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Old 20-11-2014, 07:23   #1
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Problem with Negative Terminal Corrosion

Greetings! I have a problem with corrosion on and around the negative battery terminals only. Furthermore, this corrosion only appears to affect certain metals such as the bolt and wing-nut that secure the wires to the terminals. If i can figure out how to attach a picture i will.......

Has anyone come across this problem before?

Bit of background:

It's been ongoing for about a year and a half now but nothing has changed in the battery system for about 4 years. Both batteries are showing this problem. Initially the boat was out of the water and batteries were charging via shore power. I figured it was a grounding issue but it didn't go away when it was re-launched. Now charging via solar. Batteries are 2 x lifeline 8Ds (AGMs). Battery system is simple. Batteries in parallel, grounded through engine (no corrosion at the engine terminal and the zinc on the end of the prop shaft is fine. The one in the heat exchanger always disappears pretty quickly so i replace that about twice a year and have been doing so since before this problem occurred) and connected to panel via a negative collection plate. On the positive side it goes from the batteries to a switch (which is always left on) and then to the engine and panel distribution. Any ideas at all would be much appreciated! Battery performance is still excellent, but something bad must be happening surely? My chief concern is that more reactive metals in the engine are corroding like this but i just can't see it.
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Old 20-11-2014, 07:25   #2
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Re: Problem with Negative Terminal Corrosion

After you clean off the terminals and or replace them. Spray them with this every few months and it should prevent it from happening.

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Old 20-11-2014, 07:27   #3
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Re: Problem with Negative Terminal Corrosion

You can also use this to clean the terminals or if you are in a pinch coca cola works too. Just be sure after cleaning them to rinse with water, then apply the protector

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Old 20-11-2014, 07:34   #4
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Re: Problem with Negative Terminal Corrosion

Hmmmmm, yea i can clean them pretty easily (a vacuum cleaner works well to suck up all of the nastiness!) but i'd really like to address the root of the problem. The reactive metals are corroding, there a dampness around the terminals and some yellowishness around the vents (which i presume is sulphur from the sulphuric acid electrolyte). It's really weird too that it's only on the negative terminals......... Any ideas?
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Old 20-11-2014, 08:33   #5
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Re: Problem with Negative Terminal Corrosion

Maybe you are over charging the AGMs.

They do contain fluid/liquid that can boil off. Most can be accessed and refilled to avoid ruining them. Or so I have read by one who has done it on Lifeline AGMs.
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Old 20-11-2014, 08:44   #6
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Re: Problem with Negative Terminal Corrosion

Yea maybe. I'm charging at the voltages stipulated by the manufacturer and the fact that i've had this problem with both a shore charger and a solar system independently is a bit odd, but it is certainly possible. I will write to lifeline i think and see what they say, if anything.
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Old 20-11-2014, 09:00   #7
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Re: Problem with Negative Terminal Corrosion

The corrosion is from acid getting on the terminals. It can be from it being over charged and the gas venting onto the terminal. It could be a crack in the battery near the terminal allowing the gas to get on it, or it can be spilling acid on the battery when filling them.

Cleaning the batteries regularly and applying a preventer helps the situation. Sometimes it is normal. Frequent excessive amounts of corrosion could mean leaking battery or overcharging.
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Old 20-11-2014, 09:04   #8
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Re: Problem with Negative Terminal Corrosion

Maybe the seal between the post and the battery casing is no longer tight.
After cleaning the post, smear dielectric grease around the base of the post where it enters the casing, fit the terminal clamp, then apply more grease.
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Old 20-11-2014, 09:04   #9
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Re: Problem with Negative Terminal Corrosion

Nice, thanks very much. Why would the acid corrosion be limited to the negative terminals only? Not a crack - both batteries experiencing same thing. Also not from filling - AGM sealed batteries. I'm charging at the voltages specified by the manufacturer but could be over-charging............. I will try reducing the length of time that the charger keeps them in absorption mode. I have noticed it takes a very long time to go into float mode.

The lifeline guy got back to me straight away requesting the pictures so i will post will his diagnosis for future reference for others once he's given it.
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Old 20-11-2014, 09:15   #10
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Re: Problem with Negative Terminal Corrosion

Some other observations:

Wing nuts are not a good idea on a boat. The batteries should be the type with a threaded stud and the cable ring lug should be attached directly to the stud with a washer + hex nut and torqued properly. If these are sealed batteries most likely there is a crack in the case allowing gas or acid to escape. If these are water filled batteries the compartment must be ventilated all the time. The gases released from charging unsealed batteries must be ventilated or bad things happen.
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Old 20-11-2014, 09:30   #11
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Re: Problem with Negative Terminal Corrosion

Quote:
Originally Posted by Therapy View Post
....They do contain fluid/liquid that can boil off. Most can be accessed and refilled to avoid ruining them. Or so I have read by one who has done it on Lifeline AGMs.
You should never open AGMs as they are sealed under pressure at up to 6 PSI! Get that in your face and you won't be posting here anymore.

The electrolyte fills only about 95% of the Glass Matt, so you wouldn't see anything in there anyway. The boat next door opened up all his 10 Deka AGMs and because he couldn't see any electrolyte he filled them up. Opening is fatal because oxygen gets in, and filling just makes them deaderer!
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Old 20-11-2014, 09:51   #12
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Re: Problem with Negative Terminal Corrosion

Just like in the automotive field, it's almost always the negative terminals
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Old 20-11-2014, 10:08   #13
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Re: Problem with Negative Terminal Corrosion

The negative battery terminal is always the one that corrodes.The battery gas is positively charged & settles on the neg post.It's a normal thing.Clean & coat them as mentioned by other posts.If they crud up as bad as ur pic,in less than a year,I suspect overcharging.
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Old 20-11-2014, 10:36   #14
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Re: Problem with Negative Terminal Corrosion

Quote:
Originally Posted by deblen View Post
The battery gas is positively charged
I was not aware of that aspect but it explains a lot
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Old 20-11-2014, 10:53   #15
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Re: Problem with Negative Terminal Corrosion

How long does it take to build up that much?

Ventilate, ventilate, ventilate, just like the rest of your boat. Consider not letting it get that bad!
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