Stationary Batteries: Why they fail and what can be done to prolong battery life

Transcription

1 Stationary Batteries: Why they fail and what can be done to prolong battery life J. Allen Byrne Tech. Support & Services Mgr. Interstate PowerCare A Division of Interstate Batteries April 13, 2016 Schaumburg, IL.

2 Stationary Batteries Almost all Power Engineers consider the Battery to be the weakest link of any battery backed power system, including a UPS. The humble Battery is also the Rodney Dangerfield of the industry it gets no respect! My goal is to ensure that you recognize this Achilles heel and give it some respect.

3 Stationary Batteries Just a reminder Lead Is Not Dead!

4 Stationary Batteries Where Losing Power Isn't An Option

5 Why do batteries fail? Manufacturing defects. Natural Aging. Bad installation. Lack of maintenance. Incorrect charging. Battery Environment Temperature Humidity Dirt, etc.

6 Why do batteries fail? The lead-acid battery is a sacrificial design with unavoidable degradation over time. The lead-calcium positive plates structure will corrode and grow over time even under ideal conditions. This causes internal problems. The VRLA battery is also susceptible to loss of electrolyte over time because of charging abuse leading to loss of capacity and eventual failure because of dry out.

7 How can battery problems be eliminated or delayed? Nothing much can be done about natural aging but it can be slowed down by: Maintaining the battery properly. Charging the battery properly. Keeping an eye on the battery charger(s) Operating at the correct temperature or use temperature compensation. Monitoring the battery. Testing the battery. Replacing bad units before they affect the others.

8 Why Maintenance? Proper maintenance will: Prolong the life of a battery. Ensure that it is capable of satisfying its design requirements. Serve as a valuable aid in determining potential failure and predict the need for battery replacement. Provide for peace of mind.

9 Lack of maintenance will: X Lead to premature battery failure. X Allow for unpredicted failure. X Endanger the load and personnel. X May lead to catastrophic results. 85% of UPS & Power System failures are due to battery failures or the improper management of them. Source. B-Tech, Inc.

10 Two Main Maintenance Standards 1. For VLA (Flooded) Batteries IEEE Recommended Practice for Maintenance, Testing, and Replacement of Vented Lead-Acid (VLA) Batteries for Stationary Applications. 2. For VRLA (Sealed / Absorbed-Electrolyte / Gelled) Batteries. IEEE Recommended Practice for Maintenance, Testing, and Replacement of Valve-Regulated Lead- Acid (VRLA) Batteries for Stationary Applications. What about PRC-005-?

11 Charge the battery properly Correct Charging Voltage It is extremely important that a battery be float charged at the correct voltage. The correct float charging voltage depends upon the specific gravity (SG) of the electrolyte, battery type and chemistry and the open-circuit voltage of the battery cell. A battery cell must be charged slightly above the Open Circuit Voltage (OCV) in order to overcome and compensate for natural battery self-discharge. Rule of thumb: Specific gravity = Open Circuit Voltage (OCV) OCV V = approximate float voltage.

12 Consequences of overcharging. Overcharging will: Accelerate aging by: Causing excessive polarization of the positive plate = accelerated corrosion. Generating more free oxygen = accelerated corrosion. Promote excessive gassing, causing: Shedding of active material. Increased water consumption. Increase heat generation.

13 Overcharging Consequence of overcharging: Accelerates positive plate growth (See upcoming slides) Causes dry-out It is thought that 20% dry-out reduces battery capacity by 50% Increased heat can lead to thermal runaway

14 Natural Aging and Positive Plate Growth New Plate Aged Plate NAES Plant Managers Conference 2015

15 Look at the battery plates they are a great indicator of battery health. For VLA, check the plates, separators and electrolyte of the battery cell. The positive plates should be a dark chocolate brown or blackish. The negative plates should be light grey. The electrolyte should be clear and some minor bubbles may be present. If all the above is not the case, there is probably a problem with the battery

16 Look at the battery plates they are a great indicator of battery health. More severe growth and cracking Plate Cracks. One needs to look closely to spot these

17 Can you believe qualified personnel per IEEE 1657 looked at this battery cell for over a year and did nothing?

18 Undercharging Undercharging means that the battery does not get fully charged. Causes plate sulfation. Build-up of lead-sulfate crystals on plates. Loss of capacity which could be permanent. Plate deformation. Equalize or boost charging may fully or partially recover plates. Severe undercharging will kill a battery.

