Quote:
Originally Posted by Keith Seymore
I used regular 1.5V AA battery to replace those in my Sun tach transmitter, after I had run them down in a flashlight for a bit. They worked for probably 15 years or so; I just replaced them last weekend.
Those are my batteries (and my photo) in the top pic, btw. I still have them and use them for display purposes.
Starting with post #6: http://67-72chevytrucks.com/vboard/s...d.php?t=392461
K |
Keith......you are correct......thanks for the post
Mercury batteries (two 1.35 volt cells in series = 2 .7 v) were used in the earlier Sun tachs. The mercury style batteries provided excellent constant voltage regulation over their operating life span. As a result the mercury batteries will maintain 1.35v potential until approx. 5% of their life, where the voltage will quickly decline. AA Alkaline battery technology doesn’t have the same constant voltage regulation curve. The batteries have an initial open circuit voltage of 1.5v and initially drop approx. 6.6% - 13.3% (1.4v-1.3v) then continue to decrease over their life span.
Decreasing an alkaline battery from the initial 1.5v to 1.35v before using them in the Sun tach will work however due to their poor constant voltage regulation the Sun tach’s needle deflection, representing the RPM, will not be as accurate as if it had been used with an original mercury type battery.
If accuracy is not an issue then problem solved. If accuracy is an issue then it can be corrected by the use of a simple voltage regulator circuit; 9 volt battery, resistor and a 2.7v Zener diode.
The mercury battery was Sun part number 1766-7 and was made by Mallory, commercial part number RM12R and the Eveready part number was N0. E12N.
I am restoring to period correctness and therefore prefer not to modify but use the original technology of the day. I reached out to the company that Lee mentioned above. Hopefully they have access to the Duracell RM12R battery.