Ripple detecting polarity indicator for battery charger

A ripple current component detecting circuitry embodied in the terminal of a cable connecting a battery charger with a lead acid storage battery to improve safety of use by preventing the indication of a correct polarity of connection where a charger is energized before connection is made with the battery when in fact such an indication may be incorrect, the prevention of such an indication being accomplished by the utilization of the AC ripple component in the charger output. The circuitry detects the ripple and with its use overrides what would otherwise be given as a misleading indication of polarity.

BACKGROUND OF THE INVENTION 
1. Field of Invention 
This invention relates to the construction of a safety circuit in the 
terminal of a battery charger output cable. 
2. Description of the Prior Art 
It is known in the prior art of cable terminals which embody circuits which 
indicate a correct polarity in connecting a battery charger with a lead 
acid storage battery. However, it is not well known in the case of 
plugging a cable into a battery charger which is energized to avoid being 
misled by an erroneous indication of correct polarity. In connecting the 
cable with a battery, if the polarity in fact is correct, a small spark 
will occur. If in fact the polarity is incorrect, a very large spark will 
occur. 
It is therefore desirable to have no indication of a correct polarity when 
the charger is already energized. The operator should be alerted to remove 
the cables from the charger before making any connections to the battery. 
SUMMARY OF THE INVENTION 
It is an object of this invention to reduce the likelihood of connecting by 
cable a battery charger to a lead acid storage battery using incorrect 
polarity. 
It is also an object of this invention to reduce the likelihood of 
connecting an energized battery charger to a storage battery. 
It is more specifically an object of this invention to provide in a cable 
connecting a battery charger to a battery, a terminal including circuitry 
which when the cable is connected to an energized charger and the charger 
output is sufficient to indicate correct polarity with itself but not 
necessarily a correct polarity with the battery, the circuitry in the 
terminal detects the AC ripple component in the output from the charger, 
and the ripple component in the charger output is used to trigger a 
circuit which causes to be overridden what might otherwise be a misleading 
indication of a correct polarity and causes the operator to note that it 
is not safe to connect the charger cable to the battery. 
These and other objects and advantages of the invention will be set forth 
in the following description made in connection with the accompanying 
drawings in which like reference characters refer to similar parts 
throughout the several views.

DESCRIPTION OF A PREFERRED EMBODIMENT 
Throughout the description herein, conventional current flow positive to 
negative will be presumed. Diode symbols shall point in the direction of 
conventional flow, as is also the case with the LEDs (light emitting 
diodes) used herein as indicators. The use of an LED for an indicator is 
by way of an example and included is the concept of using visual, audible 
or other indicators within the scope of this invention. The green LEDs 
herein have minimum voltage requirements and thus function as zener 
diodes. 
It is presumed to be known in the art of battery chargers that the charger 
voltage output includes with DC voltage a large amount of AC voltage 
commonly called a ripple component and a unidirectional current component. 
Use is made herein of the minimum forward voltage requirements and the 
unidirectional current characteristics of the green LEDs; however, other 
indicators may be used connected in series with additional zener and 
rectifier diodes. 
Referring to FIG. 1, a conventional type of a battery charger 1 is shown 
comprising in cross section a substantially rectangular housing 2 having 
mounted in one side thereof a recessed polarized output connector 3 and 
having extending therefrom a power line 4 having a terminal plug 4a to 
connect to an appropriate AC power source. 
A connecting or output cable 8 is provided having a polarized terminal plug 
or terminal 5 at one end having projecting contacts 5a to plug into said 
charger connector 3. Up-facing on said terminal are indicators here shown 
as a red LED 6 to indicate incorrect polarity and a green LED 7 to 
indicate correct polarity. Also included in said terminal is appropriate 
circuitry. At the other end of said cable are a pair of battery terminal 
clamps 9 (red) and 10 (black). 
A lead acid storage battery is indicated generally by the reference numeral 
11. Said battery has a positive terminal 12 and a negative terminal 13. 
With reference to FIG. 2, a prior art circuitry 15 is first shown in 
connection with said terminal 5. Prior art includes the red and green 
polarity indicating means generally and known are the use of removable 
connectors 3 and 5. Said prior art circuit is first described so that 
there may be shown by comparison the improvements present in the circuitry 
representing the invention herein. 
