Douglas Krantz - Technical Writer - Describing How It Works

Does Replacing an Overheated Transformer Make the Power Supply Bad?

When the transformer is too hot, it means that there's too much current going through the coils of the transformer. Replacing the transformer with the same model is like replacing the wiring. Something inside the power supply or building wiring is probably using too much current, making the transformer hot.

The transformer for a power supply is made up of two coils of wire. If the transformer is hot, it is because there is too much current flowing through the wires.

Greetings Douglas,

I had a job where the two electromagnetic door holders did not work. My electrician checked for power at the door holders themselves, but they did not have any power there.

My electrician traced the power wire for holders back to the security alarm box. There we found a 24v transformer that was extremely hot. We disconnected the transformer from the alarm panel to replace it with another one, but we could not get the new one back in before the batteries died in system.

My question is, would you have to replace the bell power supply due to the electrician taking out the transformer?

Thank you, E

Pre-Existing Fault

A transformer is made up of two coils of wire. The primary side and the secondary side. There are no other electrical components inside a transformer. The only way a coil of wire can get hot is that too much electrical current passes through the wires.

Once in a great while, the windings inside the transformer can short out causing too much current to flow through the other wires, but that kind of internal short would probably burn out the fuse, or blow the circuit breaker.

The original problem that caused the transformer to get too hot is usually a problem inside the power supply itself, or a problem in the building's wiring connected to the output of the power supply.

Building Wiring Fault

Most fire alarm or security power supplies have protective circuitry inside to prevent damage to the power supply should there be a short circuit in the building's wiring. Unless there's a pre-existing problem in the power supply, the power to the building's wiring would be cut off before damage to the power supply.

Power Supply Fault

Components on the power supply circuit board is the most likely cause of the transformer being too hot. Replacing the transformer would not fix the power supply. Even though the transformer was replaced, the power supply probably needs to be replaced.

Building's Wiring

When powering up the new power supply, watch out for faults in the building's wiring. That possibly is the original cause of burning out the power supply, which made the transformer too hot.

There probably isn't a fault with the building's wiring, but keep that in mind when powering up the new power supply.


If there's batteries in the power supply, don't reuse the old batteries. Batteries are inexpensive, regularly have to be replaced anyway, and once they've been drained all the way down, they won't have the capacity to hold as long as before. You're spending a lot of money on a power supply, just spend the little bit extra for new batteries. Then you will know that the old batteries weren't the original cause of problems.


To answer your original question, taking out the transformer probably isn't the cause of the power supply going bad.

Douglas Krantz
Life Safety
This website uses cookies. See Privacy for details.
Fire Alarm Q&A Articles

No Charge - Unsubscribe Anytime

Make It Work Series of Books by Douglas Krantz
Free - Click and Download
Make It Work Series of Books by Douglas Krantz
Make It Work Series of Books by Douglas Krantz