Preventing +6 Amp surge

[Dan_Steele]

Right guys,

just moved into my university halls and brought my Peter Daniel gainlcone (300Va 25V trafo) hifi system that I built.

But, the wiring here is 'aparantly' only fit for 6 amps and so as I power them on the surge to the trafos flips the breaker (which I cant get to so I cant hold it on during power up)

The fuse in them is a 5amp so obv if i can get them on it shouldnt trip them during normal running.

Now is there any way of getting around this, preventing the surge or making it spread over a larger time period.

many thanks

Regards

Dan

 

[Frank Berry]

You need to find out what other electrical devices are on the circuit and shut them down befor you power up the amplifier.

You might also look into a soft-start circuit for your amplifier.
(hint) You may be able to start the amplifier through a 100 watt bulb. When the bulb dims, bypass the bulb.

 

[-=terran=-]

Expanding on Frank's 100W Lamp idea, perhaps you could use a NTC inrush current limiter, like those found in computer power supplies. You can check on digikey for part numbers, but here are a few links from a quick google:

Calculations:
http://www.ametherm.com/Inrush_Current/transformer_case_study.htm
Example parts:
http://www.wecc.com/inrush.html

 

[56405]

I would prefer the NTC solution.

Take care to choose NTCs specifically designed as inrush current limiters.

See as example:
http://content.honeywell.com/sensing/prodinfo/thermistors/inrush.asp

http://www.gesensing.com/thermometricsproducts/inrushcurrent.htm

 

[Dan_Steele]

Cheers guys,

I've gone for the NTC surge protection option. Should be arriving in the next couple of weeks hopefully.

In the mean time, I've got one hell of an extention lead to the hoover socket down the corridor.

Well needs must!!

Regards

Dan

 

[AndrewT]

........I've gone for the NTC surge protection option. Should be arriving in the next couple of weeks......

and add a relay bypass switch across the NTC to bring full performance back to the transformer primary.
The delay on the relay bypass can be around 300mS to 1S. A 555 and a few components hardwired on a tiny bit of vero board does this.

 

[Dan_Steele]

limited resorces / tools here, so for now its just the limiter,

as an update, just installed them and they work a treat, no more extension leads to vacuum cleaner sockets required!!

Thanks for your advice guys.

Regards

Dan

 

[-=terran=-]

Congrats on getting everything working!

Also, don't worry too much about bypassing the limiter, since they typically have very low effective resistance at their maximum current and/or after a few seconds of heating... in the milliohms range from some of the datasheets I've seen. The voltage drop at 120 or 220 VAC should have a negligible effect on your amplifier power output.

 

[AndrewT]

Also, don't worry too much about bypassing the limiter, since they typically have very low effective resistance at their maximum current and/or after a few seconds of heating... in the milliohms range from some of the datasheets I've seen. The voltage drop at 120 or 220 VAC should have a negligible effect on your amplifier power output.

I tried an unbypassed Thermistor on a ClassA amp which draws nearly constant mains load when still in ClassA and I can see the output waveform clipping bounce as the thermistor changes temperature when applying a load. This clip bounce gets worse as the load value becomes lower and the amp goes into ClassAB.

My advice, whether for resistor or thermistor, is to bypass with a relay. Minimise the upstream impedance for better performance.