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

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.

This is a very simple but ideal unit for Battery systems. I have configured one with a Battery Charger Plugged into a IOT Relay to turn the charger on when the battery is 25% low and then turn the charger off when battery is fully charged. The other Voltage Protection Module I will use to disconnect the battery complex if the voltage gets too low. The one little funny issue I had set (left button 11.5V) then you set a different voltage (right button to .5) this is wired until you understand if the full voltage is 12V and the charge voltage is 11v the different voltage is .5V. Yea I know a little wired, once you figure this out its easy to work with. On one of my units the voltage read .1V off no problem if you want true 12v you set it to 11.6v. These are very inexpensive units that do just what I needed them to do even more expensive Voltage Protection Module can't do what these little guys can do.

Another seller of this same item has excellent directions on the amazon page. This seller doesn't. I took off one star for directions. It looks to me like several sellers are selling the same item. The first one I got, from another seller, did not work at all. I opened the first one from this seller and it worked like a champ. And I have a spare. Every feature worked fine. When I lowered the voltage below the cutoff, it cut off great. When I raised it 2V over the cutoff, it came back on. I did not have to adjust the voltage, it was spot on to my meter out of the package. Perfect. I have a 24V LIFEPO4 battery, and it is nominally at about 26V. By 24V, there is almost nothing left in the battery, but my circuit doesn't like low voltage, so the cutoff at 24V makes a clean off, so if I forget to turn it off (yes, I did that once, with bad results), the circuit is protected. This is even higher cutoff than the battery pack bms (2.5V/cell=20V) .

Used these as a way to turn on and off a relay for my solar setup. I found without a device like this, my batteries would be drained below optimal levels which could damage the batteries. This turns off the relay so my EcoFlow stops pulling power from the batteries till the on voltage is achieved again.

Works so far ,but these things are super flimsy I don't expect them to last long! I already hot glued the coils to sturdy them up.

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 between Programming 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.

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..