Rolls / Surrette Battery Charging [RE-wrenches]

Fri Apr 27 14:05:04 PDT 2007

Hello Wrenches,

Several weeks ago there was a discussion thread involving our (Rolls / Surrette) batteries and some charging difficulties that were being / had been experienced.  To all of you that were kind enough to discuss these issues with me, I would like to extend our appreciation for your time, input and transfer of knowledge.  These discussion have resulted in the development of a revised Charging Bulletin of which I have attached version 1.

A brief background;

When we entered the RE / Solar market with some vigour in the mid-90's, the resounding requirements put forth by the industry were;

i) Capacity
ii) Cycle-life / durability

In fairness, these were really a combined request with the feeling that this was "needed" to survive in the RE / Solar market.  From this, we tweaked and developed our products over the past decade.  However, as we have seen, another major component is the "ability" to charge the battery (bank), which is compromised in order to attain capacity & cycle-life.   As systems have grown dramatically, undercharging has become a significant hindrance to battery performance.  Essentially, there are only a few ways to over come this hurdle;

i) Increase the charge capacity (not practical)
ii) Increase the charge voltage (described in the attached Bulletin)
iii) Lower the internal resistance (we are working on it!).

Earlier charge voltage settings / recommendations were a product of past practice and, as we have found, erred on the side of caution.  We feel the attached will be of benefit to those who are experiencing any difficulty in attaining 100% SOC with out product and I hope this creates some dialogue.

Regards,

Jamie   

James Surrette

Surrette Battery Co. Ltd
1 Station Rd.
Springhill, NS, CAN
B0M 1X0

Direct: 902.597.4027
Fax: 902.597.8447

____________________________________________________________________________________

ROLLS BATTERYENGINEERING
Salem, Massachusetts, USA     Ph 1-800-681-9914   (902) 597 * 3767 Fax (902) 597-8447
Mail:  P.O. Box 2020, Springhill, Nova Scotia, Canada B0M 1X0

Bulletin 614, PM, Charging and Discharging Batteries;
Renewable Energy Applications

Introduction

Charging recommendations for flooded lead acid batteries have been based on past practices and often presented as general statements.  In actuality, charging practices should be based on system applications and availability of charging sources.  Rolls / Surrette Batteries are designed with thick plates, high density active material; for cycling service and to minimize the impact of heavy charging.  These two design parameters, coupled with other design features, require more lead per unit which increases battery life in high cycle applications.  The disadvantage of this design is marginally lower charge acceptance. This bulletin addresses this and clearly states that Rolls/ Surrette batteries should be charged at higher voltage settings depending on RE System design and are designed for cycling use.

Charging Parameters

Bulk/ absorption set points have been derived from the automotive industry and are for two reasons only.  1) The batteries do not get excessively hot and 2) the batteries do not use excessive amounts of water.  These charging regimes also assume that excess power is available from a constantly running internal combustion engine.  Because of these reasons the charging voltages can be increased as long as temperature does not get excessive and batteries do not consume large amounts of water causing undue amounts of maintenance.

Automotive batteries are 12V and in general the batteries cells are in a 2 x 3 layout and reside in a high temperature environment.  Rolls/ Surrette batteries generally have cell layouts of simply single cells, 1 x 2 or 1 x 3 layouts.  Heat transfer (away from the plates into the acid and out of the battery case) is much better than in standard layouts or with steel trays.  This means more aggressive charge regimes (higher bulk absorption settings) can be used.  

Consideration of application of use is important and will affect how the charge regime that should be used.  In most alternative energy applications, maximum charge application is only available for 6-8 hrs.  Meaning, the majority of charging has to be completed during this time frame to avoid reliance on an auxiliary generator further reduction in the battery’s state of charge (SOC).  Consideration has to be given also to whether the system is grid tied for back up power or stand alone.

