Transformerless battery charger in combination with a battery, and method of charging a battery

A transformerless battery charger having a circuit for connecting the battery to an A.C. power source to supply charging current to the battery including: an inductive impedance in series with the battery for limiting the charging current through the battery. An electronic switch in the form of a TRIAC or SCR is connected in series with the battery, and the electronic switch is normally non-conductive thereby keeping open the charging circuit for the battery. An electronic trigger for turning on said electronic switch is provided to close the charging circuit for the battery as a function of the difference between the instantaneous voltage from said A.C. power source and the battery voltage. The electronic switch and the electronic trigger jointly operating to provide a pulsed charging current to the battery during the A.C. power cycle which is long enough to produce a significant battery-charging effect but short enough to avoid harmful internal heating of the battery. The electronic trigger advantageously includes an R--C element driving a Diac.

SUMMARY OF THE INVENTION 
This invention relates to a novel combination of a battery and a 
transformerless battery charger and to a novel method of charging a 
battery. 
In both its apparatus and method aspects, the present invention is based on 
my discovery that a battery can be safely and effectively charged from a 
conventional 60 Hz., 110-120 volt power outlet without the need for a 
step-down transformer. In accordance with my invention, an inductor and a 
semiconductor switching device are connected in series with the battery 
across the A.C. power input lines. The semiconductor switching device is 
maintained non-conductive for much of the A.C. power cycle, thereby 
open-circuiting the charging circuit for the battery, and during the A.C. 
power cycle it is caused to become conductive as a function of the A.C. 
voltage and the actual battery voltage at that instant. When the 
semiconductor switching device turns on, charging current is delivered to 
the battery. The duration of this current is kept short enough to avoid 
heating the battery deleteriously but long enough to produce an adequate 
charging effect on the battery. 
A principal object of this invention is to provide a novel combination of a 
battery and a transformerless battery charger. 
Another principal object of this invention is to provide a novel method of 
charging a battery. 
Further objects and advantages of this invention will be apparent from the 
following detailed description of two presently preferred embodiments 
which are illustrated schematically in the accompanying drawing.

