General: This is a charger/controller PCB similar to the one used in the S12UPS-3.0/12DC unit - except with component changes for 24V operation. It's designed to keep a 24V application running in the event of a power failure. The PCB is designed to be powered by automotive, truck, or aircraft battery systems or by solar panels. Any input voltage from 21.6V to 32VDC can be used. Using a larger battery allows a longer power-fail backup time. Whenever a suitable supply voltage is available (21.6V - 32VDC), the PCB directs this voltage to its output terminal and on to the user's application. Also, at the same time, the charger built into the PCB draws an additional 1A or so from the supply source to recharge the external 24V SLA battery. Once the external battery has been recharged, this additional current drops to a low level. If the supply voltage is removed from the PCB, the unit quickly switches the external battery to the output terminal. When the supply voltage is restored, the PCB's internal charger recharges the battery. The unit has an internal battery-disconnect feature. This prevents an application from over-discharging the battery below 21.6V (which could damage it). This also allows the PCB/battery to be put into storage without the PCB's circuitry prematurely discharging its battery. If the UPS is supplying battery power to the load, and the voltage drops below 21.6V, the battery is disconnected and the UPS shuts down. When the Input Supply is restored or if a fresh battery is connected to the UPS, the UPS restarts and reconnects the battery. Mounting: Use #4 hardware on all 4 mounting holes in conjunction with 3/16" (minimum) standoffs (metal or plastic). The PCB has a temperature monitoring circuit. This allows the battery charger to temperature-compensate its voltage output to suit the requirements of an SLA battery. The PCB and battery need to be mounted in the same enclosure for so the PCB can detect the battery's ambient temperature. The PCB may be mounted in any position and must be protected from the weather. Thermal Considerations: The PCB operates normally in an ambient temperature of -40C to +65C. However, this is limited by the battery's requirements. The unit's charger stops operating above +65C but automatically restarts when the temperature drops below this number. However, above +60C, the life of all SLA (sealed lead-acid) batteries is severely reduced. For the sake of battery life, mount the unit away from heat sources or direct sunlight. Connecting to the PCB: #22(0.65mm) stranded wire is recommended for application where the distance between the UPS and the load is short. For longer distances, #20(0.81mm) or even #18(1.02mm) wire may be required. The following
#20 is .020V/Amp/Foot
#18 is .013V/Amp/Foot
To arrive at the total voltage drop, make three calculations: 1: Multiply the appropriate number in the previous paragraph by the load current (in Amps) times the cable length between the PCB and load (in Feet).
2: Similarly, repeat the calculation for the distance between the PCB and the battery.
3: Similarly, repeat the calculation for the distance between the PCB and the power source. This voltage drop is for the total round trip the load current makes - from the PCB and back via the return wire. The total voltage drop when there is an active power source is 1. + 3.
When the load is powered from the UPS battery, the voltage drop is 1. + 2. As an example, using #22 wire to power a load that draws 1.5A and is 4 feet from the UPS, the voltage drop is
Block Diagram Operation Manual Electrical Specs. Mechanical Info.
+BAT terminal (+Battery): The positive terminal of the user-supplied UPS battery is connected here. The negative terminal of the UPS battery is connected to one of the COMMON terminals. OUT terminal (Output Power): This is the (+) output of the UPS which is used to power the application load. If the Input Supply is greater than 21.6V, an internal switch connects the Input Supply terminal to the Output Power terminal. If the Input Supply is less than 21.6V, the internal switch instead connects the external 24V battery to the Output Power terminal. The PCB's transfer from the Input Supply to external battery takes less than 1 millisecond. During this time, an internal capacitor connected to the Output Power pin prevents the voltage from dropping to zero during the transfer time. With a 3A load, the voltage sag at the Output Power terminal is approximately 2V during the transfer time. If the application cannot tolerate this voltage sag, then a sufficiently large capacitor should be added to the application's power input to hold up the voltage for this period. Even when the Input Supply drops below 21.6V, the PCB's charger can still operate (down to approximately 5V Input Supply) and can contribute a reduced current to the Output Power terminal. If the load is substantial, then the battery supplies most of the output current and eventually becomes discharged. However, if the load current is small, then the charger is able to provide this output current and also maintain the battery at 100% charge level. Because of this, a small solar panel in dim light may be able to keep the battery maintained at 100% charge level if the load current is small. The application load may draw up to 3.0A steady-state - whether from the Input Supply or the external battery. Drawing more than 3.0A continuously may damage the unit. However, large surge currents (up to 25A for 10mSec) may be drawn on a low duty cycle basis. A circuit breaker on the Output Power terminal has a 1 second delay and trips