Feed Back on a Surge Protector Circuit - Page 1
Forum section: electronics / beginners

author: Crawdaddy
author_rank: Newbie
timestamp: June 09, 2025, 11:47:09 am
content: This is a surge protector circuit I designed for use on US 240v/120v AC. The circuits are split up into subsections for modularity. The N-G TVS section is meant for use downstream such as subpanels. I plan to design two PCBs. One will have the TVS stage and MOV stage. The second will have the GDT stage. The PCBs will be stackable so that they can be used together in one enclosure or only one PCB can be used independently. If any sub circuit is not needed it can be left unpopulated.All components are through hole. The two pin headers are for LED connection. LEDs are designed to be illuminated unless a fault has occurred. The MOV stacks are three MOVs with one thermal fuse bound together.Looking for input on changes I should make before PCB design. Thanks.TVS Diodes:240V - Littelfuse Inc. 1.5KE400CA Description TVS DIODE 342VWM 548VC DO201https://www.digikey.com/en/products/detail/littelfuse-inc/1-5KE400CA/688073120V - Higher Capacity/Higher Voltage for Main Panel - STMicroelectronics BZW50-180B TVS DIODE 180VWM 410V Clamp 146A (8/20µs) Ipphttps://www.digikey.com/en/products/detail/stmicroelectronics/BZW50-180B/1037901120V - Lower Capacity/Lower Voltage for Subpanel - YAGEO 5KP180CA/B TVS DIODE 180VWM 292V Clamp 17.5A Ipphttps://www.digikey.com/en/products/detail/yageo/5KP180CA-B/22508771MOVs:240V - Littelfuse Inc. V480LA80CP VARISTOR 750V 10KA DISC 20MMhttps://www.digikey.com/en/products/detail/littelfuse-inc/V480LA80CP/2501525120V - Littelfuse Inc. V275LA40CP VARISTOR VARISTOR 430V 10KA DISC 20MMhttps://www.digikey.com/en/products/detail/littelfuse-inc/V275LA40CP/1009423MOV thermal fuse: Cantherm SDF DF141S Thermal Cutoff (TCO) 141C (286F) 250VAC 10A Axialhttps://www.digikey.com/en/products/detail/cantherm/SDF-DF141S/1014763GDTs: Bourns Inc. 2026-47-C2LF Gas Discharge Tube 470 V 20000A (20kA) ±20% 3 Pole Through Hole

author: Terry Bites
author_rank: Super Contributor
timestamp: June 09, 2025, 01:05:58 pm
content: Very belt and braces!Its not easy to judge what you need. What is your situation wrt surges?Note that all arrestors GDT and semiconductor/ MOV will eventually die from fatigue.MOVs especially I've found.Surge currents in MOVs are often very high and will easily take down the fuse, is that a good idea?

author: MariuszD
author_rank: Regular Contributor
timestamp: June 09, 2025, 09:00:13 pm
content: Fuse in neutral is stupid. Ask the electrician how many damaged devices he has seen due to a broken neutral wire.GDT and MOV and TVS can't be connected close to each other. GDT is slow and neds kV spike to initiate gas discharge, The MOV will prevent the GDT from firing.The TVS has a lower dynamic resistance than the MOV. It will burn before MOV can act.Capacitor in series with diode will not light an LED.GDT in paralel will not workResistor in series with surge protector will reduce effectiveness.I don't know if PCB is god idea Currents in the range of thousands of amperes cause the evaporation of traces on the PCB.@Terry BitesVaristors degrade when they absorb voltage surges. A worn-out varistor starts conducting at mains voltage and begins to burn, so a fuse is essential to reduce the risk of fire. A thermal fuse is often used.

author: Crawdaddy
author_rank: Newbie
timestamp: June 10, 2025, 01:19:21 am
content: Quote from: Terry Bites on June 09, 2025, 01:05:58 pmThis designed to be a whole home surge protector to be installed at the main breaker panel. Will be connected to a dedicated circuit breaker. It is a wear item that must be replaced/rebuilt, but that is the case with all whole home surge protector that I am aware of. The fuses I am not sure on. I think they can handle the inrush current if they are properly sized slow blow ceramic fuses. The fuses are to protect for components that fail short. Maybe a PTC thermistor with thermal fuse would be better. The MOVs are protected with a thermal fuse, which looks to be the standard for commercially available surge protectors.Quote from: MariuszD on June 09, 2025, 09:00:13 pmThe surge protector is wire to an independent circuit breaker in the main breaker panel. An open neutral will not have an effect on other devices. Most the commercial available whole home surge protectors I have looked at use MOVs with GDTs. They don't normally have TVS diodes. As far as I am aware the MOVs will act sooner and at lower voltages, but I the event that the MOVs can't clamp the surge it will cause the GDTs to fire. If the GDTs fire in this case the MOVs will most likely be damaged/sacrificed. I add the TVS diode to act sooner than the MOVs, but maybe they could still be used with the MOVs if a PTC thermistor is place in series with the TVS diodes? Maybe add a thermal fuse connected to the PTC thermistor in place of the ceramic fuse for fail short protection? I fixed the LED circuit and have attach the corrected circuit. Is the issue with parallel GDTs that if one fires that non of the others would be able to fire? The resistors in series with the GDTs is to stop the arc at the 0V crossing. The resistors in series with the TVS diodes is to help balance the load due to the diodes being used in parallel. Is something other than a PCB the normal for something like this? The currents are for very short periods of time. Would sizing the traces to the time and temp rise of the traces not work?