The circuit 15 operates as follows. The resistor 17 sets the value of the 
current through the LEDs 6 and 7 to an appropriate value for them, and 
each LED, since it is a diode as well as a light, conducts only for one 
polarity, that is, the green diode 7 for the correct polarity and red 
diode 6 for reversed polarity. 
A problem occurs when the cable 8 is disconnected from the battery after 
use but is left plugged into the charger or is permanently connected to 
the charger. If the charger is subsequently energized, the green LED 7 
will light indicating correct polarity, thus misleading the operator to 
believe it is safe to connect the other end of the cable to the battery. 
This will cause a spark at the battery. The spark will be a small one if 
the polarity is correct at the battery but it will be a very large one if 
the polarity is not correct at the battery. 
It is very desirable to prevent the green LED from becoming illuminated in 
such a situation with the likelihood of giving misleading information. It 
is desirable to have a red LED light up to indicate the charger is 
energized or some other condition may be present requiring correction 
before connecting the cable to the battery. 
Reference is now had to FIG. 3, an example of a preferred embodiment of the 
circuitry of the invention herein is shown schematically and is indicated 
generally as 15a. The reference numerals are the same as in FIG. 2 for 
like parts with a prime added for a modified part and other reference 
numerals will be applied to different or added parts. A description of the 
circuitry elements will accompany a description of the operation of the 
circuit. 
In FIG. 3, the components 6, 17, 18, 24, 25, and 7, if taken alone, would 
function as in the prior art circuit of FIG. 2 and present the same 
problem as in the case of FIG. 2. The following described entire circuitry 
of FIG. 3 sets forth the improvement herein. 
In the case that in FIG. 3, the cable 8 was plugged into an energized 
charger 1 prior to attachment to the battery 11 terminals and since the 
cable terminal 5 is keyed to always be correctly connected to the 
connector 3 of the charger 1 and since the charger output polarity is the 
same as that of said battery when correctly connected to the cable 
terminals, the green LED 7, in prior art circuitry, would light and would 
thus incorrectly indicate that connection could safely be made to the 
battery 11. However, with the circuitry herein, the green LED 7 is 
prevented from lighting by transistor 21, which turns on, and thus by way 
of its collector 21b and emitter 21a leads, shunts the current from 
resistor 24 around said green LED 7, thus preventing said current from 
flowing through said green LED 7. 
Transistor 21 is turned on by base current generated during the intervals 
of increasing magnitude of the voltage and the AC ripple component of the 
battery charger output. During these intervals, the positively increasing 
voltage of the AC ripple component of the battery charger 1 output causes 
a capacitor 19 to become charged. The resulting capacitor charging current 
also flows through the diode 20 and the base emitter junction 21a of the 
transistor 21. This current does not flow through the red LED 6 during 
this interval because the direction of the current is reverse biased 
relative to said red LED and whereas the diode 20 and the base-emitter 
circuit 21a are forward biased relative to the direction of the current. 
As the peak of the battery charger 1 output voltage passes and the 
magnitude begins to decrease, the capacitor 19 begins to discharge through 
the series circuit shown comprised of diode 25, resistor 24, capacitor 22 
(which is substantially larger in capacitance value than capacitor 19), 
the red LED 6 and the resistor 17. Said voltage does not pass through 
diode 20 which is reverse biased and also the base-emitter junction 21a is 
now reverse biased. 
Thus it is that during intervals of increases in the magnitude of the 
battery charger output, current flows through capacitor 19, increasing its 
stored charge, and said current also flows through the base-emitter 
junction 21a turning it on, thus discharging capacitor 22 and diverting 
any current which would otherwise flow through the green LED 7; while 
during intervals of decreases in the magnitude of the voltage output of 
said charger 1, the capacitor 19 discharges reversing the direction of 
current flow through it causing the reversed current to flow through the 
red LED 6, as above described, causing it to light. The red light alerts 
the operator that the battery charger is connected to a power source and 
is energized and that it should be disconnected before connecting the 
cable to the battery. 
The desirable result is that the AC ripple component of the charger output, 
in passing through capacitor 19 and alternately turning on the transistor 
21 and the red LED 6, causes the green LED 7 to remain dark but causes the 
red LED 6 to light. The circuit thus has detected the AC ripple component 
in the charger output and is caused by said ripple component to override 
the tendency of the green LED 7 to otherwise light which would give a 
misleading indication. The alternate turning on and off of said transistor 
and said red LED 6 is so rapid that the red LED appears to be continuously 
lighted. The alternation indicated results from the character of the 
current, caused by the action of the capacitor 19 in response to the AC 
ripple component present in the charger output when a battery is not 
connected to it. It is seen that the operator is alerted by the indication 
on the terminal that the charger is energized, therefore it is not safe to 
connect the charger cable 8 to the battery 11. 
