richie00boy thats amazing......ur guess is right. I tested the voltage across the relay coil and it is 8.7V. The transformer was giving 9.6Vac. But the DC voltage across the rectifier diodes was only 8.6 V. I dunno what is going on. Am i not supposed to get close to 12 V ?
The relay specs are as follows:
12Vdc Relay coil
coil resistance 270ohm
nominal current 44.4mA
Could it be that i fried the diodes while soldering ?
The relay specs are as follows:
12Vdc Relay coil
coil resistance 270ohm
nominal current 44.4mA
Could it be that i fried the diodes while soldering ?
At a wild guess, 24V
Be very careful with this circuit - there is no isolation from the mains!
edit: It depends on the load. I looked up a typical 24V relay with the same pinout, and got a coil resistance of 1440 ohms. Using that and simulating the circuit, I found that the voltage rises to about 29V. I'd guess it'd delay for about 3 seconds due to the 2x470uF
I would also prefer to use one metalclad resistor, say 50W, rather than the multiple 5W ones mounted on the PCB as shown here.
Be very careful with this circuit - there is no isolation from the mains!
edit: It depends on the load. I looked up a typical 24V relay with the same pinout, and got a coil resistance of 1440 ohms. Using that and simulating the circuit, I found that the voltage rises to about 29V. I'd guess it'd delay for about 3 seconds due to the 2x470uF
I would also prefer to use one metalclad resistor, say 50W, rather than the multiple 5W ones mounted on the PCB as shown here.
Buzzy said:
How many secondary wires from your transformer? It sounds like either you have wired it out of phase, or you have a centre tap transformer and you have incorrectly connected it. You could also have a damaged diode or a diode in the wrong way.
Check for AC voltage after your rectifier - if you read any, then you've got a bad or incorrectly oriented diode. You will also need to replace any capacitors in this case as they will have been exposed to reverse voltage.
The transformer i use has 3 terminals on the secondary side. They are 9V-0V-9V. I connected the two 9V terminals to the diodes. I have desoldered the diodes and checked and they are fine.
Is this the right way to connect the transformer ?
BTW the relay still switches on. The weird thing is that the AC voltage at the transformer sec keeps fluctuating when i connect the circuit to it.
Is this the right way to connect the transformer ?
BTW the relay still switches on. The weird thing is that the AC voltage at the transformer sec keeps fluctuating when i connect the circuit to it.
It is a centre tapped transformer.
What you should do is remove diodes D3 and D4, connect the 9V taps to D1 and D2 as they are now, and connect the 0V tap to 0V in the circuit (the -ve end of C1)
Personally I wouldve built the PCB version that uses the opamp. The circuit is shown at the end of the article. It's just using the opamp as a simple comparator circuit, when the output of the opamp goes low, it sinks current and turns the transistor on which turns the relay on, bypassing the resistors.
An externally hosted image should be here but it was not working when we last tested it.
What you should do is remove diodes D3 and D4, connect the 9V taps to D1 and D2 as they are now, and connect the 0V tap to 0V in the circuit (the -ve end of C1)
Personally I wouldve built the PCB version that uses the opamp. The circuit is shown at the end of the article. It's just using the opamp as a simple comparator circuit, when the output of the opamp goes low, it sinks current and turns the transistor on which turns the relay on, bypassing the resistors.
Buzzy said:
I run a 1000VA transformer without a soft start and have no problems with fuses.
Clearly the mains fuse needs to be 13 amp otehrwise power on surge will blow it.
The transformer does hum a little for the first second but then settles down.
The secondary fuse is 10 amps and I havent blown one yet in a few months of use.
Re: Re: ESP sound soft start
The fuse at rated current passes 3120W. For a short period, one or two seconds, it can pass 6kW without rupturing.
I suspect that there are many wires downstream of that 13A fuse that contravene the cable rating. They must all be protected by a fuse of lower rating than the cable.
Change the 13A fuse to match the lowest rated cable it feeds.
but, you do have a problem with your mains fuse.nigelwright7557 said:
The fuse at rated current passes 3120W. For a short period, one or two seconds, it can pass 6kW without rupturing.
I suspect that there are many wires downstream of that 13A fuse that contravene the cable rating. They must all be protected by a fuse of lower rating than the cable.
Change the 13A fuse to match the lowest rated cable it feeds.
Re: Re: Re: ESP sound soft start
It didnt think it was worth all the extra circuitry.
The amp doesnt have a mains switch, I use the wall switch to turn it on and off. I am only charging 10,000uF anyway so perhaps it isnt too bad.
The cable is all 13 amp cable anyway.
The earth bond is also 13 amps.
richie00boy said:
It didnt think it was worth all the extra circuitry.
The amp doesnt have a mains switch, I use the wall switch to turn it on and off. I am only charging 10,000uF anyway so perhaps it isnt too bad.
AndrewT said:
The cable is all 13 amp cable anyway.
The earth bond is also 13 amps.
Re: Re: Re: Re: ESP sound soft start
Don't you have MCB's in your house? I once powered on a 650VA transformer connected to 15,000uF of capacitance with no soft start, and it tripped the 32A ring breaker (much to the annoyance of my family!). Using a bulb in series with the live stopped it.
A soft start is hardly a lot of parts, and you can even throw in a soft-power-off switch for only a few parts more.
nigelwright7557 said:
Don't you have MCB's in your house? I once powered on a 650VA transformer connected to 15,000uF of capacitance with no soft start, and it tripped the 32A ring breaker (much to the annoyance of my family!). Using a bulb in series with the live stopped it.
A soft start is hardly a lot of parts, and you can even throw in a soft-power-off switch for only a few parts more.
Re: Re: Re: Re: ESP sound soft start
Then you will be stressing your wall switch
The amount of capacitance is irrelevant, the inrush is due to transformer magnetising current.
Your call if you think a small board is unnecessary, I'd rather have fusing that is effective.
nigelwright7557 said:
Then you will be stressing your wall switch
The amount of capacitance is irrelevant, the inrush is due to transformer magnetising current.
Your call if you think a small board is unnecessary, I'd rather have fusing that is effective.
Re: Re: Re: Re: ESP sound soft start
What kind of load is on the end of the PSU?
It would be far better for you to use a T3.1A mains fuse in the amp and a 5A fuse in the plug top and make the amp operate reliably through those.
nigelwright7557 said:
seems a bit of a mismatch.nigelwright7557 said:
What kind of load is on the end of the PSU?
It would be far better for you to use a T3.1A mains fuse in the amp and a 5A fuse in the plug top and make the amp operate reliably through those.
E built the ESP soft start a couple of years ago using Rod's board. I've built a couple of other designs. They all work, but I liked Rod's best because it seemed to me to be the most paranoid! I also put the whole thing inside a non conductive, self extinguishing box which is itself inside the amp enclosure. NO exposed mains current anywhere when the lid is taken off the amp.
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