Red Digital Voltmeter

Great for B&D 20v converted tools with the "power wheels adapter". B&D Batteries or tools dont have a low voltage shutoff circuit. Relies on the motor requiring 15v. So if you use those batteries in other tools with adapters. You can drain them to a point of no recharge. This lets you monitor the voltage on tools to ensure you never drop past 16.5 volts. You are the low voltage shutoff circuit :D

Keeps working down to about 3 volts, which is impressive. I compared measurements with my expensive multimeter and these little displays are satisfyingly accurate.

Great little voltmeter! Mounting is easy, I 3D printed a shroud to help with this and added some smoky Lexan to cut the brightness down a bit and improve the contrast. Calibration is simple and accurate, I set the 10ths digit to roll over to the next value with the input voltage reaches 0.05V (i.e. an input voltage of 12.44 reads as 12.4 on the LED, and 12.45 reads as 12.5). The accuracy is very good over the input range and the 10ths digit does not jump around excessively. Overall this is a very easy to use and acceptable voltmeter for most projects. I used it here in a mobile amateur radio setup to measure power supply/battery voltage and boosted voltage. I do wish the 3 wires were accessible so you could join the white and red (voltage for the LCD driver and voltage to measure) but they solder to the surface of the PCB under the LED, not a big deal though.

Very surprised how well these voltmeters work. We needed a simple display to augment our Automatic Testing Systems and the price was so good and size was right. I made a PLA 3d printed frame. I used 1.1 inches Hole to Hole spacing and used 3mm Socket Head Cap Screws. Opening I used was .6 x .91 inches if it helps anyone. Since there is no weight printed 2.5mm holes and tapped them with a 3mm tap. I looks like a gas station sign but it works great.

One of them came dead but the rest worked. Screen is bright. The two that I used in my project were displaying a very accurate voltage reading. I’m pretty happy with them.

I’m using this to monitor the state of charge of a LiFePo4 battery in my camper van, so I need accuracy between 12.9-13.4V. I calibrated the first unit to transition from 13.3 to 13.4 with a precision input crossing 13.35V. I’ll define a sub count as a change in the input of 0.01V. This mini DVM uses a micro with a 12 bit ADC, supporting a resolution below 0.01V, or 1 sub count (divide 30V range by 2^12). The voltage reference for the ADC comes from a cheap LDO regulator with +/-3% accuracy, which is why the calibration screw is needed. The specified variation of this LDO reference voltage suggests at most +\- 2 sub counts of accuracy loss between 50-100 degrees F ambient temperature, which is not bad. The long term drift of this reference is unspecified, and probably the most serious impact on accuracy over time. But again, a yearly recalibration should take care of that. I’ll check back in a year with an update. One last thing I’ll mention is the input (white wire) current. It is not quite zero. My measurement suggests there is a 125kohm resistor attenuator (probably 10:1) between the input and ground. So even if the unit is switched off (red wire opened) expect some current drain into input. For example, 0.1mA with a 12v input. Low enough for me to leave connected to my battery at all times, but about 10 times more current then a typical fluke DVM.

Great product, excellent prive

Great to monitor batteries.

Ça m'évite de sortir le voltmètre pour vérifié l'état des batteries. Un calibrage, par contre est nécessaire pour chaque voltmètre. J'aime bien.

remarkably accurate compared to my fluke. using to monitor 12 batteries in rv.

A lot of buzz introduced into the power line. Use a bypass capacitor.