Hi all,
My son and I are building (assembling) an amplifier for our living room. It will drive the sub when completed. The board we purchased has all the rectifier & power supply rail caps already on it, all I had to do was source a transformer (+34/-34 secondary @ 300VA). When I connect the primary winding to AC power I'm blowing a fuse even with the secondary unconnected. I've stepped up from a .125 to a .25 to a .5 amp fuse, but the fuse keeps blowing. I don't I put a 100 watt incandescent bulb in series with the primary, and leaving the secondary unconnected, the fuse does not blow and the voltage on the secondary is correct - so I do not believe there's an issue with the transformer. Is there a component that I can leave in series with the transformer primary which will accomplish the same thing as the light?
I apologize to the audience here to post such a novice question, but I'm hoping for a solution so that we can button up our project and move on to another.
Thanks in advance,
Joey C
My son and I are building (assembling) an amplifier for our living room. It will drive the sub when completed. The board we purchased has all the rectifier & power supply rail caps already on it, all I had to do was source a transformer (+34/-34 secondary @ 300VA). When I connect the primary winding to AC power I'm blowing a fuse even with the secondary unconnected. I've stepped up from a .125 to a .25 to a .5 amp fuse, but the fuse keeps blowing. I don't I put a 100 watt incandescent bulb in series with the primary, and leaving the secondary unconnected, the fuse does not blow and the voltage on the secondary is correct - so I do not believe there's an issue with the transformer. Is there a component that I can leave in series with the transformer primary which will accomplish the same thing as the light?
I apologize to the audience here to post such a novice question, but I'm hoping for a solution so that we can button up our project and move on to another.
Thanks in advance,
Joey C
The transformer in-rush current is blowing the fuse. The simplest remedy is to use a slow blow fuse.
Thanks so much! I knew it had to be a simple solution. Already ordered an assortment. I really appreciate the help here!
Joey
Joey
For a transformer with that rating, and used to power an amplifier, a fuse of 5.0 amps is more suitable.
Without knowing the details of the amp/supply, I can only speculate at this time.
Without knowing the details of the amp/supply, I can only speculate at this time.
Did you do a simulation with your set-up to determine the surge of current with X capacitance upon..."zero-time" forward?
Don't be too trusting with these so-called "recommendations" for power supplies...many seemingly don't bother with crunching the numbers.
-------------------------------------------------------------------------Rick..........
Don't be too trusting with these so-called "recommendations" for power supplies...many seemingly don't bother with crunching the numbers.
-------------------------------------------------------------------------Rick..........
WHAT COUNTRY ARE YOU IN? ..... WHAT IS YOUR MAINS VOLTAGE?
Impossible to answer without that BASIC data.
As usual, DIY Audio Members JUMP to answer without enough data 🙄
I did not. Sounds like I have some math to do as far as that goes.
I initially started with low value fuses (fast blow) because I really didn't know what the unloaded current would be and I just wanted to test the transformer outputs. When I got to a half amp fuse, I knew I was missing something because even though my knowledge is admittedly limited, I know Ohms law and that a half an amp at 110 volts is fairly considerable. And I didn't want to damage anything through ignorance.
I have another question if you guys will indulge me, The board I bought has a trace from the input of the secondary transformer center tap to ground through the mounting holes on the edge of the board. If I use brass standoffs as we were planning, this would mean the secondary would literally be frame grounded - and I'm grounding the actual ground wire from the wall plug to the chassis as well. Something seems wrong about that to me. There's a bridge rectifier in the circuit with the common also connected to the same trace. Here's the question: Is grounding the secondary center tap typical or am I about to let all the smoke out of this when I connect the amp board in this configuration (grounded secondary center tap)?
Again, thanks in advance and apologies for such elementary questions.
JC
I initially started with low value fuses (fast blow) because I really didn't know what the unloaded current would be and I just wanted to test the transformer outputs. When I got to a half amp fuse, I knew I was missing something because even though my knowledge is admittedly limited, I know Ohms law and that a half an amp at 110 volts is fairly considerable. And I didn't want to damage anything through ignorance.
I have another question if you guys will indulge me, The board I bought has a trace from the input of the secondary transformer center tap to ground through the mounting holes on the edge of the board. If I use brass standoffs as we were planning, this would mean the secondary would literally be frame grounded - and I'm grounding the actual ground wire from the wall plug to the chassis as well. Something seems wrong about that to me. There's a bridge rectifier in the circuit with the common also connected to the same trace. Here's the question: Is grounding the secondary center tap typical or am I about to let all the smoke out of this when I connect the amp board in this configuration (grounded secondary center tap)?
Again, thanks in advance and apologies for such elementary questions.
JC
If the transformer is not damaged, the primary and secondary are electrically isolated, SEPERATE.
300VA on secondary also gives 300VA on primary.
So with 110VAC that gives approx 3 amps.
Add a bit more for power on surge into capacitors and a 5 amp slow blow fuse will be about right.