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.

MC34063A PDF

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.

Comments

[twolf8]

Great idea. I had also been looking for a basic circuit to test MC34063's. Does the DMM actually run on 9v or does it step the voltage down internally?

[Mutt Man]

The DMM runs off of 9 Volts, Here we use the MC34063 to Step up the 3.7 Volts from the 18650 Battery to 9 volts used by the DMM.

[Cliffystones]

Hello Mutt Man,

A few questions regarding parts. There are differences in part values between your build and the one in the On Semi spec. sheet. R1 and R2, I'm assuming, are replaced by the pot. But there is a 1500pF cap on the spec sheet that you don't mention, along with a 0.22 ohm resistor and a 330uF cap. Could you post a copy of your final schematic? I'd like to avoid creating a cockroach-sized roadside bomb :)

Also, what did you do for the 170uH coil? There are 150uH and 20uH coils available cheap that I'll probably use in series before winding my own.

Thanks!

[neopolitan]

hang onto that dse dvm dude it's about to become a collectors item!!!

[Mutt Man]

Thinking about making an offer were you? LOL

[HerbertD1]

Best if you have a meter with a real mains switch, for meters with Buttons like on your remote the Voltage must be allways there. This converter consumes 3mA in Standby, if you use it often not a problem otherwise it may have killed the accu by deep discharge when you need it. Better to put the protection circuit of an cell phone accu in additionally, if there is place left.

[lexak]

The IC is specified for input voltages between 3-40V and seems to crap out not far below the 3V mark, so probably adding a general purpose diode in series on the input will serve as a simple undervoltage lockout ;-)

[Mutt Man]

If you read the text you will see that the Step up converter will consume no power when you are not using the DMM as the battery is disconnected when the DMM is switched off.

[techprolet]

Cool idea, I've always had the same problem with my multimeters:-)

[p_leriche]

You don't say how to charge the battery. If anyone who doesn't know better simply plugs in a mains adapter (plenty have the right kind of power plug) then there is a SEVERE RISK of fire!

[Mutt Man]

To recharge the Battery you use a Lithium Li-ion Battery charger, that is suitable for 18650 type batteries. Just like any cellphone you have to use the right charger.

[HerbertD1]

I was to lazy to doe that and simply put two in series. Bur then it is of course dangerous when you measur higher than 50 V. Because they are connected to the accu, which will not fit inside the Meter.

[HerbertD1]

The pure Display may work with 3.7V. But to measure higher Resistances there are 9V used out of convenience. And so Meter circuits for 5V are used, maybe because they are cheaper and/or more abundant.

[wold630]

This is great! Thanks for sharing your project and information!