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Burning wires...
https://slantsix.org/forum/viewtopic.php?t=24643		 Page 1 of 1
Author:  stuggin [ Sun Aug 26, 2007 6:36 pm ]
Post subject:  Burning wires...
Hey all,
So today i started my car and let it warm up, and then when i come back out to it, it smells like something is burning and my gauges and turn signal light have gone totally wonky, and my dash started to smoke. So, i shut the car off (the gauges and turn signal light still totally wonky) and i begin to disassemble my dash to try to find out what happened. To make a long story short, the two wires going to my ammeter (which run direct from my alternator without any regulation at all apparently) melted all the wires inside my dash together (or at least i assume thats what happened). I then proceeded to unhook my alternator and limp the 200 km (125 mi) home on the battery without any gauges :S.
I changed my 35A generator to a 75A alternator about two years ago, so i could run my stereo system. Strange that the wiring picked now to bite the biscuit.
I guess my question is when i replace all of these wires, should i put some kind of resistor in line with the wires going to the ammeter or something? Is this commonplace and having to do with the alternator swap or did i develop a short or something? Lemme know what you guys think.
Thanks,
Allen
Author:  sandy in BC [ Sun Aug 26, 2007 7:24 pm ]
Post subject: 
I took my car to an auto electric place when my car did the same thing on an out of town trip. They sent an old guy out who said "Valiant......must be the ammeter:"

He fixed it 20 minutes and charged me $40,,,,,,about 6 years ago. It has worked fine since. He did something to the ammeter(which still works).
Author:  SlantSixDan [ Sun Aug 26, 2007 7:54 pm ]
Post subject:  Re: Burning wires...
Quote:
I changed my 35A generator to a 75A alternator about two years ago, so i could run my stereo system.
Mmm. Without upgrading the main circuit to handle the more-than-double amperage you threw at it, it sounds like. :-(
Quote:
I guess my question is when i replace all of these wires, should i put some kind of resistor in line with the wires going to the ammeter or something?
A resistor won't do what you need. You'd need an active shunt. Or, you could take the hack way out and bypass the ammeter or slice-and-dice in a voltmeter. (guess you can guess this would not get my vote; others prefer voltmeters. Spirited discussion on the matter is here).
Quote:
Is this commonplace and having to do with the alternator swap
With a stock charging system, the ammeter connections require periodic inspection and maintenance (every couple of decades) to avoid corrosion and the increased resistance/heat/failure it can bring. But the problem you've got is the result of an incomplete charging system upgrade. It is not reasonable to more than double the max amperage that can flow through a circuit and leave the circuit itself untouched, and expect anything but eventual failure. :-(

While you are going back and finishing the charging system upgrade, be advised that the early cars (I am assuming yours is a pre-'63, because that was the year Canadian-market Valiants got alternators as standard equipment) have minimal circuit protection and have no main circuit protection. See this thread for discussion of various main circuit protection strategies.
Author:  stuggin [ Sun Aug 26, 2007 9:01 pm ]
Post subject: 
Well, in the defense of my intelligence and ego, when the upgrade was done i was 16, knew virtually nothing about cars (or automotive electrical systems) and it was done by someone else. It never crossed my mind to reinforce it because it had worked fine up until this point.
Thanks for the links and suggestions Dan, I'll look into the active shunt and main circuit protection. Should i also increase the gauge of the wires in the circuit to handle the increased amperage?
-Allen
Oh, and my car's a 62, in case you were wondering.
Author:  SlantSixDan [ Sun Aug 26, 2007 9:42 pm ]
Post subject: 
I didn't aim to impugn your intelligence or put you down -- sorry if that's how I came across.

The active shunt, carefully built, will limit the current passing through the ammeter to a value the gauge and wiring can handle. All current in excess of that amount will bypass the ammeter and go directly from alternator to battery. So there wouldn't be any real need to go bigger than factory wire in the stock circuit, because the ammeter itself would still be the smallest link in the chain.
Author:  stuggin [ Sun Aug 26, 2007 10:28 pm ]
Post subject: 
OK so i read the thread about sixsignet's shunt and the pdf on KBB_of_TMC's. I see that sixsignet's design is better fitted (or perhaps designed is the better word) to the wiring system on my car, but there's an inherent problem in the fact that the diode that he used is only rated to 60A :? . Does anyone know if he found a better diode eventually? Maybe i'll pm him. If not, does anyone see any problem with me running KBB_of_TMC's design?
Oh and Dan, all of those fusible link size recommendations are probably ok in the Upgrade section on that website, right, or should i do the four sizes down thing from the existing wires? Thanks for your help, always appreciated.
-Allen
Author:  SlantSixDan [ Mon Aug 27, 2007 8:02 am ]
Post subject: 
A diode rated for higher currents is going to be a big honkin' diode...probably better to put two 60A diodes in parallel, giving you 120A capacity and preventing total device failure if one of the diodes should fail. That said, I don't know enough about electronics to know how one would either set the device up so that it fails "safe" (all current shunted past the ammeter, rather than all current sent through it), or at least equip it with a diode failure warning indicator. You might want to ask about that in the active-shunt thread.

The "four sizes down" thing is only if you are using fusible link wire. If you are installing a main fuse instead (which is usually easier), then you go strictly by amperage...keeping in mind that you need to consider the circuit protection needs of all the circuits. If one circuit, such as your stereo, pushes the maximum amperage way up, and you put a corresponding high-amp main fuse in, that means less protection in the event one of the lower-amp circuits creates a problem for the main fuse to address.
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