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L16 explosion

miahallen

miahallen

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Dec 28, 2021
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Been doing solar for 9 years now, this is the first time I've seen a Lead Acid battery explosion. I would love some feedback as to the possible cause so I can avoid, and hopefully help others also avoid this scenario in the future.

I installed this system about 5 years ago, and it has been performing flawlessly for those 5 years, except for one wire which became corroded and was replaced about 2 years ago.

Last week, I got a call from the client telling me one of the batteries exploded (he was standing only 8-10ft away at the time. He described it as follows:
  • a hemisphere of plasma more than 1 inch in radius formed over the terminal of the battery
  • He immediately began shutting the system down
  • within about 20 seconds, the explosion occurred splattering acid on him
  • He felt the burning of the acid on his face and immediately ran to the shower to wash
  • the system was shut off for the past few days, till I was able to go assist yesterday
  • the client is fine, no acid got in his eyes and he cleaned quickly, so no ill effects
Details about the system:
  • 2S3P - 370AH Delta L16 deep cycle batteries - 12V
  • 3x Flexmax80 charge controllers (each with enough PV to peak at about 80A output)
  • 1x 3600W Flexpower inverter - 12V
  • All battery interconnects are 2/0 pure copper, with copper ring terminals
  • batteries were regularly serviced, and water kept topped up
Other notes:
  • Even after the explosion, all 6 batteries were testing in the 6.05-6.10V range, including the exploded battery
  • All battery interconnects tested at close to zero ohms of resistance
  • the inverter and charge controllers are all still functional
  • 2 batteries were replaced last year ( I did not do the work)
  • I was not the last person to work on the system
Photos of the aftermath:
photo_2023-06-15_10-38-09.jpg
photo_2023-06-15_10-38-06.jpg
photo_2023-06-15_10-38-04.jpg
photo_2023-06-15_10-38-01.jpg
photo_2023-06-15_10-37-57.jpg
 
The positive connection looks like it was pretty hot, I see three connections on the post. I'd guess it was charging heavily and gassing out the battery vent which flashed.
 
Yowsa! Glad the client is fine.

I'll guess 3rd!

The problem started here. A bad connection heated up and melted INTO the cell which ignited in the hydrogen rich atmosphere of battery being aggressively charged. I've never seen that before and I've been around a lot of batteries.


1686849141489.png
 
Poor installation practices. The terminals are not heat shrink wrapped, and if that's the case, we can probably assume the mating surfaces between the battery lugs and the cable terminal was not prepped and probably not coated with any anti-corrosion compound.

This resulted in corrosion between the mating surfaces, which lead to an eventual breakdown of conductivity and a DC arc forming, which then found some hydrogen gas and... boom....

I'm guessing that the charging profile didn't cause this and it was a hard amp-draw discharge that caused it. Something drew a lot of amps out of that bank and caused the terminal to heat up.

Before making battery connections, all terminal mating surfaces should be lightly sanded to remove any corrosion, even corrosion invisible to the naked eye. All connections should then have a liberal coating of dielectric grease (or other anti-corrosion compound) until the stuff squirts out the edges when tightened. Then smear it on any exposed metallic surfaces like screw threads etc. This isn't so important for a 30 amp connection, but anything with a 2/0 cable better be done right.

Also, when it comes to these large lead acid cells, ventilation is important. Those acidic fumes, even when invisible to human senses, will coat and corrode everything around them. Even an open door or large air vents on a battery shed are not enough... You really need a small fan running anytime the batteries are charging.
 
Note to all FLA users:

Vent caps can become plugged and not vent any more. Pressure then builds.

Couple years ago, I was watering up a bank of L-16's. Going one battery at a time - take off the fill lids, add distilled, put the lids back. Wearing neoprene gloves and safety glasses, of course. Things were charging and since I had to leave shortly, couldn't wait until evening and the charging had stopped.

On one battery, a few seconds after putting the lids back on, I could hear a faint sss-sss-sss noise. Carefully got closer - it appeared to be the middle cell of the battery. Slowly removed the lid and was rewarded by a "phud" noise as the pressure was released and the sss-sss stopped.

Yowza. That's not good...

Upon careful inspection, the sides of that battery were slightly bowed out. Not good either.

Replaced the plugged vent cap with another and verified that the sss-sss had stopped. Couple weeks after that my Water Miser caps arrived and I replaced all 12 of the OEM caps for that bank.

Monitored voltage/current/heat (with FLIR) after this episode for a couple weeks. All seemed to be OK so I didn't replace the L-16.

