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Matrix-UPS run time theory

Issue:
Where can information be found on the method the Matrix UPS calculates its estimated runtime?

Product Line:
Matrix UPS

Environment:
All serial ranges

Cause:
This information may be required during routine troubleshooting.

Resolution:

The software algorithm on the Matrix UPS calculates the "Estimated Run Time" based on five variables:

1. Age of the batteries
2. Type of battery (lead acid)
3. Number of battery packs
4. Type of battery packs (i.e. SmartCell or SmartCell XR)
5. Percentage of load being applied to the UPS.

When a fully charged battery begins to discharge (with a good size load) initially its voltage drops off rapidly. After a short time the voltage levels off for a while, ramps down steadily then drops off rapidly once again when the battery capacity is almost used. To allow the UPS to predict when the battery will be exhausted (39 VDC) it stores four numbers which represent a typical discharge curve (constants). By knowing where it is in the discharge curve, the UPS will be able to estimate the remaining run time. Three of the four battery constants are set depending on the battery type (i.e. lead acid). The fourth constant (bottom of the curve) is set after a deep discharge or by performing a run time calibration.

A calibration might establish that at 40 volts DC the batteries are 2 minutes from reaching 39 volts (which is always the end of discharge). As the batteries age, the 2 minutes to shutdown point will climb the discharge curve to a much higher value and the estimated run time displayed will be decreased accordingly.

If the UPS load is too light compared to the number of battery packs, you will observe that when the UPS is on-battery, the estimated run time will freeze since the battery voltage does not ramp down rapidly enough to cross over the set points in the discharge curve.

The estimated run time can also be inaccurate if there is a miscalibration of the fourth battery constant. When the UPS is first installed with a brand new set of batteries, this constant is set to a Hexadecimal value of "B0". To the algorithm this represents a battery that is brand new and should follow a normal curve. If the constant is too low (below "80" Hex) the UPS might begin a graceful shutdown too soon or show an abnormally short run time.

Conclusion:

Battery run time estimation is not an exact science. There could be as much as 30% error (on a good calibration). To minimize the inaccuracy on the run time display please refer to the KBase document titled "Requirements for Matrix UPS "Run Time Calibration"


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