Burping the battery

vtmaps · April 2012

Blackcherry04 wrote: »

I cut my cables at least 3 " longer than you need. The reason for this and having the batteries loose is so I can "Burp" them. I have noticed that batteries in a fixed location not subject to shaking like in a car will retain a Hydrogen bubble between the plates. I can't tell you of this will get you longer life, but it has to help their output and may with their life. I will take the battery case and rock it back and forth a couple times, you will hear it release the hydrogen. If you cannot shake them, take a small rubber mallet and tap lightly on the case and you'll hear it.

Blackcherry04 wrote: »

Has anyone besides me noticed that a day after you do a full 3 stage charge or a EQ that if you tap lightly on the case or shake a battery you can hear them release a large hydrogen bubble that is trapped between the plates ?? I call it burping for lack of a better term. Most of my battery's are in stationary mounts even though they are on boats and don't get shaken enough to release them on their own. Where I have consistently done it to them they seem to have a longer life.

mike90045 wrote: »

I find that happening when I fill the batteries, about 1/2 way 30% of the cells, I get a large burp of bubbles. 8 L16's bolted together, don't rock much.

I too have noticed this burping when I jiggle my batteries.

Blackcherry, why do you think it is hydrogen rather than oxygen?

This picture is from a Sandia document:
Attachment not found.

You can download the document here: http://photovoltaics.sandia.gov/docs/PDF/caploss.pdf

One thing that is mentioned in the document is that the gas bubble entrapment is relieved by heavy gassing in late stages of charging. That is not my experience... I find that after charging is complete I can still burp the battery. I am beginning to think that the next frontier in wise battery charging will be to add some sort of motorized battery burper to my setup. I do realize that it could be dangerous to have a unsealed motor in a battery box. It might be an interesting experience to get that passed by the local AHJ.

--vtMaps

waynefromnscanada · April 2012

Re: Burping the battery

My 10 year old L-16 batteries have never intentionally been "burped" and are still doing their job just fine. It's my opinion that the bubbles don't stay in any one place for an extended time, thus don't cause a problem. When they get big enough, they escape. Always and without fail.

Cariboocoot · April 2012

Re: Burping the battery

For what it's worth, we were taught to gently rock batteries after a "full charge" for just this reason; to release the trapped gas. The old "magic eye" batteries would sometimes need a jostle to get the eye to go to green after being charged. How severe this will be is going to vary by battery and charging procedure, but it is something to keep in mind.

One more thing that AGM's don't suffer from!

stephendv · April 2012

Re: Burping the battery

Interesting document from sandia! From the doc:

"Gas bubble removal
requires some vibration or
motion of the battery case
and/or heavy gassing."

So it seems that a normal EQ charge would achieve the same thing.

vtmaps · April 2012

Re: Burping the battery

stephendv wrote: »

Interesting document from sandia! From the doc:

"Gas bubble removal
requires some vibration or
motion of the battery case
and/or heavy gassing."

So it seems that a normal EQ charge would achieve the same thing.

In my experience, after heavy gassing such as an equalization charge, there are still retained gas pockets. Also, I don't like to think that my battery plates have all those pock marks. Maybe the forklift battery folks are on to something with their air bubblers and electrolyte recirculators.
--vtMaps

Blackcherry04 · April 2012

Re: Burping the battery

vtmaps wrote: »

I too have noticed this burping when I jiggle my batteries.

Blackcherry, why do you think it is hydrogen rather than oxygen?

--vtMaps

Well, I don't know what one it is for sure. I burp mine for two reasons. 1) I want the electrolyte to have full contact with the plates. 2) I have a mean place I have to lean over to water my batteries. I was adding water one day and a big burst let loose as soon as I starting adding water and it blew acid all over me. After the second time it happened I started burping them on a regular basis and before adding water and after EQ'ing.

