Hi,
10r suits Eva's very large load and necessarily high fuse value.
3//50r resistors will suit a smaller fuse value (maybe 1000VA to 2000VA).
2//50r resistors will suit about 600 to 1000VA.
Users with 110/120Vac will require surge resistors of about half these values.
If one were to close rate the mains fusing then higher values of resistor would be more suitable.
eg. 800VA transformer fused @ T3.1A starts reliably with 50r (100W) on 240Vac mains.
10r suits Eva's very large load and necessarily high fuse value.
3//50r resistors will suit a smaller fuse value (maybe 1000VA to 2000VA).
2//50r resistors will suit about 600 to 1000VA.
Users with 110/120Vac will require surge resistors of about half these values.
If one were to close rate the mains fusing then higher values of resistor would be more suitable.
eg. 800VA transformer fused @ T3.1A starts reliably with 50r (100W) on 240Vac mains.
Hi,
the light bulb makes an excellent test kit due to it's ability to take full mains voltage without failing.
Unfortunately, it also has a positive temperature coefficient.
As demand for power in the amp goes up, the resistance goes up, reducing the voltage available to the transformer.
A -ve temp coef is needed for soft start duty.
At start up the cold resistance is high and limits initial current to your selected value. The passing current heats the resistance and causes it's value to fall, allowing more current to pass.
After a few seconds the start value will have reduced by a factor exceeding 10. Say 5ohms down to 0.3ohms. This allows the amp to run with almost full voltage available to the transformer.
An alternative is to use a resistor with a near zero temp coef. This must be bypassed very quickly to prevent the resistor overheating. That is the circuit discussed in this thread.
Keep the light bulb for it's testing use.
BTW,
that +ve temp coef is useful for tweeter protection.
the light bulb makes an excellent test kit due to it's ability to take full mains voltage without failing.
Unfortunately, it also has a positive temperature coefficient.
As demand for power in the amp goes up, the resistance goes up, reducing the voltage available to the transformer.
A -ve temp coef is needed for soft start duty.
At start up the cold resistance is high and limits initial current to your selected value. The passing current heats the resistance and causes it's value to fall, allowing more current to pass.
After a few seconds the start value will have reduced by a factor exceeding 10. Say 5ohms down to 0.3ohms. This allows the amp to run with almost full voltage available to the transformer.
An alternative is to use a resistor with a near zero temp coef. This must be bypassed very quickly to prevent the resistor overheating. That is the circuit discussed in this thread.
Keep the light bulb for it's testing use.
BTW,
that +ve temp coef is useful for tweeter protection.
Hi,
look up the AC relay data to find the time to close.
I suspect only a maximum is quoted and it could be around 10 to 15mS.
At best that would allow less than one mains cycle to pass through the surge suppressing resistor.
The info I have seen, suggest the toroid needs three to five cycles to fully establish it's magnetic flux. That's why I design for around 300mS delay on the relay.
look up the AC relay data to find the time to close.
I suspect only a maximum is quoted and it could be around 10 to 15mS.
At best that would allow less than one mains cycle to pass through the surge suppressing resistor.
The info I have seen, suggest the toroid needs three to five cycles to fully establish it's magnetic flux. That's why I design for around 300mS delay on the relay.
I designed an LLC SMPS using a PIC.
Using a PIC gives good control over power up.
I first wait until power supply caps are charged up (uses thermistor to limit current)
Then I use a soft start to limit current draw setting LLC frequency very high.
Only then do I start regulating the voltage.
Using a PIC gives good control over power up.
I first wait until power supply caps are charged up (uses thermistor to limit current)
Then I use a soft start to limit current draw setting LLC frequency very high.
Only then do I start regulating the voltage.
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