Battery terminal corrosion

ScottVA

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A friend of mine has a '05 Highlander. She's having trouble now with it periodically not wanting to start. She has heavy corrosion at the battery terminals and went to have it looked at. The mechanic is telling her it might be the alternator causing this. Have any of you ever heard this before? I've been shade-treeing my cars for years and have never heard that an alternator can cause corrosion at the battery terminals. I've always carried a terminal post/connector cleaner brush and wrench so I can clean my terminals as needed. I just can't get to her anytime soon to clean her terminals/connectors They also suggested she replace her battery cables, which I do agree with. They say the corrosion goes deep into the insulated part of the cable.

Any thoughts?

ScottVA
 

billr

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If the alternator output voltage is too high (bad regulator), then it could be over-charging the battery, which would cause it to give off more gases than normal, maybe even bubble some liquid out the cell vents. That could increase chances of corrosion. What voltage is too high? I would say anything over 14.5V, but you have to check at highway engine speeds; if it runs 3500 rpm on the highway then you have to test voltage at 3500-4000, just a "fast idle" isn't enough. Don't worry about when it is wound up to 5000+ rpm, it won't be at those speeds for long periods (unless it is a race care!). Before replacing cables and clamps, try cleaning by soaking in a baking-soda solution. Corrosion there is like a fart, a little bit can go a long way! There may not be all that much metal-loss, even on the cable conductors up inside the insulation. Once you soak them and clean down to bare copper (an easy task with the baking-soda), then you can decide if replacement is really necessary.
 

Mobile Dan

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My opinion is that if the terminals corrode, the terminals are not sealed at the case, and the acid wicks up past the damaged seal to cause corrosion.

Why does this happen? Well, you could say the battery is at fault (defective?) but I think what happens is that people over-torque the terminal clamps during installation (or removal) and wreck the seal. How many times have you seen a battery post "lean" during service procedures? You can't tell me that can't create a leak.

I wonder if wal-mart would warranty a battery because those seals were leaking and causing problems.
 

NickD

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If the battery terminals were never touched in the last seven years, nor were protected with silicone grease, they will be corroded. Brand new Cruze came with dried terminals, first thing I did was greased them.

Practically all alternators provide full output at 5,000 alternator rpm, and are geared up about three times the engine speed. A ruler verifies this. So running the engine at around 1,700 rpm would be a worse case condition. Also the regulator has to be able to keep the voltage constant at a very light load, residual magnetism in the field can prevent this.

So just by running the engine at around 1,700 rpm with a voltmeter across the battery should show no more than 14.6 volts. But that is at 25*C Denso's have a negative temperature coefficient of 11mv/*C, so if the temperature say is 55*C or 30 above the mean, maximum voltage should be 30 times 0.011 or 0.33V from 14.5 V or 14.17V.

With the battery cables removed, easy enough to check the posts for cracks around the case.

I love aircraft voltage regulators, linear and apply a continuous DC voltage to the field that is transient free, but require large power transistors on heat sinks that adds a couple of bucks to the cost. Automotive uses pulse width modulation, cheap pass transistor that when it switches off, the stator's core is saturated with magnetic flux. When that collapses, generators a very high voltage in the neighborhood of 150 to 200 volts. Depend heavily on the battery to filter out those transients or can do major damage to your electronics.

If your battery terminals are dirty, can expect major electronic problems. Need a good solid contact, also a good battery, when its capacity declines, so does its ability to filter out these transients. Voltmeter won't show this, a scope will.
 

opelgt

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Could be a bad cell in the battery. That will draw down the battery strength (weaken the rest of the battery) and also cause the alternator to overcharge the battery resulting in the acid corrosion buildup and also cause an intermittent no start. A battery usually only lasts 5-6 years. That battery is now 7 yrs old.
 
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