Survivalist Hard Wired Charge Controller

Survivalist Hard Wired Charge Controller

WARNING: Do NOT make homemade charge controllers. To avoid potential fire hazard, electric shock or damage to electrical component, use only industry standard charge controllers. This post is for information only.

Here is the scenario, all of my integrated charge controllers have fail. All “ACME” Hardware stores have shut down. I do have rectifier diodes as a backup. I need to route straight 18v DC to my storage units. Since I am using ultra-capacitors and Nickel Iron batteries; my (M1), all I need is a simple charge controller.

This post will only cover the charge controller not sizing what devices you will power. I will cover those topic in later posts. The critical asset to charging is a diode for solar applications. Without a semi conductor, back current will damage your solar panels if sunlight is obstructed while your storage devices are charged. As a survivalist, my circuits must resist cyclic thermal degradation on diodes (semiconductors) as much as possible. Redundancy and over sizing will increase the duty life of the circuit but decrease efficiency. If all else fails, I will cover the construction of a vacuum tube diode in a later post. There are hundreds of ways to hard wire a simple controller. This is just my way.

I try to keep my circuits repairable and customizable in a survival situation. Little to no soldering, mostly clamps and snap on components are used. See YouTube link here.

  1. Load resister (Fan). The fan also bleeds current from solar panel when there is no load on the system.
  2. 24v Schottky high temperature rectifier diode.
  3. 24v relay switch with double action (NO) and (NC) contacts.
  4. One analog volt meter and one analog amp meter.
  5. Any plastic or wood container.

The circuit is simple, all that is needed is one diode sized to handle the current draw from the solar panel wired straight to the storage device. This simplicity will more than often burn out a diode fast.  I want more control over my hard wire circuits so to minimized the thermal stress to my semiconductor diode, my solar panels and my ( M1) unit. I use a case fan to serve as a load and to cool my diode, and to bleed current from my panel when there is no load. I use analog voltage and current meters so to monitor load to my batteries. A simple heat sink by the way of wire alligator clips. I then use a simple 12v automotive ice cube relay so to not overcharge my M1 battery bank.

  1. Cutout opening for the case fan, in/out ports for wiring, and openings for the meters.
  2. Mount components. For my diode, I use a heat resistant manifold gasket making sure the plastic of the cutout is not close to the diode.

3. Run the solar power feed in to the volt meter then to the diode noting the cathode connection. Also, connect the (+) lead of the case fan to this same side of the terminal. This way the fan will not bleed power from the CAPs if solar power generation has stopped (if NOT using relay).

Side view profile of “Power in” and “Power out”

  1. Run ground wire from solar panel to the (-) side of the volt meter to one side of the amp meter. Note: If amp meter needle falls below (0) under current, reverse the terminals. Attached the (-) lead from the case fan to this terminal. From the opposite terminal of the amp meter, route wire out of box to the CAP’s (-) terminal.

At this point, we are done if we will manually watch the voltage rise up to around 18 volts, then we would simply disconnect power to the CAPs.  Test ran at 2 amps across the diode at only 10 degrees above ambient temperature of the room. But let’s add a relay to make this somewhat automatic.

To Summarize: Using a 100 watt solar panel in full noon sun with no clouds with drained CAPs of no voltage, pull a current well over 5 amps thus overheating the diode. My M1 electrochemical cells will maintain at least 9 volts for most of my devices will never use voltages lower than this. Also, the M1 will regenerate back to 10 to 12 volts after discharge yet will have low power density. Full charge is a voltage maintained at 18.5 volts. If the amp draw is more than 4 amps, the solar panels can be re-positioned to an angle other then perpendicular to direct sunlight. Again, this is a survivalist manual way of charging electrochemical cells without integrated automation. All parts are repairable less the semiconductor. Future post will cover the repairs of both the meters and the case fan.

Adding a Relay

I will use the solenoid coil to open the circuit. The “ice cube relay” solenoid is rated at 24 volts and will actuate at 12 volts. By adjusting the tension spring on the pinion assembly, I can actuate the contacts at 18 volts. Over sizing the solenoid coil due to the fact that most 12 volts panels deliver voltages well over 18 volts in direct sunlight. This cube contains both (NO) and (NC) connectors.

Simple, just divert power from the solar panel to the solenoid. Then route the negative wire from amp meter to the relay’s (NC) connectors. When solar voltage reaches 18 volts, the solenoid will actuate thus opening the circuit (power to the CAPs will disconnect).  Be sure to have the CAPs connected first before connecting the solar panels to the circuit if in full sun.


Finished Product.

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