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Smoking Bridges

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#46
BrianDonegan said:
Also, there is no need to use a larger bridge. 2A 100V is totally fine for this circuit.

I am curious as to why you are using such a large transformer. 50VA would be more than enough.
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Same here.

The peak output of that transformer would be enough to weld a metal rod together and pop the tops off those capacitors if anything were to go seriously wrong.

The power consumption of the transformer while idle alone would be enough to make me reconsider using it in this manner.

As I've said before Fusing of the secondary is highly suggested.

freax said:
Just be careful, you did say earlier that the traces on the PCB were nearly burnt off because of this. Check the capacitors for shorts. (Charge them with a battery and measure it with a voltmeter, if the voltage drops quickly or it doesn't hold a charge at all then you have a shorted capacitor.) And... install a fuse onto the secondary winding.

As I said in the previous post (edited) I would just go back to having a 100VA winding.

The traces on the PCB may not be up to handling more inrush current, basically you've reached the limits of the circuit.

Don't say you weren't warned! 🙂
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#47
BrianDonegan said:
Also, there is no need to use a larger bridge. 2A 100V is totally fine for this circuit.

I am curious as to why you are using such a large transformer. 50VA would be more than enough.
Click to expand...

I Will use a fuse for sure.
Antek was out of stock on any 15v smaller than 200va. I plan to get a 50va in December when they get more. I knew it was way more than I needed but got impatient. I will not be hooking this transformer back up. I'll test and repair the circuits and PATIENTLY wait for a smaller transformer.
 
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#50
I've had great luck lately with Triad Magnetics made toroids, they are more compact and quieter in operation than the Antek, and still not too unreasonably priced even though they are more expensive.

VPT30-5330 Triad Magnetics | 237-1347-ND | DigiKey

Antek has been out of stock repeatedly when I have looked for transformers lately, and have not responded to my queries about when they will again be available, consequently I will avoid them in the future.
 
#53
I would only put one on the primary. A fuse on the secondary is sometimes useful initial testing - but it adds resistance and thus ripple at PS inputs - so its best to remove it after you are comfortable. Only if something is seriously wrong(a short or say a mistake in assembly) would such a fuse blow.

BTW the bridges on the Placids are very definitely appropriately sized for their purpose.
 
#54
Russ White said:
I would only put one on the primary. A fuse on the secondary is sometimes useful initial testing - but it adds resistance and thus ripple at PS inputs - so its best to remove it after you are comfortable. Only if something is seriously wrong(a short or say a mistake in assembly) would such a fuse blow.

BTW the bridges on the Placids are very definitely appropriately sized for their purpose.
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Thanks Russ and Brian. I while back I had the TP PS powering a ESP preamp, phono stage, and a sub filter, Basically 8 opamps. I had a 1.5 amp slo blo fuse on the primary. Seemed to work great but I was just guessing on the fuse size. Any thoughts?
 
#56
BrianDonegan said:
If you only have one fuse, it should be on the mains power, to protect you from electrocution. Additionally, it could put a fuse after the transformer to protect the circuits, but if it blows, there is generally another problem already.
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A fuse is not to prevent electrocution. A fuse is there to clear the line in the event of an overcurrent. It is a safety element. And you are correct, it belongs on the mains power. Hot, not neutral.

jn
 
#58
BrianDonegan said:
"Preventing electrocution" gets the point across though 🙂
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Yes, I agree. However, it may mislead some into thinking that it is sufficient in that aspect. Unfortunately, it tends to bypass the actual entity responsible for preventing electrocution, the safety ground. Th only reason I chipped in is because compromising the safety ground is a typical practice when hum is involved. I'd really hate to have somebody believe that if they insert a fuse into the hot line, that they can get rid of the ground and still be safe from electrocution. You did not say that of course, but some may come away with that nonetheless.

It really hit me in the face when the NEC guy explained that a fuse or circuit breaker is NOT there to prevent electrocution. It is ONLY there to protect the wires. Period.

That's why I'm so sensitive to the fuse thingy. Not your fault.

jn
 
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