2pcs 12V-36V DC Voltage Protection Module Digital Low Voltage Protector Disconnect Switch Over Discharge Protection Module

Work great, but very small so be careful not to be to rough with it..

The built in voltmeter is within a few hundredths of a volt to my Fluke meter.The disconnect was within 0.1v of the disconnect setting. Perfectly acceptable for a $5 part.Some have complained that the disconnect continues to drain the battery after disconnecting the load.In my application, I have a 12V SLA battery, an AC to DC power supply set at 13.5V (float voltage) and a load.I connected the power supply and load to the VIN terminals, and the battery to the VOUT terminals.This is opposite to the published diagram.When the AC voltage drops out, the load stays on until the battery voltage drops below disconnect (12v), then the relay opens and the battery is disconnected and has no parasitic load.When AC power is restored the relay closes and the battery gets charged.

There are some technical details which don't seem to be spelled out. One of them is that the relay output is not isolated. The relay negative output connects directly to the negative input, and the relay + output connects to the positive input when the relay is active. There are two programming set points. One is the threshold voltage, and the other is hysteresis. The hysteresis is added to the threshold voltage to determine when the relay turns back on. (This saved me from having to use two modules!) There was also a calibration, where you can calibrate the displayed voltage if you have a known accurate input. That feature doesn't seem to be documented. In fact the only documentation appears to be one of the product images on Amazon. It's a little bit tricky setting it up using the two buttons.

One thing which is not clear is the relay connects the input to the output, so it is not for a connection where the "output" just turns on or off. But you can link the output directly to a big relay.I do need to put it in a nice case though.I'm using it in my F250. While I doubt my personal electronics will kill the battery, I really don't want everything on all the time. With the engine going (including remote start), I get 14.2v. When I shut off it drops to 13.5 then slowly goes to around 12.5. This makes it easy to give a short time until it shuts off, about 5 seconds after the engine shuts off when it hits 13v, but disconnecting that jumps back to 13.4-.5V, so the turn on threshold also helps.I can do electrical engineering, and wiring to use various indicators and run them through, but it is trivial to cut a short 12V plug extension and put this board betweenProgramming is also easy. Press the left button and hold it to set the disconnect voltage, then use the left to go up and right to go down - holding them in will start a fast count up or down. You have to disconnect power to store the value (it will store the current value on the display any time power is off) Then use the right button to set the voltage above the cutoff to turn back on. In my case, I used 13.0 and 0.6 so it shuts off below 13.0v (the display stays on) and turns back on above 13.6v.

1st one lasted about 4 months on a solar configuration, now its not accurately reading voltage ( low by about 1-2 volts) but did the job. On the second one now, for cheap price still worth using to tinker with, I would spend more if you need something reliable long term.

Came exactly as shown. Will purchase again in the future.

The steady state voltage reading fluctuates .5 volt peak to peak. No load.. just measuring the battery.. I would think i had a bad module but they both do it... same amount. 0.5v ptp. Of course the absolute voltage measurement is off by about 0.4 volts between the two... connected to the same battery.. To even expect some usefulness the circuit would have to filter this reading instead of use it directly... it doesnt... the brain apparently uses every measurement to decide whether to disconnect the load... Lead acid do not have the voltage droops that enable a module this inaccurate to be used.... 12.6 is fully charged... and 11.9 is discharged.... .7 volts droop between full charged and discharged. accuracy is a must. I have to send them back.. my use was to keep 12v battery operated surveillance cameras from totally discharging the battery. I need a cutoff at 11.9v and a turn on at 12.4v. (.5v). The solar panels dont get enough light some days to keep the batteries fully up for the night. These devices just toggle all the time with settings like that... cause the voltage reading has .5v noise on it... lead acid Batteries dont have noise in the tenths of volts... in comparison.... my old $2.99 harbor freight multimeter has better voltage accuracy..

I connected my 12v li-po drill battery to this low voltage cutoff and it showed 12.3v. I then connected the same battery directly to my dedicated Klein voltmeter, and it confirmed 12.3v (12.26). I'm using a 12v Milwaukee battery with 3 cells, and it's worked for me with no issues for 2 yearsSince I have a 3 cell li-po pack, I don't want to go below 3.2v per cell which would be a total of 9.6 on this low voltage cutoff. To give a little more buffer, I set it to cutoff at 9.8, so that it cuts off when the first cell hits 3.2v. I may set it to 9.9, although the default on mine was 10v. It's splitting hairs at this point, but I like the ability to customize the cutoff depending on the battery chemistry.I'm really glad to see the voltmeter that's built in is accurate- that's an important part of setting the cut-off. I will validate the volt meter on each one of these I use, just to make sure they are set correctly