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March 10, 2017

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

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).
24 volt battery charger and UPS for  vehicles, heavy equipment,,  bussesDIN rail mountOptional DIN rail mount UPS for automobiles and cars
Click here for the 12V 3 amp car UPS controller
12 volt 10 amp car UPS module
Click here for the 12V 12A car UPS controller

Superbly Engineered Products, Retail, Wholesale, and Custom Designed!



This is a 24V DC UPS controller for use in trucks, busses, 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 10 amps, 240 watts nominal.

In addition it controls the charge of the the auxiliary battery at 0.850 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.

Fourth, it prevents the external battery from being overdischarged, 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 automobile'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-2424-10A
Max Charge Current 850 mA
Temperature dependence of charge current The charge current is reduced at higher temperatures to maintain reliable heat management. At 40°C the charge current limit is 600 mA
Maximum pass-through current 10 amps
Transient pass-through current 13A for 10 seconds
18A for 1 second
Maximum input voltage (steady state) 30V
Maximum input voltage (transient) 44V
Maximum pass-through wattage 240 watts
Transition time less than 550 microseconds from main battery to auxiliary battery
less than 350 microseconds from auxiliary battery to main battery
Charge voltage The charging circuit is current limited, so the charge voltage can vary depending on the state of charge of the battery. The maximum charge voltage is 0.5 volts less than the vehicle's bus voltage. The vehicle bus' voltage must be higher than 25.8 volts to charge the auxiliary battery. The maximum vehicle bus voltage is 30 volts.
The available custom setpoints are Main On, Main Off, Charger On, Charger Off, Aux On, Aux Off This document describes how to engineer and specify the 6 custom setpoints if desired
Type of battery charged Lead acid, VRLA, SLA, etc.
Charge algorithm Constant current until the battery voltage reaches 26.8 volts, taper charge above 26.8 volts to zero current at 28.2 volts
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 89 x 94 11mm
3.5x3.7x0.45 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 -10°C ( -40°C available upon request )
Maximum ambient temperature of 70°C
When the case temperature gets above 45°C the charge current is automatically reduced to maintain system operation at higher temperatures.
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
Weight 140 gms or 4.9 ounces

Formerly this was called the PST-DC-UPS-2424-10A 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-2424-10A-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)

Model Price for quantity 1-49 Price for quantity 50-99 Quantity 100-499 Quantity 500+ -40°C option pricing click here
PST-DCUPS-12A-N26.2-P20 $89.00
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$76.50 $65 $59.50  
PST-DCUPS-12A-N23.6-P20 $89.00
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$76.50 $65 $59.50  
PST-DCUPS-12A-Nxx-Pyy
(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.
$95.00
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$81.50 $69 $63.50  
DIN Rail mounting kit (see below)
rail not included
$3.00
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$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
$22.00
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$18.30 $15.90 $14.25  
What the 10 amp UPS for cars looks like inside This is what the circuit board looks like inside the fully potted module.
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 tophat 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 10 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 setpoints 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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