I bought one of these in 2007 and used it to charge the two deep cycle batteries in my truck camper for two years before I knew any better. Solar charging was new to me and this was cheap so I figured I would give it a go. It appeared to work fine - it showed it was charging. But my batteries never seemed to last long. I set out to find out why, and in the process learned a lot about solar charging. Along with that education came a realization of the pitfalls of charge controllers like this one.
This is an "on/off" controller. When your batteries reach 14.2 volts, it simply turns off. Your batteries will then discharge, either from something running off of them or simply by the passage of time (self discharge). Once they reach 13 volts, this controller turns on again and takes them back up to 14.2 volts, and the cycle repeats itself.
The problem is your 12v batteries are not fully charged when they reach 14.2 volts. Deep cycle batteries, especially, need more than that. Many are rated to be charged at 14.4v, some as high as 14.8v (many 6v pairs, wired in series, fall into this latter category). And when they reach that voltage they should continue to be charged at a gradually reduced current until they are truly full. When that doesn't happen they are chronically undercharged, which doesn't give you the full use of the battery's capacity. It's like having a ten gallon gas tank in your car but never putting more than 7 or 8 gallons in it. The result is you can't use as much electricity before needing to recharge again. Worse yet, chronic undercharging shortens battery life. Sulfation of the plates occurs, as well as stratification of the electrolyte fluid. Individual battery cell charges drift apart, and eventually cell failure occurs. It only takes one cell to fail and your battery becomes nothing more than a toxic lead weight.
Look for charge controllers that use PWM (Pulse Width Modulation) technology or MPPT (Maximum Power Point Tracking). MPPT is expensive and not really financially feasible for many small solar systems, but there are many PWM controllers on the market these days that are nearly as inexpensive as this cheap Sunforce on/off model.
PWM controllers charge your batteries in three stages - bulk, absorption and float. Bulk allows everything your solar panels can produce to be thrown at the batteries until they reach a set point, (14.4v for example), and at that point absorption stage takes over where the voltage is held there while the amps allowed into your batteries are gradually diminished over several hours. This really gets your batteries charged fully. At the end of absorption stage float stage takes over, which trickle charges batteries to keep them fully charged.
Renogy is one brand that is sold here on Amazon. The ten amp model uses PWM and even includes in-unit temperature compensation, but it is about ten bucks more than this Sunforce model. Even so, you'd likely save more than that in battery life. It's got its faults too though, like a short 30-minute absorption mode. If you really want a good one, look for Morningstar, Blue Sky, Rogue or Xantrex, to name a few. I've also heard good things about a very cheap Chinese brand called Landstar. Although most of these are quite a bit more expensive, they won't cut your battery life short and they will give you more battery capacity to work with. To learn more about 12v solar charging see rvsolar101 dot blogspot dot com. Part 7 covers charge controllers.
| Manufacturer | Sunforce |
|---|---|
| Brand | Sunforce |
| Model | 7-amp Charge Controller |
| Item Weight | 5.6 ounces |
| Product Dimensions | 4 x 2.25 x 7 inches |
| Item model number | 60012 |
| Is Discontinued By Manufacturer | No |
| Manufacturer Part Number | 60012 |
