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Calculating maximum battery charging current

Max. charging current 

Ib = {(Vp – Vd) – Vb} divided by Rs

 ……. 

Equation 1

 where,

Vp

 = The output voltage of the power supply

Vd

 = Forward voltage drop across D1 (0.2 V for < 1 A and 0.4 V > 10 A)

Vb

 = Battery voltage at fully discharged condition (Normally 11.4 V for 12 V

and 22.8 V for 24 V)

Rs

 = Equivalent series resistance (In this case, two 1 Ohm in parallel = 0.5 Ohm)

Assuming that the voltages of fully discharged 12 V and 24 V batteries to be 11.4
V and 22.8 V respectively, the maximum charging currents will be as follows as
per 

Equation 1

:

Charging current in factory pre-set condition

:

In the factory preset condition, resistors R1 and R2, each 1  Ohm, 35 W are
connected in parallel. The charging currents will be as follows:

For 12 V battery backup

 = (14 V – 0.2 V – 11.4 V) divided by 0.5 Ohm = 4.8 A, 

say 5A

For 24 V battery backup

 = (27.6 V – 0.2 V – 22.8 V) divided by 0.5 Ohm = 9.2 A, 

say 10 A

Adjustment to reduce the values of the maximum charging current to half

The charging currents can be reduced to half the values by disconnecting either
R1 or R2. R1 and R2 are connected using quick connect terminals. To discon-
nect, remove one of the two terminals of the selected resistor. Now only 1
resistor will be in series and the resistance Rs will be 1 Ohm instead of 0.5 Ohm.
The charging currents will now be as follows:

For 12 V battery backup

 = (14 V – 0.2 V – 11.4 V) divided by 1 Ohm = 2.4 A, 

say 2.5 A

For 24 V battery backup

 = (27.6 V – 0.2 V – 22.8 V) divided by 1 Ohm = 4.6 A, 

say 5 A

Page 6

Summary of Contents for BBM-12100

Page 1: ...Owner s Manual Please read this manual before operating your unit Battery Back up Model BBM 12100 ...

Page 2: ...Safety instructions 2 Description 2 Principle of operation 3 4 5 6 Installation 7 8 Specifications 9 Warranty information 10 INDEX ...

Page 3: ...ontain very corrosive diluted sulphuric acid as electrolyte Precautions should be taken to prevent contact with skin eyes or clothing Batteries generate hydrogen and oxygen during charging resulting in evolution of explosive gas mixture Care should be taken to ventilate the battery area and follow the battery manufacturer s recommendations Never smoke or allow a spark or flame near the batteries U...

Page 4: ... the battery terminals and the load is connected to the load terminals The voltage from the power supply is fed through the isolating Schottky diode D1 to the load and to the battery through the charging current limiting resistors R1 and R2 Diode D1 provides isolation between the power supply and the battery to prevent the battery from feeding back into the power supply circuit D1 has a forward vo...

Page 5: ...charging of the battery will be 14 V minus drop of 0 2 V to 0 4 V across diode D1 i e 13 8 V to 13 6 V Power supply voltage for 24V SLA battery backup 27 6 V The output voltage for the load and for float charging of the battery will be 27 6 V minus drop of 0 2 V to 0 4 V across diode D1 i e 27 4 V to 27 2 V As long as the power supply is operating normally it will supply the load as well as charge...

Page 6: ... to approximately 5A Battery backup application using 24 V 100 AH battery When using this unit in the preset condition for 24 V 100 AH battery backup application the charging current will increase approx two times to 10 A which is equivalent to approximately C 10 0 1C Please check with the battery manufac turer if this maximum charging current of C 10 or 0 1C is acceptable for the 100 AH 24 V batt...

Page 7: ... resistors R1 and R2 each 1 Ohm 35 W are connected in parallel The charging currents will be as follows For 12 V battery backup 14 V 0 2 V 11 4 V divided by 0 5 Ohm 4 8 A say 5A For 24 V battery backup 27 6 V 0 2 V 22 8 V divided by 0 5 Ohm 9 2 A say 10 A Adjustment to reduce the values of the maximum charging current to half The charging currents can be reduced to half the values by disconnecting...

Page 8: ...n and possibility of fire Hence for safety a very fast acting fuse of appropriate current capacity should be connected in series with the positive cable and should be placed as close as possible to the positive terminal of the battery Type ANN series fuses and Fuse Block No 4164 made by Bussmann or similar are recommended The following Table gives the recommended sizes of cable and fuses Current C...

Page 9: ...n on page 3 Switch off the power supply Connect the positive and negative output of the power supply to the input terminals of the unit marked INPUT POSITIVE and INPUT NEGATIVE respectively Connect the DC load to the terminals marked LOAD POSITIVE and LOAD NEGATIVE Connect the battery to the terminals marked BATTERY POSITIVE and BATTERY NEGATIVE CAUTION ENSURE CORRECT POLARITY OF ALL CONNECTIONS P...

Page 10: ...V battery Up to 90 A for 24 V battery Charging current to battery Up to 5 A for 12 V battery Up to 10 A for 24 V battery NOTE The unit is pre set for charging current of up to 5 A for 12 V battery and up to 10 A for 24 V battery The charging current can be reduced to half the above values by disconnecting one of the two resistors R1 R2 Please see under Principle of Operation Adjustment to reduce t...

Page 11: ...t to remedy the defect by anyone other than the Warrantor shall render this warranty void There shall be no warranty for defects or damages caused by faulty installation or hook up abuse or misuse of the equipment including exposure to excessive heat salt or fresh water spray or water immersion No other express warranty is hereby given and there are no warranties which extend beyond those describe...

Page 12: ...110 17 Fawcett Rd Coquitlam B C Canada V3K 6V2 T 604 525 3836 F 604 525 5221 e mail samlex samlexamerica com website www samlexamerica co BBM 12100_Manual_Feb2011 ...

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