Battery_Charger

• Battery Charger for (14.4 and 18.0) V NiMH Tool Batteries Experimental
• Requires External 24+ V, 2 A, DC power supply.

Revision 3

• Adjusted Footprints.
• Bias network for RV1 adjusted.
• Bleed resistors added to large capacitors.
• Cascode circuitry added to +BATT monitoring to protect MAX713 sense input.
• D2 replaced with Q2 to provide more ideal diode behavior and provide reverse input protection.
• External temperature monitoring circuitry added.
• Low pass RC filters added to +BATT and -BATT sensing pins.
• Reverse input protection added to the DC input and Battery Outputs using P-Channel power MOSFETs.

Revision 2

• Restructured board to have separate analog and switching ground planes (stared)

Prototype 0

• Resistor Footprints are WAY too big.
• MAX713 Will regulate voltage across BAT- to BAT+ when measured using resistive load.
• Device successfully achieves current regulation during fast charge.
• At 24 V DC Input the LM7805 Gets hot, may need heatsink.
• Q2 was originally a 1N4001; Replace with 1N5821 due to excessive heating.
• Target Batteries get HOT near end-of charge sequence.
• Device has NOT been observed to perform DV/dt charge termination.
• In absence of reverse input protection, installing a charged battery backwards will destroy R7...R10.

Revision 0

• Design is experimental, based on MAX713 Charge Controller.
• Concept: Replace the Linear Regulated Supply with a Buck Converter.
• Design is intended to charge at C/2 (~1.8 A)
• No use of temperature feedback is employed.
• No effort is made to reverse-input protect board.