Negtaive terminal of battery keeps on corroding (snowing)

[Cicada]

Hello

My gate motor is power by 240VAC and has an internal 12V 7Ah battery (+ charger) similar to the ones used in a UPS. The negative terminal keeps on corroding after I clean it with baking soda. The corrosion cause the system to stop working since it runs from the battery even with 240VAC present. I have not replaced the terminal lead but I have replaced the battery. The unit is exposed to very hot outside temperatures.

Why does the terminal keep on corroding.
1. Could it be due to a grounding problem? Only the negative terminal corrode.
2. Could the warm temperatures cause acid to leak out of the battery that causes the terminal to corrode? If so why does the + terminal not corrode. Maybe the leak only happens close to the - terminal each time. I see no stuff acid leaking out. It is a CSB branded battery.

I have searched this forum and others but cannot find a satisfactory answer.

Thanks for any pointers and help.
Cicada

[Gyro]

It could well be coincidence that only the negative terminal is affected. It doesn't take much for a very small leak path to form between the terminal and battery molding / epoxy fill.

The standard treatment for Lead acid battery terminals is petroleum jelly (Vaseline), spread it on the terminal before re-making the connection and then liberally cover all of the exposed connection. That should hopefully solve your problem, best to do both terminals while you're at it.

[elecman14]

Does the battery have a hold down strap or something similar? I have seen cases in the past where over tightening a battery hold down can cause a small crack in the epoxy/case near the terminal causing battery acid to attack the connector (can be internal). This came to mind since you have had the same problem with two different batteries. If this is not the problem you may be receiving batteries with damaged cases. It might be a good idea to attempt to source a different brand battery from a different supplier.

[Cicada]

Thanks Elecman14

Does the battery have a hold down strap.

No it is loose standing in the enclosure.

If this is not the problem you may be receiving batteries with damaged cases. It might be a good idea to attempt to source a different brand battery from a different supplier.

The first battery was the original from the supplier. The second battery was from local battery company. So different source.

[Cicada]

The standard treatment for Lead acid battery terminals is petroleum jelly (Vaseline).

Will use Vaseline. Sounds sensible. Thanks Gyro

[MyHeadHz]

I always take a drop of engine oil and thoroughly finger each pole before I put the terminals on.  As far as I can tell, they never corrode after that.  The last battery I had I did that day one and seven years later (when it failed), the terminals were still pristine.  I imagine petroleum jelly would work just as well, but I've never tried it.

[coppice]

I always take a drop of engine oil and thoroughly finger each pole before I put the terminals on.  As far as I can tell, they never corrode after that.  The last battery I had I did that day one and seven years later (when it failed), the terminals were still pristine.  I imagine petroleum jelly would work just as well, but I've never tried it.

Engine oil works for a while, but its not a great moisture barrier. Perhaps your environment didn't really stress things. Vaseline will keep the terminals pristine for many years in pretty much any environment fit for humans. It is non-hygroscopic, and has the right consistency to stay where you put it.

[Gyro]

Engine oil (unlike gear oil for instance) is actually hygroscopic - it's designed to bind up moisture from the engine until it can be evaporated off when it gets up to temperature. That's why it's so good at forming a persistent white emulsion when your head gasket goes! It doesn't separate out as normal oil and water would.

That's why you should always pick a gear oil rather than engine oil when looking for something for a general lubricating task.

Vaseline is a thing of wonder in the lab (aside from it's other domestic duties ) It's great for stopping contact surfaces oxidizing and lubricating things like 4mm terminal threads, contacts on precision resistance boxes etc. ... and of course battery terminals.

[MyHeadHz]

Awesome, thanks for the info.

In general, I usually clean the area with water/baking soda to neutralize the area first, then wipe it clean before applying.  Any reasons to not do that?

Also, would there be general mechanical/electrical situations where it would be advisable to avoid using vaseline?

[Gyro]

No, neutralizing with an alkali (baking soda is as good as any) is a good way of stopping the corrosion - it's the  method recommended by car repair manuals for battery corrosion and acid spills. I suppose if the leak around the terminal is REALLY  bad there's a chance of some of it getting into the cell, but not a practical risk.

I've only used Vaseline on non arcing electrical contacts -  I wouldn't use it on switch contacts that arc (it's probably flammable!). It's effect on brass contact resistance is nothing short of remarkable. I've used it in difficult low signal automotive connectors (ABS sensor wiring) to cure intermittents. I'm not sure about its lubricating properties for heavy loads, although terminals are very smooth after applying it to the threads and never seize.  The good thing is that it is effectively medical grade so won't do you any harm. if you get it on your skin. As MyHeadHz said, it has the advantage that you can completely cover (smother) exposed contacts in the stuff to repel moisture and it will stay where it's put, much more effective than WD40.

P.S. At this point it looks like I'm far too acquainted with Vaseline and its uses so I'd better shut up! 

[SeanB]

R3 or R5 with the battery mounted on its side I will guess. Replace the complete leads with new ones, from the control board connectors to the battery, and check the battery voltage is under 14.0V on float charge ( battery charging for at least 4 hours with no gate operation). If over 14V change the power supply, they tend to get wonky with age, and will either have a higher output voltage with some ripple on it, or a low output, depending on which capacitors died first.

The vaseline on the connectors is good ( I use a very nice white grease though, which is very good at water repelling as well, but it is rather expensive as it only comes in 2 sizes, 20l and 205l), just make sure you take the new leads and put a little blob inside the spade side, plus crimp the spade tighter using some gentle pressure from pliers, so the connector is a little stiff going on, and makes good contact. The acid venting from a battery being slightly overcharged ( the charger is supposed to have temperature compensation but this is often a little optimistic) will corrode the spade connection which is closest to the outside air as the gas escapes, and this is the negative terminal in these. Plus if there is poor contact there will be heating which accelerates the action of the corrosion along with it being closer to damp outside air.

Same gate motors, though the ones I have at home are decades old, and as it is a complex we went to a separate control box and a 30AH battery for backup as well. At work the R5 ate the lead after 2 years, a new one ( at least new to the gate, it was originally a Samsung aircon loom with 1/4 spade connectors in sleeves on the one end, and good ones at that) with a clean up of the battery and tensioning of the contacts kept it perfect for over 5 years now, though the battery tends to get changed every 4 years with the rest of the UPS batteries, as it is one of the old ones being repurposed to lower duty use.