Huamai 20A 12V/24V MPPT Solar Charge Controller, Upgraded Intelligent Waterproof Solar Charge Regulator 15-45V DC Input Overload Protection Temperature Compensation

Updated March 2019: I have purchased a total of 13 of these genuine MPPT charge controllers. I have only had 1 failure which the vendor replaced promptly. These are the best deal on Amazon. Now that I have a lot of experience with these I have updated to 5 stars.Updated March 2018: I have purchased a total of 10 of these MPPT controllers. They all work very well overall except the last 2 I purchased were upgraded. At first I thought the last 2 were defective in that the voltmeter did not come on when I made the battery connection like the first 8 did. However, the last 2 have an extra circuit board in place of the internal fuse where it now monitors whether solar input is present. Once I made the solar panel connector the MPPT powered up properly. This is a huge improvement in that the batteries no longer run down overnight at all (12.8V in the morning, not the 12.5-12.6 I was experiencing with the first 8 purchased). In my opinion, with the upgraded circuitry, this MPPT unit is worth at least $70 compared to other MPPT controllers with similar features.Feb 2018: I have purchase 8 of these controllers and being a retired electrical engineer you can take this review as fact, My solar system is 400W of solar panels, with another 1000W to be added and 420AH of 12V battery capacity with which I run a 12VDC to 120V AC 1500W converter. This true low cost, no frills, MPPT scans the solar panels voltage vs current curve 8 times per minute to calculate the MPP. I measured the conversion efficiency at three different solar power levels 130W, 50W, and 10W and found the efficiency to be right around 95%+/-. Below 10W the efficiency falls off steeply due to the controllers needing electrical power for running its own electronics. The previous PWM controller I had never produced more than 110W in midday summer sun. It's mid February here in Massachusetts where the sun is only about 60deg above the horizon so to get 130W in full sun is was incredible. You will see more current flowing into the batteries than what is flowing in from your panels!! What follows is the pros, cons, and nuances to this controller. BOTTOMLINE IS THAT I AM GOING TO ORDER AT LEAST A HALF DOZEN MORE OF THESE AFTER I SUBMIT THIS REVIEW.PROSTrue MPPT with very low cost relative to it functionality (conversion efficiency).Seems to be very well built both in terms of ruggedization and workmanship.Charge voltage settings options for multiple 12/24v battery topologies.Small in sizeCONSThe MPPTs voltmeter is not accurate. It measured anywhere from .2V to .5V high from the actual battery voltage. Because the inaccuracy was variable based on the charge rate I suspect there is a resistor used for current sensing between what the MPPT says is the battery voltage and the actual battery voltage at the MPPT battery connector.The MPPTs voltmeter and associated electronics remains powered even when PV is low to nil (night, extreme overcast conditions). It draws between .05 to .1amps which would make it less suitable if you have a battery and/or solar panels with low capacity.The owners manual (one sheet of paper) written in Chinglish is pretty much useless. For example: It makes no mention of what the switch settings do. I figured out the switch settings by experimentation. Setting #1 is for gel, nicad, lithium cells which have lower charging rate and voltage requirements (13.2V). Setting #2 is for flooded lead acid or AGM batteries (hard charge to 14.2V, no float mode however). Setting #3 is for equalization of flooded lead acid batteries (15.5V). Setting #3 should be used only occasionally to equalize and de-sulphate your batteries per your manufacturers instructions.As far as reliability is concerned there is nothing in the owners manual so time will tell. Based on my experience as an electrical engineer if you push the controller to its limit of 300W it won't live as long as it would at say 200W or less. This brings me to a closing comment. This item is enclosed but not waterproof, this is good to keep contamination out but is bad in that heat generated internally has no way out except for conduction/convection through the housing. You do not want any sunlight or any moisture getting in contact with this device.

Updated 05/03/2018I ordered the other one. This unit works very well. So I updated to four stars.———————————-Original reviewWithout many reviews, I purchased this controller with doubt. When it arrived, I tested on the 100w solar panel and was pleased to see its MPPT function which converts panel voltage (~17V) to battery voltage (~12V) with 20-30% higher currents. It has exact functions as the other reviewer described in the long review.However, it stopped working after only two days. I turned off it and reconnected several times, it still didn’t come back. How disappointed! I think their QC needs improvement.

Does a good job of getting the most out of the solar panels, however has a poor charge controller. Simply regulates the output at a fixed voltage of 12v, 14.2v, or 15.6v. It does not drop down to a float voltage and will kill AGM or any sealed lead acid battery in a short time. It also generates a lot of RF noise which interferes with radios.

ABSOLUTE TRASH! 24volt ‘auto’ does not function. Measured 29vdc off panels to inputs. Outputs at 15vdc. I am removing this piece of trash. and purchasing two 12vdc Battery Tenders- because they really work and are sealed against moisture. THIS IS NOWHERE NEAR WATER-RESISTANT! comes in a high quality metal enclosure. No documentation on Mystery Three Mode switch. There is a HOLE to access the switch.... hello water! Likewise the LED is not sealed to case. Both sets of wires not sealed. No epoxy on electronics. Pure fraud to claim anything like waterproof! Fraud to claim 24vdc. The ‘mystery switch’ appears to increase output 1vdc each step with 3 the highest step/volts. What a waste of time installing this, siliconing all gaps to find out it is UTTER RUBISH.

This is a surprisingly inexpensive controller that (so far) has worked very well. I'd give it 5 stars, but the instructions are somewhat confusing, and the switch that selects the charge mode is pretty much impossible to access without taking the unit apart, although you normally would only need to do this once. I have two 100w solar panels that I run in series to the controller, and in normal sunlight around here, I can easily get 150+ watts into the battery bank of my RV. I am not totally sure if it is really an MPPT controller, but I do notice that it periodically seems to go into a sense mode where it adjusts output voltage to maximize battery charge current.

Unlike some other MPPT converters I've tried, this one actually does raise the working voltage on the solar panel to the 16 - 18 volt range and step the voltage down to 12 volts with reasonable efficiency.

Hi my controller did not come with any instructions, what do the I II III mean? Also there is no outer switch to move the dial from I II III, I had to unscrew the case and the little switch is tiny, not sure if this was intentional or a larger switch broke off that was supposed to poke through the outer box. I have not hooked it up yet as I am not sure what these settings mean or what they will do to my battery.

Unfortunately, there is zero documentation for this device, and the seller is not willing to answer basic questions about it's operation, resulting in an UNSAFE product.Because the different modes are unclear, this controller cannot be used without severe safety and equipment risk.