How to get 24 v AC from 27 ?

Question

Please don't laugh at the silly question, but what component should I buy to reduce the power output of a transformer from 26.4 volts, down to 24 ?

This is an AC transformer that supplies power to the circuit board of a home heating furnace. It takes line voltage in on one end and should have an output of 24 Volts AC.

Two wires in, two wires out; grounding through its metal case. The actual voltage going in is 118v and the output is 26.4v to 27.4v (two voltmeters used).

The circuit board feeds the thermostat (among other things) and the output on the thermostat leads is 27.11v

Do I need to install a resistor? If yes, what capacity?

Edwin Pawlowski · Accepted Answer

How do you know it is truly 26.4 volts?  Maybe your meter is off.   Besides, a plus or minus is always normal.  Don't lose any sleep.

FDR · Answer

Once you put a load across the transformer output it will probably drop a bit.  I'm sure that 24 volts +/- 10% will be ok.

TURTLE · Answer

this is Turtle.Michael , i've done this hvac work all my life and the voltage of the gas furnaces is called 24 volt ac but ranges from 20 volts to 28 volts ac. The transforner that puts out the 24 volts ac normally for the gas furnaces with out no load on it will normally put out 26 to 28 volt ac. With a load on them from the gas furnace and cooling system running . it could run the voltage down to 17 or18 volts. So if you have a 28 volt ac without a load on it,  that is very good.Michael , your good to go but just don't know it.TURTLE

Michael Stoic · Answer

OK, I've made my peace with it. Thank you for your help!                ..MS

How to get 24 v AC from 27 ?

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