Surge protection for appliances - Page 1
Forum section: electronics / general

author: ultrarunner2018
author_rank: Contributor
timestamp: September 04, 2023, 05:06:54 pm
content: Hey guys;We just replaced a microwave oven that was only about 2-1/2 years old. It was a Panasonic 2.2cu ft, 1250W model.While I am not at all certain that the failure was caused by a surge, I thought it best to add POU surge protection to all our expensive appliances.We have a whole-house unit that is wired directly to the electric service panel through double-pole 30A breaker, but I thought adding POU for the appliances - I already have them on my computers - would be wise.When I shopped for surge protectors, I looked for single outlet devices with the highest energy (joule) rating. I purchased the [ETL Listed] Cable Matters 2205 joules, 1875W units on Amazon.After plugging them in, I found that these units have a 'let-through' voltage of 900V, compared to the Tripp Lite Spike Cube which has a 600V let-through, but only 600 joules.In addition, the Cable Matters units do not have H-G or N-G (only H-N) protection, while the Tripp Lite has all three (H-N, H-G, N-G), with let-through of 400, 500, 500.Considering that I already have whole-house protection, it would seem logical that I wouldn't need the higher joule rating, but could benefit more from the lower let-through voltage.Now, I'm not exactly sure what is meant by let-through (as listed on the Tripp Lite spec sheet) compared to MOV clamping voltage. From what I have read so far, clamping voltage refers to the voltage at which the MOV begins conducting 1mA current. As MOV current rises, so does the clamping voltage.So, my question is whether I should return the Cable Matters devices and buy the Tripp Lite devices with a lower let-through voltage but lower energy rating.Thanks for your helpUltrarunner

author: Miyuki
author_rank: Frequent Contributor
timestamp: September 04, 2023, 06:34:43 pm
content: Devices shall withstand it if they are up to specifications, but nobody cares nowadays, so can just die.The only way to have lover clamp voltage is to have a big TVS, which is pretty expensive and exotic, or some thyristor crowbar

author: ultrarunner2018
author_rank: Contributor
timestamp: September 05, 2023, 12:51:52 pm
content: Thanks for your advice;I'm probably overthinking this, as I do everything.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 05, 2023, 01:30:51 pm
content: There is one other technology: clamp it with a dumb ass diode and (electrolytic) capacitor. These are somewhat popular as long(er)-life protection, with a low clamping voltage; I'm not sure exactly about energy capacity, or size or cost, but it's a good solution for surges up to some maximum amplitude and duration (lest the capacitor be overcharged, eh), without the wear mechanism of MOVs. Electrolytics do age in general, particularly under bias and at elevated temperature. (Should still be decades of service, for something that sits on the floor or outlet near ambient temperature.)Indeed this is the primary mechanism of most power supplies; very small ones (under 50W, say) may benefit from enough DCR (and LL) in the CMC to allow FWB + input cap to do the clamping, and larger supplies have more than enough capacitance (and rectifier capacity) to do it directly. Likewise anything with a (mains frequency) power transformer, the leakage inductance plus output cap provides ample surge immunity. The main issue these days is when PFC is required (which is most/all the time), in which case the electrolytic doesn't clamp the input directly, but is fed through PFC choke(s); or synchronous rectification, or both (bridgeless PFC), in which case a MOV is likely included to reduce peak voltage and current through the active devices. (An inrush / PFC bypass diode is commonly used, anyway, which gives a direct surge path from rect to cap, but the MOV is still helpful.)Mains rated TVSs have essentially unlimited life, but are fuckoff massive (as diodes go; they're still smaller than the corresponding electrolytic capacitor though!). Very pricey, but may be a good idea if you're in an extremely surge-prone area.MOVs wear under surge duty; at typical ratings, one might be suitable for some thousands of strikes. Which is plenty to survive a decade or more product lifetime. The downside is, when they go,they go; they're somewhat notorious because the vaporized remains of leads and disc are rather graphic (and maybe destructive too), and of course repairpersons see them all the time, driving confirmation bias. One must keep in mind it's a given that the unit has failed in some way already, to get to repair, and without the MOV it would've failed MUCH sooner -- and from much more complicated means (i.e. you'd have to replace all the power transistors and controllers on the primary side -- BER).Surge protection is often combined with series impedance, which is most feasible on a base unit, or a larger power strip, and probably not acceptable in a plug-mounted unit (where I would expect a couple MOVs plus thermal fuses and that's it); and may not be acceptable installed for a whole facility (SPD unit), partly because if it's off to the side (on its own branch circuit?), impedance would worsen performance entirely, but also because, even if it were in series with the facility feed, that impedance affects regulation and fault current capacity of subsequent circuits.Tim

author: tszaboo
author_rank: Super Contributor
timestamp: September 05, 2023, 02:27:37 pm
content: I was renting an apartment and it came with a fridge. Every time it stopped the compressor of it, it made a huge kickback to the network, so large, that it made my coffee machine make a popping sound. So surges come from all kinds of appliances with electric motors, not just from the outside of the house. I honestly don't have a good idea how to resolve problems like that, other than buying more efficient models with brushless motors and drivers.