Note: Descriptions are shown in the official language in which they were submitted.
ELD OF THE INVENTION:
This invention relates to electrical circuits having shunt
control circuits therewithin, and more particularly to battery
charging circuits having a shunt control circuit that precludes a
battery from discharging back through the shunt control.
Basically, the invention relates to circuits where the current
through a control coil of a regulated input device, such as a
saturable reactor is controlled by a shunted member across the
coil. Such type of circuit is disclosed in Applicant's United
States Patent No. 3,8~8,173, issued November 12, 1974 for 5TORAGE
BATTERY CHARGING APPARATUS~
BACKGROUND OF THE INVENTION:
Circuits for charging heavy duty batteries are well
known and are in wide spread use in industry. Batteries being
charged are typically found in industrial trucks, communications
equipment, or float charge rectifiers, and may have amp-hour
ratings of from 200 amp-hours to 1800 amp~hours, more or less.
Motive power batteries are usually re-charged overnight, a
period which could range from eight to sixteen hours;
communications batteeies are continually on charge. Motive power
batteries may need to be charged from a virtual zero charge to a
full charge for use the following day, which is done by an
initial high constant current at an appropriate voltage, followed
by a constant voltage tapering current charge, followed by a
trickle charge -- all as taught in the aforementioned patent.
Other charging procedures may simply be carried out first at a
constant voltage, then at a constant current; or simply in a
constant current float charging mode. In all events, the energy
t
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pplied to the battery is derived from an AC source through
suitable rectification, and under suitable surveillance of the
battery condition and control of a synchronous switch in the
output to alter the rate of energy input to the circuit.
An example of one such circuit is the inventor' 5
Canadian patent 1,111,104 issued 20 October 1981, for a "Battery
Charger and Surveillance System"O All such circuits, in any
event, derive the power that controls the input synchronous
switch -- that is, the control current through the control coil
10 of the synchronous switch -- from the DC output side of the
circuit. They also derive the power for the sensing circuit that
controls the control coil from the DC output side of the circuit;
but the sensing power is a very low power requirement at all
times, whereas the control coil power may, at times, be a very
15 high power requirement.
It is therefore an object of the present invention to
provide a circuit where the control power requirements are
separated from the sensing power requirement.
Control of a constant current or tapered current
20 charging circuit is often accomplished by a shunt control
circuit, an example of which is discussed in the inventor's
Canadian patent No. 822,798 issued on 9 September 1969. Such a
shunt control is used to control the amount of current flow
through the control coil of a saturable reactor or other
25 synchronous switch device having a control coil, such as a
magnetic amplifier. The shunt generally consists of a transistor,
the base of which is connected to the output of a sensing and
control circuit.
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When a substantially fully discharged battery is
connected to the charging circuit and the charging circuit is
turned on, the amount of current to initially charge the battery
may be at a maximum, as determined by the status of the battery
being sensed by the control circuit. Resultingly, the output
from the control circuit causes current flow through the control
coil as discussed hereafter, which in turn permits the saturable
reactor gates to transfer a controlled amount of power to the
transformer. Thus a controlled amount of DC charging current is
10 available to the DC output for charging the battery. Usually, if
the battery is substantially in a state of discharge, the current
through the saturable reactor or other controlled input device
will be at a ma~imum, and the DC output current will also be at a
maximum.
When the battery becomes fully charged, the control
circuit provides a signal to the shunt transistor, which is
thereby fully turned on. As a consequence, very little, if any,
current flows through the saturable reactor control coil. In
turn, the saturable reactor gates permit very little, if any,
power to be delivered to the transformer and ultimately to the DC
output portion of the circuit.
A problem that has previously occurred, however, is one
of reverse power flow from a partially or fully charged ba~tery
especially in the event of a failure of the AC input power. In
this circumstance, reverse power flow from the battery travels
back through the circuit to the control coil. It is highly
undersireable to supply power from the battery back through the
control coil, since the battery can become discharged during AC
power failure. It is acceptable, however, to supply a very small
~ount of power to the sensing circuit.
