tardishead
Well-known member
How much are heater filaments on power transformers over-engineered? If a 6.3vac winding is specified for 2 amps can it be pushed to 2.3A for example?
Transformer Heater Specs
- Thread starter tardishead
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Kingston
Well-known member
All manufacturers pretty much have their own idea about this, and it is rare you will even get this specification from them. It's impossible to draw a general conclusion based on that.
Hence, always over-specify them yourself. I have my own rule somewhere in the 70-80% of maximum current used in the worst case scenario. The way at least toroidal transformers are usually designed that's roughly the point where the core starts saturating more and more (ie. losing efficiency) and will start to turn into a heat generator.
Running any power transformer over the maximum spec. is gambling at best. Usually when they "melt" it's just a single winding and a dead trafo, almost like an expensive fuse. But with ill luck they run too hot and start burning and melting things around them. This fire hazard can be easily avoided by observing the above rule.
[edit]
see the first three posts here: http://www.groupdiy.com/index.php?topic=28274.2760
And further, I would not mind seeing some real data on this topic. I got that 70-80% number from a friend who had been observing the voltage drops and general behaviour on some toroidal transformers, but that was just one manufacturer (Trafox) who are really trustworthy. I would trust most manufacturers less based on some melting experiences.
Hence, always over-specify them yourself. I have my own rule somewhere in the 70-80% of maximum current used in the worst case scenario. The way at least toroidal transformers are usually designed that's roughly the point where the core starts saturating more and more (ie. losing efficiency) and will start to turn into a heat generator.
Running any power transformer over the maximum spec. is gambling at best. Usually when they "melt" it's just a single winding and a dead trafo, almost like an expensive fuse. But with ill luck they run too hot and start burning and melting things around them. This fire hazard can be easily avoided by observing the above rule.
[edit]
see the first three posts here: http://www.groupdiy.com/index.php?topic=28274.2760
And further, I would not mind seeing some real data on this topic. I got that 70-80% number from a friend who had been observing the voltage drops and general behaviour on some toroidal transformers, but that was just one manufacturer (Trafox) who are really trustworthy. I would trust most manufacturers less based on some melting experiences.
tardishead said:
This is a good question. I imagine an absolute meltdown failure could vary from one manufacturer to another. Unlike the HT winding I've always ran filaments pretty much right at rated load and avoided going too much lower. On the bench I've ran 100 -200ma high but never on a build because I didn't want to risk long term failure. I think part of my hesitancy was never seeing any older commercial gear that ran filaments over spec.
I'd call Hammond or Edcor and speak with one of their engineers.