19 Has the appearance of glitter or crystals on the edges of the positive plates. Sulfation It can be normal on negative plates. The presence of this white lead sulfate can occur when the battery has been left in a discharged state for some time. It also occurs if the battery is being undercharged. Once the plates have been sulfated the performance of the battery is impaired and it may not be possible to restore the battery to full state of health. Undercharging means that the battery does not get fully charged..

20 Charger An unsuitable charger (one that is poorly regulated and has a noisy output) may mean: High ripple output current which causes: Increased positive plate corrosion. Increased temperature. Shorter cycle life? Poor regulation of the charger output can result in undercharging or overcharging.

21 Comply with manufacturers charging requirements. Note the recommended float charging voltage on label Also other important details. Even similar batteries can have different charging voltages

22 Temperature Lead-acid batteries are temperature sensitive. Particularly lead-calcium VRLA s In the USA, capacity and performance are base-lined at 77 F (25 C) E.g. 100 Ah at 77 F to 1.75 Volts-per-Cell (VPC) Above this temperature the cell will have increased capacity but life is reduced. Below this temperature, the cell will have reduced capacity but life is extended.

23 Temperature How is the battery life affected by temperature? For every F above 77 F, the battery life is halved. E.g., A 10 year design life VRLA operating at 94 F would only have a life of 5 years. More realistically, the practical life of 5 years would be reduced to 2.5 years. Below 77 F, the battery will potentially be undercharged.

24 Temperature Compensation It is common with modern battery charging equipment for temperature compensated charging to be employed. This is where the battery temperature is monitored and a compensation circuit lowers or raises the float voltage as necessary. The compensation voltage varies slightly depending on the manufacturer and battery type but the rule of thumb is 1.67 mv per degree Fahrenheit.

25 Temperature Compensation Sample Calculation Say a battery is operating at 62 F 77 F - 62 F = 15 F 15 x 1.67 mv F = mv ( V) Say the recommended float V at 77 F is 2.25 VPC 2.25 V V = VPC Therefore, the temperature compensated float voltage would be VPC If this was a 60 cell, 120 V battery then the correct float voltage would be 60 x V = 136.5V and not 135V

26 A Little Bit About Ohmic Measurement Ohmic Measurements. IEEE Std defines Internal Ohmic Measurement as: A measurement of the electronic and ionic conduction path within a cell or unit, using terms defining conditions commonly known as impedance, conductance, or resistance. Three Basic Types of Battery Internal Ohmic Values. Resistance. Conductance. Impedance. All are IEEE and NERC approved. None are 100% accurate. NAES Plant Managers Conference 2015

27 Ohmic Measurements and Load Testing. Load Testing. Ohmic measurement, although fairly accurate (90% plus) cannot determine with full certainty a battery s state of health. The only really accurate method to establish this is a full load test using either the battery s actual load or a load bank. A load test is a battery discharge test that may be required to: Determine if the battery will meet the battery duty cycle. Determine if there is problem with a battery. Confirm that other indicators are correct in indicating that there is a problem with a battery. The IEEE does make recommendations but the requirement for a full load test is often a judgment call by the battery owner and may depend upon the criticality of the battery.

28 Record Keeping Record Keeping is recommended and is a NERC requirement. It is recommended that forms be prepared to record all data in an orderly fashion and in such a way that comparison with past data is convenient. A meaningful comparison will require that all data be converted to a standard base. Information, readings and data should be recorded at the time of installation and then with each inspection and test. Data records should also contain reports on corrective actions. Correct interpretation of data obtained from inspection, corrective actions, and tests are important to the operation and life of the batteries.

29 Summary Stationary batteries of the lead acid type can offer a good, cost effective and reliable option for providing back-up power. How they perform is mainly up to you!

30 Stationary Batteries Thank You For Your Attention QUESTIONS???

31 J. Allen Byrne Technical Support & Services Manager Interstate PowerCare A Division of Interstate Batteries Tel allen.byrne@ibsa.com