Hildebran R/C Aero-Modelers

Volume 4, Issue 3

AMA Charter # 3470

April 2003

Club Officers:

President: Ron Bachman
VP: Jim Holder
Sec/Treasurer: Brett Springall

Web Site http://www.hrcam.com/
Appointed Officers:
Field Marshall: Jessie Wylie
Safety Officers: Elbert Cook

Intro Pilots:
Ivan Vrooman
Elbert Cook


From The Oval Office

Our membership is currently quite low compared to previous years. For this reason we have decided not to have our family fun fly in May. We will wait until later in the year, giving the opportunity for any new members we gain during the summer to take part.

Thanks, see you at the next meeting.

Ron Bachman

President

 

 

 

 

Next Meeting:
Sunday, May, 11, 2003 at 3:00pm
Location: Flying Field


Please record your work credits on the list in the club house. Next years dues will be calculated based on these recorded work credits.


Notes from the last club meeting

It was decided to postpone the family fun fly until later in the year. This was done because we are currently at a low level of membership.

A work evening was planned for May 1, to put up some new safety fence, and install a wire gate across the driveway.


UP COMING EVENTS

5/14 - 5/17, Joe Nall Giant Scale, Greenville, SC

5/31 - 6/1, Carolina Classic Control Line, Huntersville

6/7 - 6/8, Giant Scale Fly In, Statesville, NC

6/15, Fathers Day Fly In, King, NC

6/21, Frenchbroad Fly In, Asheville, NC

6/21, Balsa Buzzards Big Bird, Duncan, NC

7/11 - 7/13, Alabama Big Birds, Huntsville, AL

 

 

 

 

Portions of this newsletter are reprinted from the AMA national newsletter Academy of Model Aeronautics.

TIP TIME

CARE AND FEED OF SEALED LEAD ACID BATTERIES
By RED SCHOLEFIELD

Lead acid gel cells should be charged with a constant potential charger specifically designed for these batteries. These chargers can be referred to as Constant Voltage Chargers (CVC). You can charge them with a constant current charger, but you must terminate the charge when the voltage reaches 14.7 volts. You should not exceed the C/10 charge rate. If you have a 7 Ah battery in your field box, the maximum constant current charge rate should not exceed 700 mA. It takes about 14 hours to charge from a fully discharged state (voltage less than 12 volts.).

A CVC is exactly what the name implies. It is clamped at a certain voltage and puts out all the current it can until the battery reaches the clamp voltage, usually around 14.5 volts. Then, the current drops off to maintain this voltage. A CVC is characterized as one having a current capable of supplying a fixed voltage to whatever load is applied. A constant current charge on the other hand will provide whatever voltage is necessary to force a fixed value of current through a load. Constant current charges have a much higher internal resistance than the load so that any variation on the load will not change the current being supplied. Constant voltage charges have a very low resistance as compared to the load and will supply whatever current necessary to maintain a given voltage at the load.

Many inexpensive chargers used for sealed lead batteries are what are called taper chargers; these are set up so the voltage tapers off as the full-charge voltage is reached. True constant potential chargers can be quite expensive so a compromise is made in the design to control costs.

We have used the term sealed lead battery in this discussion. These batteries are not truly sealed as cylindrical Nickel Cadmium (Ni-Cd) batteries are. They have a gelled electrolyte system where there is a modest recombination of the oxygen in overcharge in some designs. All require venting of the oxygen and hydrogen byproducts of charging and discharging. You should never totally seal these in a field box where these gasses can accumulate. Mixtures of oxygen and hydrogen can cause a spectacular "event" if a spark is provided (from an electric fuel pump motor).

How much charge is there in the battery? Unlike Ni-Cds, you can read the remaining capacity quite easily with a voltmeter. After the battery has been on rest for a few hours, read the voltage (no load). A reading of 12 volts is essentially fully discharged while 13 is fully charged. This is a fairly linear relationship so a reading of 12.4 volts means you have 40% of the capacity remaining.

Never leave a lead acid battery in the discharged condition or sulfation will result. The sulfuric acid in the electrolyte reacts with the sponge lead active material and forms lead sulfate. It is a poor conductor. This, coupled with the H20 left after you take all the S out of H2S04, is also a poor conductor, so trying to charge requires a lot of voltage to push the current through to convert the active material back to the charged state. Sometimes they just cannot be brought back from the sulfated state.

The good news is that sealed lead batteries retain their charge much longer than Ni-Cd; at room temperature, it's well over a year. All you have to do is make an occasional open voltage check to see if you need to charge it.

from Hear Ye!
Valley Forge Signal Seekers 
Marilyn Ayres, editor
Glen Mills PA