[time-nuts] OT Gel Cell question

Brooke Clarke brooke at pacific.net
Mon Jul 28 15:45:45 EDT 2014

Hi Ed:

I don't know.  When I got the unit the batteries had been removed.  The power supply consists of two 723 based voltage 
regulator curcuits the first to drop the line voltage to about 20 V (float charging 3 each 6 V Gell Cells) and the 
second 723 circuit to take in battery voltage and supply a lower voltage to run the unit.

The key problem was the short distance between the batteries and the hot oven.  Maybe the oven was also heating the 
batteries. Something to keep in mind today.

Have Fun,

Brooke Clarke

Ed Palmer wrote:
> As I understand it, the only time that any sealed lead acid battery will vent is in the case of gross overcharging.  
> The battery is designed so that normal charge rates and correct float voltage will result in recombination of any 
> hydrogen and oxygen produced. Was there a fault in the charging circuit or perhaps, the charging circuit didn't have 
> proper temperature compensation of the charge voltage?
> Ed
> On 7/28/2014 10:56 AM, Brooke Clarke wrote:
>> Hi:
>> Using lead acid batteries and a precision frequency standard is not a good thing if they are too close together.
>> A number of decades ago (before the Time Nuts or the internet) I was able to purchase a rack mount Gibbs 5 MHz double 
>> oven frequency standard that used a very nice Bliley glass tube crystal because it was not as precise as is was 
>> supposed to be. It used GelCell backup batteries that were physically in the same rack chassis as the oven.  The 
>> fumes from the batteries when charging etched some traces off the PCB inside the oven defeating the temperature 
>> control but leaving the oscillator. It took a long time to reverse engineer and repair it.  I've added a photo of the 
>> cord wood construction of the cylindrical oscillator.  The core of the cylinder holds the glass bottle crystal and 
>> the glass piston coarse tuning capacitor, surrounded by the first heater, circuitry for the oscillator and dual 
>> temperature control circuits on ring shaped boards.  These fit inside a cylindrical cavity which is the outer oven.  
>> I've added a photo of the inner assembly at:
>> http://prc68.com/I/office_equip.html
>> Have Fun,
>> Brooke Clarke
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