Need to replace failed FLA battery bank

[montana]

I have a battery question that I also want an educated opinion on.

I have a solar system SMA SunnyBoy inverters that is normally grid tied but I have a Sunny Island and battery bank that I can switch my house to during power outage. I installed the system 5 years ago and the batteries mostly sit on a Iota 48VDC float charger and I leave the Sunny Island powered down. The batteries are qty=8, 6VDC, Energizer GC2, I had one explode while sitting on float charge in Aug 2016, I replaced the one battery and had another explode when turning on the Sunny Island inverter 1 month ago. I decommissioned the battery bank after the 2^nd explosion. I was not able to identify the cause of the exploding batteries, there was not any heat or loose connections during either explosion.

I always maintained the water level in these batteries although they did not use much water sitting on float charger, I equalized the batteries every 6 months or so.
How long would you expect this relatively cheap battery bank to last sitting on a float charger?
I suspect the batteries shorted internally and ignited the Hydrogen, exploding the battery case, does that sound plausible?

I am trying to figure out if I did something wrong to these batteries? I would like to replace the entire battery bank and trying to decide what brand and model would make sense for my application of limited use. The hazard of future exploding batteries is my biggest concern for future battery bank, cost is of lesser concern.

The Sunny Island is a 6000 watt inverter, 48VDC to 120VAC, seems like those GC2 batteries were 220Ah?

Seemed odd to me that one explosion was with Sunny Island off, charging on Iota float charger and 2^nd explosion was with Iota powered off and starting up the Sunny Island (some inrush current but should not have been excessive)

[Mike90250]

Batteries explode from Steam (extremely high amps causing boiling and flash to steam) or charging and a spark sets off the hydrogen. If you had even fairly decent venting, it's tough to build up enough hydrogen, leaving a current fault (internal short) or super high amps flashing the 2 gallons of acid/water into steam.
Careful exam of the pieces should have shown how it blew up.
Many, many banks of flooded batteries are in use with no problems. Your having 2 blow up, suggests some sort of site issue causing it, Lithium batteries will be a really spectacular event to watch burn. Did the fire department come up with a reason ?

8, GC2 batteries can never fully power a 6KW S.Island They can provide enough power, maybe 1-2KW, to keep the lights on for 20 min, but that's the limits

[SunEagle]

There are too many possibilities as to why those batteries exploded.

Without a lot more information (including a wiring diagram and hardware specs) it will be hard to figure out if you just have a bad system design, an issue with wiring connections, bad batteries, bad charge controller, uncontrolled charging circuit, to name a few.

[montana]

battery 2.JPG

Thanks for the comments thus far, I will provide a few more details in case that helps. The wiring is 3/0, I have a 200 amp fuse on the positive cable as it heads to Sunny Island. There is not much to show in a wiring diagram since there are eight 6VDC batteries in series with a 200 amp fuse. I was careful to pre bend the 3/0 so it was not putting stress on the battery terminals.

I pasted a picture of the 1^st exploded battery, this one destroyed the case a little more spectacularly than the 2^nd. During the 1^st explosion the bank was charging with a

[montana]

I wrote a lot more information but the forum seems to truncate it, how do I get around that? I would like to paste the rest of my comment.

[SunEagle]

Unless there was a strange wiring issue with either the Sunny Island or the Iota it is still hard to determine why those 2 batteries may have been creating more hydrogen gas then the others 6 in the system.

Did you get any voltage or current measurements to and from the batteries before the problem happened?

A possible reason the second battery blew up when you turned on the Sunny Island may only be due to hydrogen gas being present and a spark being generated when the equipment was turned on as opposed to some type of surge.

Loose battery connections or some form of "bridging" between the pos and neg terminals may also be something to look at.

[SunEagle]

I wrote a lot more information but the forum seems to truncate it, how do I get around that? I would like to paste the rest of my comment.

Sometimes the "paste" function does not work well. I end up writing out my posts instead of using any copy/cut/paste shortcuts.

[Sunking]

OK a lot more details are needed. What was the voltage of the charger set to? How many amps is the charge?

Only way for a FLA battery to explode is a sever over charge voltage being applied with enough current. Batteries do not gas until they reach Gassing Voltage which is roughly 2.4 volts per cell depending on temperature. On a 48 volt FLA battery is 58 volts. Float Voltage is roughly 52 to 54 volts well below gassing voltage.

Now it is possible even at float voltage for a battery to explode. If you have a bad cell or battery in the mix like a shorted cell(s) would cause surrounding cell voltages to go above gassing voltage. Howver there are a few warning signs and conditions have to be met. First you would notice three things:

1. Excessive charge current and batteries running warm. Batteries on Float do not use current. They are fully charged and very little charge current flows and they would be cold.
2. You would hear them boiling and fizzing. .
3. Strong noxious rotten egg smell that would make you gag.

Lastly it would take very poor ventilation and an ignition source. In order for hydrogen to explode requires a saturation of 4% or greater. Does not sound like much, but in reality is a lot and the area would have to be sealed up and the batteries gassing heavily. Something like being in a cabinet, box or a tightly sealed room. You would not be able to tolerate the odor of rotten eggs. Then it has to find an ignition source like a flame or spark.

My guess is you had a perfect storm, a failed battery, coupled with to high of a voltage like an EQ charge. There is no reason to ever EQ a battery maintained on Float. Equalization is only required on a battery that is cycled regularly.

Edit Note

You said you used 3/0 AWG cable. Where is it? That is not 3/0 in your pictures.

[montana]

I could not figure out how to paste my comments in as text so I will try as a .jpg

battery text.JPG

[montana]

Sunny Island can invert 5300 watts for 30 min at 77F
8400 watts for 1 min at 77F
max battery charging 110 amps,
recomended battery bank size 100Ah to 10,000 Ah

[montana]

Any recommendations for batteries to replace this failed battery bank? What do you think about Trojan L16RE-B

also, I recently bought a Deka Hydrometer and it says to remove the foam that is in the glass tube, I removed the rubber pieces from both ends of the glass tube and it is not obvious to me how to get the foam out, seems fragile and I don't want to break it.