Automatic Float Cum Charger For Monitoring Starter Battery Of DG Sets & Fire Fighting. You might have always felt that there is a need for an external Float cum Boost Charger for the Starter Battery of the DG Set. Even though the Dynamo coupled to the DG Set is meant for keeping the starter Battery in charged condition, the same is not normally effective. Because the battery can get charged through the dynamo, only when the dg set works for some time. Since usually the DG Set is not in operation for many days, the dynamo is not effective to keep the Battery in charged condition. As a result, the state of Charge of the Battery Set goes down and down every day and ultimately when the DG set has to started, there will be no sufficient energy in the Battery for starting the DG Set. It is for this reason. There is always a need of an external Float cum Boost charger. Which will keep the Battery Float charged or Boost charged. Depending upon the requirement of the Battery.

The following are the essential functional requirements of the External Float cum Boost Charger that monitors the state of charges of the Starter Battery of a DG Set.

Caution

• The main function of the External Float cum Boost Charger is to keep the already charged Battery in fully charged condition, by compensating the continuous internal Losses taking place in the Battery; this will ensure Battery to be in a fully charged and healthy condition. to be able to provide the full power for starting the DG Set, whenever called for.
• The second requirement of the external Float Charger is that it should changeover automatically from Float mode of Boost mode. Whenever the battery is down and upon boost charging the battery. The charger should return automatically to the Float mode. This automatic changeover from Float to Boost and vice versa, not only eliminates any Manual attention to Battery, but it also ensures the Battery to be in a full state of charge all the time.
• The Float cum Boost Charger should be necessarily be an SCR Controlled Charger having DC Output stabilization of +1% in both Float and Boost mode, so that even if the AC mains input Voltage goes up or down, the DC Output Voltage of the Charger will remain stabilized within ±1%, eliminating any fear of Undercharging or Overcharging of the Batteries, that can caused due to AC Mains Voltage Fluctuation. A Manually controlled Charger without DC Output Voltage Stabilization is as good as not having the External Charger.
• The Floating Voltage is set at 2.20 V Per Cell i.e. 26.4 V For The 24 V Battery and the Boost Charge Voltage is a Constant Voltage of 2.40 V Per Cell i.e. 28.8 V for the 24 V Battery.
• In the Boost mode, the maximum charging current is Limited to 6 Amps. In case of DC Set using a 24 V 180 AH Battery with 2 Nos. of 12 V 180 AH Batteries in series. In case of higher rating DG Set, where an effective 24 V 360 AH Battery is used with 4 Nos. of 12V 180 AH Batteries in series / Parallel, than the maximum Boost Charging Current will limited to 12 Amps.

Principle Of Operation Of Automatic Float Cum Boost Charger
The Principal of Operation of the Float cum Boost Charger ment for the starter Battery of the DG Set & Fire Fighting is a under :

• Normally when the charger is energized with the fully charged Battery of 24V across the charger will choose the Float mode, provided the Battery is in charged condition. Due to the soft start feature, the charger will energized in Float mode and since the Battery is quite fully charged, The charger will continued in Float mode only. The Charger Operating in its Float the Battery at 2.20 V per cell stabilized within ±1%
• If the Battery draws an excessive Current, of more than. 1.2A. The solid state Current Censor will sense the same and through the Mill volt Amplifier (MVA), it will drive a relay, to change over automatically the mode of operation of the Charger from Float mode of Boost.
• The Charger in Boost mode will charge the Battery at a higher constant voltage of 2.40 V per cell. Providing adequate charging current to the Battery. If the Battery is fully starved, The Battery will draw at the beginning of its Boost mode charging, its proper charging current.
• The total output Current of the Charger will limited to 6 Amps., being the practical charging Current for the 24 V 180 AH Battery of the DG Set.
• As the Battery picks up charge the charging current through it, will progressively decrease, Thus the Boost charging carried out at a constant applied voltage of 2.40 V per cell allowing the Battery to draw its required charging current not only initially, but thereafter also as Battery picks up charge As the charging Current through the Battery decreases progressively, a moment will come for returning the charger to its Float mode operation This is done by sensing the falling current through the Battery below a specified charging current level, for which a level of 1.2 Amps or below is fixed for changing over the mode of charger from Boost to Float, Thus when the falling current goes below 1.2 Amps the solid state sensor Circuit (MVA) operates to drive a relay, to put the charger back automatically to its Float mode. in the Float mode, a constant voltage of 2.20 V per cell is applied across the Battery still needs some charging, the Float mode operation itself will help to charge the Battery at lower Currents, over a long period, to complete the very small balance charging required.
• In the Float mode operation, the charger will float the Battery at 2.20 V per cell and if for some reason, the discharged Battery tends to draw over Trickle Charging Current beyond 1.2 Amps. it will change over to Boost mode and then return to Float mode.
• The Float cum Boost Charger is also provided with manual mode of operation In the manual mode of operation of the charger, one manually applies the Voltage as required either for charging or for Floating by selecting the switch SW 1 to manual position, In the manual mode one has to manually adjust the voltage as required and bring back also manually. in Manual mode, the selection, adjustment of Voltage /Current, retraction back to normal etc. are manually done. Normally, the manual mode is not restored to, except when Auto made fails or when one wants to give an extended Boost Charge to the Battery with full manual attention.
• The Charger also incorporate a Single Pole 2 way Toggle Switch to bypass the Automatic selection of Float / Boost operation and decide at will, we there we want to consciously select Float mode or Boost mode for any sort duration, Over riding the Chargers Logic to Automatic Changeover between Float and Boost mode.
• In case of 24 V 360 AH Battery, the applicable current values will be double the above values.

New System Traction Battery Charger
The conventional Traction Battery Chargers not only do not have any controls for setting the starting or Finishing Currents, but there is also no feature of constant Current charging in them. The serious disadvantages of charger can be summarized as under.

• Longer Recharging Durations due to Non - adoption of constant Current Charging.
• Lack of provision for Setting /Controlling Starting and Finishing Rate Charging Currents.
• No Reliability in the method of determining the point of termination of charging.
• Strong possibility of undercharging before gassing Over Charging after Gassing.
• Wide Variations in Battery Charging Current due AC Mains Input Voltage Fluctuations.

You might to be able to completely eliminate the inherent disadvantages of the conventional Older Design of Traction Battery Chargers, when you go in for New System Traction Battery Charges. The SCR controlled New system Traction Battery Chargers are of Constant Current type, both in respect of higher starting current require due to the point of Gassing and also the Lower Finishing Current after Gassing. When the Gassing occurs, the New System Charger charging the Battery at a higher Current of Staring Rate Level. Automatically changes over to a lower constant current charging at the finishing Rate Level. For instance, the New System Charger of the rating that you require , Charges 72 V Traction Batteries at a starting rate Constant Current of 20 Amps But when the Gassing occurs at the 2.35 V per cell, the charging Current automatically reduced to the Finishing rate Constant Current level of 10 Amps. This continues, till the voltage signifying the End of Charge, namely 2.65 V Per cell is reached, at which point the charger is automatically de-energised, terminating the charging, whether it is the Staring Current or Finishing Current, the same remains stable within + 2% of the set value. Further the New System Battery Charger's provide you the flexibility ti re-set Staring Current and the Finishing Current at any desired value, which facility is totally unavailable in the Conventional Traction Battery Chargers of Old Design.