Unusual heavy crystal formation on NEGATIVE terminal

williaty

This is a new one on me. This is from a battery power system that has over time become a glorified UPS rather than a daily use system. It's been on float for.... well... a VERY long time because it's easy to forget the system is even there. I was startled to remember its existence today and figured I'd better do a safety check since the batteries are relatively old at this point. To my surprise and annoyance, when I opened the battery box, I was greeted by HEAVY blue-green corrosion on the NEGATIVE (not positive) terminal of the battery that serves as the negative terminal for the whole bank. There's also some copper-brown colored tendrils shooting out of the crystal formation as well. The negative terminal of the battery in series with the real offender also has some of the same crystals on it though to a much smaller extent.

1) What is this/why is it on the negative terminal (I'm used to seeing greener crystals on the positive terminals only on cars)?
2) What's the safest way to deal with it?
3) Does it indicate I need to do some kind of maintenance or repair?

Thanks as always!

mike95490

Blue/green is copper.  Yellow is sulfur.   Somehow, acid has gotten to the cables or terminals.  Either acid mist from charging, or simply the vapor. 

The cables need to be taken off, when it's safe to power down the system.  Then with a toothbrush & baking soda water, clean the terminals.  If you are lucky, only the terminals have corroded, and they are likely thick enough to safely reuse.   Lightly wipe the battery terminal down with baking soda water, but don't let any get into the vent cap areas.  You may need new nut/bolt, if so, use SS.

If you discover the cable strands are the source, then you need new cables, when acid wicks into cables no way to clean it, and the conductors are compromised /eaten away

williaty

They're AGM batteries, so they weren't supposed to do this at all. *grumble*

I can see it's eaten the nickle plate off the terminal ends and exposed the bare copper. I have no way to see if it extends up under the heat shrink tubing to the cabling. I hadn't even thought of that.

Estragon

Normally, lead battery terminals would be anodic to the copper wire, so galvanic corrosion would result in the loss of lead to the copper cathode. This is common, for example, where copper water distribution pipes are directly connected to lead mains.

In this case though, the constant float voltage maybe overcoming the galvanic voltage, so you get electrolytic corrosion (forced reversal of anode/cathode) instead of galvanic? The electrolyte could be from the battery, or could be environmental (eg salt water mist). Once cleaned up, and if needed, wire replaced, a coating of vaseline over the connection should help avoid contact with electrolyte and slow the process.

littleharbor2

NO-OX-ID A-SPECIAL Is the best product made for battery connections. Not expensive and superior to other terminal coatings.

mcgivor

Looks like copper sulphate crystals, copper with sulphuric acid, would probably the nesesary ingredients, but the question is why or if are the batteries venting, if so, too high a voltage perhaps, what are your charge  settings, is there an EQ involved, is temperature compensation utilized , all relevant questions. Are the batteries in a ventilated box or otherwise? Too long without discharge, saturating the batteries and effectively overcharging... rolling stones gather no moss, comes to mind. All speculation naturally.

706jim

I've experienced corrosion on my battery terminals although I would clean it off before it got this bad. I'm making up a second set of cables so that I can change them out and clean off the terminals every few months. I figure #4 cables are large enough for a maximum current of 40 amps in my system.

mike95490

corrosion seems heaviest at bolt terminal, not the wire end.

WaterWheel

How sure are you that the batteries have been only in float without some short regular charging such as when a solar charge controller comes on each morning and charges for a few minutes possibly overcharging the batteries causing venting?

williaty

Absolutely sure. It's a manual charge controller. I have to twiddle dials to change it from float up to Bulk/Absorb and then back down when the amps drop.

littleharbor2

Does this controller have a name and model #?

williaty

It's a CC/CV power supply from a company called Volteq. It's the 30A/30V model.