I had a friend, also in the electrical field, ask me a question about a buck/boost xfmr running hot, and I thought I'd go straight to the experts. He has a 2kva, 1-phase, 240v to 120v transformer, that has no real load, maybe a couple amps, using it for 120v controls. He said it is very hot to the touch, maybe not enough to burn you but hot enough to think that something is wrong. Any idea why it would be so hot, or can this be normal? Thanks for your input.
Buck/Boost Xfmr Overheating?
- Thread starter SPierce
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kwired
Electron manager
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- NE Nebraska
Very well may be normal. I have seen many separately derived system transformers that get pretty warm even with no load, to the point you are uncomfortable touching them.
gar
Senior Member
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I do not think you would call the transformer a buck-boost. It is probably a step-down transformer with the secondary isolated from the primary, therefore not an auto-transformer.
Power transformers are designed to run somewhat into core saturation during the cycle. How far into saturation at nominal voltage is a design criteria. The overall goal will be to get maximum efficiency within design constraints at some percentage of maximum rating.
I believe you will find many small transformers under no-load will run fairly hot to the touch. But you will find this quite sensitive to excitation voltage. A transformer designed for a nominal 117 V input will be much hotter at 135 V input than at 100 V. Many industrial plants run on the high side of 120 when referenced to the 120 level. At my home I typically run around 125 V. Equipment I have in auto plants is at 130 V many times. In a commericial building I checked the voltage at about 110 V and it was a stiffer source (lower sourcre impedance) than my home supply. Lower source impedance means less voltage change with a 1500 W change in load.
If you have a bad transformer, shorted windings, then the transformer would run hotter than it should.
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I do not think you would call the transformer a buck-boost. It is probably a step-down transformer with the secondary isolated from the primary, therefore not an auto-transformer.
Power transformers are designed to run somewhat into core saturation during the cycle. How far into saturation at nominal voltage is a design criteria. The overall goal will be to get maximum efficiency within design constraints at some percentage of maximum rating.
I believe you will find many small transformers under no-load will run fairly hot to the touch. But you will find this quite sensitive to excitation voltage. A transformer designed for a nominal 117 V input will be much hotter at 135 V input than at 100 V. Many industrial plants run on the high side of 120 when referenced to the 120 level. At my home I typically run around 125 V. Equipment I have in auto plants is at 130 V many times. In a commericial building I checked the voltage at about 110 V and it was a stiffer source (lower sourcre impedance) than my home supply. Lower source impedance means less voltage change with a 1500 W change in load.
If you have a bad transformer, shorted windings, then the transformer would run hotter than it should.
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kwired
Electron manager
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- NE Nebraska
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- Wisconsin
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- PE (Retired) - Power Systems
If you can hold your hand against a transformer it is barely hot.
Most buck-boost transformers are 'sealed' units with a normal full load internal temperature of up to 115?C which is 239?F.
Most buck-boost transformers are 'sealed' units with a normal full load internal temperature of up to 115?C which is 239?F.
- Location
- Massachusetts
If it was wired wrong or overloaded it would have let the smoke out already.
As has been mentioned that size transformer is usually a sealed unit with the exterior getting very hot.
Have your friend look at the temperature rise rating on it.
As has been mentioned that size transformer is usually a sealed unit with the exterior getting very hot.
Have your friend look at the temperature rise rating on it.
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