© copyright 2010 by philadelphia scientific llc lead purity: the mother of all vrla problems harold...
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© Copyright 2010 by Philadelphia Scientific LLC
Lead Purity: The Mother of all VRLA Problems
Harold VanasseDan JonesWill Jones
© Copyright 2010 by Philadelphia Scientific LLC
Presentation Outline
• Lead purity makes a difference
• Lead purity and battery life
• Measuring lead purity
• Solutions for managing lead purity
• Conclusion
© Copyright 2010 by Philadelphia Scientific LLC
Why Lead Purity is Important
• In the early 1980’s a European battery company made the 1st VRLA starter battery for cars.
• Imagine – no more watering of car batteries!– This was a wildly anticipated product.
• The first European built prototypes worked great. – Tests were conducted in the hot southern USA.
• USA factory was built to produce these batteries. – The same European specification and tooling was
used.
© Copyright 2010 by Philadelphia Scientific LLC
What Happened?
• Catastrophe!
• Many batteries were produced and they failed all over the country.
• The financial losses were in the millions!
• The factory was closed.
• The resulting investigation could not determine the cause of the failure.
© Copyright 2010 by Philadelphia Scientific LLC
The Rest of the Story
• 20 years later the cause was determined. • It all had to do with the purity of the lead. • The prototype batteries used lead from Europe. • The production batteries used lead from US.• Both Euro and US lead was in spec.
– But not in the same place within the spec.
• But how could this happen when spectrometry was used to measure the lead purity?– Maybe they are not the right tool to use?
© Copyright 2010 by Philadelphia Scientific LLC
Time for Some Science
• There is a direct and scientific link between battery life and lead purity.
• There is a delicate voltage balance within a VRLA cell. – Voltage is shared between positive and negative plates.
• Too many impurities in negative active material throw off the balance leading to: – Excessive gassing– Increased current draw– Short life
© Copyright 2010 by Philadelphia Scientific LLC
Voltage Evenly Split
• This is the ideal – it is what we want!
• Reactions are in balance.• Unfortunately it is not
what is typical for VRLA.
Negative Plate Voltage
Positive Plate Voltage
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Voltage All on Positive Plate
• Typical VRLA problem• Negative plate discharges
while on float charge.• Leads to:
– Increased gassing– Capacity loss– Increased float current & cell
temperature – Cell dryout– Corrosion of positive plate – Early failure.
Negative Plate Voltage
Positive Plate Voltage
© Copyright 2010 by Philadelphia Scientific LLC
VRLA on Float Charge
• Oxygen is produced on positive plate and recombined with hydrogen on negative plate. – This pulls down voltage of negative plate
• Impurities cause greater gassing on negative plate.– Lead + Acid + Impurities = Hydrogen Gas
• If the rate of gassing is too high the see saw shifts off balance leading to cell failure.– Negative plate self discharges.
© Copyright 2010 by Philadelphia Scientific LLC
Key Points to Remember
• There are multiple reactions to keep in balance within VRLA cells.
• Impurities in the lead drive the self discharge of the negative active material.
• If there was a way to prevent the gas from depolarizing the negative plate then lead purity would not matter so much.
© Copyright 2010 by Philadelphia Scientific LLC
Mass SpectrometryUsed to measure purity
• A computerized detector counts where ions are in the e/m spectrum. – Location on the
spectrum identifies the element.
– Count of ions determines purity.
© Copyright 2010 by Philadelphia Scientific LLC
Mass Spectrometry
• Spectrometry is used to measure the amount of individual impurities.
• Each individual impurity has a specification that limits maximum amount allowed.
• Sum total of impurities or net effect is not addressed.
• Not all impurities are created equal!
© Copyright 2010 by Philadelphia Scientific LLC
Culpin’s Clever Contraption
• Measures self discharge based on gassing rate.– More impurities = more gas
• Charge a single negative plate.
• Put it under acid in a graduated beaker.
• Collect evolved gas.