I have noticed that a badly sulfated battery will retain them until they displace the electrolyte and it runs out the vent holes. If you tilt the battery on it's side it will let loose, then look in the cell and the electrolyte will be way back down. The sulfate seems to build around the top and sides of the plates.

It's a to each their own thing, I do it and I believe in it, if other don't, well thats ok to.

RCinFLA · April 2012

Re: Burping the battery

Picture looks like stratification which happens due to continuous light float charging without occasional gassing to mix up electrolyte. Higher acid concentration sinks to lower regions where it makes discharging reaction greater then diluted top region, eating plates up more at bottom.

Negative plate generates hydrogen gas. Positive plate generates oxygen gas. This is why positive grid has issue with oxidation (corrosion of grid).

vtmaps · April 2012

Re: Burping the battery

RCinFLA wrote: »

Picture looks like stratification which happens due to continuous light float charging without occasional gassing to mix up electrolyte. Higher acid concentration sinks to lower regions where it makes discharging reaction greater then diluted top region, eating plates up more at bottom.

Hi RCinFLA, If you read the Sandia pdf, they have another illustration of what stratification looks like. The plates are indeed eaten up more at the bottom, but without all the pockmarks.

--vtMaps

john p · April 2012

Re: Burping the battery

I f you are keen enough you can use a fish tank pump tp pump air through the batteries in a similar way to how some battery manufacturers recommend.
I did a full test on this some time ago and the post is on this forum somewhere.
It does improve battery charge times and certainly reduces plate build up..
BUT it has to be done continuously for best results,and that uses consiserable power over long term to the air pump.

Back in Philippines I just take my batteries in the back of my small truck then drive them over a bumpy dirt road for 30 mins it improves their charge take quite a bit... mabe they just like to go for a ride in the countryside??

niel · April 2012

Re: Burping the battery

i know how this is going to sound, but why not buy a vibrator and try that?

Blackcherry04 · April 2012

Re: Burping the battery

I have a couple ways of burping them. Rock them a little , A few light taps with a rubber mallet. The ones I have in boxes, I have a pry-bar long screwdriver I slip under the corner of the box and raise it up maybe 3/8 inch and let the screwdriver slip out and let it fall. Over the years I did away with all my buss bars and went to flexible cables, so it would be easy to do. I never had good luck with Buss Bars because of Positive Post growth anyway.

I am thinking that it's the condition of the battery and the type / make up of the separator that makes it more of a problem on some batteries. Say in a 10 battery bank, it may only occur in 2-3 of them.

After reading this ( http://photovoltaics.sandia.gov/docs/PDF/caploss.pdf ) I don't feel so silly for worrying about doing it. Again, it's a personal thing to burp or not to burp.

techntrek · April 2012

Re: Burping the battery

vtmaps, thanks for the link to that pdf, very interesting reading.

neil, you could build a vibration table and set the battery boxes on that. You can buy expensive tables used in the concrete biz, but I see instructions online for building your own.

< resisting urge to take neil's post and run with it... too many jokes coming to mind... >

john p · April 2012

Re: Burping the battery

The only problem with battery shaker tables. You need them to be shaking the bateries all the time for best results. I know I have done this experiment. The problem then is the amount of power you need to opperate the shaker tables .. remember lots of batteries are big weight so not that easy to vibrate .
When I did the experiment one battery actually cracked and spilt its internal fluids everywhere.. quite expensive to get cleaned up.. it was not violent shaking either. but for 4x200ahr batteries it needed a 1/2 hp motor to do the job. our smaller shaker table 1/4 hp had problems with the weight.

techntrek · April 2012

Re: Burping the battery

You don't need to do it 24/7, only during daylight when they are charging assuming a PV-only system. It doesn't even need to be constant. Set a timer to do it for a few minutes an hour during daylight hours (and maybe once more just after sunset), that would be enough to dislodge any trapped bubbles.

