Why my Solar System has Two Charge Controllers

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My solar system currently consists of two lead acid batteries from Wal-Mart, two MPPT charge controllers form eBay/amazon, and solar panels from Harbor Freight. My solar system works better than expected considering one battery is over 3 years old.

The MPPT charge controllers available on eBay and Amazon are not without issues but overall for the price are fantastic. I started with one charge controller but ended up deciding to add an additional controller for a few reasons. Although just one controller would handle my array of solar panels just fine below will explain why I added a 2nd.

Theoretically I could add an unlimited number of charge controllers just wired in parallel. Each controller should be able to either supply voltage to the system or not based on the voltage threshold. If power is leaving the system and solar power is available then it should ultimately supply the electricity into the battery.

The charge controllers on eBay have nice control threshold over the load output. Load discharge can be stopped at a specified voltage and restarted at a specified voltage. This will protect the battery so that it never goes less than 50% capacity. Any discharge less than 50% can be damaging to the battery.

Additionally the controllers are able to supply load based on solar status. It can only supply voltage from dusk to dawn or vice versa.

I added a 2nd charge controller so that I will have additional solar capacity in the future and so one controller can supply voltage only at night and the other can supply voltage 24 hours a day. I want my LED lights to operate form dusk to dawn while the wireless access point operates 24 hours a day if the battery level is above 12.1 VOLTS. Should the battery be less than 12.1 Volts the wireless access point will shut off.

For 35$ USD I now have up to 1,000 watts solar capacity and double control over load output. Furthermore with 2 separate charge controllers I can also now operate more than one type of solar panel and not lose and efficiency.

Additional Solar Capacity

Having multiple solar charge controllers also allows you to continue to charge your battery while having multiple kinds of solar panels. It is generally good to keep your solar voltages the same if you're wiring in parallel and good to keep amps the same if wiring in series. Having a 2nd charge controller allows me to have thin film solar panels on one and then mono-crystalline on the other. The voltages may vary even though they are right next to each other - 2 different kinds of solar technologies.

With the additional charge controller I am able to use both technologies together and not loose any efficiency.

Benefits of two charge controllers

1. Double solar amperage.
2. Additional Load customization.
3. Have mix matched solar voltages without becoming inefficient.
4. Charge batteries with more than one kind of solar panel.

Charge Controller Owners Manual

Click to enlarge Amazon Version B MPPT charge controller owners manual.

Click to enlarge the original version, commonly sold on eBay owners manual.