SUMMARY OF THE INVENTIOM:
The present invention provides a shunt control circuit
in a battery charging circuit that includes a pair of diodes
adapted to preclude a back flow of current from the charged
battery back to the control coil. In practice, a negligible
amount of current discharges from the battery to the sensing and
control circuit, which current is significantly lower than the
current that might flow back through the control coil without
the inclusion of the isolating diodes. The negligable sensing
current is acceptable in such charging circuits, as it will not
significantly diminish the amp-hour capacity of a charged
battery. By isolating the control power from the sensing power,
without the necessity of a separate power supply -- which
additional power supply is precluded by the provision of the
isolating diodes -- a soft walk-in after an AC power outage is
assured. That means that, when the circuit re-starts after AC
power is restored, there is a gradual buildup of control current
and DC saturation over the ~irst 6 to 12 cycles, during which the
synchronous switch reactor absorbs most of the input AC energy,
thus preventing high inrush currents.
BRIEF DESCRIPTION OF THE DRAWIMGS:
This invention will now be described in association with the
accompanying drawings, in which:
Figure 1 shows a basic single phase battery chargirlg
circuit having diode means for precluding current flow from the
battery;
Figuee 2 shows a circuit similar to Figure 1 except that
the voltage in the control circuit is doubled;
Figure 3 shows a circuit similar to Figure 1 except that
the main rectifier is a bridge circuit;
Figure 4 shows a bridge circuit similar to Figure 3
except that it is a three phase bridge circuit;
Figure 5 shows a circuit similar to Figure 4 except that
it is a six phase star circuit;
Figure 6 shows a circuit similar to Figure 1 except that
10 a PNP transistor is used.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS:
Figure 1 is a simplified schematic of a basic single
phase battery charging circuit of the present invention. The
15 circuit consists of a primary side 20 and a secondary side 22, on
either side of transformer 24. The transformer, of course, has a
primary winding 26 and a secondary winding 2~. The secondary side
22 of the circuit is divided into an AC portion 30 and a DC
portion 32 around or at the dash-dot line 34.
The circuit is adapted at its input for connection to an
AC source of electrical power 36 at its inputs 37, 38. The AC
power is passed into transformer 24, and it of course provides
the power for the DC portion 32 of the secondary side 22 of the
circuit. The DC portion 22 of the circuit is adapted for
25 connection to a battery 40 at outputs 41, 42 with 41 being the
positive terminal of the output and 42 being the negative
terminal of the output.
The power available to the primary side 26 of the
transformer 24 is of course largely passed over to the secondary
3.~
de 28 of the transformer 24, usually at a different voltage
level, in order to facilitate the voltage level of the battery
being charged. In order to rectify the AC power available at the
secondary side 28 into DC power, diodes 60, 62, 64 and ~6 are
used. Main diodes 60 and 62 form rectification means for
providing the battery 40 with DC power and they are power
diodes. Auxilliary diodes 64 and 66 form rectification means for
providing the shunt circuitry 68 with power, and they are low
current diodes. These rectification means provide a full wave
unfiltered DC power. Not shown is any filtering means for
filtering the full wave DC power into nearly ripple-free DC
power, if necessary for communication battery charging purposes.
This present circuit arrangement differs from the prior
art, as found for example in the inventor's prior Canadian
patents 1,111,104 and 1,159,110 noted above, in the following
respects. In these prior patents, the two power diodes, which
are equivalent to main diodes 60, 62 of the present invention,
provide DC power for the battery being charged, the control
circuitry, and the shunt circuitry. In the present invention,
the leads at the negative end of the diodes, which lead to the
shunt circuitry, have been placed ahead of the main rectifying
diodes 60, 62 and are in direct connection with the transformer.
Auxilliary or control power diodes 64, 66, are typically low
current diodes, and have been included ~o provide the required
rectification.
The amount of power passed to the primary side 26 of the
transformer 24 is dependent on the ampere-turns transductor --
more specifically a saturable reactor 44. Equivalently, another
type of ampere-turns transductor having a control coil could be
ed, such as a magnetic amplifier. The transductor shown in
Figure 1 is configured in a parallel manner, but alternatively it
is possible to have a suitable transductor configured in a serial
manner. Also, in bridge configuration circuits, the transductor
could be located on the secondary side oE the transformer instead
of on the primary side.
