surge protection?

rh71

No Lifer
Aug 28, 2001
52,853
1,048
126
Can someone explain how a surge protector works to protect electronics connected to it? I recently had a thunderstorm that kicked my power off and it came back on instantly. In my bedroom, I have a landline handset, a 50" tv (was not on), chromecast, and a digital projection clock connected to this surge protector. The clock wouldn't come back on, even with a button battery that it also uses as alternative power. Why was it the only one that died/fried? I know it's cheaper, but can someone explain why it was more susceptible? The green "protected" light on the surge protector has always been lit, even now.

The clock (received for free and am now claiming warranty):
https://www.amazon.com/Jensen-Radio...pID=412c1rhsR6L&preST=_SY300_QL70_&dpSrc=srch
 

ultimatebob

Lifer
Jul 1, 2001
25,135
2,445
126
How old was that surge protector? Those suckers (especially ones like the cheaper 750 joule model you were using) don't last forever.

How long they last really depends on how good your power quality is. Cheap surge protectors lose their protection after just a few power surges, though.
 
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tynopik

Diamond Member
Aug 10, 2004
5,245
500
126
it might not have even been a surge that did it in

many power supplies react . . . poorly . . . to undervoltage situations
 

mindless1

Diamond Member
Aug 11, 2001
8,052
1,442
126
Imagine three parallel resistors, representing two devices and one surge protector, with the surge protector being as low a resistance as possible, but only conducting above a certain voltage to complete a circuit to ground.

If that voltage is never exceeded, your surge protector is doing nothing to shunt surges to ground. This is a trip point for all surge protectors. If the trip point were too low, they would wear out from everyday surges coming from things like your refrigerator or A/C motor shutting off, so certain devices will fail before a surge protector even does anything because those devices were cheaper to build without any protection, and based on the components may be more susceptible to damage from higher voltage.

Now imagine a surge that exceeds the trip point so the surge protector passes the surge to ground. Every reasonable (cost effective) effort might be made to make the resistance to ground as low as possible, but it is not 0.00 ohms. There is still a little resistance so a certain fraction of the surge is still making it through the other two parallel resistors which are the two other devices.

The best method of surge protection is whole-site, which shunts surges at a power distribution box with a short path to earth ground, and incorporates additional shunts for any other surge route (like a roof antenna or telephone line), rather than running through dozens more of feet of wire and wire connection losses, before it's right there at the equipment outlet.

The clock probably had the bare minimum voltage regulation necessary to make it work, and its AC adapter, no surge protection at all. It's likely that somewhere some bean counter determined that the extra cost of making the design more immune to surges would be higher than the warranty replacement cost, or they just followed the lead of other consumer electronics manufacturers.
 
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Lanyap

Elite Member
Dec 23, 2000
8,106
2,157
136
The surge was either above 750 Joules or the surge protector is old and no longer protecting as it should. Also, some electronics can handle a surge better than others which would explain why some devices survived and some didn't. You should buy a better surge protector especially since you have a 50" TV.

EDIT: What mindless1 said.
 

rh71

No Lifer
Aug 28, 2001
52,853
1,048
126
I'll definitely get a new surge protector.

Separate question, I have an iRobot vacuum on a surge protector, but only the charging station is plugged in directly - the robot sits on top of metal contacts on the station. IF I DIDN'T have a surge protector on it, would it hit the robot too or just the station?