Why do some electronic devices die after a black out?

Thread Starter

StrongPenguin

Joined Jun 9, 2018
219
We had a black out test the other day on the ship I am on. The generator was shut with the Emergency Stop button, and after we had the ship up and running again, one monitor to the integrated alarm system was dead, and a CCTV control box (which was not the first box to go, I'm told)

What happens during a black out, is it a voltage spike that kills random (poorly designed?) equipment? Or is it a slow surge that does the trick?

And when we are looking for 24V DC earth faults, we have to switch off some breakers, cutting power abruptly. Does this off-switching cause a spike, or surge? Neither?
 

CROSSBOLT

Joined Dec 9, 2008
21
Your gear is probably beyond my experience as an IC Electrician and Chief Snipe 40 years ago but will give it a shot! Is your emergency stop "blackout" button killing the prime mover (piston or turbine engine) or disconnecting the generator from the buss?
 

Thread Starter

StrongPenguin

Joined Jun 9, 2018
219
It kills the engine, cutting fuel. It usually goes down "slowly", giving low voltage alarms on the main bus bar, but some breakers on sub boards switch during this slow down, looking for power elsewhere.

Thoughts?
 

Hymie

Joined Mar 30, 2018
762
Many switch mode power supplies incorporate an auxiliary primary transformer winding, which provides the low voltage to supply the primary switching circuit. Before the power supply is up and running (with power from this auxiliary winding) the primary switching circuit starts based on power from the rectified mains.

I have experienced this start circuit failing on my home security cctv system. The cctv system is powered 24/7 – but once the power was lost, the switch mode power supply cannot re-start.
Replacing a faulty capacitor in this start circuit repaired the PSU.

It may be that this fault is waiting to manifest itself on equipment employing switch mode power supplies, only evident once the mains power is interrupted.
 
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