Automotive Transient Protection on yacht - Page 1
Forum section: electronics / projects

author: WaldPinkler
author_rank: Contributor
timestamp: January 29, 2022, 02:55:05 am
content: I don't know how many circles I've been around trying to decide on transient protection.I've found dodgy forum stuff, TI pdfs, etc, etc.Where can I learn about what I reasonably need to do to add circuit protection.At the moment I want to use a pic18, CAN bus and a TI chip on a yacht. Low power stuff. Maybe lightning but that's a bigger issue.Also, running PI boards, esp32, etc.

author: WaldPinkler
author_rank: Contributor
timestamp: January 29, 2022, 04:42:20 am
content: Also information I find is 2014:https://www.ti.com/lit/an/snva717/snva717.pdfHave things progressed here much?

author: peter-h
author_rank: Super Contributor
timestamp: January 29, 2022, 08:40:39 am
content: Lightning protection is (obviously) very hard.Probably a big thing is transients from the starter motor on the engine. Yachts usually have a small engine. There is an IEC spec for that; something like 200V pulses for a few ms - surprisingly hard to deal with, so you use an LM2940 rather than a 7805, for example.

author: WaldPinkler
author_rank: Contributor
timestamp: January 29, 2022, 09:29:58 am
content: This yacht has a 50hp motor. 80A alternator. Fridge motor turning on and off. Bilge pumps up to 10A running. Lithium BMS disconnects. It's not a clean supply at the end of the day.I tried to find schematics of marine electronic gear. No luck there.

author: Dabbot
author_rank: Regular Contributor
timestamp: January 29, 2022, 11:02:23 am
content: Assuming a 24v system?What's your expected load? Can't be very much if you're just running some chips.

author: WaldPinkler
author_rank: Contributor
timestamp: January 29, 2022, 01:48:50 pm
content: 12V. It's just a current shunt chip, mcu and can bus transceiver.

author: fcb
author_rank: Super Contributor
timestamp: January 29, 2022, 02:13:50 pm
content: Quote from: WaldPinkler on January 29, 2022, 01:48:50 pmJust use a series resistor in front of your 7805 and a transzorb/TVS across that to gnd.Your current shunt IC may (or maynot) be the big issue, assume load dump is around 50-100V.

author: jonpaul
author_rank: Super Contributor
timestamp: January 29, 2022, 04:12:28 pm
content: Use Motorola MR2525 alternator load dump diode.Large transorb TAZAddd EMI filterJon

author: Faringdon
author_rank: Super Contributor
timestamp: January 30, 2022, 03:08:50 am
content: There is a way of doing transient protection with a current clamp and a TVS.....when the transient comes, the TVS shunts it......but the current gets clamped by the FET of the current clamp...and your circuit is across the TVS...and gets protected.....basically the FET takes the hit...takes the overvoltage....as in the sim attached, its in the free LTspice.Also, you can just have a comparator to literally just switch the supply rail off your circuit when the overvoltage transient comes along....so a comparator reading a divider...and the comparator switching off a series pass FET.

author: floobydust
author_rank: Super Contributor
timestamp: January 30, 2022, 05:00:18 am
content: For the 12VDC power, I would use a fuse, diode, TVS + bulk capacitance to give filtered DC with some hold time. I use massive 6,600W automotive TVS VishaySM8A27which clamps to 40V with 75A impulse. It's a simple solution proven to be robust. Depends on how many $$$ the electronics is downstream.The RPi SMPS thus does need need to tolerate the TVS clamping voltage, so good to 40V although the TVS does around 30V with smaller surges.OP can you comment on the grounding on the boat, for lightning discharge ideas.I don't know marine practices but I thought the engine gets grounded through the metal driveline and prop. But I see a ground plate is involved, and creates a new issue for galvanic corrosion between the two unless it's zinc. There is a ground busbar used as well on boats I see.

author: WaldPinkler
author_rank: Contributor
timestamp: January 30, 2022, 10:03:23 am
content: Quote from: floobydust on January 30, 2022, 05:00:18 amI have a bonding system set up that links all through hull fittings, tanks and rigging together so they are at equal voltage. Yes, there are zinc anodes. The new standard allows the bonding system to be linked to the ground with specifications on wire gauge for lightning protection.There are differing thoughts on overall lightning protection. From putting a chain from the rigging into the water which some say may increase lightning attractiveness. A friend has such an ion dissipater as in the above image. The idea being that it draws in static from the air creating a dead zone. The other is sticking laptops and such in the oven as a faraday box.Interestingly the garmin can bus includes a different connector to the bus for the wind meter to protect the rest of the bus from lightning. The $700 wind meter will get blown away on top of the mast but ok.But that's the bulk lightning system. I still want to make my own devices and protect them. I've pulled out the pcb of the anemometer. Maybe it can gives some clues on good transient protection. I'll try take a photo.