Update and Photos

Over the last two days we have been refining the circuitry and putting all the pieces together. Below are some photos and any changes that were made to the solar node.

Firstly, the safety diode for the measuring circuit  has switched positions. Now it only sits on the ground node which grounds the LEDs and op-amps' Vss. In the previous diagram it would shift the reference voltages by the forward diode voltage of 0.8 V which made the circuit a bit more inaccurate than necessary. Simple fix still reaps the benefit of not blowing the op-amps in the event of powering the circuit with reverse polarity. To see a diagram look at the Full Schematics page.

Full Unit:
The solar panel, deep-cycle battery, 3 LED house lights, phone charger (up to 4 phones) and control module.

The circuit which measures voltage of the battery to estimate state-of-charge and also the current coming from the solar panel. The LED's will represent either 0.25 V starting at 11.75 V all the way to 13.5 V for  voltage measuring. This can be thought of as 0-100% of battery charge. When measuring current each LED represents 1 Ampere and the circuit can display 1-8 Amperes. The black variable resistor will change the reference voltages on the voltage measuring branch is black while the blue one is for calibrating the current reference voltages.

The circuit board fitting into the box. The 8 LEDs do most of the positioning.

This photo shows the box with all pieces inserted. The circuit board is placed inside first and the screw connectors (which we like to call sugar cubes) rests on top with a small piece of foam separating the board and the connectors. These connectors are great because they are rated for 20 A and all that is needed to make and change strong connections is a small screw driver. You can also see the MP9100, the 100 W 0.1 Ohm resistor, directly inserted into a sugar cube. The path which the resistor is on must be rated for 10 A and so putting it on the circuit board was not possible. Not only that but the legs of this unit would not have fit. The system diagram shown on the Full Schematics page will explain what is connected to what via the sugar cubes.

Soon we will label each wire and its slot on the array of screw connectors with colors and symbols to allow for easy connection making without having to look at circuit or system diagrams.

This is a good view of the control module. The three switches in the upper left corner of the box are used to switch on and off the three LED lamps that come with each node. The large switch in the upper right corner has three positions. In the center position the battery is disconnected. This could be used as a safety measure or if you would like to not charge or discharge the battery. Switching left will connect the battery into the circuit and turn on the phone charging modules. Switching right will connect the battery but not turn on the phone charging modules. The green LED left of the large black switch is on when the solar panel receives light. It simply indicates that the solar panel is working.

The three switches in the center left are used to choose measuring modes. the left most toggle switch chooses between measuring current and voltage. The little red push switch in the middle powers the measuring circuit and for voltage mode will display the voltage. The big push switch on the right will divert current through the ballast resistor and so if measuring the current from the solar panel you must have the toggle switch on current mode and then simultaneously push  the red and black push switches to see the current reading.

Soon an overlaying template will be put on the front of the box to indicate which switch does what with both English and diagrams. The diagrams are doing to be designed to be as simple as possible but while in Uganda we are hoping that the community can tell us what are the best diagrams to help them use the device and then those can be put on the module.

The black wire running out of the top of the box is to the solar panel. The black wire running out the bottom of the box goes to the battery. The two black wires running out the side go to the USB phone charging modules. One of them is sticking towards the camera in the image. Each of these thicker wires were sealed by using the glands which are featured in a previous post. The thin blue wires just seen on the right of the box go to the LED lamps. These thin wires were sealed by just making a very small groove on edge of the box where the lid attaches and the lid compresses the wire against the grove to make a seal.

To connect to the solar panel we removed the normal generic wire which had solar industry specific plugs and connected our own wire which ran directly to the control box. If wanting to disconnect the solar panel or  anything from the circuit you would need to open the control box and unscrew it from the sugar cube. The image below shows the original solar panel wires connected in a box on the back of the solar panel.

Spade Connectors:

These seemed to have been a great investment. They attach to the thick 18 AWG wire by just inserting into the back and clamping hard over the middle of the connector with some pliers. They come with a nice plastic sheath which is perfect insulation.

Fuse:

We have now implemented a 10 A fuse. It is the same type used in cars which is good because it should therefore not be hard to find and naturally is designed for the types of voltages we are using. (12-24 V). The fuse is directly in series with the positive terminal of the battery. If something was to short and cause the deep cycle battery to draw many amps (it can supply a peak current in the hundreds of amps) then the fuse will just break the circuit and prevent other components from breaking or the unit from overheating. Our spade connectors were very useful in this regard because they just slotted right in.