I've been using these for years to charge 12v deep cycle batteries with solar. They work great in the north florida sun and humidity. Out of about 35 of them I've only had a few fail over the years. Slightly expensive but far better than the cheaper solid state charge controllers.

I have used this product before and it worked great. was just replacing an old one. This one is defective and doesn’t work either. Not sure where quality control went.

I've had mine for over a year and it's just perfect for what it is. Vastly better charging than the dumb threshold on/off units. Temperature compensation is excellent. Albeit not MPPT, it really gets your batteries charged to their peak charge by floating the proper temperature-compensated voltage/amps to them. I.e., cold mornings you'll see like 14.6v, hot summer afternoons 14.2-ish.How it works: When your battery needs charging, it directly connects your solar panel to your battery, so your solar panel voltage drops to battery voltage (below optimal, which is why MPPT is better). As the battery is charged, the voltage climbs to meet the target (say, 14.4v), it starts pulsing the current very rapidly to the battery to give it just the right amperage it needs to hold the target voltage. You'll see the solar panel voltage rise above battery voltage as this starts to happen. The target voltage is held and over time, the amperage taken from the panel decreases. Cool.My application is my first dip into solar to maintain two big batteries in my Dodge diesel pickup that isn't driven often and is not located near an outlet. And when it is driven, the system only puts out 14.0 volts, not 14.4 like many other cars do, so while batteries certainly get a charge while driving, short drives can't replace all the energy taken on start-up. Compare that to say my 2008 GM which puts out 14.7v for the first 15 mins or so, then 14.4.Even in the short winter days, a 10 watt panel is overkill, probably could have gotten by with a 5 watt panel. Again, my use is not "charging", it's "maintaining." I agree a 50W panel is about the max you can use on this, which is rated to be 4.5A at 12v (54 watts), or ~3.8A at 14V. That's still a pretty good charging rate for a single battery in applications where it is discharged.I might put the solar panel in the interior (factory tint side windows block quite a bit) and see how it goes. Then again, I might bring the batteries to the basement for the winter and treat them to weeks of desulfating from my BatteryMinders.I use a "Watts Up" on the solar side and battery side to monitor Whr, amps, volts, etc and a voltmeter on the batteries. Neat stuff![Dec 2016 update], mine's still working ok, but the voltage compensation seems to be not working (14.1 is common at low temps - reached out to support, just past the 5 year warranty though). It hasn't gotten much use in the last year or so. With my common flooded lead acid batteries, floating most of the day at peak charge voltage caused more water loss than I expected/wanted (then I over-watered them, they leaked...then I turkey-based out some out and put in a jar for later...hassle & mess). I updated to a smarter Tracer 1210RN MPPT with the MT-5 display and while additionally being MPPT, after the bulk charge, it has a lower float voltage, solving my water loss issue, and batteries are happy. Sure, the MPPT+display is more expensive (around $100), but I'm happier with it... and it's a hobby...note 100 watt panels have dramatically come down in price this year to ~$120 (fine for the Tracer, not for the SunGuard).

Nice small controller for solar setups that generate less than 4.5 amps, it works well and has a low internal consumption rate. You will need to provide your own monitoring gauges/meters to see it "working" as it has no indicator leds whatsoever. It's also not designed to drive a load as many other controllers are, which is not critical for my use.I'm not seeing any obvious advantages to the claimed: "high performance circuitry as the more expensive SunSaver line." After monitoring this controller for many hours using a volt/amp meter it seems to work no differently than any other PWM controller I have used. It does have a 5 year warranty, so for some that alone may justify the price. As such, I'll probably use a competitor's 5-amp controller (at half the cost) for the next small project, but I am pleased overall with the performance of this one.

Never had a problem always on time

This is OK, but there are better choices for low power applications. I bought this planning to use it to power a remote sensor project. I understood that this controller drew 6 mA, but I didn't understand that the current draw applied even after dark, when the device should be off. Since everything else in my project averaged 4 mA, this device dramatically reduced my battery life. I ended up going with the Genasun GV-4, which draws only 0.125 mA during the day and only 90 uA at night! The GV-4 more than doubled the battery life of my project, and my battery has been charging whenever the sun is up, regardless of cloud cover. I found the GV-4 to be a far better choice for my application, but it's not water proof like the SG-4

I bought this to replace a cheap controller that I use with a 15watt solar panel to keep a Jeep battery charged. The cheap controller just switched on and off and didn't have PMW to 3-stage charge the battery.The good- It is ruggedly built with heavy duty wire in and out. It's in a heavy duty plastic shell that's filled with "potting compound" to make it water proof. The 4 wires come out through the potting compound. (They do warn you to install it so water doesn't collect in the open end of the shell.)- I hooked up a voltmeter and it's not contstantly turning on and off like the prior one. Now I'm getting a steady (in the short term) voltage based on the battery's state of charge.The bad- There aren't any LEDs. You can't tell if it's working without a voltmeter and then you can only see one measurement at a time. (Volts in, volts out.)- There are cautions all over the instructions about not shorting out the solar power leads or it will ruin the controller. If you'll frequently be connecting/disconnecting the solar panels, install a short proof automotive connector that also prevents you from reversing the polarity.

Mine has never worked and it's unclear if it didn't work out of the box or there was an installation error.Note the instructions state a VERY specific battery / panel connection sequence that they advise must be followed or you can brick the device. The lack of any indicator or connection lights limit troubleshooting to multimeter based following a relatively complex instruction sheet.While I believe Morningstar makes a quality product, you can purchase a controller for less that offers LED and charging data. I'd look elsewhere before purchasing this product again.