Inrush current on AV800 stereo power supply - diyAudio
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Old 20th July 2004, 09:28 PM   #1
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Default Inrush current on AV800 stereo power supply

Hello,

My AV800 (800W amplifier by Anthony Holton) power supply is complete. I ordered a 2kVA toroid from Rockna Electronics. Upon connecting it up to the power supply and switching on the mains (US 120V) the breaker tripped. After as bit of thinking I figured out it was inrush current tripping the breaker when the transformer is connected to the power supply. When it's left unconnected, it operates normally, but inrush sometimes trips the breaker, depending on what part of the sine wave hits it first. What do you guys suggest with inrush suppressor thermistors or circuits. The maximum current I plan on drawing from the wall is 19A, so what do you guys suggest?

Thanks.
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Old 20th July 2004, 10:14 PM   #2
johnnyx is offline johnnyx  United Kingdom
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Default Inrush

This has been discussed before, but I don't know which thread.
The two methods are;-

Use a negative tempco thermistor designed for the purpose. they run hot, but are cheap and would be easy to fit. A 5ohm (when cold) one would be suitable,depending on the winding resistance of the transformer primary.

Another approach would be to use a fixed resistor chosen to limit the current to a suitable value, which is shorted by relay contacts after some short interval. This is not as cheap or easy, but maybe the anti-thump circuit of the amp could drive another relay.

Circuit breakers come in different types, I think it's the "D" type that is designed for motor circuits, and has a higher surge current capability before it trips. not sure if these industrial types could fit in domestic fuseboards.

I suppose you have three options to choose from. I think the relay option is possibly the best, one I would choose. I've seen all three used effectively.
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Old 20th July 2004, 10:26 PM   #3
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johnnyx,

For now, I'm going to use the thermistor. I just need something to make it work, then I'll use the relay. Digikey sells KC016L-ND, which is a CL-160. This will do despite the fact it will run hot?

Thanks.
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Old 20th July 2004, 10:44 PM   #4
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BTW, the resistance of the primary reads 0 on my ohm meter.
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Old 20th July 2004, 10:46 PM   #5
johnnyx is offline johnnyx  United Kingdom
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I'm not familiar with the type number, but it's probably ok. RS components don't list the part no, just the resistance and current rating.
You might find that you have no need to replace it. Some wirewound resistors don't like inrush currents either.
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Old 20th July 2004, 10:55 PM   #6
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johnnyx,

I'm not replacing, I'm trying to find something do use with this power supply. As you said, I will try one with 5R cold resistance and see how it goes. If it doesn't do the trick, I'll use the relay.

Thanks again for the help.
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Old 20th July 2004, 10:59 PM   #7
johnnyx is offline johnnyx  United Kingdom
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In that case, I would double check the wiring. The primary should read something, even if its just ohms. My 300VA torroidal reads 43 Ohms, for 240v, so 800va on 110v must read 5 - 10 ohms.
Maybe this is the cause of the inrush problems. I would expect the secondary to read 1 ohm or so, but not the primary.
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Old 21st July 2004, 12:51 AM   #8
Eva is offline Eva  Spain
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I would try connecting a simple 100W light bulb in series with the primary of the unloaded power supply and find out what happens. If the light bulb doesn't stop lighting after some seconds then there is probably a short somewhere
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Old 21st July 2004, 01:16 AM   #9
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Default Re: Inrush current on AV800 stereo power supply

Quote:
Originally posted by emuman100
<SNIP> The maximum current I plan on drawing from the wall is 19A, so what do you guys suggest?

Thanks.

Unless you have an outlet specifically wired for 20A then I am afraid you are limited to 15A from a regular 120V houshold AC outlet, this is standard wiring code and 20A service to an outlet would require rewiring and installing a different breaker.

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Old 21st July 2004, 01:35 AM   #10
Eva is offline Eva  Spain
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Some facts usually overlooked :

Power drawn from rectified mains [rectifier with filter caps load] produces three times the RMS mains current than power drawn from sine mains [resistive load]

1200W RMS of resistive AC load produce 10A RMS in a 120V AC line while 1200W RMS of rectified DC load [audio amplifiers] produce 30A RMS. This means that mains wires heat as if there were 3600W of resistive load

This happens because those 1200W of rectified power are actually seen by the mains line as pulses of 3600W drawn during 33% of the time and no power drawn during 66% of the time

120V lines are inefficient, even more inefficient when rectified. Fortunately any non-class-A 800W audio amplifier channel tends to draw less than 200..400W average when driving a speaker load at full power with music signal
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