Voltage indicator fits into cigarette lighter socket and utilizes light emitting and Zener diodes to display three levels of battery voltage. Indicator is superior to typical conventional electrical system indicators in that it gives a positive discrete indication of battery voltage. It is simple, inexpensive, and rugged

Miller, R. L.

English

NASA Technical Reports Server

L3	
R1, R 2, R3=47Q 
R4 = 39 Q 
= 9. 8 volt zener diode 
3	 Z2 = 11. 1 volt zener diode 
Z3 = 11. 5 volt zener diode 
L 1 - L3 = light emitting diodes
December 1973	 B73-10249 
• 
NASA TECH BRIEF
	
11 11 
Lewis Research Center 	
_4V 
NASA Tech Briefs announce now technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Reliable Low-Cost Battery Voltage Indicator 
for Light Aircraft and Automobiles 
Figure 1 
A new solid-state battery voltage indicator which fits 
into a conventional cigarette lighter socket utilizes light 
emitting and zener diodes to display three levels of 
battery voltage. Three zener-light emitting diodes are 
arranged so that two lights indicate normal voltage, three 
lights indicate overvoltage, and one light indicates low 
voltage (Figure 1). An audible alarm can easily be added 
also to signal low voltage (Figure 2). 
This indicator is particularly useful for small aircraft. 
The nominal operating voltage for most small aircraft is 
typically 13.8 volts and must be maintained within ±0.5 
volts. Prolonged over- or undervoltage is detrimental and
iscan be destructive to the electrical system, causing failure
of navigational and communications equipment. Conven-
tional charge-discharge ammeters indicate current flow 
and certain types of electrical system malfunction but do 
not show battery voltage level. Particularly, they do not 
indicate whether a battery has been restored to normal 
voltage after a heavy discharge as in starting the engine. 
Conventional discharge warning lights have the same 
shortcomings. Conventional voltmeters are usually not 
sensitive enough to indicate the relatively small voltage 
changes which can cause electrical system failure. Ex-
panded-range voltmeters resolve the problem but are 
somewhat delicate in construction and take up consider-
able space on the instrument panels. The lack of a positive 
(continued overleaf) 
This document was prepared under the sponsorship of the National 	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States 	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States	 will be free from privately owned rights. 
https://ntrs.nasa.gov/search.jsp?R=19730000249 2020-03-17T07:14:45+00:00Z
Figure 2
.. 
L3
R5 = 4.7 K 
1 1 = 2N3904 
D 1 = silicon diode 
D 2 = germanium diode 
indication of battery voltage level can result in unnoticed 
malfunctions of electrical system components, sudden and 
unexpected depletion of the battery, and failure of 
electrical power causing an emergency situation. 
As shown schematically in Figure 1, the light emitting 
diodes L 1 , L2 , and L 3 turn on, respectively, ati 1.2, 13.3, 
and 14.5 volts. The "turn on" voltage is determined by 
the drop across the zener diodes Z 1 , Z2 and Z 3 and the 
common resistor R4 . Resistors R 1 , R2 and R 3 limit the 
current through each light emitting diode. R 4 is used to 
maintain relatively constant brightness from each LED as 
it turns on, as the voltage ranges from the lowest "turn 
on" voltage up to 16 volts. 
This indicator is superior to typical conventional 
electrical system indicators in that it gives a positive 
discrete indication of battery voltage. It is simple, 
inexpensive, and rugged. The components are housed in a 
plug which fits into a conventional cigarette lighter 
socket; thus it is portable, requires no installation, and 
does not take up instrument panel space. Pilots, auto-
mobile drivers, and other vehicle or equipment operators 
can carry this battery voltage indicator with them for use 
on whichever machine they are operating. Of course, a 
similar unit could be more permanently wired into an 
instrument panel.
	 -
Note: 
No additional documentation is available. Specific 
questions, however, may be directed to: 
Technology Utilization Officer 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Reference: B73-10249 
Patent Status: 
Inquiries concerning rights for the commercial use of 
this invention should be addressed to: 
NASA Patent Counsel 
Mail Stop 500.113 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135
Source: Robert L. Miller
Lewis Research Center 
(LEW-1 2020)
. 
. 
B73 . 10249	 Category 01


Reliable low-cost battery voltage indicator for light aircraft and automobiles

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