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Best Power Patriot SPS450VA Uninterruptible Power Supply Information

"Another day, another forgotten piece of technology..."

This page aims to provide some comprehensive and hopefully useful information concerning the Best Power Patriot SPS450VA model uninterruptible power supply. It may apply to similar models as well. Best Power itself has long since been absorbed into several other companies, and information about this particular product seems to have vanished into the ether. I contacted Eaton Powerware regarding this unit and was told that any information regarding this unit had been thrown away when they moved out of the building Best Power had been situated in. No employees from that time are still with the company. They were, however, quite cooperative and tried to be helpful.

Thus, this page's "raison d'tre".

Picture of a Best Power SPS450VA Uninterruptible Power Supply.

The SPS450VA product itself seems like quite an old design. A patent number printed on the underside of the unit dates from late 1989 and another patent referenced by the first, describing how the inverter itself maintains regulation, dates from early 1986. Both patents were assigned to Best Power and a contracted manufacturer of electronics known as Pensar Corporation. Incidentally, Pensar itself was bought out, later became an independent company once again, and went through a number of hands before ending up as a part of Ducommun, Incorporated. Only one inventor's name appears on both patents, that of a Richard V. Baxter, Junior.

(Admittedly almost all of the above paragraph is search engine bait, instead of information that most people would ever care about. It is my hope that by perhaps placing such information on this page, that someone affiliated with Best Power, this product's design or its manufacture, might happen across this page, contact me and provide more information about some things I don't know about. Information in particular that I'm looking for would include a schematic, service information, user's manual, what if any end-user purpose J1 on the circuit board has and purpose of the four DIP switches on the main board near the microcontroller.)

And oh by the way: Uninterruptible Power Supplies can be dangerous if misused, modified, handled inappropriately, or poorly maintained. Power inversion circuits in general handle great quantities of electricity at hazardous voltages and frequencies. It's easily possible to kill or seriously injure yourself by being any of curious, careless or stupid around this sort of equipment. Even if you survive, a power inverter subjected to unwise experimentation probably won't. Further, the author of this page presents any information offered in good faith. He does not, however, make any guarantee, warranty or statement of any kind the information presented is accurate. Readers are encouraged to use common sense before doing anything, especially when unsure. To the maximum extent possible under law, this page's author disclaims any liability or responsibility stemming from anyone's ability or inability to use the information provided.

This page is not affiliated with or approved by Best Power or Eaton Powerware.

Here's what you really need to know.

Replacement Battery

The Patriot SPS450VA uses a single twelve volt lead acid battery. When it was new, it probably called for a battery capacity between 7-8 amp-hours. Nine amp-hour twelve volt lead acid batteries with the exact same form factor exist today and you might as well use one of them. The charging circuit appears not to have any issue with a slightly larger battery. Those looking to connect larger, externally situated batteries are on their own, and MUST carefully consider the warning below!

WARNING: The SPS450VA UPS charging circuit is NOT isolated from the AC powerline! For your own safety, you absolutely must disconnect the unit from line power by removing the power cord from the outlet (and preferably, the IEC socket on the UPS itself). Also unplug any attached loads. Don't forget to turn the unit's power switch off before you remove the battery, as the unit's inverter will try to start up and carry any attached load the moment a new battery is installed!

Another wrinkle to be aware of: The SPS450VA uses smaller terminals than are found on modern replacement batteries. You can cut these off and replace them with larger ones (14-16 AWG), with heat shrink tubing pulled over any exposed contact areas. Or you can do as I did, taking the lazy approach by abusing a bladed screwdriver and some pliers to widen the existing connector. Done carefully, modifying the connector appears to be safe.

Rather curiously, the SPS450VA only charges its battery when its power switch is turned on and its outlets are powered up. This complicates simply storing the unit if it is otherwise not in use.

Battery Removal and Reinstallation

Best Power chose to install the SPS450VA battery in a unique metal cage. Several heavy paperboard shields inside the UPS may come out when you remove the cover. It's essential that these be put back exactly as they came out. If you don't have them, it should be possible to fashion replacements from heavy posterboard. I don't believe there is any special flame retardant aspect to their design. They serve primarily to keep the circuit board and battery leads from shorting out or becoming pinched within the case.