Before explaining the disclosed embodiments of the present invention in 
detail it is to be understood that the invention is not limited in its 
application to the details of the particular arrangements shown since the 
invention is capable of other embodiments. Also, the terminology used 
herein is for the purpose of description and not of limitation. 
DETAILED DESCRIPTION 
Referring to FIG. 1, the present battery charger is energized from a 
conventional 110-120 volt A.C. power source 10 connected across a 
conventional socket 11. 
The battery charger includes a conventional pronged plug 12 which is 
insertable into the socket 11 to have the A.C. voltage applied across 
respective insulated, current conducting input lines 13 and 14 connected 
electrically to corresponding terminals of the plug. A conventional 
current-limiting fuse 15 and a toroidal inductor and 16 are connected in 
series in line 13 between the corresponding terminal of plug 12 and the 
upper input terminal 17 of a full-wave rectifier bridge 18 of conventional 
design. A "Triac" silicon semiconductor device 19 of known design is 
connected in line 14 ahead of the opposite input terminal 20 of rectifier 
bridge 18. 
The rectifier bridge has a first rectifier 21 with its anode connected to 
input terminal 17 and its cathode connected to a first output terminal 22. 
A second rectifier 23 in the bridge 18 has its cathode connected to input 
terminal 17 and its anode connected to the opposite output terminal 24 of 
the bridge. A third rectifier 25 in the bridge has its anode connected to 
input terminal 20 and its cathode connected to output terminal 22. A 
fourth rectifier 26 in the bridge has its cathode connected to input 
terminal 20 and its anode connected to output terminal 24. 
The battery B which is to be charged has its positive terminal 27 connected 
to the first output terminal 22 of rectifier bridge 18 through an ammeter 
28 of conventional design. The negative terminal 29 of the battery is 
connected directly to the second output terminal 24 of the rectifier 
bridge. 
The "Triac" 19 acts as a bidirectional switch under the control of a timing 
circuit including a "Diac" semiconductor device 30 of known design that 
functions as a bi-directional trigger to turn on the "Triac" 19 briefly 
once each half cycle of the A.C. voltage across the input terminals 17 and 
20 of the full wave rectifier bridge 18. As shown in FIG. 1, the upper 
terminal 31 of "Diac" 30 is connected directly to the control electrode 32 
of "Triac" 19. The lower terminal 33 of the "Diac" is connected to the 
input line 14 through a first capacitor 34 and through a first resistor 35 
and a second capacitor 36 connected in series with each other across 
capacitor 34. The junction point 37 between resistor 35 and capacitor 36 
is connected through a fixed resistor 38 and an adjustable resistor 39 to 
the lower input terminal 20 of rectifier bridge 18. Capacitor 34, resistor 
35, capacitor 36 and resistor 38 together provide a dual R-C time constant 
network acting as a phase shifter to control the firing of "Diac" 30. 
FIG. 2 shows the essentially sinusoidal input voltage appearing across the 
input terminals 17 and 20 of rectifier bridge 18. During each positive 
half cycle, shortly before the input voltage reaches its positive 
sinusoidal peak of 117 volts the "Triac" 19 is turned on to conduct 
positive current from right to left in FIG. 1. This happens when the 
"Diac" 30 applies a triggering signal to the control electrode 32 of 
"Triac" 19. This completes a path for positive polarity current as 
follows: from line 13 through fuse 15 and inductor 16, rectifier 21 in the 
rectifier bridge 18, ammeter 28 and through the battery B and rectifier 26 
in the rectifier bridge, and through the "Triac" 19 from right to left in 
FIG. 1 to the other A.C. input line 14. The positive current pulse through 
the battery is shown at 40 in FIG. 3. It is of short enough duration not 
to cause harmful internal heating in the battery being charged but long 
enough to produce a significant charging effect. The practical upper limit 
of the pulse duration, as a percentage of the half cycle interval of the 
A.C. input voltage, is about 60% and the practical lower limit is about 
0.01%. That is, for the usual 60 Hz. A.C. input voltage, the current pulse 
40 may be as long as about 5 milliseconds or as short as about 1 
microsecond. Within these limits, the present battery charger produces an 
adequate charging effect on the battery without overheating it to the 
extent that the battery would be damaged. 
The triggering pulse from the "Diac" 30 which turns on the "Triac" 19 does 
not last as long as the current pulse 40 delivered to the battery B 
because, once turned on by the triggering pulse from the "Diac", the 
"Triac" remains in a current-conducting state until the current pulse 40 
drops to virtually zero. 
When the "Triac" 19 is conducting current, the toroidal inductor 16 is 
virtually the only impedance across the A.C. input lines 13 and 14 because 
the battery B, the ammeter 28, and the current path through the rectifier 
bridge 18 each provide virtually no impedance. 
In one practical embodiment, the output current pulse during each negative 
half cycle of the power supply voltage is 80 amperes and during each 
positive half cycle of the power supply voltage it is slightly less than 
80 amperes. For a battery having a nominal voltage of 12 volts, the 
current pulse increases the voltage across the battery by about 8 volts. 
The point in the positive half wave of the A.C. input voltage at which the 
"Triac" 19 begins to conduct depends upon the difference between the 
instantaneous A.C. input voltage across input lines 13 and 14 and the 
actual battery voltage at that moment, as well as on the values of 
inductor 16, capacitors 34 and 36, and resistors 35, 38 and 39. In one 
practical embodiment, capacitor 34 is 0.1 microfarad, capacitor 36 is 0.1 
microfarad, resistor 35 is 15,000 ohms, resistor 38 is 2,200 ohms, and 
resistor 39 has a maximum value of 100,000 ohms. 
During each negative half cycle of the A.C. input voltage across lines 13 
and 14, when the "Diac" 30 fires and triggers the "Triac" 19 on, the 
positive current path through the circuit is from input line 14 through 
"Triac" 19 from left-to-right in FIG. 1, through rectifier 25 in rectifier 
bridge 18 and ammeter 28 to the positive battery terminal 27 through the 
battery B and from the negative battery terminal 29, through rectifier 23 
in rectifier bridge 18 and inductor 16 to the opposite A.C. input line 13. 
As shown in FIG. 2, each current pulse through the "Triac" 19 produces a 
corresponding voltage transient 41 in the A.C. input voltage across the 
rectifier bridge's input terminals 17 and 20. 
This battery charger is not limited to use with 12 volt batteries. It may 
be used to charge any battery with a rated voltage from about 1.5 volts to 
about 75 volts. Of course, the lower the rated battery voltage, the 
shorter should be the percentage of time that the "Triac" 19 is on in 
order to prevent deleterious heating of the battery being charged. The 
time interval during which the charging current is on (i.e., the charging 
circuit for the battery is closed) during each half cycle of the A.C. 
power supply is deterined by the setting of the adjustable tap on resistor 
39. The higher the nominal battery voltage, the smaller should be the 
resistance provided by resistor 39 so that the charging current will be on 
a higher percentage of the time. 
FIG. 4 shows a second embodiment of the present invention which omits the 
rectifier bridge 18, the ammeter 28 and the "Triac" 19 of FIG. 1. Elements 
in FIG. 4 which correspond to those in FIG. 1 are given the same reference 
numerals plus 100, and the detailed description of these elements will not 
be repeated. 
The terminal 131 of "Diac" 130 is connected to the control electrode 50 of 
a silicon controlled rectifier 51 of known design. The cathode of SCR 51 
is connected to the A.C. input line 114. The anode of SCR 51 is connected 
to the negative terminal 129 of the battery being charged. 
The SCR 51 functions as a half wave rectifier under the control of "Diac" 
130, such that SCR 51 is turned on only during a positive half cycle (and 
not in a negative half cycle) of the A.C. input voltage across lines 113 
and 114. As with the "Triac" 19 in FIG. 1, once it has been triggered on 
by the "Diac" 130 the SCR 51 will remain conductive until the current 
spike or pulse drops to virtually zero.