Versatile Volt, Ampere, and Power Meter

Intro: Versatile Volt, Ampere, and Power Meter

Multimeters are suitable for many purposes. But usually, they only measure one value at a time. If we deal with power measurements, we need two multimeters, one for voltage and the second for Ampere. And if we want to measure efficiency, we need four multimeters. Here we will build small and inexpensive meters to do these measurements.

You can watch my video about building it if you want:

STEP 1: Bill of Material

Such a meter is a simple build. It consists of these parts:

- 1x Meter

- 1 x 3D printed case

- 5 x Banana plugs

- 1 x 9V battery incl. connector

- 1 x switch

- 4 x 3mm screws

STEP 2: The Meter

We get them in three versions: For 33 volts and 3 or 10 amperes and for 100 volts and 10 amperes. For small projects, I recommend the smallest version. Because it shows two decimal digits instead of one. The prices for all three versions seem to be the same.

The accuracy of the smallest version is sufficient for most normal hobby measurements. It will not be enough for very low voltages and small currents like deep-sleep measurements. But most Multimeters are also not very good at measuring low currents.

STEP 3: The Box

First, you have to download
the STL files and from Thingiverse:

https://www.thingiverse.com/thing:2789890

and print the box on your 3d printer. If you do not have a 3D printer, you can use any other case. You find them cheaply on Bangood or Aliexpress. My boxes measure 8 x 8 cm and are 4 cm high.

Just print them with your 3D printer. If you plan different versions, maybe you select the color accordingly.

Next, you have to connect banana plugs to the cables of the meters.

STEP 4: Connect the Wires

We use Banana Plugs as connectors and connect one black plug to the thick black wire and one to the thick red one. The two red plugs have to be connected internally.

The yellow wire is connected to the green plug.

The thin black and white wires have to be connected to a 9-volt battery connector. Insert a switch into the red wire to switch the device off if you do not need it. The battery will last around 50 hours.

STEP 5: Connectors

I use connectors without isolators and heat-shrink tubes for isolation. For crimping, I use the tool shown in the picture.

STEP 6: Assembly and Test

Assemble everything according the diagram. Connect the two red banana plugs with a 20 AWG wire and fix the meter and the switch with hot glue if necessary.

Laber the input and the output pins and connect the input to a power supply or battery. Connect a resistor to the output and check if your meter shows values bigger than zero. If you do not trust the values double check with your multimeter.

Comments

[cwarmbold]

Why do we need those 2 red banana plugs? They are not hooked up to anything. Couldn't we just have 3 Plugs? (Input, Output, Voltage)? or does it have any practical benefits?

[Andreas Spiess]

If I remember right two are input, two are output for current and the green one is for voltage. It has to be connected to the input or the output or to the load if you have long wires.

[Andreas Spiess]

The red banana plugs are connected to in and out.

[JerryE4]

Very nice. I have one of these meters laying around somewhere. I recall I purchased it to be used in a power supply I was building however I became angry that the blasted thing took so long to get here from China, so I went ahead and used a much earlier model with fewer bells and whistles. I never did get around to changing the meters and the one I have installed does a good enough job so in the future box it went. Then when the wife became so very ill, my daughter came to clean the house so the wife could get around with her walker and most of my projects disapeared in a cloud of dust, in a box stored somewhere that only God and my daughter know.

[JackSoldano]

Just finished watching your Youtube video where you used this, once I've finished with my LoRa project I think this is next on the to-do list! :)

[RodyK1]

Is it useful to protect it with a fuse like 3A fast blow. And yes where would be the best place ?

[Andreas Spiess]

Because the meter costs less than 10 $ I did not include a fuse. You can include one in either of the thick wires because it does not matter which cable your fuse interrupts.

[oragamiunicorn]

the in and out markings spoil the look of the case, could you not adapt the 3d printing file for the case to have the words embossed?

[Andreas Spiess]

Maybe. I did not try.

[russ_hensel]

Note that the two "ground" connections are not actually at the same potential, the shunt for the current measurement separates them and causes a small voltage drop. Do not connect them together external to the meter.