Guru
Joined: 09/08/2007
Location: AustraliaPosts: 4406
| Posted: 10:42pm 13 Mar 2021 |
Probably the worst type of load for transformer heating would be airconditioning.
That could run constantly for many hours on the very hottest of of days.
I asked my mate, the guy that wound my own Warpverter transformers about heating. He said at 5Kw it would take about three hours at full load to reach final maximum temperature for the largest transformer, and that would be about 40 Celsius over ambient sitting in free air without a fan.
That is a shell type transformer using E and I laminations which is worse than a toroid for dissipating heat, and it was wound for four amps per mm sq current density.
I arranged things so that my air blower blows onto the middle of the vertical heatsink.
Half the air blows up along the heatsink channels, and half straight down along the heatsink onto the transformers to stir the air. In over three years of occasional 40 Celsius days, the air blower has NEVER come on.
I cannot recall anyone here ever having serious transformer overheating problems. Transformers of this size will absorb a lot of heat just through the sheer mass of copper and steel for a surprisingly long time. They also take a long time to cool down.
So for the occasional very heavy load, such as large power tools, an air compressor or welder for example, the load could be huge for several minutes at a time, with rest periods in between.
Heatsinking the mosfets will be a bigger problem than the transformer, there is much less thermal mass.