bayite Pack of 5 Three-Wire Calibratable DC 0~30V Red Digital Mini Voltmeter Gauge Tester Mount Car Motorcycle Battery Monitor Volt Voltage Meter 0.36" Red LED Display Panel

Great size, excellent function.

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.

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 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

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 have put these on a lot of equipment - The battery for the generator, batteries for the boat, monitors for load testing. They are small, easy to install and don't use much current.

Well illuminated. I wish there was a mounting base, but 1/4" stall mat works. The wires are small and not long, but adequate. I've added plug and jack leads for my temperature and bias feedback terminals. I plan to power two from one 9V battery. So 9V battery leads: plugs/jacks and some way to mount because as shown the backs are exppsed.

This woks good. You can also power with the signal and not from external source if you don't mind about the accuracy of the measurement. Now if you do, you better make sure to adjust all of them separately is using more than one because their factory settings come all different from one to another. For the same current, different displays from the same package will show different results (not much, just variation of the precision, mostly after the dot). Make sure you "zero" them out and use the calibrate function.

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.