Power amps and supply voltage spikes

Michael John

Michael John

Junior
Jun 25, 2011
352
9
18
Sydney, Australia
eclipseaudio.com
At events on the weekend a power spike took out some power amps and some other gear. A Lake Contour blew a fuse. A Lab PLM 14k (not on) started pouring smoke. (A 400VDC electrolytic popped on the lower power supply board that feeds the Lake board. All fixed now.) Smoke also came out of two QSC's - a PLX3002 and a PLX1804. Back home I opened them up and couldn't find any sign of burning nor leaking electrolytics. I cleaned out dust from behind the fan, turned them on and they pass audio just fine.

QSC service said that if they're passing audio, they could test them at high power on dummy loads for a few hours and see what happens. So I bought 800 watts of dummy load resistors and I plan to do something similar.

Anyway, has anyone experienced something similar with QSC amps? Any advice?

Cheers,
Michael
 
Re: Power amps and supply voltage spikes

keep in mind that the wattage rating on resistors is the "just about to burn up" rating.. to run them at full power for more than a burst you'll have to put them on a huge heatsink or in a bucket of water.

Jason
 
Re: Power amps and supply voltage spikes

Thanks. I just bought another 800 watts of resistors!

This power spike was a good excuse to buy an Arduino (EtherTen) and over Christmas I built and programmed a power meter and logger. It uses the Arduino's 6 analog inputs to measure active and neutral on all phases up to about +-580 volts peak and has protection for higher voltages. I can detect miss-wired neutrals and these indicators, along with RMS and peak voltages, are displayed on a LCD shield. I've also installed a web server for providing data to anyone on the network. If anyone's interested, I could maybe post the circuit diagram for the inputs and the code.
 
Re: Power amps and supply voltage spikes

Michael Smithers said:
Thanks. I just bought another 800 watts of resistors.
Click to expand...

Easiest and cheapest way to build a dummy load is using heater elements. As with any form of resistive dummy load, it will be the wrong type of load , but it doesn't matter for his kind of test.
 
Re: Power amps and supply voltage spikes

Michael Smithers said:
Thanks. I just bought another 800 watts of resistors!

This power spike was a good excuse to buy an Arduino (EtherTen) and over Christmas I built and programmed a power meter and logger. It uses the Arduino's 6 analog inputs to measure active and neutral on all phases up to about +-580 volts peak and has protection for higher voltages. I can detect miss-wired neutrals and these indicators, along with RMS and peak voltages, are displayed on a LCD shield. I've also installed a web server for providing data to anyone on the network. If anyone's interested, I could maybe post the circuit diagram for the inputs and the code.
Click to expand...
I was thinking about a similar idea.

I was going to isolate the measurement device and use either wireless or optical fiber for communication.

I'd be interested to look at your soulution.
 
Re: Power amps and supply voltage spikes

Michael Smithers said:
At events on the weekend a power spike took out some power amps and some other gear. A Lake Contour blew a fuse. A Lab PLM 14k (not on) started pouring smoke. (A 400VDC electrolytic popped on the lower power supply board that feeds the Lake board. All fixed now.) Smoke also came out of two QSC's - a PLX3002 and a PLX1804. Back home I opened them up and couldn't find any sign of burning nor leaking electrolytics. I cleaned out dust from behind the fan, turned them on and they pass audio just fine.

QSC service said that if they're passing audio, they could test them at high power on dummy loads for a few hours and see what happens. So I bought 800 watts of dummy load resistors and I plan to do something similar.

Anyway, has anyone experienced something similar with QSC amps? Any advice?

Cheers,
Michael
Click to expand...

Just because the amp still works after the over-voltage event does not mean it completely escaped harm. There may be some subtle device deterioration that won't show up immediately. Sometimes there are protection circuits that sacrifice themselves to protect the rest, while they often fail open.

If QSC service say burn and go, then burn and go...

JR

PS: Water heater elements (in water) apparently make decent large amp loads.

[edit] When making your power monitor you are likely using a hot circuit front end (not isolated from mains) to make measurements. Be very careful you do not inadvertently expose humans or valuable gear to shock hazards. [/edit]
 
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Re: Power amps and supply voltage spikes

A 1500 Watt oil filled room heater would make a nice 9.6 Ohm dummy load.
At least for this type of testing.

I too would be interested in the power monitor circuit.
 
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