APPLICATION NOTE 007
Benjamin Bacon, Owner, Plane Space Design
Warning: You have to be a very good mechanic to do this. Do not endanger yourself or you car if you are not an expert in the structure and functions of the automobile.
As you made have noticed in your study of the MISO product line, the voltages that the units are designed to operate at are very similar to the voltages that are commonly used in the automobile's electrical system. Under the hood of an automobile is a 12V lead-acid battery and an alternator that operates at voltages from 13.5V to 14.5V DC. This situation makes a MISO an ideal product to help avoid one of the common problems to occur for automobile owners in the winter months. That is, the loss of battery power due to cold weather.
What can the MISO do? In conjunction with the solar battery chargers that are available on the market today the MISO can switch a charging current onto the battery, when the vehicle is no longer running and the alternator has stopped charging the battery. The solar charging current will keep the battery warmer, and it will keep the terminal voltage from falling as fast.
To hook up the MISO under a car hood requires a little bit of creativity. First you must find a space for it. Next you must mount it securely in its place, and finally you must connect the wiring so that the desired switching action takes place. The first two requirements will vary from vehicle to vehicle, but in general, there is some empty space around your battery, or on that side of the vehicle. Mount your MISO there. Mount it with anything ranging from duct tape to screw clamps. That portion of the installation is your prerogative. If space is really tight, you can take the circuit board out of the MISO and devise your own enclosure and mounting method. As for the wiring, it is very simple. There are wires coming from the alternator charging circuit going to the battery. Disconnect the alternator wire from the battery, and then connect it to the MAIN terminal of the MISO. The terminal of the MAIN port can connected to ground or be left unconnected. Connect the wires from your solar battery charger to the SECOND terminals of the MISO. The final connection is to connect the OUTPUT terminals of the MISO to the terminals of the battery. Red to plus and black to minus. You might have to get creative in your installation, so that you will not have to open the hood every time you want switch to solar charging. That is the purpose of the MISO. To switch to the solar source automatically when the engine is shut off. Don't waste that utility. Wire your solar charger in permanently.
One concern for the connection is the presence of the starter motor on the alternator output port that connects to the battery. The battery and starter motor are connected in parallel to each other. Another concern is the chance that the MISO will not survive the high current events that might happen to it. Therefore, the safest installation will use protection circuitry that diverts high currents around the MISO. Use a surge protection device that routes the current around the MISO when it reaches 12 A.
Now when the engine is running the alternator charges the battery through the MISO with its greater than 13.5 V charging power. When the engine shuts off, the solar charger charges the battery through the MISO with its greater than 12 V to 15 V charging power.
Try to avoid solar chargers that can rise above too far above 12V while the engine is running as this situation will cause the alternator voltage and current to blocked and replaced by the solar voltage and current. Solar charging current is typically less than the alternator charging current and is appropriately applied to the battery only when the engine is not running.
Variations on this reserve power theme are possible. For example an extra battery in the trunk can be wired onto the SECOND terminal to provide emergency cranking amps. Or if you are really the inventive maker type, wire in an emergency battery that is charged by a wind turbine. A combination that will never fail you. The important point is that using the MISO makes an easy chore of taking these extra measures against not having a safe functional automobile during cold weather . You may feel less afraid of using the battery power to actually heat the cold cab of the car when the freezing cold comes around and the car engine is not running.