capacitor before bridge rectifier

[lanchile]

I would like to use .01uf 400v capacitor before the bridge rectifier (secondaries) to filter some noise like a snubber. Will this be a good benefit to the bridge?. last time I use 4 of these caps but I put them attached in chain with bridge.sorry I can not find pictures for example, but if you see the schematic of Hafler HD220 you will see cap#405

[rsdio]

Is C405 10,000 uF in the Hafler? I always get confused by 0.01 mF ... is that millifarads or microfarads?

[lanchile]

Caps #403 and #404 are 10.000uf 75v. the one I am talking about is the #405 that is .01uf 1000v.

[lanchile]

Originally Posted by rsdio

Is C405 10,000 uF in the Hafler? I always get confused by 0.01 mF ... is that millifarads or microfarads?

Converting uf-nf-pf


microFarads (µF) nanoFarads (nF) picoFarads (pF)
0.000001µF = 0.001nF = 1pF
0.00001µF = 0.01nF = 10pF
0.0001µF = 0.1nF = 100pF
0.001µF = 1nF = 1000pF
0.01µF = 10nF = 10,000pF
0.1µF = 100nF = 100,000pF
1µF = 1000nF = 1,000,000pF
10µF = 10,000nF = 10,000,000pF
100µF= 100,000nF = 100,000,000pF

1 millifarad is 1000uf

[rsdio]

Originally Posted by lanchile

Converting uf-nf-pf

microFarads (µF) nanoFarads (nF) picoFarads (pF)
10µF = 10,000nF = 10,000,000pF

1 millifarad is 1000uf

Oh, right, 0.01 mF would be 10 uF (not 10,000 uF; but it would be 10,000 nF)

In any case, 0.01 mF is not 0.01 uF

[AndrewT]

Originally Posted by lanchile

I would like to use .01uf 400v capacitor before the bridge rectifier (secondaries) to filter some noise like a snubber. Will this be a good benefit to the bridge?. last time I use 4 of these caps but I put them attached in chain with bridge.sorry I can not find pictures for example, but if you see the schematic of Hafler HD220 you will see cap#405

Curl had a message for us on Capacitor across the AC.
He was specifically referring to directly across the mains supply, but the argument could equally apply to the secondary side.

From what I can remember, he was suggesting 10uF plastic film metal cap across the 110/220Vac lines to present a low impedance to the HF on the mains. Trap it at source would be my equivalent phrase and would locate the 10uF at the distribution board where power enters the house.

Adding some uF to the secondary will do similar and since there is resistance and inductance between the first mains cap and this secondary cap it should work well as a secondary HF filter.
I sometimes add another cap across the +- of the rectifier. This pair of caps form a cross in the middle of the bridge rectifier. one from ~ to ~ and one from + to -.

[frank1]

Originally Posted by AndrewT

From what I can remember, he was suggesting 10uF plastic film metal cap across the 110/220Vac lines to present a low impedance to the HF on the mains. Trap it at source would be my equivalent phrase and would locate the 10uF at the distribution board where power enters the house.

If my calcs are correct, a 10uF across 240v mains would cause approx 180VA of (reactive) power consumption. Not heat but you still pay for reactive current.

Far better to use an LC filter for such things.
I would also locate such a filter inside the equipment as power-line noise is also created on the local house wiring by domestic appliances.
Frank

[AndrewT]

We as domestic consumers do not get charged extra for having a lagging power demand.
Commercial and industrial consumers do pay extra. To avoid the extra cost, they install capacitor banks or similar technologies to reduce the lag of their power demand.

If you add a capacitor across your supply, you are adding to the lag reducing effect on the whole grid system.
The electricity supply companies will love you for helping to reduce the I^2R transmission and generating losses that increase considerably with a lagging demand.

The capacitive reactance does not increase the rate at which your meter reads your consumption.

Please inform if any part of my comment is not correct.

[lanchile]

Originally Posted by AndrewT

Curl had a message for us on Capacitor across the AC.
He was specifically referring to directly across the mains supply, but the argument could equally apply to the secondary side.

From what I can remember, he was suggesting 10uF plastic film metal cap across the 110/220Vac lines to present a low impedance to the HF on the mains. Trap it at source would be my equivalent phrase and would locate the 10uF at the distribution board where power enters the house.

Adding some uF to the secondary will do similar and since there is resistance and inductance between the first mains cap and this secondary cap it should work well as a secondary HF filter.
I sometimes add another cap across the +- of the rectifier. This pair of caps form a cross in the middle of the bridge rectifier. one from ~ to ~ and one from + to -.

Thanks Andrew! Do you have any kind of pictures of how the 10uf goes? pictures tell more lol.

[AndrewT]

Look up part1 of Curl's preamp thread.

"Search" in this thread might help finding the references.