[RE-wrenches] cycling flooded batteries is not necessary

[Howie Michaelson]

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 redwoodalliance.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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