Arduino Dual Output Power Supply
23/10/21
In this post, I am going to be showing you my build process for a dual outlet DC power supply. The main reason for the build was, I needed another DC power supply. I also wanted my son to safely use a small DC power supply for testing and repairing his own RC cars. My power supply was too powerful for his intentions and could easily destroy his precious RC vehicles. As the title suggests, my son and I are also very interested in Arduino projects that nearly always require 2 DC power supplies. We intend to learn to print 3D plastic components, for RC car modifications and parts that are no longer available. During some of my own testing, using 2 separate supplies is cumbersome, untidy and unsafe. Therefore, in this situation a dual DC supply was in order for me and my son.
This information is for demonstration purposes only. I will not be held responsible for any person's injuries, losses, damages or death, whilst trying to replicate this item. This device will be powered from a 240VAC supply that will kill indiscriminately. If you have no knowledge in electrical practices, please do not attempt this build. Please stay safe guys and acknowledge your limits.
Enclosure
First of all I needed an enclosure, and for it's intended use, I bought an off the shelf ABS design as shown below.
The outer dimensions of the enclosure are shown. It has a handy carry handle and offers double insulation properties required for this design and intended use. Enclosure are usually very expensive, however this particular case was only £12 delivered. That, in my experience, is quite inexpensive and a bargain in my humble opinion considering it's dimensions. This enclosure was originally intended (and modified) for another project. However, I came up with another face plate design, incorporating the already made modifications/holes/reveals and can be seen below.
With the new face plate design complete (and with the old modifications incorporated), I was happy to move on. It was now time to transfer the dimensions to the plastic plate.
After transferring the dimension to the plate and adding the hole diameters, I centre punched the centres of each hole that would need to be drilled. This punch mark creates a start point and ensures that the drill bit will stay in place during the drilling process providing greater accuracy.
Another picture of my marking out with some of the intended components and tools I used can be seen above. I will also be using a drill bit called a stepper bit shown above, which drills with 2mm increments with 5 steps. Stepper bits are perfect tools for this type of work. I really rate them. When I was happy with my marking out, it was time for drilling.
I drilled all of the holes first to the specific size as can be seen above. I was very happy with the result quality of the holes using the stepper bit. They leave a very high quality cut with no burrs or marks.
It was time to use my rotary tool to open up a reveal (hole) for the second display and the power switch. I am using cutting disk as can be seen above. The hatching on the marking out is the material that will be removed.
After cutting out the excess away (and nearly losing an eye), the front plate was complete. After completing a test fit of the intended items, I was happy to move on. I had purchased a small SMPS (switched mode power supply) for another project, that will be repurposed for the variable voltage circuit on this instrument.
With the enclosure open, I could see an immediate problem of which I had been expecting. The problem with these types of generic enclosure are the position of the plastic screw points. They very rarely (if ever) line up with any fixing points of the components intended to be installed. This was certainly the case for the SMPS I will be using. I had to get creative.
I wanted the SMPS over the case vents for obvious cooling reasons, so I took apart the SMPS and lined it up with 2 of the case fixing points. I then drilled the SMPS alloy case as can be seen above.
I could now secure 2 fastening points for the SMPS, which is enough as it is a very light component. There is a plastic insulator sheet that goes above the new screws, and this will insulate the internal electronics from potential short circuits. I then simply rebuilt the SMPS with the parts I originally removed.
The above picture shows the SMPS fastened to the base of the enclosure. You may think it a waste to put a display on the fixed voltage output as I already know the voltage. However, I want to know how much current is flowing, hence the display. It is also wise to use a measuring instrument when building prototypes as voltage and current could rise under fault conditions. As you can see, I have also glued some mounting points to aid in the installation of the remaining components.
As you can see (above), I have not made any adjustments to the rear panel. I have instead mounted the inline fuse and power inlet to either side. This means I can fit it flush on a shelf and off the work space. As you can see the fuse is on the right, and the power inlet on the left.
Components
Many of the components I will be using here are being repurposed from other redundant projects or appliances. The AC/DC converter is new and cost £7.39, including delivery. It has a 12Volt output with 38Watts of power. This equates to around 3Amps, so it still packs quite a punch.
As you can see the SMPS is quite small, compact, yet reasonably priced DC supply. Over the many years, I have used these types of converter without a problem. They are always a reliable and safe DC power source.
The above LCD display is a repurposed item from another project. I think it cost about £7.50, at this time last year. They are still widely available and super easy to wire in. This display has 8 functions, which I love. The display is a little hard to read but I can live with that. This display will be employed on the variable DC circuit.