In any event, the ampere-turns transductor such as the
saturable reactor 44 has a control coil 46, which is part of the
DC portion 32 of the circuit. The amount of current in the
saturable reactor 44 is related to the curren~ in the control
coil 46, which is determined by the state of conduction of the
shunt transisitor 48. The state of conduction of the transistor
48 is determ~ned by a signal from the control circuit 50.
Typically, the average current when the transistor 48 is fully
shunting is higher than the average current through the control
coil when fully controlling.
The control circuit 50 monitoring includes sensing means
for measuring the amount of current flowing to the battery being
charyed, by means of a metering shunt, which is used in the
circuit in the usual and accepted manner for shunt.
When the signal from the control circuit 50 is present,
the transistor 48 is switched on and therefore is in a state of
conduction, which channels current away from the control coil 46.
All current flowing through the shunt circuitry 68, which
comprises the control coil 46, the shunt transistor 48, and a
current limiting resistor 52, must flow through the resistor 52
and is divided between control coil 46 and shunt transistor 48 --
depending on the state of conduction of the shunt transistor 48.
If the shunt transistor is turned off, again by the
3~ B~
ntrol circui~ 50, it is in a low state of conduction and
virtually all of the current flow in the shunt circuitry ~8 is
directly through the control coil 46 -- a state of maximum power
delivery through the saturable reactor 44.
The control current throuqh the SR control coil 46 is
derived from the unfiltered full wave DC supply and as a result,
the transistor 48 is switched on for part of each eyele, and is
switehed off for the remaining part of the cyele. The situation
where the transistor 48 is eondueting partially is substantially
precluded.
When the transistor 48 is switehed on, it conduets a
relatively large amount of eurrent but has a very low saturation
voltage drop aeross it, sinee partieularly all of the voltage
drop would be aeross the resistor 52. Resultingly, the power
eonsumption is relatively low, sinee power eonsumption is a
produet of the eurrent flow and the voltage drop. Alternatively,
when the transistor 48 is switched off, very little current is
flowing through it~ which again minimizes the power eonsumption.
The situation of having the transistor 48 conduct
partially, whieh would also produee a substantial voltage drop
aeross it, and a eorrespondingly high power consumption, is
avoided. This is advantageous, in that the transistor runs cooler
due to the low power consumption.
The amount of time the transistor 48 is switehed on in
eaeh eyele is inversely proportional to the state of eharge of
the battery, and is determined by sensing the voltage eross
output terminals 42. During the initial stages of eharying, the
battery requires full eharging eurrent. The signal from the
eontrol eireuit 50 would be virtually non-existent, whieh keeps
3~3
~ e transistor 48 from conducting. Correspondingly, the control
coil 46 has full current flowing through it resulting in maximum
DC current for battery charging. As the battery becomes charged,
the control circuit 50 provides a signal to the shunt transistor
48, which turns the transistor on Eor that period of time. During
that period of time current does not flow through the control
coil 46, and resultingly the saturable reactor 44 does not allow
AC power to be provided to the transformer 24, thus effectively
reducing the DC current used to charge the battery.
When the battery is ~ully charged, it can be seen that
the control circuit 50 would turn the transistor 48 on
continually, thus shunting and bypassing the control coil 46,
which results in no power being supplied for battery charging.
The control circuit 50, however, does require a smal~
amount of sensing current to keep it operating. This sensing
current cannot be supplied by the AC power source, since the
power source is effectively shut off. The power may be supplied
by an independent power supply; however, it is quite
satisfactory to provide the sensing power to the control circuit
from the charged battery 40. Due to the high internal
impedence of the control circuit 50, this sensing current is
limited to a virtually insignificant level, and thus does not
materially affect the amp-hour stored energy of the battery 40.
The shunt circuitry 68, however, does not have a high
impedance, and any back current flow therethrough would be of an
amount great enough to affect the amp-hour stored energy capacity
of the battery 40. Therefore, there must be means provided to
preclude such back current flow through the shunt circuitry 68.
