interesting failure of a AG3000 surge protector.  - Page 1
Forum section: electronics / general

author: johansen
author_rank: Super Contributor
timestamp: July 10, 2025, 05:09:33 pm
content: I can add photos later if anyone is interested but I pulled an AG 3000 surge protector out of a dumpster and found that of course the green LED didn't light up.So I took it all apart and everything looks good. turns out there is a fiberglass spring loaded blade inside the MOV assembly (mersen 150tpmovsl ) that upon the MOV heating up hot enough to melt the solder joint, the blade slides between to help contain the arc flash, and that blade bottoms out on a micro switch which is connected in a way to short out the led.But that's not what happened, instead the LED had burned out. It was wired with 30K resistor and single diode in series so ~4mA. its a 3mm green led.the mov inside is a ls40k150qpthe voltage at 1ma should be less than 240vdc, and 395 volts at 300 amps.Usually in the case of repeated surges, the mov's get damaged, leakage current goes up, they get hot. no evidence of that.so i'm wondering if there is another overlooked failure path. I can test the mov's later.

author: floobydust
author_rank: Super Contributor
timestamp: July 11, 2025, 02:49:04 am
content: I have seen the usual: mains->rectifier diode-> resistor -> LED... easily fail.What happens is any voltage spike exceeding the rectifier's rating it avalanches and kills the LED with a little reverse current. I can get even >1kV on a 24VAC system with a brief short. Your MOV assembly should have protected all this - but there must have an open due to oxidation (blade switch)?The diode is likely slow several usec reverse recovery so that might contribute. Or the dropping resistor is not really good for say 400V, or they run hot and age turn brown LED too.I just put a small diode 1N4148 across the LED, or use a SMT bridge rectifier and they last a long time.Also I have seen some LED's just fail with age, very dim, some go open.ThatMOVis huge so I expect it to be alive. Even lightning 20kA 15x is OK for it.Or the rectifier diode is not much for PIV.

author: johansen
author_rank: Super Contributor
timestamp: July 11, 2025, 03:46:26 am
content: Its a 1 time only switch, if the mov heats up the solder melts.Unfortunately i may have lost the board with the led and diode. But in my mind you would need a lot of repetitive surges to kill even a 200v rated diode with a 3mm led through a 30k ohm resistor. (you just dont have enough energy to cause the diode to fail). but, the led.. cumulative avalanche damage?The led got fried, i looked at it under a microscope. But the resistors are both half a watt, 15k in series across just half the line at 120vac. (Two mov's)

author: floobydust
author_rank: Super Contributor
timestamp: July 11, 2025, 04:00:25 am
content: Once the rectifier avalanches, that is very hard on the LED even though the 30k limits some current. LED's reverse-current rating is small something like 5uA though.Enough fault current to visibly damage the die? so when you say the LED fried - the die is burnt or bonding wires melted etc.?To me that means there was an arc across the resistor(s) but again, the MOV is supposed to be. So this failure not making sense so far.

author: coppercone2
author_rank: Super Contributor
timestamp: July 11, 2025, 05:36:43 am
content: 1 point for neons

author: johansen
author_rank: Super Contributor
timestamp: July 11, 2025, 03:28:34 pm
content: Quote from: floobydust on July 11, 2025, 04:00:25 amthe die was darkened where the bond wire attached to it. if i can find it i'll look at it again because it seemed to be one of those weird led's with two bond wires instead of one.

author: johansen
author_rank: Super Contributor
timestamp: July 12, 2025, 02:16:17 am
content: Quote from: floobydust on July 11, 2025, 04:00:25 amI found the board with the led and diode. the diode is a GP230... not sure if its really a gp02-30 but it looks like any common 1n400x diode.

author: floobydust
author_rank: Super Contributor
timestamp: July 12, 2025, 04:31:39 am
content: GP225, GP230 diodedatasheet... uh so much for my theory it's rated PIV 3,000V!