Written by Bill Willcox-KF6JQO
The Monstrosity Solar Generator is an ongoing project to provide a semi-portable, high-capacity, 12 VDC power supply for amateur radio and limited power for household appliances.
I’ve coined the name because it consists of bits and pieces spliced together like Frankenstein’s monster.
100 Ah (90 Ah usable) lithium ion ferric oxide battery.
All electrical/electronic elements mounted to a single plexiglass plate mounted above the battery.
Battery electrical and physical isolation and secure mounting.
Epic PWRgate smart battery charger.
- Can be powered by conventional power supply
- Can be powered by Solar Panel
- Multiple battery chemistries supported
- Multiple charge rates supported
- Automatic switching between power supply or battery
Overcurrent protection for branch circuits.
Multiple levels of current distribution.
All elements mounted in a weather-tight, wheeled box with extendable handle that provides support for a 50W solar panel.
The overall arrangement is shown in Figure 1.
Inside the box there is a lower compartment and an upper deck.
Figure 2 shows a simplified photo of the upper deck.
The battery isolation switch is located in the upper left corner. To the right of the switch is a 75 Amp distribution bus fed by 6 Ga duplex wire (white) that is connected to the high amp battery bus located under the upper deck. To the right of the 75 Amp bus is the Epic PWRgate and a volt/amp current meter. More on this meter later. A fused cable connects the battery terminal on the PWRgate to the high amp battery bus located under the upper deck. There are ample holes in the upper deck for cable routing and battery ventilation. The upper deck plexiglass plate is mounted to a poplar wood frame that has stand-offs to support the upper deck above the battery. The battery is visible below the upper deck.
Figure 3 shows a photo of the upper deck fully populated.
In addition to the elements noted in Figure 2, the lower right corner shows an MFJ switching power supply connected to the power supply terminal of the Epic PWRgate. The out terminal of the PWRgate leads to the transceiver. The solar panel terminal leads to the solar panel. There are two automotive style 12 VDC receptacles shown. One is fused and connects to the 75 Amp distribution bus. The other connects to one of the MFJ distribution panel fused outlets.
Note: Everything connected to the PWRgate and at each smaller gauge cable must be provided with circuit protection, as shown. All cables are connected with Anderson power poles for flexibility.
Figures 4 and 5 show photos of the battery compartment.
The battery sits on top of a piece of plywood that is cut to snuggly fit into the bottom of the box. Cleats are mounted to the plywood to secure the battery with plenty of ventilation around it. Figure 5 shows some removable chocks between the cleats and the battery to assure is does not move during transport. The box must not be tilted more than 30 degrees from vertical.
Figure 6 shows a photo of the underside of the upper deck.
The red and black battery lugs attach to the battery plus and minus terminals respectively. The other end of the red battery cable is directly connected to an 80 Amp fuse for overall circuit protection. From the fuse there is a red cable leading to the battery isolation switch. These two functions, circuit protection and battery isolation are mandatory in any battery box for safety. From the battery isolation switch a red cable leads to the high amp battery bus, located at the bottom center of the photo. The black battery cable leads directly to the negative side of the high amp battery bus. All the high current cables are either 4 or 6 gauge. All the terminals are crimped and include shrink wrap to protect the terminal to cable joints.
As previously mentioned, there is a volt/amp meter connected in series with the PWRgate and the high current battery bus. It is used to monitor the charging voltage and current from the PWRgate to the battery. However, it is limited in its current carrying capability, only indicates charging current and is difficult to read in sunlight. I plan to extract it and install a hall-effect sensor and panel that can totalize Ah in and out of the battery and provide a better means of monitoring the battery state of charge. The sensor and panel are shown in Figure 7. The sensor will mount to the bottom of the upper deck and the plus battery cable will pass through the sensor. The panel will be mounted to the top of the upper deck and powered by the battery with the power cables fused.
Power to an inverter
Another future change is the addition of a 4 Ga pig-tail to the high current battery bus that terminates in a large connector above the upper deck. This connector will feed a 15-foot, 4 Ga cable leading to a 600W, sine wave inverter. The inverter will be located far enough from the battery box to avoid harmonics (I hope). This system, when fully-charged, should run a refrigerator/freezer for a few hours during a temporary power outage.