The above display is also a reclaimed item. It is an LED voltage and current measuring device which will be used for the 5VDC fixed output circuit. These displays are widely available for around £5 and are very reliable and robust. As I stated earlier, you may find using a measuring device on a fixed voltage output a waste of a display. However, with this display I can monitor the current flow of the 5VDC supply and ensure everything is good.
As you can see in the above picture, both displays are identical in size. With the display units selected, I now need a device to adjust the voltage and current.
I will be using a trusty LTC3780 buck and boost converter. This circuit board is brand new and cost me £13.99 delivered. Not the cheapest deal I could get but, he is a very trusted supplier and delivers his items super fast. If you have read any of my other posts, you will know that I really like these modules. They are highly reliable and have excellent efficiency properties. They also operate at quite a cool temperature and are really compact. This small module can be problematic to setup if you don't know the procedure of which I will comment upon later in this post.
The above picture shows a small 5Volt/170mAh transformer (front and left). This is a reclaimed item and was taken from an old telephone answering machine power pack. This may prove to be too small/weak for the use intended, but I do have others to replace it. Further math is in order to ensure there will be no overloading of this small transformer.
There are obviously many more smaller components like potentiometers, a DPST (dual pole, single throw) switch, insulated outlet sockets, a 240VAC input socket and many other components that will be used in this project that I will not explain as I am sure you know what they look like. With most of the parts ready to go, I needed a circuit to follow.
Circuit Diagram
It is always important to have a circuit diagram for many reasons. I will draw many circuit diagrams for every project until I iron out all the problems I find. Yes it is tedious, time consuming task, but it is also a very necessary operation for both the advancement of the device, problem solving, having a record of what has been done to the device and it's capabilities or specifications.
Above is an image of the circuit diagram, with every electrical component in it's intended electrical position. It is quite a simple diagram as I intended. I have also written many notes and instructions on the above diagram so you can print it, if you decide to copy and build this DC supply. As always, I will be using mechanic electrical joins wherever possible and insulated with heat shrink/tubing. As the diagram above illustrates, both the fixed DC output voltage supply and the variable output DC supply are fully isolated from each other via separate transformers. This will ensure they will not conflict with each other during operation, nor distort their respective output readings. Now I had an acceptable diagrams, it was time to implement and test each circuit without mains voltage. These are known as "Dead Tests". The term dead test refers to an electricians testing and proving the circuits are good before connecting it to the mains supply of 240VAC.
The first test I conducted was the operation of the LTC3780, buck and boost module. With a 12VDC supply (not the SMPS) connected to the module, the red FAULT LED is illuminated. To rectify this, we need to adjust the under voltage micro potentiometer (top arrow) anti-clockwise until the green LED illuminates, as shown below.
Another picture of the potentiometer that needs to be adjusted (orange arrow) until the red LED goes off and the green LED (yellow arrow) comes on. Basically we have programmed the module to accept a base supply voltage with the adjustment of the potentiometer.
Once the adjustments have been made and the green LED is illuminated, we are good to go. At this point, I set the output voltage of the LTC to 13.8VDC.
My next test was to connect the LCD display to the LTC3780. As you can see in the picture above, the display is reading the 13.8Volt (pink arrow) output from the module. I also adjusted the CV (constant voltage) potentiometer and the changing voltage is correctly displayed.
Above is a picture of the inner progress so far. The yellow arrow on the right is pointing to the AC/DC 5Volt isolated supply. This small AC/DC converter is powered from a join in the mains input on the SMPS, and will be switched from the front panel also.
After this picture was taken, I made a massive mistake. I removed the miniature potentiometers and added the cable extensions. I then made the mistake of powering on the module and without potentiometers fitted, it simply destroyed the module. DOH.
After ordering a new LTC 3780 and was waiting for it, I decided to build up the 5Volt supply and display.
To test and complete the fixed 5Volt supply, I used the banana sockets from the variable supply, added them to the 5Volt supply and ordered another 4 from EBay. As you can see in the above picture, I had to move the position of the LCT3780 to accommodate the output banana sockets. It's getting quite busy with wires already, but they are quite tidy.
The picture above shows where I had to situate the LM2596 converter. It is not ideal, but it is the best I can do for the moment and it is fully isolated and insulated from the metal case. The 5Volt output circuit was tested and works as it should. The LM2596 has had it's output set to 5VDC output, based on a 12VDC input and will serve as a power source for the green LED.
