jfsimon – June 2018 Low-voltage cutoff circuits Using a TL431 or similar: Battery Guardian (Silicon Chip, 2002) http://www.qsl.net/9w2lw/guardian.htm LM336, comparator, N-channel MOSFET on high side driven by isolated SMPS Forum post, LV alarm, MikeML (15 March 2010) https://www.electro-tech-online.com/threads/12v-battery-low-voltage-monitor.104886/#post-856427 TL431, LED driven by NPN BJT Forum post, LV disconnect 1, MikeML (4 February 2011) https://www.electro-tech-online.com/threads/12v-battery-low-voltage-monitor.104886/page-2#post-950306 TL431, P-channel MOSFET, hysteresis resistor Same circuit from RONV (13 February 2016) https://forum.allaboutcircuits.com/threads/voltage-cut-off-tl431.120827/#post-965055 Same circuit from Hero999 (20 February 2017) https://www.eevblog.com/forum/projects/power-the-load-only-when-car-supply-voltage-is-above-14- volts/msg1140485/#msg1140485 Variant of the same circuit with ATL431 (20 February 2017) https://www.eevblog.com/forum/projects/power-the-load-only-when-car-supply-voltage-is-above-14- volts/msg1140526/#msg1140526 Forum post, LV disconnect 2, MikeML (11 February 2014) https://forum.allaboutcircuits.com/threads/tl431-battery-cut-off.94148/#post-696553 TL431, P-channel MOSFET, push-button, battery voltage is measured at MOSFET drain Forum post, Ian.M (9 August 2016) https://www.eevblog.com/forum/renewable-energy/efficient-way-to-disconnect-battery-when-voltage- drops/msg1000473/#msg1000473 TL431, NPN emitter follower, Schottky diode, P-channel MOSFET jfsimon – June 2018 Driving a relay directly with a TL431, push button to start Note: I tested this one but I haven’t been able to get reliable triggering of the relay. I observed that the voltage across the TL431 increased gradually around the triggering point. That was not sharp enough and the relay was switching slowly at unpredictable voltages. I didn’t know if that was to be expected or if I was doing something wrong; I had limited time for debugging so in the end I used this circuit instead: Units available for sale: Victron BatteryProtect https://www.victronenergy.com/battery_protect/battery-protect KEMO M148 https://www.kemo-electronic.de/en/Car/Modules/M148A-Battery-guard-12-V-DC.php (Some others on Amazon or eBay) jfsimon – June 2018 Using a MAX8212: LV disconnect from Maxim app note 926 (1996) https://www.maximintegrated.com/en/app-notes/index.mvp/id/926 Versatile Micropower Battery Protector, by Peter Smith (Silicon Chip, 2004) http://www.learningelectronics.net/circuits/versatile-micropower-battery-protector.html LV cut-off using max8212, Brian Dorey (February 2013) https://www.briandorey.com/post/low-voltage-cut-off-using-max8212 Miscellaneous: Forum post, MikeML (March 2009) https://www.electro-tech-online.com/threads/wind-turbine-battery-controller.90598/ 555 as a Schmitt trigger, linear regulator as voltage source and voltage reference Undervoltage protection, DanyK (October 2011) http://danyk.cz/p_ochr_en.html Zener diode, PNP transistor, N-channel MOSFET on low-side LifeSaver for Lithium or SLA batteries, by Nicholas Vinen (Silicon Chip, 2014) http://www.hobbielektronika.hu/forum/getfile.php?id=234807 LDO regulator, comparator, N-channel MOSFET on low side Forum post, MLXXXp (19 June 2014) https://www.eevblog.com/forum/projects/12v-low-battery-discharge-cutoff-circuit/msg463975/#msg463975 Zener diode, dual comparator, N-channel MOSFET on low side Forum post, Ian.M (17 October 2016) https://www.eevblog.com/forum/projects/designing-low-voltage-battery-protection-circuit-good-reference- designs/msg1049653/#msg1049653 LTC1440 and a P-channel MOSFET on high side Forum post, Ian.M (25 October 2016) https://www.eevblog.com/forum/projects/battery-undervoltage-lockout/msg1055771/#msg1055771 LT6650 and a P-channel MOSFET on high side Forum post, nfmax (31 October 2016) https://www.eevblog.com/forum/projects/battery-undervoltage-lockout/msg1060148/#msg1060148 LM10 and Schmitt trigger Forum post, Ian.M (20 February 2017) https://www.eevblog.com/forum/projects/power-the-load-only-when-car-supply-voltage-is-above-14- volts/msg1140421/#msg1140421 Modifying a Velleman MK138 thermostat kit .