Off Grid Systems

Off grid systems generally consist of solar PV panels and a battery bank.  With these components the following voltage settings are recommended:

Charge Stage
Volts per Cell (VPC)
12V
24V
48V

Min * Mean * Max
Min * Mean * Max
Min * Mean * Max
Min * Mean * Max

Absorption / Bulk
2.40 * 2.45 - 2.50
14.4 * 14.7 * 15.0
28.8 * 29.4 - 30
57.6 * 58.8 - 60

Equalization
2.58 - 2.63 - 2.67
15.0 * 15.8 - 16.0
30.8 * 31.6 * 32.0
61.6 * 63.2 *64.0

Float
2.20-2.22 -2.23
13.2 * 13.3 - 13.4
26.4 * 26.6 * 26.8
52.8 * 53.2 - 53.5

When a voltage setting is chosen the length of time the bank is being held at constant voltage is to be considered.  If only a short absorption time is possible then the voltages settings should be at the higher levels.  If a long absorption time is possible then the voltages should be lowered.

For example with a large PV array, small battery bank and minimal loads the lower settings should be chosen if it is apparent the battery bank can be held at the bulk/ absorption voltage for a minimum of fours hours.  When the battery bank is put through the first 10 normal cycles the specific gravity (SG) of a pilot cell should check and recorded and if the bank is receiving full charge each cycle the SG should be slightly increasing as the battery gasses and loses water due to overcharge.  Please refer to bulletin 609, Voltages, Specific Gravity and State of Charge for further info on determining cycle depth and full charge.

If the battery bank is large in relation to the PV array (C/20 min) and loads are large then the batteries will require a higher voltage setting.  Also the battery should be cycled deeply (i.e. to 50%) before starting an auxiliary charge source such as a generator.  Once every three months the bank should be discharged to the low voltage set point before starting the generator.  This is usually dependent on the cut-off of the inverter which is usually 11 volts on a 12V system.  The batteries are designed to be cycled and a deeper discharge forces electrolyte deeper into the active plate material and helps open up fresh reaction sites.  With large battery to PV systems, it is imperative that the battery bank is returned to 100% SOC once every 30 days.  Full charge can be determined by charge acceptance, which is ~2% of capacity at 100% SOC.

OpportunityEqualization

Systems with smaller PV arrays in respect to the battery bank should be also equalized more often.  Bulletin 605 describes the differences between “preventive” and “Corrective” equalization.  “Corrective” equalization should be avoided as it is bothersome, time consuming and can increase generator run time.  It is recommended to “opportunity equalize” the batteries when it is known sun will be available at a convenient time.  The auxiliary charging source (generator) should be started in the morning, with minimal loads running and bank brought to the bulk/ absorption voltage.  The bank should then be put on an equalization charge and brought up to a specific gravity of 1.265.  This should be continued until the SG is at 1.265 or the electrolyte temperature reached 115ºF in temperate climes.  (125ºF in hot ambient conditions).

Grid tied systems-Back up battery banks

Normally these systems see very little cycle service and, at most, are cycled once a month.  If cycled, the banks should be charge for 3 hrs at the mean voltage setting.  After charging, the water level should be checked and a specific gravity reading taken.  If the specific gravities are not 1.265 the bank should be further charged.

Commissioning a Battery Bank

When a bank is first put into service the electrolyte levels and specific gravities should be check and recorded.  As a battery is charged, water is electrolyzed into hydrogen and oxygen gas.  Original electrolyte levels should be noted and replacement water should be added back to this level.

The battery bank should be placed on a bulk / absorption charge and voltage settings should be set at the maximum level of the above table.  This voltage should be held for 6 hours and final current, if monitored, should be 2% of the 20 hour capacity rating.  If not the bulk / absorption charge should be continued.

Technical Assistance

Surrette Battery has built our business on providing direct and timely customer support / assistance.  Please call our technical Assistance line if there are any questions or concerns;

T: 1 800 681 9914

--
[Non-text portions of this message have been removed]

- - - -
To send a message: RE-wrenches at topica.com

Archive of previous messages: http://lists.topica.com/lists/RE-wrenches/read

List rules & how to change your email address: www.mrsharkey.com/wrenches/etiquette.php

Check out participant bios: www.mrsharkey.com/wrenches/

Hosted by Home Power magazine

Moderator: michael.welch at homepower.com
--^----------------------------------------------------------------
This email was sent to: michael.welch at homepower.com

EASY UNSUBSCRIBE click here: http://topica.com/u/?bz8Qcs.bz9JC9.bWljaGFl
Or send an email to: RE-wrenches-unsubscribe at topica.com

For Topica's complete suite of email marketing solutions visit:
http://www.topica.com/?p=TEXFOOTER
--^----------------------------------------------------------------