Proposed setup to add extra voltage to modern transformer feed to activate mechanical air whitsles.

[Birds]

I have been trying to think of a way to add a compensation voltage in-line with a full wave bridge rectifier (sound activation circuit) for use with MRC's Pure Power and Pure Power Dual so that postwar mechanical air whistles can be activated and trains won't slow down. Lionel Postwar transformers have a secondary compensation winding built into them, but the MRCs don't in order to protect newer sound boards.

This is the solution I came up with and was wondering if the electrical savvy folks think this would work:



Basically the idea is to feed a secondary low voltage transformer through a full wave rectifier, and use a normally open momentary switch to send the modified wave form and the extra voltage to the track to activate a mechanical air whistle.

Think this would work?

Thanks,
Birds

[phillyreading]

Should work but don't use newer trains or newer accessories on that track. Don't forget to tie in the neutral wire, may have to test it a few times to make sure the polarity is correct.
Lee F.

[lionelsoni]

I'm afraid not. The two sources, the main transformer and the bridge rectifier, will be trying to put different voltages on the track at the same time. Rather than adding, they will just cause fault currents to flow.

I think that the diode scheme that has frequently been mentioned on the forum is probably your best option. This involves connecting in parallel two series strings of diodes, each string's diodes facing in the opposite direction, then shorting out all but one of one string to unbalance the waveform and make a DC component.

The downside of this circuit is the loss of voltage normally. However, you could put that auxiliary transformer in series with the main transformer, to make up for the voltage lost in the diodes when the whistle is not blowing.

[johnandjulie13]

Hello Bob:

Adding on to the discussion to my questions yesterday, does the diode setup eat up some power when it is not activated? It would seem to me that instead of putting in another transformer, it would be better to bleed off a little of the power within the activation unit, so that there would be no (or little) current loss when the button is activated. While some top end speed would be lost, the operation of the loco would be much smoother when the button(s) are activated. If the diode setup does not accompli***his, is there a way to add some resistance to the circuit?

Regards,

JO

[Anonymous]

When using th diode circuit,when you jump 5 diodes you are actually boosting voltage by the equivalent of 1.75 volts RMS. The diodes use little current but do consume a small amount of power generating heat as they become warm. The 6 paired diodes drop the total voltage by 4.2 volts so if using a ZW you still get 16 volts at full throttle,more than enough for most trains..Modern whistles do not require much boost,air whistles need more. I you ran postwar only,you could string 8 diodes and jump 7,this would leave a equivalent of a 2.8 RMS boost and would reduce slowing when the whistle is activated.

Sometimes people ask about boosting voltage to assend a grade. Running this arrangement, you could jump some or all of the diodes using a relay and insulated rail actually boosting voltage.

Dale Hz