is Digital Low Voltage Protector Dconnect Switch Cut Off 12V Over-Dcharge Protection Module for 12-36V Lead Acid Lithium Battery Low Voltage Cutoff for Solar Panel Lighting System Camper

I hooked up this handy little gadget to the battery backup system we use to power my camper when we don't have grid power. The little relay on this circuit board can't handle the current that my inverter draws; so i simply connected this cut-off device to a hefty 250A relay which switches my inverter on or off. Now, when my battery drains below a pre-determined voltage, this little device turns off my big relay which, in turn, cuts off power to my inverter. (So, i no longer have to worry about draining my battery below a certain depth of discharge.) The other nice feature about this thing is the "differential" setting. I've now set the device to shut off at 11.4v and not kick back on until the battery reaches 12.6v. ONE LITTLE NUANCE: According to my multimeter, this thing reads about 0.2 or 0.25 volts less than the actual measured voltage of the battery. So i had to accommodate for this error factor when i set it up. I want it to cut off at 11.4 volts, so i set the cut-off voltage to 11.2. I want it to kick back on after the battery has reached 12.6 volts; but, because this thing is apparently off by 0.2, i therefore want it to kick back on at 12.4. The "difference" between 12.4 and 11.2 is 1.2. So that’s where I set the “differential” setting.

This device is intended to prevent over-discharge of the battery (or batteries) in a system like a solar panel-charged battery bank. Rechargeable batteries of any type can be damaged by being overly discharged in use. There are such things as "deep cycle" batteries, which are more resistant to these problems, but they still have a minimum voltage to which they can repeatedly be discharged without causing permanent damage. This module is a very simple, but very capable, device which basically allows the user to set a minimum voltage, and when the battery voltage drops below that value, it cuts off the output of the battery, shutting down the powered system. I set it up in a test circuit with a variable voltage power supply, to see how well it worked, before using it in my actual circuitry, and was able to verify that this module did exactly what it's intended to do. Then I set it up in a battery capacity testing system, to be used to verify the condition of an aircraft battery. I was interested in applying a moderately heavy load to a fully-charged battery. I wanted to discharge the battery to a reasonable point, but then shut off the load so as not to damage the battery. I was interested in monitoring the capacity of the battery to power that load, while not hurting it. I set the module to allow the battery to discharge to 10 volts. The fully charged battery had an open-circuit voltage of 12.6 volts. I then applied a 100W resistive load (just under 8 amps at the beginning). I monitored the time it took to drop from 12.6 to 10 volts, and then looked at the time it took to do that, using another electrical timer. This allowed me to leave the testing setup alone, without worrying that I would over-discharge the battery. It worked exactly as it was supposed to. As the voltage fell about .1 volts below 10 volts, the relay on the unit opened, and shut off the load. The other setting, the "difference value" keeps the circuit from cycling quickly after the load is removed. As the battery hits 10 volts, it shuts off. That immediately allows the voltage on the battery to increase, due to the loss of the load. If it did not have this "difference setting", that alone might allow it to reset and turn the circuit back on again. This would cause it to cycle off-on-off-on for a while, until the battery didn't recover to above the 10 volt setting. This behaved exactly as I needed for my intended use. If one was using this as it's intended for, in a solar system, for example, without the "difference setting", as soon as the battery output was shut off, when solar charging started again, it would immediately turn on the load again, and the battery wouldn't charge. One would use this device to ensure that the battery (or bank of batteries) is charged above the desired voltage before the load was again enabled. For example, as the system was used to power, say a small lighting system, or a waterfall pump, when the battery falls to below the set minimum safe level you choose, say 9 volts for a deep-cycle battery, it would disconnect the load. You could set the "difference value" to 4 volts. The next day, when the sun came out, the battery would charge, without powering the load, until it reached a level of 13 volts. The load would then be enabled, and if needed power would flow again to the load. Then, when the sun goes down, it would continue to power the load, until the battery reached 9 volts again, when the load would again be disconnected, and the cycle would repeat. This device seems to be very stable. It has a voltage display (red LED digits) to show the battery voltage. I found this to be very accurate, at least within .1 volt DC. And the battery/load cutoff is also very accurate, again within no more than .1 volt DC. The same display is used with the two switches to select and set the minimum voltage and the "difference value". You select "min voltage" by holding the left switch until the display flashes, and then use the two switches to set the value, up or down. When you leave it alone for a few seconds, it reverts back to the normal monitoring mode, and indicates the battery voltage again. You do the same thing with the right switch, to set the "difference value". It's pretty easy to set up once you figure this little finger dance out. It's not that tough, and you will likely only need to do it once. There is a small red LED that lights whenever the relay is energized (ON) and the load enabled. When it trips and turns off the relay/load, the LED is off. So you can tell at a glance what the status of the load is, and at the same time, what the battery voltage is at any given moment. Basically, the thing just works. The setting is persistent, in that it stays after power is disconnected until you manually change it. If you have a need for such a module, you can't beat this to control a moderate load. The relay is marked as being rated for a 20A load. It can handle a battery voltage up to 36 volts.

I purchased this disconnect to help prevent the battery in my kids’ toy car from being discharged too much from either use, or from the little toy radio not being turned off. The item itself is self explanatory in its installation, but instructions are provided nonetheless. The instructions warn that the device itself consumes power and will over time discharge the battery it is connected to. This should be expected, and doesn’t present a problem as it’s designed to prevent over-discharge - in my two weeks of testing this module, I have found it to work flawlessly. As mentioned, it’s easy to install - I used a 3D printer to make a little mount, but a few standoffs would work equally well. After setting the device up by patching it into the circuit and setting the threshold, it’s ready to go. The LED display is crisp and easy to read and shows currently voltage passing through the device. It has worked great for the post two weeks in my application. When the device shuts off the toy car, I disconnect the battery and recharge it so it’ll be ready to go the next day. I was pleasantly surprised by how straightforward the device is. The price is very reasonable and I’m considering buying more for other projects in the future.

Still going strong afters many years of service. It protected my battery from over drainage. So far i am pulling 7 amp from the battery.

Despite relatively high amp rating, the terminal blocks are rather small and took some creative solutions for connecting 10AWG gauge stranded wire. If you are buying this make sure you have the correct size compression terminal lugs on hand. Beyond that, this is an amazing little product that does exactly what it says AND can be calibrated easily to match your measured voltage. You can very easily adjust the low voltage shut off and reconnect differential. Using mine between the inverter, baby lithium battery bank, and a snitty cheap charge controller, and has greatly reduced the amount of pouting my charge control does.