As you can see from the above picture, the 5Volt fixed supply powered up via it's own miniature transformer. I have also fitted and wired the green "ON" indication led. As I indicated in the wiring diagram, I had to add a 200R 1/4watt resistor in series to the LED based on the 5Volt supply. The actual resistor value was calculated at 193.333R however, I rounded it up (never down) to 200R.
As you can see, I have also fitted an inline fuse holder to the incoming Line (240VAC Live) conductor, to ensure it's safe operation. It will be fitted with a 2amp quick blow fuse, again to aid a fast disconnection from the incoming mains supply.
Another picture of the fuse holder, this time from the inside. As you can see, it is a perfect fit and does not fowl any other component and is well insulated.
I have placed a broken LTC3780 into the case to enable me to work on the layout of components and wiring routes. The mains switch is now also wired in and works perfect for the LED indication. The 240VAC side, is still awaiting a live test but it has passed a continuity test. All conductors have been given identification labels to aid future upgrades or repairs.
The front panel (above) as you can see has been removed to install the extension wires to the conventional potentiometers.
As you can see, I have extended the inputs on the 200KR potentiometer to reach the LTC3780 buck and boost converter. This particular potentiometer controls the current adjust. I still have to wire a 500KR potentiometer that will control the voltage adjust. The empty space I once had, is quickly disappearing, as I had expected. However, there are only 5 more wires to install and then this area is complete.
I decided to print off some identification labels for the front panel. They are colour coded as far as was possible, from the small selection of colour labels I have. At least they give a clear concise meaning to each control or output which is all that is needed.
I actually borrowed the banana sockets from another instrument as I couldn't wait for the news ones to arrive. Can you see where I got them. LOL.
Then these arrived later that same day. DOH!!
And these.
And this. In fact I got all the parts needed to complete this supply.
I firstly removed the front panel to access the potentiometer site as can be seen above.
With the front panel removed, I quickly wired up the 500KR potentiometer and fitted it to the front panel, ensuring it was not fouling any other component on it's journey. With the front panel complete, I could start to wire in the new LTC3780, starting with removing the micro potentiometers for the constant current (200KR) potentiometer and the constant voltage (500KR) potentiometer. These will be replaced by the conventional potentiometers via the extension leads from the front panel.
As you can see from the above picture, I have soldered the extension leads from the conventional potentiometers on the front plate to the corresponding pads where the micro potentiometers were originally sited. It was now time to install the mains input socket.
As you can see, I went with an IEC C8 type socket, as it is compact and does not require and earth as this device is double insulated against electric shock. I purposefully mounted it on the side as I want to mount it on a shelf to keep the work space as tidy as possible. A tidy bench is a safe bench.
One last picture (I hope) of the inside of the case before I close it up. I will not be using the screws provided with the case until it is fully tested, I will instead use duck tape for ease of access.
Live Test
Remember this unit has not yet had mains electricity connected. I have however successfully tested each circuit separately, so there should be no issues to worry about. Time for a mains test.
And yes, without issue it has come to life. Happy days!! As I stated, I had tested each circuit without issue, so I knew it was good to go. I will however, put it through many tests before I finally seal it up.
As you can see, I have connected a 5VDC relay to the 5VDC outputs. The relay is drawing an expected 70mA to sustain the closed circuit. There are obviously many more tests I need to perform to ensure it's electrical integrity, calibration and operation.
In the picture above I have set the output variable voltage to 5Volt and cycled throught the menu of the display whilst adjusting the voltage.
In this picture I have adjusted the voltage to it maximum output of an expected 32.8VDC. This is an awesome little display and reads a lot of parameters for the size and cost. It cost around £10 but is well worth the money. I didn't use this display as I thought it was broken. However, the reason I didn't use it was because it was slightly out of line but is in fact fully functional.
The enclosure, I bought was perfect, however I was not as accurate as I should have been. This was due to this project running on as it did. I started designing this in mid September and it's now 23rd of October, so around 5 weeks of spare time was used up in this project. However, I am more than happy with the results and my son will love it, as will I.
I hope you have enjoyed reading this post and hopefully gained a little knowledge from it. If you do decide to recreate this in any way, please be careful and stay safe. I hope to return very soon with a new RC Car modification, news or luckily a build.
Until my next post fellow RC enthusiasts, take care!!
CatXLS
23/10/21
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ReplyDeleteThank you my friend and you are very welcome!!
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