Deciding to go cordless for your vacuum cleaner or portable vacuum is a big decision, or at least it used to be a big decision.  In today’s market many manufacturers are offering models without cords (non-tethered).   It’s not limited to just vacuum cleaners.  It seems as though everybody wants to sell cordless (battery powered) home equipment.

Of course, all home equipment that runs on battery power is actually still tethered to a wall outlet.  The only difference is one of convenience of not having a cord always attached to your home equipment during operation.  A battery allows for operation of equipment with great mobility.  A user is suddenly free to trip on everything they used to trip over, just not a power cord.

The hard truth is that having a battery powered vacuum has simply changed a user’s focus from a power cord to a battery.  Now a user must be concerned with run times, battery replacement, hazardous waste disposal, and not seating equipment correctly in the charger cradle correctly and having too little charge to vacuum, or no charge at all.

For vacuum cleaning machines there are a number of variables that will affect the acceptance of battery driven machines over tethered machines.  The most obvious consideration is that of our old friend ‘power’.  Will a battery driven machine have sufficient ‘power’ to be useful, or will it be marginally useful and ultimately more trouble than it is worth?

To best understand the new realities of cordless vacuums and portable vacuums, a little time needs to be spent in understanding what makes a machine portable and cordless.  There’s more to this than one first expects.

Perhaps the greatest challenge facing all manufacturers is that of ‘run time’.  Run time is the amount of time a vacuum can maintain a sufficient airflow so as to remove floor contaminants.  The takeaway key is maintaining sufficient airflow.  A battery that is running down is unable to provide sufficient volts and current to keep the vacuum power plant running at speed.

Everyone is familiar with having to replace batteries in flashlights.  A similar problem exists with cordless machines and their batteries.  Although replacing a machine’s battery is not always needed, the principal is the same of having to stop and recharge a battery when it runs low.

Manufacturers have addressed this problem on two fronts.  The first is to find a battery that has as much capacity as possible without it being too awkward and heavy.  The second is finding a motor that uses less power to operate and still provides the same airflow for a length of time that is acceptable.

A battery can hold a charge, and pump ions and electrons through it’s chemistry for only so long.  When the battery has run low and its internal chemical reactions are exhausted, the battery is labelled ‘dead’.

A dead battery, while still able to pump some electrons through an external path, can only do so at a decreasing rate.  The quantity and availability of electrons essentially govern it’s useful life.  Without the internal movement of ions, the battery pump simply won’t work and the motor on the vacuum will not turn.

A battery, in the field of electronics, is considered to be a pump.   When not in use (no external electrical path between the anode and cathode ends of the battery), the internal chemistry remains quiet and waiting for a path.  Once a path is established the chemical reaction starts in earnest to move ions between the cathode and anode ends of the battery.

The traditional alkaline battery is a disposable battery that has a limited amount of chemical reaction time where it will convert a chemical reaction into electrical energy.  It does this by using two metals: manganese dioxide as the positive (cathode) electrode, and an internal zinc cylinder as the negative (anode) electrode.  The battery is constructed of a metallic conductive shell which is coated internally with a manganese and coal dust mixture.  Then a separator paper soaked in potassium hydroxide or sodium hydroxide is inserted followed by powdered zinc which will become the anode part of the battery.  A brass pin is inserted into the zinc and presented at the open end of the battery cylinder as a raised bump.  It is electrically isolated from the metallic casing of the battery so as not to have a runaway discharge.

The alkaline battery gets its’ name from the alkalinity of the hydroxide compound used in the paper separator between the zinc and manganese.

A charged battery has great potential for providing its’ electrons, but without an electrical path it remains just a potential energy source.  Once an electrical path is provided, the battery will pump its’ electrons through the electrical path to the positive pole of the battery.  It will continue to provide the negative electrons until one of two things happen.  The electrical path is interrupted so that negative electrons have no where to go, or the chemistry inside the battery can no longer internally move ions.

All batteries are comprised of individual cells wherein the chemical reactions take place to generate electrical energy.  A cell has a specific voltage that can be generated, and a specific amount of current.  Through the combination of cells either in parallel or in series, changes can be made in the overall voltage and current.  Most battery packs used in  household appliances are comprised of multiple cells connected in parallel and in series surrounded by a plastic case.

A lithium-based battery works similarly, but has the distinct advantage of being rechargeable as opposed to alkaline batteries that are single use only.

A lithium-based battery works similarly, but has the distinct advantage of being rechargeable as opposed to alkaline batteries that are single use only.

When attaching a battery to an electric motor, the motor will spin at a certain number of revolutions per minute determined by the voltage.  If a load is attached to the motor (resistance to the spinning action), the motor will need more current to overcome the resistance while maintaining the same revolutions per minute.  Resistance is sometimes described as the grip of a dog owner’s hand on a leash.  Less grip (low resistance) and the leash extends, more grip (higher resistance) and the leash doesn’t extend as easily.

A battery needs to be able to provide sufficient voltage so as to spin a motor, and needs to have enough current to overcome resistance in the airway, maintaining sufficient airflow to move floor contaminants.

A battery has only so many ions available to move internally from one pole to another.  After the ions are used up, the battery can no longer pump electrons out and it is dead.  The flow of ions is also affected by chemical compounds that build up on the plates as a part of normal battery usage.

To measure this phenomenon engineers came up with a measure of a battery’s ability to maintain a voltage at a specified resistance level.  The measure is the Ampere named after Andre-Marie Ampere (1775-1836).

