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August 16, 2023

24V DC UPS controller for use in vehicles with 12A pass through

Bus 24 volt battery charger and UPS for  vehicles, heavy equipment, busesDIN rail mount for bus mounting
Optional DIN rail mount

24 volt DC UPS module keeps 24 volt equipment alive in vehicles and airplanes using an external sealed lead acid battery and acts as a battery back-up (BBU). Also available in a stand alone enclosure including battery.
battery backups for buses, transit, fire trucks, vehicle instrumentation
More battery backups for buses, emergency vehicles and vehicle instrumentation
12 volt 10 amp bus or car UPS module
Click here for the 12V 12A car and bus UPS controller
Model Price for quantity 1-49 Price for quantity 50-99 Quantity 100-499 Quantity 500+
PST-DCUPS-12AR-N26.2-P20 $135
Call Call Call
PST-DCUPS-12AR-N23.6-P20 $135
Call Call Call
(xx is your choice between 30 and 18 volts
yy is your choice between 26 and 18 volts) Delivery time for samples of the custom voltages can take up to two weeks.
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DIN Rail mounting kit (see below)
rail not included
$2.75 $2.25 $2.10
In-line fuse kit, consists of 2 in-line automotive spade fuse holders for the battery+ and load+ lines. Includes 10 amp fuses.
in-line fuse, click for larger image
$18.30 $15.90 $14.25

This is a 24V DC UPS controller for use in trucks, buses, boats, and wherever a constant supply of 24 volts is needed. It allows equipment in vehicles to continue running when the power is temporarily interrupted by starting motor operation, or when you just need to run under battery backup with up to 12 amps, 290 watts nominal.

In addition it controls the charge of the the auxiliary battery at 2 amps.

The features are as follows:
First it allows you to safely charge an external lead acid battery from the vehicle electrical bus by isolating and current regulating the connection to the auxiliary battery.

Second it isolates the extra battery from the vehicle so it won't be discharged by the vehicle electronics, and it won't try to participate in starting the vehicle.

Third it powers your equipment in the vehicle using the vehicle electrical system, but switches to external battery power when the vehicle's battery is removed, stolen, or drops below a predetermined voltage. It is not necessary to run an extra sense wire to the ignition, voltage sensing takes care of the decision making.

Fourth, it prevents the external battery from being over discharged, keeping it from being damaged.

Fifth, it prevents your equipment from running the vehicle's battery down so the vehicle can't be started. In one configuration it cuts off the vehicle's battery when the voltage gets below 26.2 volts, then switches over to the external battery, in other words, it switches over to the auxiliary battery when the engine is shut off and the alternator stops.

In another configuration the crossover voltage is lower, say 24 volts. This allows your equipment to run off the vehicle's battery but cut off while the vehicle's main battery still has enough power to safely start the engine.

Sixth, it prevents your equipment from losing power, powering down or rebooting while the vehicle is cranking the starting motor.

To solve these problems we invented this battery backup (BBU) charging board. The idea is that you can connect the module to the vehicle's electrical bus and it will charge an external 24 volt lead acid battery of your choice. Your equipment, which can be a computer, telemetry equipment, or a vehicle alarm, is connected to the module. This equipment runs off the vehicles's electrical bus until the voltage of the bus drops below a preset voltage, the "N" voltage (from 27 to 18 volts, depending on your needs). Then the external battery takes over. When the external battery drops below the "P" preset voltage (Between 20 volts and 18 volts depending on your requirements) the power is cut off to either prevent damage to the external battery or to run your equipment as long as possible.