Without the ripple component detection capability of the circuit, as 
presented, the green LED 7 would be lit and would be misleading, as the 
charger 1 output is of the correct polarity to cause the green LED 7 to 
light. 
Thus FIG. 3 shows the ripple component detecting circuit 15a. In further 
description of circuit 15a, resistor 17 limits both the base current to 
the transistor 21 during periods of increase of the magnitude of the 
charger output and also the current to the red LED 6 during periods of 
decrease in the magnitude of the battery charger 1 output to values which 
are safe for these two components. 
Capacitor 22 is necessary because, although the transistor 21 diverts 
current from the green LED 7 during intervals of increasing output of the 
battery charger (cable 8 connected to the charger 1 in energized condition 
but not to the battery), the transistor 21 is off during periods of 
decreasing output. The green LED 7 would light during these periods and 
give a misleading indication, except that the capacitor 22, which is being 
charged by the current during these periods of decreasing charger output 
causes the current to flow around the green LED 7. Said green LED, acting 
as a zener diode, has a minimum requirement of voltage to turn it on. This 
voltage is not reached if capacitor 22 is sufficiently large in 
capacitance. During the periods of increasing charger output, the 
transistor 21 is turned on, and it then again discharges the capacitor 22. 
The diode 20 may be deleted from the circuitry. It is shown herein because, 
while not always required, it does assure that the green LED 7 will light 
when the battery is properly connected and is being charged. Although the 
battery does reduce the ripple component from the charger to a value which 
is usually insufficient to cause either the red LED 6 or the base-emitter 
junction 21a of the transistor 21 to conduct, nevertheless when cable 8 is 
sufficiently long and the charging current is large enough ripple 
component may be developed as a result of charging current flowing through 
its resistance to flow through the red LED 6 and the said base 
emitter-junction. Diode 20 increases the ripple component necessary for 
this to happen and so helps insure that the LEDs 6 and 7 are indicating 
correctly (green, and not red) when the battery is being correctly 
charged, even though the output cable 8 is large in length and resistance. 
Reference is now had to the embodiment of circuitry 15b herein as shown in 
FIG. 4. In this embodiment it is never necessary to correct the polarity 
of the connections 9, 10 at the battery 11. Instead, the charger output 
connector 3' and the terminal 5' are not polarized but may be reversed 180 
degrees in rotation with respect to each other. In addition to the red LED 
6 and the green LED 7 appearing at the top or front surface of the 
terminal 5 as shown in FIG. 1, an additional red LED 6' and the additional 
green LED 7' will appear at the rear or bottom surface of said terminal 5' 
but not here shown. In FIGS. 4 and 5, the legends (TOP) and (BOTTOM) mean 
at the top or bottom of the terminal plug or terminal 5'. 
The circuit of FIG. 4 is described utilizing the ripple component detection 
capability which is the salient feature of this invention, for without it, 
in the situation of cable 8 being first plugged into the energized charger 
before attempting to connect to the battery, whichever green LED 7 or 7' 
is upfacing will light. The ripple detecting circuitry to prevent this 
works as follows. The AC ripple component of the charger output will flow 
through the double capacitor 19' (which may be a single non-polarized 
capacitor), and alternately first through the red LED 6' and the 
base-emitter junction 21a of the NPN transistor 21, then through the 
base-emitter junction 28a of the PNP transistor 28 and the red LED 6. Thus 
said red LEDs 6 and 6' are lighted, indicating the error of connection to 
the charger before connection to the battery. 
The transistors 21 and 28 will also be alternately turned on, discharging 
their associated capacitors 22 and 29, thus preventing green LEDs 7 and 7' 
from lighting and falsely indicating that there is a correct sequence of 
connection. There is not sufficient voltage developed across said 
capacitors during the intervals when the said transistors are off to cause 
either of the said green LEDs to become energized; thus, both said red 
LEDs are lighted, but neither said green LED is lighted. The operator is 
thus warned of an unsafe sequence of operations, to wit, attempting to 
connect already energized charger clamps 9, 10 to the battery 11. 