© Copyright 2010 by Philadelphia Scientific LLC
What is Good About It?
• It is better than mass spectrometry because it measures the combined effect all of the impurities.
• It is the net effect of all the impurities that we are ultimately concerned about.
• We ran this test for VRLA cells from multiple manufactures.
© Copyright 2010 by Philadelphia Scientific LLC
What we found
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0 5 10 15 20 25 30 35
Elapsed Time (Days)
Hy
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Ah
at
90
°F (
32
°C)
FA
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AS
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5
© Copyright 2010 by Philadelphia Scientific LLC
Lessons from the Test
• Worst battery produced 10 times more gas than best battery.
• All batteries claimed to use “pure” lead.
• There is large variability in the purity of the lead used.
• Disparities in test are what we see in real world performance of VRLA cells.
© Copyright 2010 by Philadelphia Scientific LLC
The Bottom Line
• Controlling total amount of impurities is the key to VRLA performance.
• A mass spectrometer may not give the full picture for measuring VRLA lead purity.
• Lead purity is not being managed adequately for VRLA batteries.
© Copyright 2010 by Philadelphia Scientific LLC
What Can Be Done?
• Three options exist: – Use very pure primary lead.– Use super refined secondary lead.– Use a catalyst
• None of these solutions are new.
© Copyright 2010 by Philadelphia Scientific LLC
History
• Mid 1990’s: VRLA problems abound.
• Will Jones and Dr. Dave Feder repeatedly show that VRLA batteries won’t deliver design life.
• Various solutions presented to correct the problems.
• Root cause always the same: Lead purity not exact enough for VRLA.
© Copyright 2010 by Philadelphia Scientific LLC
Use Very Pure Primary Lead
• Primary lead comes directly from mines.
• Worldwide demand is increasing.
• It is getting harder to obtain.
• It is becoming more expensive. – The greater the purity
the greater the price.
• May not be sustainable.
© Copyright 2010 by Philadelphia Scientific LLC
Use Super Refined Secondary Lead
• Secondary lead has been used before and then recycled.
• Refining to a higher purity standard is a must for VRLA.
• The very things that we need to add to other battery types are poisons to VRLA. – E.g. Silver from automotive
batteries.
© Copyright 2010 by Philadelphia Scientific LLC
Use Super Refined Secondary Lead
• Impurities from lead recycling stream are expensive to remove.– The greater the purity the greater the price.
• More exact purity standards and testing are needed to ensure a practical purity level is constantly maintained.
• Concern: How do you know which battery is made with good lead and which manufacturer cuts cost and quality?
© Copyright 2010 by Philadelphia Scientific LLC
Use a Catalyst
• A catalyst will recombine hydrogen & oxygen to make water in the cell.
• It prevents gas from depolarizing the negative plate so that it does not self discharge.
• Cell stays in balance – See saw is in the good middle position.
• Compensates for fluctuations and variations in lead purity.
• May be the most cost effective.
© Copyright 2010 by Philadelphia Scientific LLC
Will’s Experiments
• Early experimentation showed that VRLA cells gassed too much.
• Oxygen and Hydrogen leaving cell had to be reduced to obtain long life.
• A catalyst reduced gassing to good levels.
• Proof that this problem could be solved.
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ay/1
00 A
.h.
20 year life
10 year
5 year life
3 year life
Catalyst Cells Standard Cells
© Copyright 2010 by Philadelphia Scientific LLC
The Mother of all Problems
• Managing lead purity is the main problem with VRLA cells today.
• Most of the other problems have already been solved.
• Until this problem is solved VRLA cells will not live up to their design life.
• The sad part is that the information is not new. • It is all about lead purity!
© Copyright 2010 by Philadelphia Scientific LLC
Which is the best solution?
• The solutions are: – Primary lead– Super refined secondary lead– Catalyst
• All three solutions will increase cost of the battery but the longer life will justify it.
• Battery buyers/users must specify what they want! – Battery companies build what users specify.
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