Voltage Question for Project

I'm not familiar with the K-Line board and why it must have AC, but taking your question at face value a diode array is probably the most practical way to reduce 14V AC to about 11V AC - maybe about $1 in parts.

https://ogrforum.com/t...g-a-single-accessory

The above thread also describes some other methods of reducing one AC voltage to another AC voltage.  It also has links to Dale H's write-up with more technical details on the diode array method.

Soo Line 

This good valuable information.

Thanks, John

Thanks Stan

Here are some additional pics.

All things being equal..........

Using the buck converter (output in DC) I require an additional 3 volts to get the same amount of smoke I get from direct transformer hook up on AC.

I'm trying to understand this and for this and future uses an AC to AC with a control knob for voltage adjustment would be handy to have, to control various accessories at their optimum voltage operation. 

Would you know where such an item might be bought?  I cannot seem to find it on E bay.

Thanks

Dave

So it does function with DC.  From what I can see in the pics that should be the case.  You just have to choose wisely and apply the "+" DC to the correct Red wire (50-50 chance).  Otherwise the heater will function but the fan will not spin.

In theory if you apply the same AC or DC voltage, you should generate the same amount of smoke.  Where is your AC voltage coming from?  Many hobby meters do not accurately measure the so-called RMS voltage (effectively the heating-voltage) of some train transformers.

I am not aware of a continuously-variable AC-to-AC converter module similar to the AC-to-DC (as you have) or DC-to-DC modules.  As mentioned in the other thread, in principle an AC train controller such as the MTH Z-xxx can do this.  You supply it with a fixed AC-voltage such as from their 18V AC "brick" and use the knob to "chop" this AC voltage to a lower one.  But these controllers are somewhat bulky by comparison and of course run tens of dollars rather than a few dollars.

I think the other thread or similar threads usually throw in the use of a variable resistor (aka rheostat) of suitable power rating. 

If one were of the DIY ilk, you could cobble together such a widget using modules and parts from eBay for, say, $10 or so but that's another story.

Thanks Stan ............I did figure out the need to put the DC + to the positive side of the smoke unit. 

The AC power source I am using is a basic Lionel toy transformer...output 18 V  3A.

Just for bench use.

I used a standard hobby meter to determine voltage.

Please see attached pic.

Working voltage AC 220

Max Power 500 W

Voltage regulation  AC O volts to input voltage.

I know it's overkill but would this work?

Thanks

Dave

That looks like a typical lamp dimmer.  In principle this works the same as the Z-xxx train controllers using a semiconductor device to chop the incoming AC sinewave to effect a lower AC output voltage.  Such lamp dimmers are sometimes suggested in OGR threads for the purpose you want.  Problem is these are designed to chop incoming AC at wall outlet voltages (e.g., 120 or 240).  They do not work if the starting voltage is "only" 18V AC or whatever; I'm not saying they don't exist but I have not run into one that does.

I see on eBay low-cost lamp dimmer "kits" where you assemble the components to make a board like this.  I suppose with some re-design one could modify such a kit to operate with an incoming voltage of 18V AC.  Again, that's in the realm of a DIY'er.

And while these modules say they output from 0 volts (up to the input voltage), do NOT be fool-hardy telling yourself you'll only operate this at the lower end of the range. Don't even think of going there.

So what to do. Since your smoke unit runs on DC, I'd go with the buck regulator approach.  For general purpose bench testing I'd do what you have been doing.  That is, first see if the accessory operates on DC.  If it requires AC (such as a vibrator-motor) then use a variable output train transformer to find a suitable voltage.  Then use the diode dropping method to reduce the AC voltage.

As shown in the other thread, if you have multiple accessories that require AC voltage you can use a single array and tap off different points for different accessories.  Obviously this lead to a wiring jungle distributing multiple voltages from a central point; since diodes are pennies a piece you may find it easier to adjust the voltage at the point-of-use from a single AC accessory voltage "bus" running around the layout.

On a case-by-case basis you might choose to use another voltage conversion technique so in the end the answer is to simply pose your question on OGR!

Yes Stan ........most likely best way to go.

Buck converter for the accessories that will run on them and diodes for the rest.

AC to AC with the option to regulate would be far more handy if I could ever find some.

The demand must not be there.

I found this item that would be handy .........a little more money but nice features over the simply plain jane models.

Appreciate your help Stan

Dave