be purchasing replacement vehicles. The two we are looking at is a Chevrolet Equinox and Chevrolet Malibu. I am not sure about the Equinox battery, but the 2008 Malibu we looked at had a plastic cover over the batter and a device next to it. The electrodes are not side mounted but the older type vertical ones with a plate that clamps on. There is a good sized screw that looks like it could clamp down on a reasonably heavy duty lug for connections to the battery.

Any thoughts on using this connection?

Also, is the proper procedure to only fuse the positive side at the battery, or do you recommend fusing both positive and negative?
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NA0AA
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Posts: 1043




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« Reply #1 on: May 14, 2008, 12:42:50 PM »

If that bolt is part of the battery cable clamp assembly, it sounds good.

I hear people go back and forth on the fuses thing - I fuse both sides myself - safety I suppose.  Never had a problem.
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KB1LKR
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Posts: 1899




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« Reply #2 on: May 14, 2008, 08:16:12 PM »

GMNA Engineering Centers
General Motors Corporation
"Radio Telephone / Mobile Radio Installation Guidelines", Dated January 2002 states in part:

5. Radio Wiring and Connection Locations

A. Connecting radio power on General Motors vehicles is model dependent. The installer must decide which one of the following four methods will be appropriate.

1.) Connect the positive and negative leads directly to the battery terminals (illustrated in this guideline).

2.) Connect the positive lead to the auxiliary power terminal (located at the underhood fuse center or identified by a red plastic cover in the underhood area) and connect the negative lead directly to the negative battery terminal.

3.) Connect the positive lead to the auxiliary power terminal and connect the negative lead to the battery body connection point (identified by a short #10 AWG or larger wire running from the negative battery terminal to the body of the vehicle).

4.) Connect the positive and negative leads to the Special Equipment Option (SEO) wiring provided for this purpose.

B. If connections are made directly to the battery terminals, the GM approved methods of connecting auxiliary wiring include the adapter package illustrated in Figure 2, NAPA-Belden replacement battery bolts (part # 728198), or drilling and tapping the hex end of the original battery bolts 10-32 X 3/8" deep. NOTE: It is recommended that a fuse be placed in the transceiver negative lead to prevent possible transceiver damage in the event the battery to engine-block ground lead is inadvertently disconnected.

See: http://service.gm.com/techlineinfo/radio.html for full text.

 
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KF6IIU
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Posts: 293




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« Reply #3 on: May 16, 2008, 10:35:58 AM »

I know that this is a religious issue, but could someone describe to me a fault scenario under which a fuse in the negative conductor near the battery would provide protection? I just can't seem to think of any, and in fact it seems possibly dangerous, in that if the fuse were to open, you would be returning all current via your chassis ground without knowing it.
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KB1LKR
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Posts: 1899




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« Reply #4 on: May 17, 2008, 11:22:47 AM »

From the GM Engineering Center bulletin http://service.gm.com/techlineinfo/radio.html
posted above:

"NOTE: It is recommended that a fuse be placed in the transceiver negative lead to prevent possible transceiver damage in the event the battery to engine-block ground lead is inadvertently disconnected."

The failure mode is one where a high (relatively) resistance or open occurs in the battery to engine block cable causing the negative return cable directly to the battery (and the antenna coax shield conductors to become alternate high current return paths to the battery for the starter motor current (until the fuse at the battery in the negative line opens, or the negative wire melts and breaks.) Note that the positive wire in this case does not see any excess current.

Compare this to the different fault scenario where a positive wire to  chassis fault occurs and short circuit current flows from the battery thru the frame to the frame/battery ground cable (until the fuse at the battery in the positive line opens or the positive wire melts and breaks the circuit.) In this case, unless the battery to chassis ground cable also fails w/  high resistance or opens, the negative fuse doesn't see any excess current.

Connection to a point slightly removed from the battery (e.g. engine block, frame ground point or SEO connection (if you have one) may eliminate the need for the Neg fuse, but may increase noise on the power lines at high current draw.

"...and connect the negative lead to the battery body connection point (identified by a short #10 AWG or larger wire running from the negative battery terminal to the body of the vehicle).
4.) Connect the positive and negative leads to the Special Equipment Option (SEO) wiring provided for this purpose."

Note that is is not the primary function of either of these fuses to protect the radio from internal faults (though they may as a secondary function)), but to to protect the wiring leaving the battery. The radio primarily is protected by the fuses in its leads at the radio end.

As well, while the wire failures are glibly described above as "melts and breaks..."  the reality is there is likely an accompanying wire insulation and perhaps nearby objects fire, never a good thing in the engine campartment or under the dashboard, carpeting, etc. of a motor vehicle!

Ford also has (briefer) recommendations for land mobile radio installation/wiring, see: http://www.fordemc.com/docs/download/Mobile_Radio_Guide.pdf

Hopefully the links are of assistance.

73
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K0BG
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Posts: 9834


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« Reply #5 on: May 20, 2008, 03:08:05 PM »

There's a little more to it than just connecting to the battery. If you want more info, look over the various articles on my web site.

Alan, KØBG
www.k0bg.com
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N4ASX
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Posts: 13




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« Reply #6 on: September 01, 2008, 06:33:55 PM »

I your grommet fails and the hot lead is shorted to ground and the hot side fuse does not blow, then the return current may blow the negative side.  There should be fuses on both sides of any pass through.  Unfortunately for the return current theory,  there are many paths from ground fault to the battery minus.  The other reason I guess is that many car systems are not hot switched but ground switched.  This is why a horn can go off when the ground wire is grounded short of the switch.
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