Instead of a table or portable concrete vibrator (which would definitely damage a battery), there are several power tools which could be picked up cheap, used, which might do the job. Jig saw, handheld rotary sander, handheld drill with an off-center weighted bit to make it vibrate. Strap one to each battery. Thinking outside of the battery box...

Cariboocoot · April 2012

Re: Burping the battery

You could even program your charge controller's AUX function to operate the "battery burper" once Float is reached ...
Make sure there's enough cable slack if you use the rocking method.

john p · April 2012

Re: Burping the battery

Techntrek . Your ideas of vibrating batteries with simple power tools like a jigsaw or sander just wont work.. Well not if you are using above 100ahr batteries . Most would be using 2 or 4 at least.. thats a lot of weight to vibrate and it needs to be at a relatively slow rate . A jigsaw would be far to fast even if it could do it. Another thing to think about the current draw of those tools . most tools like that draw about 400 to 800w. thats a lot of power consumed over a long period of time even if only used 8 hrs a day. And most hand power tools are not designed for continuous use.
After having done all the experimental testing of vibrating batteries I discovered its not as easy as it seems and uses a lot of power to do so.

westbranch · April 2012

Re: Burping the battery

Blackcherry04 wrote: »

.

After reading this ( http://photovoltaics.sandia.gov/docs/PDF/caploss.pdf )

URP....I believe...

Blackcherry, any idea of the age of that publication?

BB. · April 2012

Re: Burping the battery

The PDF was created in August of 1999, the latest referenced document was from 1998--So, I think that is a pretty accurate answer.

-Bill

waynefromnscanada · April 2012

Re: Burping the battery

So, after checking the link provided by Westbranch, I realize my L-16's have always been well charged, and this may well be why they've survived 10 years and are still going strong without being "burped".

"To date, laboratory and system testing
consistently identified the incomplete recharge of PV batteries as the predominant
cause of premature capacity loss resulting in a lower than rated cycle-life. Incomplete
battery recharge introduces battery degradation mechanisms such as electrolyte
stratification, gas bubble entrapment, excessive sulfation, and degradation of the
positive active mass."

Blackcherry04 · April 2012

Re: Burping the battery

waynefromnscanada wrote: »

So, after checking the link provided by Westbranch, I realize my L-16's have always been well charged, and this may well be why they've survived 10 years and are still going strong without being "burped".

"To date, laboratory and system testing
consistently identified the incomplete recharge of PV batteries as the predominant
cause of premature capacity loss resulting in a lower than rated cycle-life. Incomplete
battery recharge introduces battery degradation mechanisms such as electrolyte
stratification, gas bubble entrapment, excessive sulfation, and degradation of the
positive active mass."

Sounds like your doing something right. I have a customer that Sings to his, Please, Please, Oh'Please keep on going a just a little bit longer........lol

Cariboocoot · April 2012

Re: Burping the battery

waynefromnscanada wrote: »

"To date, laboratory and system testing
consistently identified the incomplete recharge of PV batteries as the predominant
cause of premature capacity loss resulting in a lower than rated cycle-life. Incomplete
battery recharge introduces battery degradation mechanisms such as electrolyte
stratification, gas bubble entrapment, excessive sulfation, and degradation of the
positive active mass."

We should sticky that; it'd save having to retype the info over and over again as we do now. :roll:

john p · April 2012

Re: Burping the battery

When you think about it lead acid batteries are really not suitable in most cases for solar recharging.
In many cases the user draws down the battteries overnight to say 60%. Because of economic considerations the solar panels are only adequate to recharge them in about 4 hrs. OK no problem you say. But there is . 4 hrs for most people is about the max available solar isolation time. Therefor no time or very little time available for equalizing. In reality most of the time they will not even reach their fully recharged voltage and when this happens over a long period sulphation starts .
Now lets look at say forklift batteries used in a forklift.. Average daytime use max 9hrs that gives the battery charger 15 hrs to really charge up the batteries. with zero interuptions.. ie no overcast days no clouds or rain.
Same goes for any batteries used in installations charged by mains battery chargers.
When all things are taken into consideration its amazing lead acid batteries last even reasonably long times.
The ones that do are ones charged by an "ovesized" panel array. or receive suplimentary mains battery charging sometimes.

