Hello Everybody!

I too have a bubbling/fizzling sound when charging my brand new AGM batteries and I'm kind of worried.
I have 2 pieces of BSB Power sealed lead acid 150 Ah batteries (AGM, VRLA) wired in series in a 24V system.
I charge them from solar panels. The charge controller is a Victron Energy BlueSolar MPPT 100/15 charger with 3 charging stages: bulk (apply as much current as possible), absorption (apply 14.4V per battery) and float (apply 13.7V per battery).
The battery manufacturer recommends a charging voltage of 14.4-14.8V during the absorption stage and 13.6-13.8V during the float stage.

The bubbling sound only starts in the absorption stage (14.4V per battery, 28.8V in my 2-battery system) and stops in the float stage (13.7V per battery, 27.2V in my 2-battery system).
I did measure the voltage of the batteries when the sounds is audible and the voltage stays all the time at 28.8V, which is at the lower and of the charging voltage recommended by the manufacturer for this stage. I also touched the batteries and they are not hot, they are not even warm a little bit. So I think it's not likely that they are being overcharged.

This bubbling sound seems to be coming more from one of the batteries than from the other, although it's hard to tell because they are right next to each other. I measured the fully charged voltage on them individually and they both stay at around 13V with no load when fully charged, so it's unlikely that any of them have damaged cells.

The opinions on the Internet are different. Most people say that AGM batteries should not make a bubbling sound. A few people say that it's OK. What do you think, should I be worried? Is it possible that it's only because the batteries are new and it will go away with time? Maybe I've been sold some defective or old batteries?

 

Hello,

You just hijacked an old existing thread:
Should a 12V 75AH AGM battery make noises during charging?

This we do not like over here.
Now you have a thread of your own.

Bertus

 

AGM batteries should not bubble during normal charging.
That will eventually boil off the electrolyte and kill the battery.

 

Bertus, sorry for the "hijacking". Didn't know it's a bad thing to do. I apologize. Thanks for creating this new thread instead.

crutschow, Ok, they should not bubble. But why are they bubbling then? According to all signs they are not overcharged. They are not warm. Their voltage is the correct one (14.4V). The chraging current is 2-6A and the manufacturer specifies that the maximum charging current is 37.5A. That means that I'm charging them with less then C/20 and with far less current than allowed. So why are they making the bubbling sound?

Thanks!

 

Any other opinions about the bubbling sound? I actually asked the manufacturer, but I doubt they'll respond as they are a huge company and they probably don't deal with individual customers...

 

Did you measure the voltage on each battery separately when the bubbling sound was occurring?
Perhaps the charger is staying too long in the absorption phase.

 

the only way thebattery will make hissing noise is when the current is more than the battery can absorb chemically. At that time, water electrolysis occurs and hydrogen and oxygen are produced creating gas pressure which is vented by an over pressure valve. the battery is getting more current than it needs after bulk charge phase.

 

Thank you for your answers!

It is not a hissing sound. It sounds more like boiling or bubbling. Like bubbles are moving in liquid. The manufacturer talks about gas recombination system. Perhaps it recombines later? Or is it just commercial bla-bla?
I didn't measure the voltages individually, but together for the two batteries in series. It was 28.8V, as it should be. Yet they bubble... both of them.

 

They are not warm.

In absolute terms, or relative to ambient? Charging voltage should be decreased with temperature increase. Does your charger have temperature compensation? If not, the top-up voltage may be above the recommended value.

 

The charger does have temperature compensation and it is 32mV/degree. The battery manufacturer recommends 30 mV/degree, so it's kind of OK. Anyway, the charger and batteries are sitting next to each other in a room where the temperature is 15-20 dgrees. The charger is calibrated for 14.4V/battery I think at 20 degrees. So that should not be a problem.
By the fact that the batteries were not warm I mean I put my hand on their sides and they were just as cool as any other plastic object in that room.

 

if you keep insisting that everything your charger is doing is correct, and the many experieced answers we are giving, telling you the battery is essentially being charged to fast are ignored... what more exactly do you want from us?

 

I would like alternative explanations regarding what else (except overcharge) could cause this
On another forum another experienced user swears that AGMs do have this behavior and it's completely fine. I'm puzzled...

 

I would like alternative explanations regarding what else (except overcharge) could cause this
On another forum another experienced user swears that AGMs do have this behavior and it's completely fine. I'm puzzled...

The fact that gas is being generated means, "bad". Overcharging is the only way to cause gas bubbles except maybe taking the batteries up in an airplane or baking them in an oven like a roast chicken. There is no, "alternative" explanation that is actually true. You can continue to ask random strangers on many websites until you get the answer you want.

 

OK, let's assume that indeed the bubbling is bad. In this case what steps do you recommend to take to fix the problem?
Should I reduce the absorption voltage of the charger, even though I'm at the low limit recommended by the manufacturer?
Should I limit the bulk charging current to less than 5A, even though the manufacturer says that 37.5A is the maximum?
What can I do to try to fix the bubbling?
Should I try draining the battery to see if after a deeper discharge the bubbling still exists? Until now I've only managed to discharge it to about 90% (almost full) before the charging began the next day.

 

I expect you're aware of the charging recommendations here. Does your charger accurately follow this profile?

 

To stop the bubbling, you lower the charging voltage (and current) until the bubbling stops.

The electrolyte knows exactly when to bubble, regardless of what the manufacturer said. When the battery can absorb energy, the electrolyte does not bubble. Adding more energy after the charging has completed or adding it too quickly simply exceeds the ability of the battery to absorb energy. When the battery can not absorb energy as fast as you are adding energy, the water in the electrolyte uses up that energy to make hydrogen and oxygen. There is no magic chemical in there that bubbles because it's happy or sad. It's just acid and water.

 

Alec_t, I'm a frequent visitor of BatteryUniversity, but I don't think I've read this particular article. I will now! Thank you!
Also thanks to #12! I will try to modify the charging voltage for the absorption stage, see what happens...

One more question: this bubbling happened 3 times (on 3 days) so far for about 30-60 min each day. Do you think it could have caused any major damage?

 

Bubbling is merely the destruction of water. If the batteries are not sealed, replace the water with some really clean water like, "deionized" or at least, "distilled". If the battery is sealed, you can't fix the water level.

 

They are sealed, VRLA AGM batts.

 

They are sealed, VRLA AGM batts.

That's why people are getting irritated here. You have been damaging the contents of the battery in a way that can't be fixed. STOP doing that! Listen to the battery. Reality is happening. Adapt to the reality of the situation. Reading the instruction manual to the battery will not fix this.