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Circuits designed by David Johnson, P.E.
Last Updated on: Thursday, April 07, 2016 02:04 PM

Master Category List - Dave's Circuits

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Battery Monitor Circuits

12v Battery Voltage Monitor-Expanded Scale  -  The circuit below expands the battery voltage monitoring scale for a 12v battery so a more accurate voltage reading can be made.  The numbers printed onto the face of a standard 0v to 5v meter are changed so the scale ranges from 10v to 15v… [Hobby Circuit designed by David Johnson P.E., 10/16/05]
 

3 Volt Low Battery Voltage Flasher -  This circuit is designed to monitor two alkaline cells (3v) that form the battery often used in portable electronic equipment… [Circuit by David A. Johnson P.E., 12/24/98]

 

6v NMH/NiCd Battery Tester -  I designed this circuit to test rechargeable six volt battery packs under constant current conditions.  As designed, the circuit applies a 10 Amp load to the battery pack.  A heat sink must be used on the main power transistor… [Circuit by Dave Johnson P.E., 12/12/04]

9v Battery Voltage Monitor  -  This circuit turns on a LED whenever the voltage of a standard 9v battery connected to the circuit drops below 7.2 volts.  It uses a LTC1440 comparator, which also contains a 1.18v reference diode.  In standby mode, the circuit draws only 4uA . . . [Circuit by David A. Johnson P.E.,  07/09/06]


Alkaline Low Battery Voltage Indicator  -  In many battery powered systems a user would like to know when it was time to replace the batteries  before they were completely discharged, causing the device being powered to fail completely.  Alkaline batteries have an open cell voltage of about 1.5 volts.  As they are discharged, the voltage slowly drops.  When the cell voltage reaches about 1.25v, they have delivered about 90% of their stored energy . . . [Circuit by David Johnson P.E.,  06/17/12]


Expanded Scale 12v Battery Voltage Monitor  -  The circuit below expands the battery voltage monitoring scale for a 12v battery so a more accurate voltage reading can be made.  The numbers printed onto the face of a standard 0v to 5v meter are changed so the scale ranges from 10v to 15v. http://archil . . . [Circuit by David Johnson P.E.,  10/16/05]


Lead-Acid Battery Low Voltage Indicator  -  Lead-acid batteries should not be discharged below a certain voltage.  Discharging a cell below about 1.8v and can often damage it, which will result in a lower Amp-hour capacity.  Large battery banks are critical in off-grid energy storage systems.  One . . . [Circuit by David A. Johnson P.E.,  07/30/06]


Lithium Battery Tester  -  I bought some lithium ion rechargeable batteries a while back. I was planning on using them to modify some solar powered LED spot lights.  What I like about these new batteries is that they are the same size as a standard 1.5v alkaline AA cell . . . [Hobby Circuit designed by David A. Johnson P.E.,  02/05/12]


Low Battery Voltage Flasher  -  This circuit is designed to monitor two alkaline cells (3v) that from the battery often used in portable electronic equipment. It use an inexpensive IC from Panasonic that is connected to an efficient LED flashing circuit. When the battery voltage drops below a certain point the circuit flashes the LED. In the off state the circuit draws only 1uA, while in the active flashing state it draws 20uA.  . . . [Circuit by David Johnson P.E.,  01/01/98]


Low Voltage Indicator for Lead-Acid Battery  -  Lead-acid batteries should not be discharged below a certain voltage.  Discharging a cell below about 1.8v and can often damage it, which will result in a lower Amp-hour capacity.  Large battery banks are critical in off-grid energy storage systems.  One . . . [Hobby Circuit designed by David A. Johnson P.E.,  07/30/06]


Nine-Volt Battery Voltage Monitor  -  This circuit turns on a LED whenever the voltage of a standard 9v battery connected to the circuit drops below 7.2 volts.  It uses a LTC1440 comparator, which also contains a 1.18v reference diode.  In standby mode, the circuit draws only 4uA . . . [Circuit by Dave Johnson P.E.,  07/09/06]


NMH/NiCd 6v Battery Tester  -  I designed this circuit to test rechargeable six volt battery packs under constant current conditions.  As designed, the circuit applies a 10 Amp load to the battery pack.  A heat sink must be used on the main power transistor . . . [Hobby Circuit designed by David Johnson P.E.,  12/12/04]


Voltage Monitor for a 9v Battery  -  Nine voltage batteries are used in a wide variety of electronic devices.  But, you often don’t know when it is time to change the battery until the device stops operating.  The hobby circuit below provides a visual indication when the battery needs to be . . . [Hobby Circuit designed by David Johnson P.E.,  07/09/06]

 

More Battery Monitor Circuits

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