Said red LEDs, optionally, may be deleted in FIG. 4 and a direct connection 
made from resistor 17 to the bases of the transistors 21, 28. Although not 
preferable, one or both of the resistors 17, 23 may also be omitted. The 
green LEDs will still provide the necessary indication, the 
ripple-detecting feature of this modified circuit is unchanged. As before, 
diodes 25 and 32 protect the components with which they are associated 
from excessive reverse voltage. 
Another modification of the circuitry herein designed to detect the 
presence of a ripple component is indicated as 15c in FIG. 5. This is an 
addition to, and an improvement of, the prior art circuit of FIG. 2, with 
the further change of connectors 3' and 5' to the reversible or 
nonpolarized type. 
This circuit provides for green LEDs 7 and 7' to be at the top and bottom 
of the terminal 5' connected in inverse parallel with a shunting circuit 
including a latched current means 34 shown here as a triac, all in series 
with a current limiting resistor 24. The triac 34 is gated by the circuit 
comprised of the non-polarized capacitor or double capacitor 19' with 
capacitor 35 and the diodes 36 and 37. Capacitor 35 is substantially 
larger in capacitance than is capacitor 19'. Said triac embodies an 
internal built-in resistor (not shown) connected from its gate 34a to its 
second main terminal 34c. The first main terminal is indicated at 34b. 
With the cable 8 plugged into an energized charger before the cable is 
connected to a battery, the ripple component detecting portion of said 
circuit 15c triggers the triac 34 on to a conducting state between its 
first and second main terminals 34b and 34c, thus shunting current away 
from the LEDs 7 and 7" permitting neither to light. The ripple component 
detection is described as follows: The capacitor 19' blocks the DC content 
from the battery charger output but allows the AC ripple component from 
the charger output to pass through, alternately causing diodes 37 and 36 
to conduct and diode 36 passes this current into capacitor 35 during those 
instants when the charger output is rising and diode 37 provides a return 
path for current back into capacitor 19' when the charger output is 
falling. Over the course of several cycles of AC ripple component, the 
capacitor 35 is charged to a voltage sufficient to trigger the triac 34, 
which then shunts out the green LEDs, permitting neither of them to light. 
This will alert the operator to unplug the cable from the charger before 
connecting to the battery. Removal of the cable from the charger will 
reset the triac. The time delay before said triac is triggered on is on 
the order of a hundred milliseconds. The triac 34 serves conveniently in 
the circuit 15c as described in being a bidirectional device. Replacement 
or substitute elements for said triac 34 could be a four-diode bridge 
connected to a silicon controlled rectifier (SCR), a field-effect 
transistor (FET), or a bipolar (NPN or PNP) transistor. Red LEDs could 
replace the diodes 36 and 37. 
With reference to FIG. 6, circuit 15d is shown as a modification of the 
circuit 15c to the extent of substituting for the triac 34 and its 
controlling elements 35-37, the capacitor 22', the diode 41-44 and an opto 
electronic isolator or opto coupler 42. For purposes of illustration, the 
opto electronic isolator 42 having a photo Darlington output transistor 
42c inside a four-diode bridge 41, has bidirectional input IREDs (infra 
red LEDs) 42 a,b as shown. Capacitor 22 must now be changed to a 
non-polarized type of capacitor 22' as shown. Because of the additional 
voltage drops of the Darlington transistor 42c and the diodes 41a and d or 
41b and c, the capacitor 19' will not be completely discharged by the 
phototransistor 42c when it is turned on by the infra red light emitted by 
the IREDs 42a and b when AC ripple component passes through the capacitor 
22' and thereby through the said IREDs. Diodes 43 and 44 are therefore 
included to allow the capacitor 22' to charge up to a higher voltage 
before allowing the green LEDs 7 or 7" to light. The desirable additional 
voltage drop across the diodes 41 and Darlington transistor 42c is thus 
seen to be sufficiently offset by the diodes 43 and 44 to prevent the 
green LEDs from lighting. 
It is seen that the essential novelty herein is the prevention of an 
indication of correct polarity when the battery charger is in fact 
energized before connection is made to the battery with the cable. The 
prevention of a misleading indication of correct polarity is accomplished 
by the detection of the AC ripple present in the battery of the invention 
herein which, generally stated, consists in an apparatus capable of 
carrying out the objects above set forth, in the parts and combinations of 
parts disclosed and defined in the appended claims.