I guess the take away here is that you can also have H2 UNDER PRESSURE in a FLA battery under certain circumstances, which means there's a lot more of it than there would be at a no-pressure situation. I watch more carefully now for any physical deformation of the case.

The "plasma" observation certainly sounds like H2. Does anybody else remember the "electrolysis of water" experiment from high school chem class? When you ignited the H2 that was produced with a wood splint, you would get a "bark" and a blue flash.

I have given some thought to a fixture (probably made from an old battery top) that you could screw caps onto and then pressure up with compressed air to check if they are plugged. Haven't gotten around to it.
 
Depending on how the batteries were wired in parallel, the outer batteries could have been overcharged or over discharged, while the inner batteries were undercharged or under discharged. That may not the be cause of the explosion, but it could have been a contributing factor.
 
MurphyGuy said:
Poor installation practices. The terminals are not heat shrink wrapped, and if that's the case, we can probably assume the mating surfaces between the battery lugs and the cable terminal was not prepped and probably not coated with any anti-corrosion compound.
Click to expand...

What compound would you recommend ?
 
Regular automotive grade dielectric grease.. any auto parts store will have it. Coat everything.
 
HRTKD said:
Depending on how the batteries were wired in parallel, the outer batteries could have been overcharged or over discharged, while the inner batteries were undercharged or under discharged. That may not the be cause of the explosion, but it could have been a contributing factor.
Click to expand...

Wiring was like this:
1686956131491.png
 
Last edited:
That's not bad, but not optimal. Take a look at the Wiring Unlimited document in the first link.

diysolarforum.com

Wiring Unlimited

Wiring Unlimited is a great resource that covers many many common topics and questions relevant to DIYers. It is a free E-book from Victron Written by Margreet Leeftink. Check it out! Download
diysolarforum.com diysolarforum.com

For a more in-depth discussion of how to wire parallel batteries, check out this thread.

diysolarforum.com

Calculation of parallel string battery currents

Hi, everybody! I'm a retired EE. I didn't want my EE skills to fade away after retirment, so I exercise them when I can. Whenever I see a non-trivial circuit analysis problem on one of various forums I frequent, I challenge myself to solve it. Recently I watched Will's video about current...
diysolarforum.com diysolarforum.com

Here's a summary. Assume the batteries are 1, ,2 and 3, going from left to right. I consider the two 12 volt batteries wired in parallel to be a single battery for this.

The negative cable has to be repositioned between batteries 1 and 2. The positive cable has to be repositioned between batteries 2 and 3. It's easier to reposition the cable if you're using metal bus bars between the terminals.
 
HRTKD said:
Your inverter can still create an imbalance in the batteries. Why are you trying to dedicate a charge controller to each 24 battery?
Click to expand...
They are L16s (6V per unit), 12V per string.
Putting a CC on each string balances the charge current.
How would you balance things better?
 
miahallen said:
They are L16s (6V per unit), 12V per string.
Putting a CC on each string balances the charge current.
How would you balance things better?
Click to expand...

By arranging the cables to the battery as defined in the Wiring Unlimited document or the thread I linked to or post #12 of this thread.

You've improved the balance of the charge, which isn't bad.
 
I was very young when I saw a lead acid go boom.

Hood was open on the car as well.
 
HRTKD said:
By arranging the cables to the battery as defined in the Wiring Unlimited document or the thread I linked to or post #12 of this thread.

You've improved the balance of the charge, which isn't bad.
Click to expand...
It seems that to improve this further, I should switch to bus bars....unfortunately, the posts on these L16s are not lined up, and each one would still require a soft jumper to the bus bar....seems overly complex/expensive for the minor gain.
 
Also when looking at events such as this, it is helpful to ask:
Were the batteries properly watered & maintained ?
What were the Hydrometer readings ?
Was the acid clear or murky in the Hydrometer ?
When the cells were topped up, what kind of water was used ?
(you'd be shocked to find out how many people do not pay attention to it, no matter how many times they are told, the common refrain "it won't hurt just this one time".)

Diagnostic questions such as that can help to determine causes. If plates get exposed & covered again, a milky white residue can appear in the acid. If it looks rusty then other things are happening. If the cell plates have been air exposed that creates a LOT of hydrogen and can arc and explode.

The point on Cleaning Vents ! SO TRUE !!! Very few ever clean the vents, which should be checked at every watering/inspection.

Gotta say it, I really do not miss FLA in any way !
 
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