Lead Purity: The Mother of all VRLA Problems

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Transcript Lead Purity: The Mother of all VRLA Problems

Lead Purity: The Mother of all VRLA Problems

Presentation Outline

Why Lead Purity is Important

• In the early 1980’s a European battery company made the 1 st 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.

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 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?

Lead Purity and Battery Life

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

Negative Plate Voltage Positive Plate Voltage

• 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

Voltage All on Positive Plate

Positive Plate Voltage

• 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.

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.

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.

Measuring Lead Purity

Mass Spectrometry Used 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.

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!

Culpin’s Clever Contraption

• Measures self discharge based on gassing rate.

What is Good About It?

• It is better than mass spectrometry because it measures the combined effect all of the impurities.

What we found

2000 1800 1600 1400 1200 1000 800 600 400 200 0 0

5 10 15 20 Elapsed Time (Days) 25 5 30 35

Lessons from the Test

• Worst battery produced 10 times more gas than best battery. • All batteries claimed to use “pure” lead.

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

Solutions for Managing Lead Purity

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.

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.

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.

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.

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.

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.

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. 150 Catalyst Cells 125 100 75 50 25 0 Standard Cells 3 year life 5 year life 10 year 20 year life © Copyright 2010 by Philadelphia Scientific LLC

Conclusion

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.

Lead Purity: The Mother of all VRLA Problems

Transcript Lead Purity: The Mother of all VRLA Problems