Failure due to harmonics 1

[RajT]

I am on a project where we are commisioning new installed equipment.
The plant UPS system feeds several 110Vac “Beacons” ( stroboscopic lights used by the PA system) . The unit ratg is about 50VA.

We are finding that these beacons are failing after a few days in service.

The supplier of the beacon has carried out bench testing of the units at upto 135Vac and has found no failures.



The strobe units do have intricate electronic circuitry.

The strobe unit design is also some five years old and thus considered proven.



My thoughts are that could it be that the harmonics given out by the ( though less then 5% max) UPS may have some significance to the sensitive beacon circuitry.

As an experiment, I am thinking of fitting some type of RC network filter blocks on the input term of the beacons to see if it is indeed the harmonics that have any connection to the failures.

Any suggestion appreciated.
Guidence to small "filter blocks" supplier web site would also be appreciated.

 

[OperaHouse]

I suspect the problem is external. A 120KVA has to have a lot of other stuff connected to it. The simple power supply acts as a capacitive snubber on the entire system. If you put a 5 ohm resistor in series with the power of each strobe, I'm sure the problem would go away.

 

[jimkirk]

tequilasunrise has a good point. Many electronic loads are essentially constant power, so a low line voltage is often more stressful to a fuse than high line. I'd also wonder about inrush current to a xenon strobe...charge cap/discharge and repeat...

800mA fuse for a 500mA load is not much margin. Is the fuse being used to protect the circuit or as a safety device? It can be a bit of a philosophical question. I wouldn't recommend a higher curernt fuse, but there are different trains of thought regarding the proper use of fuses.

 

[RajT]

The beacons were bench tested at 190-135V which is their design limits with no fuse blown faults found.
The fuse is used to provide internal short circuit protection. The fuse size is considered acceptable.
The irony is that the design is some 5 yrs old with thousands of units sold ( so says the manufacturer).

The use of non UPS supply is not an option on the project which is a offshore facility.

 

[BobbyNewmark]

tequilasunrise has it: inrush current. Try plugging one of the strobes into a power strip and flip the switch on and off a bunch of times. I'll bet it pops the fuse.

One solution: bigger, slower fuse

Another solution: use an electronic relay that switches when the AC line crosses zero. (Somebody makes these, right?) This would greatly reduce the inrush current.