[RE-wrenches] cycling flooded batteries is not necessary

John DeBoever jdeboever at trojanbattery.com
Tue Feb 21 12:42:05 PST 2012


Wrenches,

Howie,



Too much equalize charge accelerate the ageing of flooded lead acid battery. Avoiding equalize charge certainly ruin the life of flooded lead acid battery. Two correct statements.

Ideally, with perfectly balanced cells battery + that has no acid stratification, then you do not need to do an equalization charge. The case you described of not full recharge actually shows that you will end up by having unequalled cells and possibly stratification over time (application specifics, temperature specific). Indeed your described partial SOC operation will result into a combination of sulfatation, stratification and cell S.G. not equaled.  Fortunately, in the case of flooded lead acid, equalization is possible to fix this challenge.  It is not obvious to foresee / predict the true dynamics of an application, considering the actual loads and its variations, the energy source and its variations, and the maintenance and its variations, assuming an adequate initial system design and adequate system install & commissioning.  Any attempt to understand how the flooded lead acid battery is actually used over time with regular monitoring of the S.G. is a positive move. S.G. is a great reference point, provided temperature adjustment of the reading is applied. 15 to 30 points delta is a range to consider @ 77F, as  a trigger for equalization.

 For memo, recommended few steps re S.G. monitoring:

o   If the batteries are discharged, only add water if the plates are exposed. Add just enough water to cover the plates, then charge the batteries. Once fully charged, add water to the proper level indicated above.

o   Recharge the battery fully per battery manufacturer requirements (up to float charge mode, typically for 2 hours for the float charge)

o   Refill the water up to indicated levels by the battery manufacturer (otherwise the S.G. might indicate higher level due to lack of enough water)

o   Let the battery standing still  for 1-2 hours (no charge, no loads), then measure the S.G. and record the temperature. Adjust the S.G. reading using the temp de-rate factor.

Equalizing is required if the specific gravity value of any individual cell varies 30 points (delta = 0.030).

When taking specific gravity readings, corrections must be made for variations in temperature of the electrolyte. For each 3°F (1.67°C) in temperature of the electrolyte above 80°F (27°C) add one point (.001) in specific gravity to the observed hydrometer readings; and for each 3°F (1.67°C) in temperature below 80°F (27°C) subtract one point (.001) in specific gravity from the observed hydrometer reading.
Examples: Reading Hydrometer Cell Corrected to and Reading Temperature Correction 80°F (27°C)
1.280 sp. gr 70°F (20°C) -.003 (3 points)= 1.277 sp. gr.
1.280 sp. gr. 86°F (30°C) +.002 (2 points)= 1.282 sp. gr.
                                                       1.280 sp. gr. 95°F (35°C) +.005 (5 points0= 1.285 sp. gr.

o   The Equalization charge will balance the cells and also stir the electrolyte, which ultimately is important for proper readings.  Depending application specifics, equalization typically shall happen every 30 charge cycles, so typically every 4 weeks. Larger batteries might require equalization, depending the application specifics, every 2 weeks.

o   Once the S.G. have been correctly set up and the water levels are adequate, subsequent measurement of the S.G. with temp adjustment calcs will provide a fairly accurate SOC level reading.

Note: Bad (dead) cell: if the S.G. are < 0.050 (50 points) difference, there is not yet a certain indication of a “possible” bad cell. The SG variation of 0.050, in any one or more individual cells particularly within a bank that has been equalized is an indication of a dead or troubled cell.



I hope this helps,



John

-----Original Message-----
From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Howie Michaelson
Sent: Tuesday, February 21, 2012 1:56 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] cycling flooded batteries is not necessary



Thanks John for your continued helpful explanations.



With respect to equalizing in a cycling application (e.g. off-grid), if the battery cells are getting a regular bulk/absord charge which brings them back to full at least every 3-7 days, and they are being kept or brought up to a high state of charge (maybe 90%) at least every day or 2 in between the full charge cycle, and the SG is kept under a 30 point spread (I've always heard 15 points or less), is there a need for an equalize charge?  My understanding is that the equalize charge addresses the two issues you reference: stratification and unequal SOC across the bank.  If the bank is staying even and there is regular cycling to prevent stratification, I've tended to think that an equalizing charge is not indicated.  Am I missing something here?



