Introduction: Lithium Li-ion 18650 Multimeter
Getting the wrong Voltages on your Multimeter, Battery always flat when you need to use it.
Sick of buying expensive 9 Volt batteries for your Multimeter, That only last a few months.
Then build this simple 3.7 Volt to 9 Volt Step up Converter circuit and forget about buying another 9 Volt battery.
Simply recharge it when it goes flat.
Step 1: Fitting the Battery Inside the Multimeter
First thing is to dis-assemble your Multimeter and drill a hole to suit the DC socket. (Used to recharge Battery)
Then using a sharp Knife cut the Plastic case to fit the 18650 Battery.
Put the case back together to check battery fitment .
Note: Will not fit smaller sized Multimeters Due to size of the 18650 Battery. 65mm x 18 mm
Step 2: 9 Volt Step Up Converter PCB
Now assemble the 9 Volt Step up Converter on a piece of Vero board or make a PCB from from the supplied Eagle board file.
Part values are not critical as a Trim pot is used to set the final Voltage.
Parts Youll' Need:
1 18650 Lithium Lion Battery
1 Dc power socket
1 22k or 27k Resistor
1 180 ohm Resistor
1 10k or 5k Variable trim pot
1 22uF or 47uF Electrolytic Capacitor
1 100uF Electrolytic Capacitor
1 10pF to 50pF Ceramic Capacitor
1 MC34063A DC to DC converter IC
1 IN5819 Diode
1 170uH inductor
A piece of Vero board or make a PCB
Step 3: Put It All Together
Solder a wire from the Positive of the battery and then to the center pin of the Dc Socket.
Solder a wire from the Negative of the battery and then to 1 side of the Dc Socket switch.
Solder a wire from other side of the Dc Socket switch and connect to the negative input of the step up converter PCB.
Note: the DC Charging Socket is wired so it dis-connects the Stepup converter when charging the Battery.
Solder a wire from the Positive of the battery to the unused contact of the Multimeter switch
Solder a wire from the other side of the Multimeter switch to the Positive input of the step up converter PCB
Now solder the 9 Volts input wires from the Multimeter to the outputs of the step up converter PCB.
Note: The Positive Lead from the battery To the Stepup converter is dis-connected when the Multimeter is switched off.
Adjust the trim pot so that the Step up converter delivers 9 Volts at its output. (can output up to 27 Volts)
Now fit it all back in the Multimeter and reassemble.