westbranch · April 2012

Re: Burping the battery

Hope this is right, as I have only read the article once, but I took from it that a low DoD is also a factor in that longevity.

ie the lower the DoD, and the longer the charging time, especially float, the longer the life span
PLUS the 1.3 RATIO of Array Ahr to Load Ahr

For VRLA bulk charging ASAP at the upper limits of the recommended range and "longer finish-charge time'' is also a factor

Cariboocoot · April 2012

Re: Burping the battery

westbranch wrote: »

Hope this is right, as I have only read the article once, but I took form it that a low DoD is also a factor in that longevity.

ie the lower the DoD, and the longer the charging time, especially float, the longer the life span
PLUS the 1.3 RATIO of Array Ahr to Load Ahr

For VRLA bulk charging ASAP at the upper limits of the recommended range and "longer finish-charge time'' is also a factor

Right you are; less discharge + proper charging = longest life.

Hence the endless repetition of "you need more panels for that amount of battery."

The short-cut rules-of-thumb may skip over the explanations of "why" but in the end they get you a system that works.

Eric L · April 2012

Re: Burping the battery

Because of economic considerations the solar panels are only adequate to recharge them in about 4 hrs. OK no problem you say. But there is . 4 hrs for most people is about the max available solar isolation time. Therefor no time or very little time available for equalizing. In reality most of the time they will not even reach their fully recharged voltage and when this happens over a long period sulphation starts .

I agree, although it may be the case that the economics of the situation are changing for the better in this respect as panel prices fall and battery prices rise.

I've been experimenting with a very high panel:battery ratio in my current system; enough for a greater than C/5 charge rate from the panels (based on 20 hr. ah battery rating), although I've set up the system so that the batteries never see that much current.

So far, it's working nicely, although the real question will be whether it's economically better than the more traditional 'C/10' panel:battery charging ratio.

I hope to report some of my findings from my little experiment after it has run a while longer.

BB. · April 2012

Re: Burping the battery

And why, we (I) try to account for all of the major losses... A full off grid system from solar array > charge controller > battery bank > AC inverter > AC load has around around 52% operating efficiency (can be better, can be worst--depends on your exact installation, usage and needs)--And 1/0.52=1.92:1 Panel AH to Load AH ratio...

Daisy Chaining losses and power conversions is ugly. No way around that. A 95% efficient inverter or charge controller sounds great--Multiply everything together--not so great.

-Bill

Eric L · April 2012

Re: Burping the battery

Question: what are panel amp-hours? Is it something like average watt-hours per day/battery system voltage?

westbranch · April 2012

Re: Burping the battery

I would like to think it is Amps out from CC to battery less line loss X # hrs /day (AVG) for planning purposes.

Cariboocoot · April 2012

Re: Burping the battery

Comparison of power produced by panels to power used by loads expressed as Amp hours across a consistent Voltage.

BB. · April 2012

Re: Burping the battery

Amp*Hours is sort of Watt*Hours without the voltage:

Amp*Hours * Volts = Watt*Hours

So, from a very "simple" point of view, once you define the voltage--they are identical.

In reality--It is much more complex. The relationship between Voltage, Current, and Power is highly dependent on the power sources and loads...

For example, we are all familiar with:

Voltage = Current * Resistance

If the Current goes up, the voltage goes up... etc. Change it around, a heater may look like:

Current = Voltage / Resistance

If you have "high line voltage" at your home, your heater will use more current--Not really a loss because:

Power = Voltage * Current

So, using more current, you get more heat (and pay the utility more money). All washes out in the end.

