Lower the voltage of MTH Z-750 brick

Don't use resistors, use dropping diode pairs.  Each diode pair will drop about .7 volts.

Resistors change the voltage drop based on current, so anytime the current to the load changes, the voltage to the load will also change.

Use as many diode pairs as needed to achieve the desired voltage.  You can also use bridge rectifiers to replace two sets of diodes, makes wiring easier and also the whole assembly more compact.

LTJ,

You need to add another resistor to your diagram, at the far right, and only temporarily for analysis purposes.  It will represent the load that you're trying to power.  To make this work, and determine the value of the temporary resistor, you need to know several things.

First, how much current will your 14 VAC load be drawing?  Next, is it a static load, i.e. constant like a lamp, or does it vary over time, like a motor-driven accessory?

Once we have a value for this temporary resistor, from the answers to those questions, then we'll determine the values of R1 and R2.  After that hook up the circuit, replacing the temporarily resistor with your desired load.

I have a feeling though that, unless your load is quite small, R1 and R2 will have to be high-power devices (quite high wattage).

For that reason John's solution is better.

Mike

I'd start with four diode bridges, those should drop about 6 volts.  Note that when you apply a load, the open circuit voltage of the transformer will drop.

@gunrunnerjohn Is there a particular diode you recommend? Just to reiterate, the power brick outputs 21VAC (@3.75 amps) and I am looking to drop it to 14VAC. Thanks for your help.

Troy

How much current do you plan to draw?  The diode rating has to be higher than the maximum current.  Also, as I said, even though the brick puts out 21VAC open circuit, that will drop when it has any appreciable load on it.  You will want to make the diode array deliver the voltage desired at the typical current that will be drawn.

Some of these 6 amp SMC UG6KB60TB Diode Bridge parts should handle any load you choose to use on that transformer.

@gunrunnerjohn posted:

How much current do you plan to draw?  The diode rating has to be higher than the maximum current.  Also, as I said, even though the brick puts out 21VAC open circuit, that will drop when it has any appreciable load on it.  You will want to make the diode array deliver the voltage desired at the typical current that will be drawn.

Some of these 6 amp SMC UG6KB60TB Diode Bridge parts should handle any load you choose to use on that transformer.

Thanks John. 6 amps will be plenty. I will take a look at the diodes you mentioned.