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March 3, 2023

12V UPS controller and DC UPS for use in cars and buses with 12A pass through

battery backups for buses, transit, fire trucks, vehicle instrumentation
More battery backups for buses, emergency vehicles and vehicle instrumentation
12 volt battery charger and UPS for buses and cars DIN rail mount for busesOptional DIN rail mount
Automotive battery backup system

12 volt DC UPS module or battery backup (BBU) keeps 12 volt equipment alive in cars and taxis using an external sealed lead acid battery.
Price for quantity 1-49 Price for quantity 50-99 Quantity 100-499 Quantity 500+
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PST-DCUPS-12A-N11.8-P10 $135.00
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(xx is your choice between 9 and 13.1 volts
yy is your choice between 12.9 and 6 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) $6.00
$4.20 $3.80 $2.95
In-line fuse kit, consists of 2 in-line automotive spade fuse holders for the battery+ and load+ lines. Includes 15 amp fuses.
in-line fuse, click for larger image
$18.30 $15.90 $14.25
UPS for buses, vehciles and cars
Click here for more vehicle battery backup products
24 volt 10 amp car UPS module
Click here for the 24V 12A car UPS controller
5 amp DC/DC automotive UPS controller with status output
Click here for 5 amp version with status output
What the 10 amp UPS for cars looks like inside This is what the circuit board looks like inside the fully potted module.

This is the big brother of the PST-DC-UPS-1212. It allows equipment in cars to run under battery backup with up to 12 amps, 144 watts nominal.

In addition it charges the auxiliary battery at up to 0.8 amps.

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

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

Third it powers your equipment in the car using the car electrical system, but switches to external battery power when the car's battery is removed, stolen, or drops below a predetermined voltage, acting as a battery backup (BBU).

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

Fifth, it prevents your equipment from running the car's battery down so the car can't be started. In one configuration it cuts off the car's battery when the voltage gets below 13.1 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 12.0 volts. This allows your equipment to run off the car's battery but cut off while the car's main battery still has enough power to safely start the engine.

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

To solve these problems we invented this charging board. The idea is that you can connect the module to the car's electrical bus and it will charge an external 12 volt lead acid battery of your choice. Your equipment, which can be a small computer, telemetry equipment, or a car 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 13.1 to 11.9 volts, depending on your needs). Then the external battery takes over. When the external battery drops below the "P" preset voltage (Between 10 volts and 3 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, high and low temperatures.
Detailed Specifications PST-DC-UPS-1212-12A
Max Charge Current 800 milliamps.
Maximum pass-through current 12 amps continuous
Also comes in 3 amp and 5 amp versions
Transient pass-through current 13 amps for 40 seconds
20 amps for 5 seconds
Over 20 amps immediate shutdown
Maximum input voltage (steady state) 15V
Maximum input voltage (transient) 40V
Maximum pass-through wattage 120 watts
(180 Watts on special order)
Transition time less than 50 microseconds from main battery to auxiliary battery
less than 50 microseconds from auxiliary battery to main battery. We have a capacitor to keep the voltage up during the transition and have not had any problem with customer's equipment dropping out during the switchover.
Charge voltage Factory selectable, default is 13.8V
Type of battery charged Lead acid, VRLA, SLA, etc.
Charge algorithm Constant current until the battery voltage reaches 13.4 volts, taper charge above 13.4 volts to zero current at 14.1 volts
Nominal Battery Voltage 12 Volts
Battery Capacity 1 to 33+ Amp-Hours (larger batteries may be used but they may take a long time to charge)
Size of module 100 x 66 x 18 mm
3.92 x 2.6 x 0.72 inches
External battery connects when the input voltage to the module drops below 13.6 to 12.9 volts, see suffixes below
External battery is disconnected from the load when the external battery's voltage drops below: 12.9 to 6 volts, see suffixes below
Battery charging circuit turns on when main is above: 13V
Battery charging circuit turns off when main is below: 12.4
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
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 -20°C to 70°C
Connection 6 Faston spade terminals, clearly labeled
3 Ground terminals
External battery positive
Load positive
Car positive
Status connector 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
LEDs or 12V relays can be attached as shown below
Weight 140 grams or 4.9 ounces
PDF Data sheet Click here for the PDF data sheet
Installation Instructions Click here for the PDF installation sheet
3-D cad models IGS model STEP model
Ordering See the shopping cart below

The PST-DC-UPS-1212-12A can be ordered with a range of "N" and "P" values, as explained in the following table.
Suffixes* Voltage at which car battery is cut of from the load Voltage at which auxiliary battery is cut off from the load Why?
N13.1 (most common choice) 13.1 ±0.2 volts   Load is disconnected from the car electrical bus when the ignition is switched off
N12.9 12.9 ±0.2 volts    
N12.8 12.8 ±0.2 volts    
N 12.7 12.7 ±0.2 volts    
N12.6 12.6 ±0.2 volts    
N12.0 12.0 ±0.2 volts    
N11.9 11.9 +0.1 -0 volts   Allows the load to be powered by the car battery most of the time but still start the car (barely).
N?? Tell us what you need, the range is between 9.0 volts and 11.9 volts. The tolerance is ±0.2 volts    
P10 (most common choice)   10 volts When deep cycling of the auxiliary battery is desired.
P3   6 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 12.9 volts and 6 volts  
Tolerance Tolerance for N values is ± 2.5% Tolerance for P values is ± 2.5%  
**(For example PST-DC-UPS-1212-12A-N13.1-P10 would be a module which disconnects from the car battery when the car voltage falls lower than 13.1 volts and turns the auxiliary battery off when it falls to 10 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 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 unit 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 car exceeds its N value).

3. Q: What do you have for 24 volt systems?
A: Use the 24 volt version of the 12 Amp backup module which will use 24 volt auxiliary batteries in a 24 volt vehicle.

4. Q: What is the recommended fusing?
A: If you fuse both the input positive and auxiliary battery positive with a 20 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 20 amp fast acting fuse as well.

5. Q: I need a signal to tell me what the status of the UPS, whether it is on the main circuit, the auxiliary battery, or turned off.
A: This has "dry contact" annunciation, in other words a switch closes to indicate that the system is on auxiliary battery power.
6. Q: I am charging a very small battery with this, the 1.5A 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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Bus battery backup system, car battery backup system, truck battery backup system, vehicle BBU

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