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.
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.
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.
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.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.
Maybe this is the cause of the inrush problems. I would expect the secondary to read 1 ohm or so, but not the primary.
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
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
Good points guys. I measured the primart again, it reads 0R2 (0.2 Ohms), and both the secondarys read 0R1 (0.1 Ohm). This was the toroid I got from Rockna Electronics. From what I hear, they sell a good product and make some really nice toroids.
Eva, I've done my calculations and realize this. I'm going by the schematic provided from Anthony.
Frazzled, I will be wiring some 20A outlets, this was just to test.
I connected a 12Vrms center tapped transformer I had laying around to the power supply. Everything worked the way it should (I never loaded it, just used a volt meter) and I got 8VDC on the positive and negative outputs. I think inrush supression will do the trick. If not, I'll have to get another transformer.
Anything else I'm missing?
Thanks.
Eva, I've done my calculations and realize this. I'm going by the schematic provided from Anthony.
Frazzled, I will be wiring some 20A outlets, this was just to test.
I connected a 12Vrms center tapped transformer I had laying around to the power supply. Everything worked the way it should (I never loaded it, just used a volt meter) and I got 8VDC on the positive and negative outputs. I think inrush supression will do the trick. If not, I'll have to get another transformer.
Anything else I'm missing?
Thanks.
Any Pictures?
emuman100
I would be EXTREMELY interested in seeing any pictures you might have of your amp, and I mean anything, any state of completion, and I would be really interested in your thoughts and impressions of the sound from this amp, are you using a Zoebel network?
I have purchased my transformers and once I finish moving, I will be in the process of putting "IT" all together, I am using a output delay and a triac soft start circuit, 50,000uf of smoothing caps per channel and a kick a$$ wind tunnel heat sink seen in this thread.
thanks!
emuman100
I would be EXTREMELY interested in seeing any pictures you might have of your amp, and I mean anything, any state of completion, and I would be really interested in your thoughts and impressions of the sound from this amp, are you using a Zoebel network?
I have purchased my transformers and once I finish moving, I will be in the process of putting "IT" all together, I am using a output delay and a triac soft start circuit, 50,000uf of smoothing caps per channel and a kick a$$ wind tunnel heat sink seen in this thread.
thanks!
Frazzled,
I'm glad to hear you are building this too. As of now, I have built the power supply. This consists of the two bridges, 20000uF per rail, and the 10kR 5W resistors. I drew up a layout on a 6x6 pcb and etched it. I flowed thick solder to make really thick traces to be able to handle the current. I used wiring terminals that accept 4 AWG wire. Everything was from digikey except the board and etching supplies. If I had a digital camera, I'd take a picture, but I have no digital camera. The 2kVA toroidal transformer is a 117V primary, 2x65V secondaries at 15A per secondary. I ordered it from Rockna electronics. The peak AC output from this transformer just might pop the capacitors, because the voltage is about 10 or 20V higher than the caps are rated for. I might have to order new ones and use them. I also ordered parts for the first AV800 PCB. I ordered a delayed relay and a resistor and also a few inrush thermistors to try out. Once the inrush is not a problem and the power supply is operating, I'll start assembly on the AV800 pcb.
I'm glad to hear you are building this too. As of now, I have built the power supply. This consists of the two bridges, 20000uF per rail, and the 10kR 5W resistors. I drew up a layout on a 6x6 pcb and etched it. I flowed thick solder to make really thick traces to be able to handle the current. I used wiring terminals that accept 4 AWG wire. Everything was from digikey except the board and etching supplies. If I had a digital camera, I'd take a picture, but I have no digital camera. The 2kVA toroidal transformer is a 117V primary, 2x65V secondaries at 15A per secondary. I ordered it from Rockna electronics. The peak AC output from this transformer just might pop the capacitors, because the voltage is about 10 or 20V higher than the caps are rated for. I might have to order new ones and use them. I also ordered parts for the first AV800 PCB. I ordered a delayed relay and a resistor and also a few inrush thermistors to try out. Once the inrush is not a problem and the power supply is operating, I'll start assembly on the AV800 pcb.
Re: Inrush
Another approach that I like is to use a thermistor and relay. In this case you could select a resistance value for the thermistor that would be higher than usual because you don't have any problem with continuous dissipation. Also, at the instant before closure, depending on how long the thermistor is given to heat up, the relay contacts will probably have a lower voltage across them than with a resistor setup. Less chance of "chirping the tyres".
johnnyx said:
Another approach that I like is to use a thermistor and relay. In this case you could select a resistance value for the thermistor that would be higher than usual because you don't have any problem with continuous dissipation. Also, at the instant before closure, depending on how long the thermistor is given to heat up, the relay contacts will probably have a lower voltage across them than with a resistor setup. Less chance of "chirping the tyres".
Re: Re: Inrush
I saw this in an industrial 60A constant current source, for an ionizing machine. I had to replace the thermistor, which had gone open-circuit., probably due to the faulty switching transformer.
There are so many ways to achieve the same result, Choosing one is sometimes difficult.
Circlotron said:
I saw this in an industrial 60A constant current source, for an ionizing machine. I had to replace the thermistor, which had gone open-circuit., probably due to the faulty switching transformer.
There are so many ways to achieve the same result, Choosing one is sometimes difficult.
Re: Re: Inrush current on AV800 stereo power supply
Actually, a 20A breaker will trip at 18A continuous current (120VAC) and the time it takes to trip is described on it's trip time curves for that particular circuit breaker. If the surge lasts longer than the trip time for that much surge current, the breaker will trip. Of course you wouldn't have a 20A breaker unless you had 12 Gauge wire, I don't think 14 Guage is used for power anymore, but if it is 14 Guage, than a 15A breaker will give you almost 13A.
If you are charging large capacitors with the transformer, you are probably putting a capacitive load on the line, (secondary impeadence is reflected through the primary) dispite the inductive reactance in the windings. If the surge is too much, you could use 220V if possible, or construct an SCR circuit to initially use 25% - 50% of the power sine wave, and slowly increase the percentage to 100%.
I would not use an industrial breaker in a house circuit for saftey reasons and starting a
Frazzled said:
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.
Actually, a 20A breaker will trip at 18A continuous current (120VAC) and the time it takes to trip is described on it's trip time curves for that particular circuit breaker. If the surge lasts longer than the trip time for that much surge current, the breaker will trip. Of course you wouldn't have a 20A breaker unless you had 12 Gauge wire, I don't think 14 Guage is used for power anymore, but if it is 14 Guage, than a 15A breaker will give you almost 13A.
If you are charging large capacitors with the transformer, you are probably putting a capacitive load on the line, (secondary impeadence is reflected through the primary) dispite the inductive reactance in the windings. If the surge is too much, you could use 220V if possible, or construct an SCR circuit to initially use 25% - 50% of the power sine wave, and slowly increase the percentage to 100%.
I would not use an industrial breaker in a house circuit for saftey reasons and starting a
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