Such a means is provided for in the form of main or isolating
odes 60, 62. Any back current is blocked from flowing between
the positive and negative termina1s 41, 42 of the battery 40 by
these main diodes 60, 62. In order that the shunt circuitr~ 68
can be protected in the above described manner by these main
diodes 60, 62, yet be supplied with full wave rectified power,
auxilliary diodes 64, 66 have been included.
Another problem that is created by back current flow
from a charged battery when means to block such flow does not
exist, is that the control coil 46 becomes DC biased by this back
current. This DC bias would cause the control coil to be in a
conductive state when a load is connected to the outputs 41 and
42. When power is subsequently supplied to the circuit, an
immediate inrush of DC current to the battery occurs, which is
undesirable. However, in keeping with this invention, with the
back current flow blocked, there is no DC bias across the control
coil 46, and thus the coil is precluded from being in a
conductive state. When the AC power is subsequently returned to
the circuit, the control coil 46 has a response time of about 6
to 12 cycles of the power source to reach its fully conductive
state. This prevents a sudden inrush of current to the battery,
and instead provides for a "soft walk-in" current, as noted
above.
In the preferred embodiment, an NPN transistor has been
used in conjunction with the control coil 46, and of course is
connected to the negative side of the circuit. This is an
advantageous configuration because the circuit is easily
adaptable for interfacing with micro-chip based equipment, such
as digital meter chips or timing chips.
In an alternative embodiment of the device, it is
contemplated that a silicon controlled rectifier could be used
in place of the shunt transistor of the preferred embodiment.
This silicon controlled rectifier could be turned on 50 as to
conduct and turned off so as not to conduct, in a manner similar
to the above mentioned shunt transistor. It could conceivably be
controlled by the same type of control circuit as the shunt
transistor, with little or no modification to the control
circuit.
Reference is now made to Figure 2, which shows a circuit
that is similar to Figure 1, but includes two basic changes. One
change is that the negative side 80 of the circuit is connec~ed
to an end terminal of the transformer 82, and not to the centre
tap terminal, and that the power diodes 84 and 86 have been
reversed. Correspondingly, the output side of each diode, in
this case the positive side, has been connected to the negative
side 80 of the circuit. The smaller rectification diodes which
provide rectified power to the shunt circuit 88, are connected
one to each end terminal of the transformer. The negative side
of the circuit has been connected to the opposite end terminal of
the transformer than are the power diodes, instead of to the
centre tap terminal as in Figure 1. Correspondingly, the voltage
across the shunt circuit 88 is twice the voltage supplied in the
circuit of Figure 1, thus providing it with more control power
and correspondingly better control characteristics. This
configuration is tyical in lower voltage circuits. The output for
charging the battery is also centre tapped in this embodiment,
thus keeping it at the same voltage as in Figure 1.
~5~f~;3
The second change includes re-arranging the saturable
reactor ga~es 90 into a series configura~ion. This has been
included to illustrate that either a parallel arrangement or a
series arrangement is acceptable.
Reference is now made to Figure 3, which shows a circuit
that is similar to Figure 1 except that it uses a bridge circuit
equivalent to the rectification circuit shown in Figure 1, to
obtain full wave rectification. Also, the saturable reactor gates
100 have been included on the secondary side 102 of the
transformer 104. Having the saturable reactor gates 100 on
either side of the transformer 104 is acceptable in a bridge
configuration circuit; and it is also possible to connect the
auxilliary diodes directly to the secondary winding of the
transformer as indicated by a dashed line at 103.
An alternative embodiment of the device is shown in
Figure 4, which shows a three phase bridge circuit that is
otherwise similar to Figure 3.
A still further alternative embodiment of the device is
shown in Figure 5 which shows a circuit similar to that shown in
Figure 1 except that there are six secondary windings on the
transformer, the windings being configured in a star arrangement
such that a six phase output is produced.
A final alternative embodiment is shown in Figure 6. It
is very similar to the circuit of Figure 1, except that it
25 employs a PNP transistor 200 across the control coil 202, both of
which are directly connected to the positive side of the DC
portion of the circuit.
Other modifications and al~erations may be used in the
design and manufacture of the shunt control circuit of the
present invention without departing from the spirit and scope of
the accompanying claims.
