Volts, Amps, Power and Temperature Tester

15/8/21

Hello my friends and RC enthusiasts from around the World. I hope you are all well.

In this post I will be showing you this super useful voltage, current, power and temperature tester. I named it Cyclops, as the first version only had one display that read only the voltage and current. In this second version, I changed the display to an OLED tester that has lots more functions. I also found I needed a temperature tester in certain circumstances, so I installed one on this device. The device can show me a lot more results without me switching out my multi meter and changing ranges. Using this device also uses less wires, which is a lot tidier, therefore a much safer device to use. If you read my post on the 300 watt test rig, you will know I built this little device in a hurry and I forgot to take pictures. 

The front and rear panels are made from reclaimed fire retardant marine plywood. The case is from the inside of an old desk top pc and was actually a HDD caddy/holder. The 2 displays I used were actually new and were for another project however, it was a lot cheaper to use the displays rather than buy 2 new multi meters. I have since replaced the displays for the other project. Inside the case is a LM 2596 buck converter used to power the temperature display. The converter was £3, the top display was £9 and the temperature display was £5. At the rear are 2 pairs of gold plated binding posts, which were £5. I would have preferred to use plug in sockets but there was not enough space inside the small enclosure.  A total of £22 spent on this device. It's not cheap, I realise but it perfect for my needs. It also frees up my main multi meter to be used elsewhere. This unit looks like a piece of scrap as it was built in a massive hurry. Again if I get time in the future, this is another project that needs re-casing.

As always, if you choose to follow these instructions, I take no responsibility for any injuries, damages or losses. Please double check your wiring and test your connections. 

As I built this device on the fly, I did not (at that time) make any circuit drawings but I have since drawn up diagrams for your convenience and can be found below.

At the top of the page is the diagram to wire in the volt, amp and power meter. It only uses 4 of the 5 wires. The fifth wire is not needed in this particular setup. In the middle of the page is the wiring diagram that shows the wiring for the temperature display. At the bottom of the page shows the LM 2596 buck converter. The pick star indicates were it should be situated and wired.

I decided to make a new drawing showing exactly how the LM 2596 is wired. The micro potentiometer must set the output voltage to 5VDC as this is the correct voltage to operate the temperature display. The LM 2596 can operate up to 28VDC and the output is now set to 5.0VDC.

 The above picture is of an actual LM 2596 buck module. In this picture I am using one in another project. I do not have any new ones to show as I have ran out. I must order some more of them as they are handy to have in your spare parts. On the left of the converter are the DC inputs and has a input voltage maximum of 28VDC. The blue micro potentiometer in the converter can adjust the output voltage but only under the input voltage (ie less than the input voltage). I have used many LM 2596 modules over the years and I have found them to be ultra reliable and super robust. I have never had a problem with them so far. They are also quite inexpensive to buy in packs of 5. 

The picture above shows the 2 pairs of binding posts. One pair of inputs and one set of outputs. As I earlier stated, I would have liked to have used plug in sockets when building it. I may, at a later date modify the back plate with sockets if space allows. If you intend to use binding posts, buy some decent ones, as the cheaper ones fall apart after a short period of time. Believe me, I have used them in the past and had to replace them quite early due to cheap parts and sub par materials. 

In the picture above is the top volts, amps and power display. This module is constantly testing the voltage, current and power.. It also has accumulative power, capacity and time. It also shows internal temperature. The display is an OLED type and although small it is very clear to observe. The display is currently reading 7.3 volts, 3.14 amps and the supply has a power of 22.92 watts. It has been running 4 minutes and the internal temperature is 30 degrees centigrade. I has discharges 653mAh with a power of 4.7Wh. As you can see, this display is quite comprehensive and come with instructions shown below.

The picture above shows the various wiring methods that can be used. As you can see the display have a working voltage range of 4 to 20VDC, which is enough for me. If I wished to read higher voltages (which I can), all I need to do is put a 9V (PP3) battery inside on the inside connected to both displays. This will then isolate both voltage supplies.

The second page of the instructions (above) details the operation of the display module. It also lists specifications and tolerances. I am quite impressed with the functions of the little device and will use them in future projects. 

The picture above shows the unit being powered from a 2S LiPo battery and is showing a voltage of 7.8VDC. It is reading 0.00 amps as the is nothing on the outputs to act as a load. The temperature in the room is a balmy 27.1 degrees centigrade. 

In the picture above you can see the unit being used to test and develop my load rig. On that test I am using a 7.2 volt NiMH battery pack and under load is at 7.3volts with 3.14 amps passing through. The display at the bottom is reading the temperature of the big alloy heat sink and has a reading of 28.3 degrees centigrade. All I did was plug it in and record the results with different resistances and temperatures, easy. Also there are enough cables there already without the need for more multi meter test leads. In the picture above you can see a red glow coming from inside the case. This is only the red LED operation light of  the LM 2596 and is normal.

As you can see, I have copied the dimensions of the unit and built another case which can sit on top. The unit at the top is a NiMH and 2S automatic battery charger I built and will be my next post. 

You should now have all the information you require to build your own multi meter. The only other thing you will require is an enclosure to house all the components to make it safe. Ensure all your connections are strong and insulated. Test the continuity of the cable and ensure the are no possibilities of short circuit. Again, if you decide to follow my instruction, please be careful.

I hope you have enjoyed this post and found it of use.

Until my next post, take care.

CATXLS.

15/8/2021

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