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Prune 15th September 2004 08:48 AM

Electrolytic polarity
 
When making a non-polar by putting two polars in series, do you put the two negative or positive terminals together, or it doesn't matter?

peranders 15th September 2004 09:00 AM

It doesn't matter how you do, plus to plus or minus to minus

Sch3mat1c 15th September 2004 09:02 AM

I don't think it matters...

If you want to ensure they get equal always-positive signals, put diodes across them to prevent reverse voltage. Note that when the capacitors are uncharged, one diode switches on and apparent C is just one; on the next cycle, the caps are charged and will look like two caps in series, i.e. C = C/2.

Electrolytics aren't good for continuous AC use, hence motor start caps are smaller than motor run caps, which are film in oil.

Tim

Geek 15th September 2004 09:26 AM

Nope, doesn't matter. They will eventually fail either way ;)

Prune 15th September 2004 09:56 AM

Which way do I do it for mains DC blocking (with the antiparallel diodes across them)?

BTW, I only found 6A diodes locally, whereas I need 10A. When I parallel them, do I need to put resistances in front? Somewhere I read that should be done, to drop 0.3-0.5V, otherwise as the diodes aren't a perfect match, one will conduct most of the current. But that means 0.05Ohm diodes, and I can't find anything like that.

Sch3mat1c 15th September 2004 04:37 PM

Yes, a bit of resistance will level out current sharing. The only thing it costs you is dissipation and voltage drop, whether that will be a problem is up to you.

With or without diodes, direction doesn't matter, as long as the (cap+diode)'s both point in opposite directions.

Wazza mains DC blocking about? :confused:

Tim

Prune 16th September 2004 02:58 AM

2 Attachment(s)
Sometimes my mains has about 0.2-0.4 VDC and makes transformers buzz more. I got the attached schematic from the forums here; I'm not using the filter part, and I assume I can put both caps on the same line rather than around the transformer?

Geek 16th September 2004 06:16 AM

The mains DC is from an asymmetrical waveform due to incorrect power distrobution, loads or interference on the lines. Because of that, the circuit is, IMO, useless.

Prune 16th September 2004 07:19 AM

Well, you can hear it working. Toroids especially simply don't buzz as much (even better when I use an EMI/RFI filter instead of a regular IEC power connector).

On the other hand, lately I've not seen as much DC occuring; maybe someone took out a light dimmer or something.

peranders 16th September 2004 07:40 AM

Quote:

Originally posted by Geek
The mains DC is from an asymmetrical waveform due to incorrect power distrobution, loads or interference on the lines. Because of that, the circuit is, IMO, useless.
Have you tested it? It works actually.


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