This uninterruptible power supply control module is specifically designed to withstand the harsh electrical and temperature requirements of automotive equipment including spike, dropouts, load dumps, jump-starting, and high or low temperatures.
Detailed Specifications PST-DC-UPS-2424-12A
Max Charge Current 2000 mA
Maximum pass-through current 12 amps
Transient pass-through current 13A for 10 seconds
18A for 1 second
non making or breaking above 12A
Maximum input voltage (steady state) 30V
Maximum input voltage (transient) 44V
Maximum pass-through wattage 240 watts
Transition time less than 6 milliseconds from main battery to auxiliary battery
Charge voltage 29.4V charge, 27.6V float
The available custom set points are Main On, Main Off, Charger On, Charger Off, Aux On, Aux Off This document describes how to engineer and specify the 6 custom set-points if desired
Type of battery charged Lead acid, VRLA, SLA, etc.
Charge algorithm Constant current until the battery voltage reaches 29.4 volts, taper charge at 29.4V until the current drops to 120 mA, then switches to 27.6 float voltage
Nominal Battery Voltage 24 Volts (28 volts by airplane nomenclature)
Battery Capacity 1 to 33+ Amp-Hours (larger batteries may be used but they may take a long time to charge)
Size of module 70 x 108 x 23mm
2.75 x 4.25 x 0.90 inches
External battery connects when the input voltage to the module drops below 30V to 18 volts, see suffixes below
External battery is disconnected from the load when the external battery's voltage drops below 26 volts to 18 volts, see suffixes below
Temperature Range Minimum ambient temperature -40°C
Maximum ambient temperature 70°C
Storage Temperature -10°C to 100°C
( -40°C available upon request )
Connection 6 Faston spade terminals, clearly labeled:
3 Ground terminals
External battery positive
Load positive
vehicle positive
Status Connector There is a connection diagram below.
The mating parts for the status connector are: Connector shell = Molex 43645-0400 Connector pins = Molex 43030-009 or similar.
There is a connection diagram below.
Pin 1 connected to +5V, 30mA source which may be used to power LEDs
Pin 2 will be closed to ground when the main battery is connected
Pin 3 will be connected to ground when the auxiliary battery is connected
Pin 4 is internally connected to Power Ground
24V relays can be attached as shown below
Fail safe If the Auxiliary battery is lost or goes below the cutoff voltage the main battery is reconnected.

Formerly this was called the PST-DC-UPS-2424-12A can be ordered with a range of "N" and "P" values, as explained in the following table.
Suffixes* Voltage at which vehicle battery is cut of from the load Voltage at which auxiliary battery is cut off from the load Why?
N26.2 (most common choice) 26.2 ±0.2 volts   Load is disconnected from the vehicle electrical bus when the ignition is switched off
N25.8 25.8 ±0.2 volts    
N25.4 25.4 ±0.2 volts    
N24.0 24.0 ±0.2 volts    
N23.8 23.8 +0.1 -0 volts   Allows the load to be powered by the vehicle battery most of the time but still start the vehicle (barely).
N?? Tell us what you need, the range is between 30 volts and 18 volts. The tolerance is ±0.2 volts    
P20 (most common choice)   20 volts When deep cycling of the auxiliary battery is desired.
P18   18 volts When longest possible system operation is desired regardless of loss of auxiliary battery cycle life.
P??   Tell us what you need, the range is between 26 volts and 18 volts  
Tolerance Tolerance for N values is ±2.5% Tolerance for P values is ±2.5%  
Users Manual Click here for the User's and Installation Manual    
**(For example PST-DC-UPS-2424-12A-N26.2-P20 would be a module which disconnects from the vehicle battery when the vehicle voltage falls lower than 26.2 volts and turns the auxiliary battery off when it falls to 20 volts)

Hook up diagram:
Connection diagram

Connection to the status connector dimensioned drawing of the PC-DC-UPS-1212-Nxx-Pyy
Dimensions, click on drawing for larger view

DIN rail mounting option, click for a larger picture Din rail mount option fits both 31mm and 15mm top hat profile rails
din rail mount Din rail mount
DIN rail mount from the bottom DIN rail mount system viewed from the bottom

DIN rail mounting option (shown here on the 3 amp version of the DC UPS)

Questions and Answers

1. Q: My application needs more than 12 amps pass-through current, what can I do?
A: A 15 amp version is available, call and let us know your requirements.

2. Q: When the module turns off because both batteries are below their set-points when does the module turn back on?
A: The module turns back whenever the main battery or auxiliary battery is greater than their N or P values (this is an improvement over the 3 amp UPS module which turns on only when the vehicle exceeds its N value).

3. Q: What do you have for 12 volt systems?
A: Use either the 12 volt 3 amp UPS or 12 volt 12 amp UPS versions
4. Q: What is the recommended fusing?
A: If you fuse both the input positive and auxiliary battery positive with a 15 amp fast blow fuse the module will be protected from reverse polarity and short circuit conditions. In addition, if the load can source current it should have a 15 amp fast acting fuse as well.

5. Q: I am charging a very small battery with this, the 850 mA charge rate is too high according to the battery manufacturer.
A. The charge algorithm used is kind to the batteries even when the maximum charge rate is over the C/3 rate specified by the battery manufacturers. For more information click on this link.

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