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Overview
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Batscan is a battery monitoring system built as a modular data acquisition system where a PC computer evaluates and stores the data collected from decentralized measuring devices (modules) containing analog to digital converters. A RS485 serial bus network provides the communication link between the PC and all connected modules. The bus also supplies power to the modules.
Safety issuesA battery has normally only two connection points, the + and - terminals, in a large UPS battery there is one thick cable connected to each terminal. These cables can carry a very high current and the voltage is often several hundred volts, it is therefore very important to protect the cables from mechanical stress and ware to avoid any risk for a short circuit. The cables must also be well isolated for human protection. This is not a very big problem with only two cables between the battery and the UPS.However, if a battery monitoring system is installed the number of connections required to the battery can increase to several hundred. Each of them adding a potential risk for battery discharge, short circuit and human injury. Batscan recognizes this as the most critical safety issue with any battery monitoring system and uses several combined methods to address this particular problem.
High Voltage Isolation TransformersThe voltage measuring modules are internally isolated with a high voltage transformer that separates the digital side connected to the communication bus from the analogue side connected to the hazardous battery voltage.
Current Limiting ResistorsAll connections to the battery cells to be monitored are made trough protective high ohmic resistors. These resistors provide the primary protection barrier between the monitoring system and the battery.By using resistors instead of fuses maximum worst case current is limited to a safe value under all conditions. For example; Even if the measuring wire from the +terminal of the first cell accidentally is shortened directly to the −terminal of the last cell in a 500 Volt battery, the current through the protective resistor cannot exceed 250µA (0.000250 A) with a maximum heat dissipation of 0.125W. |
Under normal, no fault, condition the maximum current drawn from the battery is less than 30µA (0.000030 A).
Separate power supplyAll measuring modules are powered from the communication network and do not rely on the monitored battery for its operation. This also preserves the battery's integrity.
Observe Without AffectingBatscan is a true monitoring system intended only to observe the battery, without any means of affecting it in any way, not even in the event of a fault condition in the monitoring system itself.This means that Batscan can not inject any current, AC or DC, into the battery, nor will it attempt to send any commands to the UPS to initiate a test procedure. However, Batscan is fully compatible with any automated scheme for battery tests initiated by other components in the power system, including periodic discharges or reduction of charge voltage used by some UPS's for determining battery condition.
No missing dataSince Batscan continuously monitors all parameters of the battery at full speed, the results from any power outage or battery test - whether automatically or manually initiated, will always be recorded at maximum resolution by the PC.For each complete measuring cycle, which is typically repeated every 5 seconds, all individual channels are measured simultaneously and their new value are compared to the last value saved by the PC if the difference exceeds a predefined minimum-change-to-save-threshold the new value will be saved together with a timestamp. All measured values are also compared to predefined low and high alarm thresholds, when all channels measures within their respective limits a normally open (NO, 1B) isolated relay contact will be activated to indicate 'Battery OK' status. This relay contact functions as a summary alarm and is typically connected to the site's central alarm system. |
Simplified schematic diagram
In a battery of good condition the values shall balance well around the average of all voltages within the battery.
The graphical user interface gives a clear view of all cells deviation from their optimal value. A too high or too low value will be indicated with color marking of the faulty cell.
A serial COM-port or a USB-port is used for connection to the Batscan Network Interface Module (BNIF) that links to the RS485 serial bus via an isolation transformer, and to an external alarm system via a floating relay contact.
The relay contact will only be activated (closed) when all measured values are within specified limits. In all other situations the relay contact will be open.
A small AC-adapter serves as power supply for all modules connected to the network. The adapter is typically connected to the same AC source as the PC computer. Alternatively the bus can be powered from a DC source with 9-15V.
The Batscan network uses standard modular cables and connectors internally inside the IP65-enclosues and for short external distances of up to 50m. For longer cable lengths or noisy environment high quality DeviceNet cables is required. Belden type 3084A can be used for total network length of up to 250meters. And the thicker cable Belden type 3082A allows the network to extend to 1000m.
The voltage measuring modules can be individually placed along the battery, or grouped together in IP65 enclosures, in both cases with wires connecting to the battery terminals via protective resistors.
The network links through each module. From the last module in a battery the network may continue to the next battery.
This simplified schematic diagram shows an example with a small 24 cell battery, requiring only three voltage modules. A typical UPS battery with 192 cells will require 24 voltage modules.
A common battery configuration that is gaining increased popularity for UPS is 2 or more strings with 32x12V SLA block-batteries in each string, this will require 4 voltage modules per string.
Besides cell and block voltages, Batscan can measure and record several other parameters from up to 15 batteries simultaneously:
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| Safe Voltage | |
| Low Current | |
| Hazardous Voltage & High Current | |