1. Shut down all loads attached to the UPS. Turn the toggle switch off.
2. Disconnect all loads from the UPS.
3. Disconnect the UPS line cord from the AC outlet or turn off the power supplying it. Clearly mark any switches, circuit breakers or fuses controlling power to the UPS and its load, so that no one will mistakenly turn them back on. (You must do this, as the battery circuit is LINE CONNECTED! Very dangerous!)
4. Flip the UPS over so the bottom panel is visible.
5. Remove the four screws at the outer edges of the case.
6. Turn the UPS back over and carefully slide the cover off.
7. Disconnect the battery leads.
8. Remove the two screws holding the battery cage in place.
9. Slide the battery and its cage out.
10. Remove the old battery from the cage, and place the new one exactly as the old one was situated.

If you don't know how the old battery was in place or don't have one, refer to the illustration below.

11. Slide the battery cage back into place and fasten its retaining screws. Be sure the power switch on the UPS is turned off. The two rubber pads on the battery cage face toward the outlet panel on the UPS.
12. Reconnect the battery leads, being sure to connect them correctly. (I believe the SPS450VA is protected against reverse polarity, but couldn't swear to such being the case.)
13. Replace the paperboard guides and route the battery wiring through them.
14. Slide the UPS's top cover back into place, flip it over once again and fasten all four screws.
15. Reconnect all loads to the UPS, and plug its power cord in or restore power to the circuit.
16. Turn the UPS power switch on. Allow several hours for the battery to charge.
Best Power Patriot SPS450VA Battery Installation - Illustration Copyright  2015 William R. Walsh.
Computer Communication

Present on the SPS450VA back panel is a nine pin serial port. Unlike modern UPS units, this port is limited in what information it can exchange with an attached device. This method of signalling is usually considered as a "dumb" method. Modern UPSes that still have an RS232 serial port usually use a so-called "smart" signalling method. This port is optically isolated for safety purposes.

A web page details not only the pinout of the monitoring port, but also how to make the SPS450VA work under Linux. The pinout below is taken from that page. I have not personally tested it.

UPS DB9 Pin / Function
PC Serial Port DB9 Pin / Function
1 - Shuts down the UPS when held high for five seconds.
4 DTR - Shuts down the UPS when held high.
3 - Normally open, connects to ground when a power failure occurs.
8 CTS - Indicates the loss of AC power.
4 - UPS Ground
5 Signal Ground
5 - Normally open, grounded when UPS battery is low.
1 DCD - Indicates safe computer shutdown when low.

You will require a pullup resistor (10K ohm) to provide for reliable signalling from the UPS to an attached device. These resistors are indicated as being installed on the PC end of the cable, going from pin seven (RTS) to pin eight (CTS). These parts should be readily available at RadioShack or any reputable electronic components dealer. The author of the previously linked page indicates that while the signalling levels used do not comply with RS232 specifications, that it worked for them.

Windows NT 4.0 and later include UPS monitoring software. It should be possible (though, again, I've not tried it) to configure this software to work with the SPS450VA. This information may also work with other operating systems that support "simple" or "dumb" UPS signalling. It may also be possible to create a simple visual signalling device with LEDs and a few supporting components.


Signalling will also occur via an audible alarm. In a rather clever bit of engineering, this alarm sounds more frequently as the battery level drops. What I've not found is a way to shut it off, short of physically removing it from the circuit board. (Which I generally do, as I find them irritating enough to warrant removal.) None of the DIP switches have any obvious effect on the alarm or its frequency. To Best Power's credit, their beeper implementation is nowhere near as irritating as other brands and models. When the beeper sounds, the unit's front panel LED turns off. It too cycles more frequently to off as the battery level decreases.

A less drastic solution would be to place a switch (with only nonconductive parts able to come in contact with the end user) in series with the beeper.

