Archives and Special Collections at the University of Minnesota

Today, I had the chance of a very short tour of Archives and Special Collections that are managed, in part, by the University of Minnesota’s Libraries. Housed under the Elmer L. Andersen Library, a set of football-field-lengthclimate controlled caverns house the materials for the Charles Babbage Institute, YMCA Archives, and one of the largest Sherlock Holmes collections, among many others.  While wandering around with the small group, I took a few pictures.

Cold Weather, The Coop and Heat Transfer


_DSC6863-2A few weeks ago, we bought a new waterer for the coop.  There was nothing wrong with the current waterer other than being an energy hog.  Throughout December, we struggled with keeping the coop’s battery charged enough power the waterer.  The waterer’s 100 watt heating element was just too much. Think of it like this: the waterer’s draw (outflow) on the battery is greater than the solar panel’s ability to recharge (inflow) the battery.

\(Outflow > Inflow\)

_DSC6854-2The new waterer, branded as Cozy Hen Waterer, is from Neora Inventors, LLC. From a cost perspective, it was expensive.  Around $70 for the waterer, a hanging chain, and a heater.  The waterer consists of two buckets – one ¾ gallon bucket nested within a larger pail. Inside the larger pail, there is a layer of thin insulation.  The outer pail is only used as a convenient way to capsulate the inner pail in insulation.  The water, contained in the inner pail, is able to get out to the chickens byway of a chicken nipple (pictured to the right).  The other interesting bit of engineering is the encasement of the chicken nipple in an aluminum pipe.  The pipe extends into the water pail by several inches.  This is subsequently encased in a bit of insulation with an outer shell made of a PVC plumbing part.  Finally, inside the water pail, there is a 15 watt aquarium heater.  It will keep the water at around 77°F.

The aluminum pipe is clever because of what it allows: heat transfer.  Although not entirely analogous (it is a pipe and not a rod), you could get a sense of the heat transfer by using a partial differential equation (Partial Differential Equations for Scientists and Engineers is also a good place to look).  There are actually several energy-flows going on in these coop-systems if you think about it.

The heat is transferred from near the center of the water pail down to the chicken nipple byway of the aluminum pipe.  This allows for the nipple to stay mostly ice-free on those -20°F days.

A bit of welding - the new waterer needed a bracket to hang on.
A bit of welding – the new waterer needed a bracket to hang on; rebar scraps that I had laying around.

If you recall from a previous post, the first-replacement waterer had a thermostatic switch that kept the water at 35°F.  In my mind, that seems like a valid temperature for water – it would minimize the energy consumption.  The new waterer with the aquarium heater and its 77°F temperature seems, on the surface, like it will use too much energy.

But, there are a few things that make the new waterer-system much easier on the consumption of electricity.  First, the larger waterer has 1.⅔ times the surface area as that of the new, insulated waterer.  More surface area results in faster transfer of energy from the warm water to the cold air.  Second, and this is likely the most important factor, the new waterer is insulated.  Top, bottom and sides – it is all insulated.  The one direct exception is the chicken nipple area, but that has the aluminum pipe to assist with heat loss (with the assumption that the heat transfer from the water + pipe is greater than the heat transfer from the end of the nipple to the air).

The more I have thought about the larger waterer and how it appears to be inefficient, the more I kept thinking of its design in comparison to the new waterer.  The larger waterer has the heating element on the bottom – the three gallons of water sit on top of the element.  This means that only one side of the element in contact with a surface that has water touching it.  That other side is hanging out in the air; sometimes, well-below-zero air.  What is the likelihood that the thermostatic switch actually switches off for any significant length of time?

A better design would be have the heating element have more contact surface with the water.  Perhaps, instead of being encased in a disc in the base of the waterer, the element would be a more rod-shaped protrusion from the base into the center of the water  reservoir.  Secondly, insulate, insulate, insulate.  The choice of insulation material is possibly debatable – the new waterer uses foil covered bubble insulation – this might be sufficient; it would certainly be better than nothing.

Solar Coop – Update II


_DSC6362 - 2015-01-25 at 16-14-33 - Version 2Since writing the first update on the solar panels on the chicken coop, we had quite the cold snap.  Along with the persistent cold, there was persistent cloud cover and strong winds.  The combination of cold weather meant the battery for the coop had diminished capacity and the cloud cover meant that there would not be enough solar irradiation to fill that reduced capacity.

Each night, I would disconnect the battery from the system and lug into the garage; connecting it to a battery charger for the night.  We also brought the chicken’s waterer into the house to prevent the need in the morning of having to thaw the water. In addition to the routine changes, I removed two things from the electrical-mix: the electric timer and the ammeter. With the battery’s stored energy being consumed so quickly and the water and battery being brought in at night, it did not seem like the timer was needed at all. The ammeter was removed because it stopped working in the sub-zero cold.  Subsequent tests, while it has been warmer outside, show that the meter still works; it just does not like the cold.

We have since made it through that cold spell, and have been in a pleasant middle ground of nice amounts of sun, above freezing day-time temperatures – several days in a row, and light amounts of wind.

