Help selecting a thermistor

Captn Dave · 13th March 2010, 02:10 PM

I need to replace a thermistor used on the primary side of a power transfo (in series with the fuse). The spec is >25 at 25C and the operating current is about 1.3 amps. It's an NTC application; while the CL-60 seems to be a diy favorite, it is only 10 ohms at 25C. I need select another (or use 3 CL-60s).

I'm always temped to oversize passive components but I wonder if more thought is required in this case. Would it be correct to say that a 5 amp component in a 1.3 amp circuit would not heat up enough to sufficiently drop it's resistance? I would imagine a 1.3 amp thermistor would fail due to the inrush. The truth must lie somewhere in the middle. An Epcos 33 ohm / 2.5 amp is available and I'm tempted to use that.

Can you suggest a rule of thumb, best practice or a calculation method for selecting the proper current rating?

Thanks

13th March 2010, 02:10 PM	#1
Captn Dave diyAudio Member Join Date: Jun 2008	Help selecting a thermistor I need to replace a thermistor used on the primary side of a power transfo (in series with the fuse). The spec is >25 at 25C and the operating current is about 1.3 amps. It's an NTC application; while the CL-60 seems to be a diy favorite, it is only 10 ohms at 25C. I need select another (or use 3 CL-60s). I'm always temped to oversize passive components but I wonder if more thought is required in this case. Would it be correct to say that a 5 amp component in a 1.3 amp circuit would not heat up enough to sufficiently drop it's resistance? I would imagine a 1.3 amp thermistor would fail due to the inrush. The truth must lie somewhere in the middle. An Epcos 33 ohm / 2.5 amp is available and I'm tempted to use that. Can you suggest a rule of thumb, best practice or a calculation method for selecting the proper current rating? Thanks

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