Beeper Module Closeup

The beeper itself is a Panasonic EFB-RD24411.

Technical Stuff

Note: I'm not an electrical engineer by trade, only someone who has a lot of enthusiasm, some knowledge and interest in electronics as a hobby. What's written here is believed to be generally correct, but like everything else in life: there are no guarantees. Don't base life or death decisions on the information presented in this section. In fact, don't base any decision or course of action on what's written here. However, if you have a correction or find something I've gotten wrong (whether major or minor), I'd certainly like to know about it.

I'll start things off by saying that some, maybe all of the heatsinks in this unit are live. I didn't check them all, but of the ones I could readily reach, they indicated direct connection to the battery. As we already know, the battery circuit in this unit is not line isolated. Definitely don't touch anything inside this unit so long as it is connected to any power source.

Inverter drive in this particular unit is provided by feedback used to monitor the transformer linking this unit's output to the outside world. Current flow through the inverter and its associated transformer are sensed to govern operation of the pulse width modulation circuitry. The transformer's operation is said to be maintained just shy of its saturation point to avoid issues with inductive pulses, oscillation or other instabilities in the inverter's power devices. A microcontroller, rather than a simple switching controller, is used to monitor and govern operation of the circuit.

This would certainly explain the formidable looking microcontroller within the SPS450VA. Even if the patents did not give signifanct insight into the age of this unit's design, the microcontroller would. It is an NEC PD78C12ACW, 64 pin DIP style IC with a massive footprint. The case is also marked "73601 FRW-0001A". NEC's datasheet places this MCU in their 78C10A family of products and indicates that it is a complete system on chip with onboard ROM, RAM, 8-bit CPU, arithmetic logic unit and an analog to digital converter. This MCU supports a low power standby mode and external ROM (of which more in just a bit). Also provided are a serial interface, and several timers with differing resolutions. Operating instructions are contained in a mask ROM.

This microcontroller is easily 3/4" of an inch wide and almost if not three inches long! It is clocked at 14.7456 MHz, right up against the 15 MHz maximum specification.

An external 93C46 serial EEPROM of unknown purpose is present on the board; perhaps it stores per-unit calibrations, battery aging information or other miscellaneous data.

For all of this sophistication in its inverter governance circuit, there is no such sophistication anywhere else. Despite not formally investigating to see how much of the microcontroller's time is taken up by its current set of tasks, I get the feeling that it is really rather terribly underutilized. No outward facing indication besides a single color LED exists, nor is there a test switch available to let the end user easily check whether or not the battery works. Scheduled self tests do not appear to be performed. Further, there is no other power conditioning capability (such as boosting or reduction of line voltage) present beyond the inverter backup circuit and surge suppression/noise filtering. A misisng, disconnected or bad battery does not produce any obvious warning. All you get is a standby inverter that is switched on to carry the load.

There would have been plenty of room on the front panel, and such would likely have been within the capabilities of the microcontroller, for display elements pertaining to line voltage and battery status. A cold start capability (the ability to produce AC power without first starting from utility power) is present. Although 50 Hz line frequency compatibility is indicated, it would appear that when cold started without an AC line reference, that the output frequency defaults to 60 Hz.

The output waveform is a modified sine wave type (more correctly: it's a stepped square wave type, where the output rests at zero for a brief period before being pulled up or down).

Other Models

I know of an SPS850VA having been made. Presumably there were models between it and the SPS450VA.

Your Help Wanted!

If you have any information regarding this UPS, no matter what it is, I'd REALLY appreciate hearing from you!

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Copyright 2015 by William R. Walsh. Some rights reserved. Your rights to reuse some or all of this material in other projects are fully detailed at the "terms and conditions" page available from the top level of this web server. In simple terms, permission is granted to use portions or the entirety of this page in your own projects, provided those projects do not contain advertising materials and no fee other than that necessary to cover reasonable duplicating or connection time expenses is charged. Such projects must also not be of an illegal, derogatory, defamatory or dangerous nature. Please don't parody my work even if the laws of your country or locale allow you to do so. Thank you.