With the warmer stint of weather, the battery has been under lighter duty. Even when the solar charge controller has been indicating that the battery is not strong enough to power the inverter, the next day’s sun will be more than enough to give the battery a good charge.

Being a curious, amateur scientist, I wanted to know a bit more about why a lead-acid battery appears to be quite poor at being able to provide energy when the ambient temperature is very low.  This inability to provide energy is quite noticeable and prevalent in colder regions during the winter.  For those who are familiar with starting a car while in the depths of a cold winter – think of how the car’s starter seems to struggle to turn the engine over.  It’s a battle between cold lubricants with a higher than normal viscosity and a lead acid starter battery with diminished capacity.  But, why does cold cause this diminished capacity.

With my day-job being at a university, and I am surrounded by academics and researchers, my first thought was to look into published research on batteries or modeling batteries.

The first paper I found was A mathematical model for lead-acid batteries co-authored by Dr. Ziyad Salameh – Dept. of Electrical Engineering, UMass Lowell, Margaret A. Casacca (student), and William A. Lynch (student).  The paper was published in the IEEE Transactions on Energy Conversion, Vol. 7, No.I, March 1992.

Aside from equations and a mention of a BASIC program that was developed (but this program is nowhere to be found in the paper), the main take aways from the paper are list of five factors that effect a battery’s ability to store energy; for the most part, the list of things is obvious.  (1) State of charge, (2) battery storage capacity, (3) rate of discharge, (4) environment temperature, and (5) shelf-life or age.

(This list is originally from the Complete Battery Book.)

We can say that our battery is fully charged (state of charge is 100% at the on set), has a capacity of 110 amp-hours, the waterer has a draw of at most 10 amps (this is likely not constant as the waterer will turn on when the water is below 35 degrees, and turn off when it reaches a temperature above this), the shelf-life or age is basically “brand new”.  Temperature is likely the deciding factor.

Looking at how temperature effects capacity, you can see that as the temperature drops, the capacity drops, as well.

Capacity vs Temperature

Assuming this graph is true (there is no documentation or available analysis), at our coldest, the battery is likely to be running at a bit over 60% capacity; meaning, we’ll only get about 66ah from it.  The inverter will shut off when the voltage drops below about 12.10V; according to another battery university article, this likely means the battery has about 50% capacity remaining.  This could roughly be translated into a capacity of 33ah at our coldest, and about 55ah at optimal temperature (which we won’t have until sometime in late May).

Now that I have some numbers that better explain the observation of why didn’t the battery last more than 8 hours on the coldest day, I still want to know why does this happen.  Why does ambient cold have such an effect on lead-acid batteries?

The short answer is internal resistance.  To understand this, you first need to know a bit about how lead-acid batteries work.

A course offered at the University of Colorado Boulder‘s Electrical, Computer and Energy Engineering department has a great set of lecture slides (or here) explaining how lead-acid batteries work.

The gist of how lead-acid batteries work are electrons drifting or flowing from the negative terminal – most often made of lead (\(\ce{Pb}\)) – to the positive terminal – most often made of lead dioxide (\(\ce{PbO2}\)).  The two terminals are submerged in an electrolyte solution.  This is usually in the form of sulfuric acid (\(\ce{H2SO4}\), where, in solution, it takes the form of aqueous ions \(\ce{{H^{+}}+{SO4^{-2}}}\)).  As you draw electricity from the battery via the positive terminal, electrons flow from the negative terminal to the positive terminal.  How easily or difficult the electrons can move from negative to positive terminals in the internal resistance.

I think of what happens with the electrolyte solution and effect of cold temperatures on it is sort of like what happens to honey when it is chilled.  It is not quite analogous but I think it gets the point across.  If little droplets of honey are running down a piece of glass and you suddenly cool the glass, the honey will begin to run much slower.

Similarly, as the electrolyte solution cools, the ability for electrons to drift efficiently to the positive terminal decreases.  The decrease in electron flow results in less power to be consumed – in our case, by the inverter and waterer.

So, what can be done be to keep batteries from losing their capacity in the cold?  Some of the documentation that I read suggested gently warming the battery to keep it from getting too cold.  This might be possible if we added another electricity generator – like a wind turbine.  We would have to build a better storage place for the battery, too.  We can’t really put the battery into the coop (where it is noticeably warmer because of sheltering from the wind as well as the use of deep-litter) because lead-acid batteries generally need venting (there is a small amount of oxygen and hydrogen released from batteries).  In addition to the idea of keeping the batteries slightly warmer (which, I will admit, I’m likely not going to do), adding capacity seems like a more viable option.  This is done by simply adding additional batteries in parallel.  With the idea of adding in a wind turbine, I have already been thinking of adding additional batteries.

To wrap things up, I just hope that the recent temperature bounce-near-and-around-freezing continues.  The battery likes not being choked by the cold; nice amount of sun – the adequate sun light we have been receiving has had two benefits: the battery is able to be recharged successfully, and, equally important, the chickens have begun laying eggs once again.

 

For a better look at the specifics of the chemical reactions that occur within a lead-acid battery, check out this page.