Maybe you could use a slightly larger fuse for now. However, it still may blow. Or better yet use two power switches in parallel. Put a resistor in series with one and turn it in first.
1.25A is what NP uses, as per the article. Just realised he uses 15k caps whilst i am using 22k..
what size (VA) is your transformer?
Fuse rating = VA * 3 / Vac.
If you're using 300VA, then fuse it with T4A or T5A.
When you come to use your soft start circuit, try that T1.2A again.
Add a time delayed bypass across the soft start resistor/thermistor. Set the delay to about 300ms. You could try 100 to 200ms, it should still let the transformer start.
The smoothing capacitance is a completely different story. with 176mF or is that +-88mF/channel or +-44mF/channel, you may need a slow charge circuit. this should be fitted to the secondary and the timed bypass should be between 5s and 20s. Thermistors probably suit this duty better than resistors.
Fuse rating = VA * 3 / Vac.
If you're using 300VA, then fuse it with T4A or T5A.
When you come to use your soft start circuit, try that T1.2A again.
Add a time delayed bypass across the soft start resistor/thermistor. Set the delay to about 300ms. You could try 100 to 200ms, it should still let the transformer start.
The smoothing capacitance is a completely different story. with 176mF or is that +-88mF/channel or +-44mF/channel, you may need a slow charge circuit. this should be fitted to the secondary and the timed bypass should be between 5s and 20s. Thermistors probably suit this duty better than resistors.
I am using a 500VA transformer.
Using that calculation i would need a fuse rating of 6.25A.
I am using 88mF per supply rail, just using the cviller boards for the PS.
NP article says use CL-60 thermistors but i cant get hold of one for another 3 - 4 weeks. What i can get hold of is the CL-40, which has a 5R resistance instead of 10R.
Using that calculation i would need a fuse rating of 6.25A.
I am using 88mF per supply rail, just using the cviller boards for the PS.
NP article says use CL-60 thermistors but i cant get hold of one for another 3 - 4 weeks. What i can get hold of is the CL-40, which has a 5R resistance instead of 10R.
Hi,
add a bank of 10r 5W resistors together for a soft start ballast.
I use between 30r and 60r for my transformers.
A pair of series 5r0 thermistors will not look like much to a 240Vac supply.
Without a soft start you may need a T8A fuse to start the transformer reliably, i.e. without nuisance blowing every month or two.
add a bank of 10r 5W resistors together for a soft start ballast.
I use between 30r and 60r for my transformers.
A pair of series 5r0 thermistors will not look like much to a 240Vac supply.
Without a soft start you may need a T8A fuse to start the transformer reliably, i.e. without nuisance blowing every month or two.
AndrewT said:
Hi,
Would there be any risks to the amplifiers circuity or transformer by using no soft start, becuase of the large inrush?
R
Your caps aren't fully formed yet so they look like a dead short to the trans. Wire up a lightbulb in series as a current limiter and let it cook for a couple hrs then try it.
Best, Bill
Best, Bill
Anything will work. When you turn it on the light will burn brightly for a second or two, then it will dim. Just let it run like that for a while and your caps will form. If the bulb doesn't dim then there problems somewhere. I start everything I build this way, Poor Man's Variac.
Bill
Bill
Zen Mod said:
I have loads of PC PSU's. Where abouts would i find the thermistor? Near the mains inlet?
Bill Fuss said:
Sounds good. Would i still need a 8A fuse whilst doing this, or should i use the standard 1.25A?
A 60W bulb will limit the current to about 1/4A so the 1.25 fuse is fine. In the end a 2A slow blow with a CL60 would probably be my choice.
Best, Bill
Best, Bill
rhysh said:
A variac would help in this situation. If you turn the voltage up slowly, and the
variac vibrates unusually, or your fuse blows, you know you have a problem
(hopefully before anything else is destroyed). I got a new 500VA one at Fry's
(in the USA) for about $70 (if I remember correctly).
Good luck,
Robert