Howie

--

Howie Michaelson

NABCEP Certified Solar PV Installer™



Catamount Solar, LLC

Renewable Energy Systems Sales and Service VT Solar Electric & Hot Water Incentive Partner http://www.CatamountSolar.com

802-272-0004





On Tue, February 21, 2012 1:29 pm, John DeBoever wrote:

> Wrenches,

>

> Sorry for late answer as I was/am busy in meetings.

>

> I will recap as follows:

>

> In a nut shell, Todd made a great point: equalizing and cycling are

> two different necessary steps in a full charge of a flooded lead acid battery.

> “Floating applications” means exactly that: they stay in floating

> mode 99% of the time. The float charge address the self-discharge of

> the battery. If the battery is seeing additional external causes for

> discharge, then it need to go through the re-charge process, which

> includes, depending the DOD, going through bulk charge, absorption

> charge and floating charge. On flooded lead acid technology, we have

> the luxury to do an equalization charge in lieu of the float charge,

> approximately after 30 cycles (typical 4 weeks, sometime earlier,

> sometime later, depending application specifics, size of battery, and, age of battery).

> For memo: equalization charge address two issues – equalizing the

> cells so you do not face more than 30 points between the cells

> (resulting on difference charge acceptance), and, mitigate the acid

> stratification in the electrolyte (thus improving the charge-discharge

> performance and reducing corrosion).

>

> Having said that, a  lead acid battery designed for true deep cycle is

> best used for cyclic applications that actually cycle the battery due

> to the application. That battery design will keep the battery in great

> condition with numerous cycles, provided you actually fully recharge

> the battery and address equalization periodically after completing

> absorption, instead of the floating mode. That does not mean that you

> need to exercise unnecessary cycle the battery for increasing life.

> Another distinction is that true deep cycle lead acid batteries

> require 50 to 100 cycles when new to reach full capacity.  Maybe that

> is where some confusion built up regarding “cycling a battery is good”.

>

> A “UPS” battery  technology is designed specifically for 99%

> floating applications. They provide power as a “parachute” if &

> only when there is a power outage. Any exercise cycling on this

> battery design will ruin the battery. Some applications are necessary

> full “floating

> applications”: the “99% of the time” is actually much less than

> that ( power outage, loads, system  losses, shadow loads, …) ,

> resulting into a larger DOD. The floating charge is therefore not

> sufficient to overcome the DOD. Now we are talking requirement of

> recharging the battery (thus actually cycling it).

> Note: On VRLA, equalization is no go, although a boost charge can be

> considered on AGM (application specifics, too long to describe here on

> the blog).

>

> The issue is to pick the right battery design for the application, and

> then make sure the battery is full charged at each cycle.

>

> Hope this helps, not confusing you more. There are so many

> perspectives to see from and one is easy confused…

>

> John

>

> From: re-wrenches-bounces at lists.re-wrenches.org

> [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of

> toddcory at finestplanet.com

> Sent: Tuesday, February 21, 2012 12:45 PM

> To: RE-wrenches

> Subject: Re: [RE-wrenches] cycling flooded batteries is not necessary

>

>

> the two battery manufacturers say that cycling of floated batteries is

> 100% unnecessary.

>

>

>

> equalizing is still important to prevent stratification of the

> electrolyte... but equalizing and cycling are different things.

>

>

>

> todd

>

>

>

>

>

>

>

> On Tuesday, February 21, 2012 6:33am, "Drake"

> <drake.chamberlin at redwoodalliance.org<mailto:drake.chamberlin at redwooda

> lliance.org>>

> said:

> In my experience, at least my batteries need to be cycled.  Here is

> the data.

>

> AC coupled backup system.  The batteries are usually only supplying

> the inverter controls, with the pair of Outback 3524 inverters

> connected but turned off at the Mate.  80 watts of pv is used for a battery maintainer.

> The 2160 W of PV usually goes straight to the grid, and is switched

> over when needed.

>

> The batteries will remain essentially dormant with self discharge and

> control power somewhat balanced by a trickle charge coming from the

> small sub array.  The batteries hold around 25.2 volts over night.

> When they drop to 25 or 24.8, I charge and often equalize them.

>

> Just equalizing will not make them hold at 25.2 V again.  Even back to

> back equalization will not keep the battery V from dropping to 25

> almost immediately.  If I switch to off grid mode for a night to cycle

> the batteries and then bulk charge them,  they will hold the 25.2 V again.

>

> I think cycling really is needed to mix up the acid.

>

> Drake

>

>

>

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