at between 3.5A and 7.0A. If the circuit breaker trips, power to the Output Power terminal is interrupted. Once tripped, the circuit breaker can only be reset by briefly disconnecting the battery and input power. PWR terminal (Signal P Power): This terminal supplies a signal to power a standard LED and is internally resistor current-limited. When the Input Supply is above 21.6V, this signal is active at 5V. When the Input Supply is below 21.6V, this signal is zero. There is about 0.4V of Input Supply hysteresis between on and off for this signal. This signal is driven from the output of an LM224 op-amp in series with 200 ohms. The LM224 can source approximately 15mA or sink 1ma. If driving a TTL circuit and more pull-down is needed, a 270 ohm resistor from this terminal to the Common Negative terminal helps somewhat. +IN terminal (Input Supply): This is the (+) input power source for the UPS. To keep the external battery from powering the output, the voltage at this terminal must be between 21.6V and 32VDC. While the voltage is at this level, the Output Power is entirely sourced by this Input Supply terminal. Also, the Input Supply operates the unit's internal charger to recharge/maintain the external 24V battery. If the Input Supply voltage drops below 21.6V, then the unit disconnects the Input Supply terminal from the Output Power terminal and instead connects the external battery to the Output Power terminal. Even if the Input Supply is no longer feeding the Output Power terminal, as long as it remains above 5V, the charger still operates - although at a much lower current level. If the current drawn from the Output Power terminal is low enough, the battery can still be recharged/maintained with this low Input Supply voltage. However, if the Output Power terminal current is above the now-limited capability of the charger, the battery still eventually becomes discharged. CHG terminal (Signal C: Charge) This terminal supplies a signal to power a standard LED and is internally resistor current-limited. This signal is driven from the output of an LM224 op-amp in series with 200 ohms. The LM224 can source approximately 15mA or sink 1ma. If driving a TTL circuit and more pull-down is needed, a 270 ohm resistor from this terminal to the Common Negative terminal helps somewhat. When the Input Supply is above 21.6V, this signal is high whenever the external battery is being charged. When the battery is fully recharged, this signal goes off. If the Input Supply is below 21.6V, this signal has a different purpose. While the Input Supply is below 21.6V and the battery is supplying current to the Output Power terminal, the unit's microprocessor monitors the battery's voltage. The signal on this terminal indicates the battery voltage level with a series of flashes (waveform shown below). ENB terminal (Enable): This terminal is normally connected to the Common Negative terminal via the unit's mating connector. Grounding this terminal allows the unit's battery to be connected to the rest of the unit's circuitry. Do not use this terminal for any other purpose. If the unit is to be stored and out of active service, disconnecting this terminal causes the UPS to completely shut down and isolates the battery from any circuitry. This prevents the battery from prematurely discharging while in storage. All batteries have internal leakage which increases with temperature. Thus, even disconnected from circuitry, the battery eventually discharges. This can be from one month to a year - again depending on temperature. For this reason, each unit should be connected to a power source periodically. Assuming the battery is charged, re-connecting the battery to the PCB re-starts it. This is done with a small capacitor injecting a startup current into the UPS circuitry. If reconnecting the battery is fumbled a bit by the operator, the capacitor may need time to discharge again in preparation for another try. This very seldom happens but, if needed, disconnect the battery, wait 15 seconds, and try again. If there is a voltage on the Input Supply terminal, this startup circuit not used and the preceding instructions can be ignored. FLT terminal (Signal F Fault): This terminal supplies a signal to power a standard LED and is internally resistor current-limited. Unlike the other two Indicator Signals, this signal originates from a 12V source in series with a 2.4K resistor. This terminal has no pull-down capabilities and needs a user-supplied buffer circuit if interfacing with TTL. If a standard LED is connected to this terminal, the LED remains lighted whenever the Output Power circuit breaker has tripped. If a LED is not connected to this terminal, Signal C is used to signal a fault. It does this with a very rapid series of flashes. The fault shutdown continues until both the battery and input supply are briefly disconnected. COMMON terminals (Common Negative): This is the negative return for the Input Supply, Output Power, and Indicator Signals. For convenience, two Common Negative terminals are provided - use either or both.
There follows a series of from one to five 62mS pulses, with a 250mS spacing, followed by a second 500mS off time. The pulse train repeats this pattern continuously. The pulse-width tolerance is +- 5%.
The number of 62mS pulses is determined by the battery voltage.
5 pulses: Voltage = 12.60V and above (approx 80% - 100% charge level)
4 pulses: Voltage = 12.15V to 12.60V (60% - 80%)
3 pulses: Voltage = 11.70V to 12.15V (40% - 60%)
2 pulses: Voltage = 11.25V to 11.70V (20% - 40%)
1 pulse : Voltage = 10.80V to 11.25V (00% - 20%)