Re: {Collins} tapping ferro resonant transformer output at 115 volts for s line

On May 19, 2015, at 12:41 PM, lorenzenenterprises@xxxxxxxx wrote:

> With the thought in mind of tapping the output of a ferro resonant transformer to obtain 115 volts for S line and A line etc. and provide some voltage regulation  ...


I don’t have direct experience in tapping the output of these things (I have tapped variacs to restore proper dial indications and reduce maximum over voltage output), but I do have some information and some suggestions:

- I assume you are talking about a “Sola” type voltage regulating transformer, and one that has 120 volt output normally.

- The larger Solas I have worked with (250 watts and up)  seem to have a more or less accessible output winding, that is, as you suggest, the output winding is on the outside of the  core and likely can be accessed.

- Based on wiring diagrams I have (a file called eleccons.pdf) the entire secondary is involved in the regulating function, so you’d have to tap the existing winding, not simply move the output connection to a different turn. (Note that this particular data sheet seems to have errors it it: the output connections are shown from transformer interwinding shield or core connection to only one end of the output winding.)

- Some/many Sola devices allow for connection for both 110 and 120 volt output voltage taps already - you only need to dope out which connections to use to get 110 volt output.

- In case you have a transformer in hand which does not have output connections for lower than 120 volts, you may be able to add a small number of turns along with the normal windings in the opposing direction to buck the output back down to 115 volts.  If you do this, I would expect regulation to be only slightly degraded, if at all.  Connections from the windings to the capacitor need to remain as they were.

- Normal Sola type transformers are naturally current limiting.  The “foldover” current depends on input voltage:  125 percent of rated current for 95 volts input, and 175 percent of rated current for 130 volts input for example. (From a file called opchars.pdf)  It appears that no harm is done with even extended periods of operation in current limiting.

- Given a Sola type transformer of 120 volt output, it would seem quite simple to add an external 5 or 6.3 volt bucking transformer to reduce the output down to 115 volts,  Of course such a bucking transformer can be used with normal line connections not involving a hot noisy voltage regulating transformer.

- If a “sola” transformer you have is not working right, replacing the capacitor will most likely restore proper operation. Typical symptoms include incorrect output voltage, poor regulation, and low output current capacity when current limiting/foldover occurs.  Most of these capacitors have a 660 volt AC rating.

- Solas meant for 50 hertz operation WILL NOT work on 60 hertz.  We have reports of Solas going up in smoke and flames when emergency generators produced NON-60 cycle power.

I/we will be glad to hear of you experience with this.


Roy Morgan
K1LKY Since 1958

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