Similar with filament light bulbs... The less voltage you present, the power/light they produce... However, even a simple lamp gets complicated. Resistance is a function of temperature, the cooler the filament, the lower the resistance, hence the more current will pass through. In the old'en days, a filament lamp was actually used as a cheap and dirty constant current source.

And you have constant power devices... Electric induction motors are, more or less constant power devices. You want 1 HP from your well pump if it is running at 212 VAC or 264 VAC (low/high line). That means that the lower the voltage, the more current the motor will draw to keep P=V*I a constant power (more complex than that, Power Factor changes too--so total current may not flow the above example).

With DC to AC inverters--They are also constant power devices... If you have a 1,200 watt load, the current required from a 12 volt battery bank may be:

1,200 watts * 1/0.85 inverter eff * 1/14.8 volts battery charging = 95.4 amps (high batt voltage)
1,200 watts * 1/0.85 inverter eff * 1/10.5 volts battery near dead = 134.5 amps (low batt voltage)

Many times, people use units that "make things easy"... For example, Lead Acid Batteries tend to be around 80-90% efficient when you measure Watt*Hours Out divided by Watt*hours In...

However, Lead Acid Batteries are almost 100% efficient when measuring Amp*Hours Out divided by Amp*Hours In... So working with Amp*Hours and battery banks tends to be a natural--you don't need to address fudge factors for losses.

With solar panels, they are "current sources" (more or less). They, roughly, output Imp from Vmp to roughly zero volts... So, your 10 amp 17.5 volt panel will output ~10 amps at zero volts too (shorted output). So, you can certainly talk about Amp*Hours very nicely with solar panels... However, we use "power" and "energy" (Watts and Watt*Hours). The Power equation bites us here:

Power = Volts * Amps
Power = 17.5 volts * 10 amps = 175 watts from a solar panel into "matched" load
Power = 14.5 volts * 10 amps = 145 watts from a solar panel into "near full" battery using PWM controller (MPPT will be different)
Power = 11.5 volts * 10 amps = 115 watts from a solar panel into "near empty" battery using PWM controller (MPPT will be different)
Power = 0.0 volts * 10 amps = 0 watts from solar panel into a dead short

So--I tend to like to work with Power (Watts) and Energy (Watt*Hours) so that we don't make a mistake and assume that "voltage" does not matter...

For example, we charge a battery at ~14.5 volts but discharging under load is around 12.5 volts--The power/energy losses would be:

12.5 volts / 14.5 volts = 86% efficiency

There are, of course, other losses (voltage drop on wiring, controller losses, float voltage/equalization current which does not "recharge" a battery, etc.)... But between uses of rules of thumb (77% efficiency, 85% efficiency, 52% efficiency) in the "right place" (designing panels, designing battery bank capacity, overall end to end efficiency, etc.) and plugging in numbers (14.5 volts charging, 12 or 12.5 volts discharging) allow me to get reasonably close and conservative numbers that are easy to use when doing a paper design. Once you have a paper design, you can go through and use some "real numbers" (inverter tare losses, winter vs summer solar panel temperature, battery losses for flooded cell vs AGM) to get "more accurate" numbers...

However, in real life--we are probably only looking at getting answers to within 10%, at best, of real numbers... Variability in sun, how "you" use your system, measurement errors, etc. all serve to muddy the numbers and why we still recommend that you only use 66% to 75% or so of your system's estimated power output daily from your solar array. Allows for clouds, occasional loads (washer, vacuum, etc.) and you have a genset to keep the batteries from being damaged by being drawn down too deeply (and shutting down optional loads, etc.).

Sorry for the long post--But even "simple" questions can have very complex answers. Hope it helps rather than confuses more...

-Bill

Eric L · April 2012

Re: Burping the battery

Thanks guys. I'll infer from your answers that there's not a fixed convention for panel amp hours (in the sense that it's not just stipulated to be, say, watt-hours/nominal battery voltage). Rather it's a 'floating' value as each input variable of resistance, battery voltage, etc. change.

Burping the battery

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