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-   -   DIY balanced power unit with dual 60v secondary transformer? (http://www.diyaudio.com/forums/power-supplies/106902-diy-balanced-power-unit-dual-60v-secondary-transformer.html)

bikehorn 14th August 2007 11:43 PM

DIY balanced power unit with dual 60v secondary transformer?
 
I have no mains filtration but would like to add some eventually. I initially was interested in a standard isolation transformer but later began reading about balanced power.

I have a few questions which searching has not been able to answer...

1) What about using a transformer with dual 60v secondaries instead of a single centre-tapped 120v secondary? I can't think of any issues with this approach except in one place I read that the centre tap must be very precisely in the middle of the 120(or 240 for that matter) volts and that those centre taps are ideally more precisely implemented than in standard power transformers. Does this mean that two secondaries of the same voltage are unlikely to be a near-perfect match and therefore are unsuitable? It seems that dual 60v transformers in high VA ratings are easier to come across and more attractively priced than centre-tapped ones with a single 120v secondary

2) just what happens when you plug a regular old non-grounded 2-prong device into a balanced power system? does that not(dangerously) put 60 volts on what used to be 0v(chassis)?

3) when using a device with an SPST power switch, what happens to the 60v pulse on the neutral conductor? and what if it is like the above 2-conductor device i.e. not grounded?

4) let's say i build an enclosure with a balanced isolation transformer. do I need to fuse it? what about omitting a power switch(i.e. always on) ?



thanks

AndrewT 15th August 2007 03:07 PM

Hi,
the dual secondary and the centre tapped secondary will both be made the same way.
The two windings will bifillar wound using the same wire diameter and the same number of turns.
The outputs from either of these windings are near enough identical.
The difference is that the centre tapped has the pair of windings soldered to a single output lead, whereas the dual has a separated pair of output leads.
All duals can easily be converted to centred tapped if one requires that.

pooge 15th August 2007 04:06 PM

Re: DIY balanced power unit with dual 60v secondary transformer?
 
Quote:

Originally posted by bikehorn
I have no mains filtration but would like to add some eventually. I initially was interested in a standard isolation transformer but later began reading about balanced power.

I have a few questions which searching has not been able to answer...


2) just what happens when you plug a regular old non-grounded 2-prong device into a balanced power system? does that not(dangerously) put 60 volts on what used to be 0v(chassis)?


Yes, but only if chassis is connected to one of the leads. This is why it is not approved for such use, and why double pole GFCIs are important to use.

pooge 15th August 2007 04:07 PM

Re: DIY balanced power unit with dual 60v secondary transformer?
 
Quote:

Originally posted by bikehorn
I have no mains filtration but would like to add some eventually. I initially was interested in a standard isolation transformer but later began reading about balanced power.

I have a few questions which searching has not been able to answer...

3) when using a device with an SPST power switch, what happens to the 60v pulse on the neutral conductor? and what if it is like the above 2-conductor device i.e. not grounded?


DP power switches are a must.

pengboon 8th February 2008 04:52 PM

If given a choice of

1) 2 separate 0-60 transformers wired in series
or
2) a 60-0-60 transformer
appropriately wired for a balanced isolation solution, which will be better or no difference?

cheers!

pmkap 8th February 2008 06:59 PM

Unless there is a groundable shield between overwound primary and secondary on toroidal transformers, (same for overwound type EI transformers) or physically separated bobbins for primary and secondary on noshielded non toroids, they make poor isolation transformers, as the capacitive leakage beween primary and secondary makes for poor isolation of noise.

A balancing mains power transformer is first and foremost an isolation transformer, and the cancellation of reactive leakage current via balacing is the 'icing on the cake'.

FWIW


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