The measurement describes the force that can be applied to an object from a battery or any electrical source for one second of time.  The force is measured in Coulombs.  The values are:

1 Ampere = 1 coulomb/second  or 1 coulomb – 1 ampere x 1 second

The number of electrons described by 1 coulomb is –1.602176565 x 10 to the -19th power.  That’s a whole lot of electrons!

The value presented on most battery labels is listed as Amp Hours (ah).  It is a measure of how long a battery takes to provide a power of  one ampere in one hour.  For ease of presentation, it is sometimes listed as Mill-Amp-Hours (Mah).  The ah value can be use as a comparative element to gauge one battery’s ability against another.  i.e. a 20 ah battery is roughly twice the capacity of a 10 ah battery.

The amp-hour rating is descriptive of the amount of energy available for use by a motor.  Motors also have an ah rating that describes their use of power under no resistance (baseline current draw).  This value on the motor should be considerably less than the battery ah rating.

Batteries are heat sensitive.  The chemistry inside a battery is sensitive to elevated temperatures and will deteriorate over time.  The plates inside a battery, when exposed to excessive heat, will deform and change the electrical characteristics of the battery.  The voltage may change, the amp hour rating may change, or the plates may bend and touch each other causing an internal short circuit and discharging the battery at an excessive rate causing the battery to heat up and potentially explode.

[ENGINEERING NOTE ==>]  Ever wonder why hand-held equipment has a warning about the battery heating up, or why there are internal thermal fuses protecting the battery from overheating?  Those protections are there to keep the battery from overheating and starting a fire, or worse.

Best to keep batteries out of the car in the summer and away from wood burning stoves or other heat sources.  When ordering new batteries steer clear of batteries coming from areas where the climate is hot.

Many people assume that batteries with a full charge will remain at a full charge until they are needed.  This is simply not the case.  As many can attest to, batteries stored on the shelf will lose their charge over time.  Just think of the batteries you have in a box in the storage room.

The process is titled ‘Self-Discharge’ and it affects all batteries, some more than others.  For Li-ion batteries, the battery will self-discharge about 5% in the first 24 hrs and then lose 1-2% per month.  If there is a cell protection circuit in the battery case, that will add an additional 3% per month.

As the ambient temperature increases, so does the self-discharge rate.  For every 18 degrees F or 10 degrees C the self-discharge rate will double. At the rates listed above the discharge rate would be approximately 7% per month. for every 18 deg F increase.

[ENGINEERING NOTE ==>]  A fully charged Li-ion battery is more prone to failure than one that is partially charged.  A Li-ion battery should never be discharged below 2.5 v per cell.

Li-ion batteries  have a protection circuit that disengages the battery from normal charging if the cell voltage drops below 2.5 volts.  Most chargers will recognize this and refuse to charge a cell below that voltage.

The reason why has to do with copper dendrites growing in the cell if the voltage drops below 2.5 volts.  The dendrites begin to form if the Li-ion battery is allowed to sit at the lower voltage for longer than a week.  The conductive copper dendrites contribute to elevated self-discharge, which could present safety concerns having to do with sudden excessive discharge rates, heating, and possible explosion.

Li-ion batteries are not forever.  An unwanted deposition of lithium on the anode electrode in the battery results from normal charge and discharge cycles.  This has the effect of the battery losing capacity over time due to depletion of lithium in the battery electrolyte.  The more a Li-ion battery is charge/discharged the shorter it’s lifespan.

So, how does one keep batteries at their peak charge and ready for action.  The most effective way is to place the batteries on a trickle charge.  Most manufacturers have a power supply that performs a trickle charge.  Simply put, a trickle charge is when the charger senses that the battery has dropped in voltage and the charger applies just a trickle of power to the battery to bring the battery back up to the desired voltage level.

Even if you don’t use your cordless vacuum the batteries are constantly being recharged by the power supply.

Even with a trickle charge batteries eventually will refuse to accept a charge.  Batteries can also fully discharge when in use and a fully discharged battery and dynamically reverse it’s polarity so that negative becomes positive and positive becomes negative.  When this happens the battery cannot be recharged and must be disposed of.

Hmmm. just how does one dispose of the new Lithium Ion batteries…

Unfortunately this type of battery cannot be thrown away in the trash.  There are far too many hazards to dumping old batteries into the trash bin.  A Lithium battery is full of hazardous chemicals like Cobalt, manganese, and other metals.  Lithium ion batteries also contain lithium salts and the ever-present plastics that house the batteries and provide internal structure.  They also contain arsenic, cadmium, lead, and copper.

A whopping 95% of all lithium batteries somehow find their way to the landfills.  Of course we won’t see the effects of this hazardous waste for a decade or so, but it is coming our way to a water well near you.  Also of concern are airborne particulates ranging from 2.5 micrometer to 10 micrometer.  These particles come from batteries that are incinerated or are ground up under the tracks of a bulldozer at the landfill.  Hydroflouric acid is a natural by-product of lithium Ion battery decay.  A surprising amount of hydroflouric acid is released in a gaseous state at the rate of up to 200MG per rated watt of power.

So, be certain to send your batteries to your local recycle center that is certified to handle Lithium based chemistry batteries.

A typical run time for a battery powered vacuum is going to be about 12-18 minutes.  After this time the battery will need to be recharged before its next use.  In a home this is not too much of an inconvenience, but if there is a significant cleaning job to be done this will definitely hamper your style.  For commercial applications a 12-18 minute window simply is insufficient to get a job completed.

There are some strategies to cope with short run times.  Using multiple batteries is always an option, but this can become expensive and dragging along a set of batteries around a building can become a burden after a while.

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