Converter In-Rush Thermistors etc, UPDATE -4
UPDATE on 17 Nov, Update 2 on 22 Nov, Update 3 on 16 Jan 14, Update 4 on 19 Oct 14. --------------- In a recent thread there was mention of how you can wreck your gizmo (in my case a converter) ...
Forum Discussion
If it is operating correctly, it should be VERY HOT, and I mean HOT. You shouldn't be able to touch it without getting burned. At minumum resistance and max current, body temp for the one you ordered will be near 240C, Yes, C not F. over 400F. Even at half resistance and 1/2 current it will be way to hot to touch.
It's a negative temperature coefficent device. Resistance goes down with increasing temperature, not up. And to get a big resistance change means a big temperature change.
The device you ordered is rated for 25A max, so current wise you are ok.
From the device specs, at max current (25A) resistance is .02ohms so power in the device is 25x25x.02=12.5W
And again from the device specs, resistance at 1/2 rated current which is probably near where you are operating is 0.06 ohms. So power dissipated is:
12.5x12.5x.06=9.5W
temp coefficent for body temp is given as 45mw/C. So for a 3W reduction in power, temp will go down by about 3,000mw/45mw/c= 66C.
Max body temp is at 65C, assuming roughly 40C operating (temp inside the converter) rather than 65C , then the 240C max body temp would be about 215C with 25A or around 150C with 9A.
Now these calculations assume the my guess for the "operating" current of 12A for the converter is 12A RMS. Since these converters have very strange input current waveforms, non sinusoidal, the 12A could be off some. However, I believe the converter you have is Power Factor corrected, so input current should be much closer to an in phase 60Hz sine wave.
rough numbers and could vary some since there is some info lacking in the specs to do an actual temp vs. power curve, but the spec's are adequate for a rough guess on expected body temperature.
Still well above boiling water.
My guess is that if you are in the "expected" design operating current range of the device, it's temperature will always be very high, well above 100C
Click on your link, and open up the data sheet. it shows resistance and temperature data.
Be concerned if the device is NOT to hot to touch after it is running with a decent load on the output!!!
Now, with very low load on the output, with input current in a few amp range, then yes, it may be pretty cool, at least cool enough to touch.
If the spec's had a resistance vs input current or temp vs input current graph it would be pretty easy to see what to expect for operating temperature.
It's a negative temperature coefficent device. Resistance goes down with increasing temperature, not up. And to get a big resistance change means a big temperature change.
The device you ordered is rated for 25A max, so current wise you are ok.
From the device specs, at max current (25A) resistance is .02ohms so power in the device is 25x25x.02=12.5W
And again from the device specs, resistance at 1/2 rated current which is probably near where you are operating is 0.06 ohms. So power dissipated is:
12.5x12.5x.06=9.5W
temp coefficent for body temp is given as 45mw/C. So for a 3W reduction in power, temp will go down by about 3,000mw/45mw/c= 66C.
Max body temp is at 65C, assuming roughly 40C operating (temp inside the converter) rather than 65C , then the 240C max body temp would be about 215C with 25A or around 150C with 9A.
Now these calculations assume the my guess for the "operating" current of 12A for the converter is 12A RMS. Since these converters have very strange input current waveforms, non sinusoidal, the 12A could be off some. However, I believe the converter you have is Power Factor corrected, so input current should be much closer to an in phase 60Hz sine wave.
rough numbers and could vary some since there is some info lacking in the specs to do an actual temp vs. power curve, but the spec's are adequate for a rough guess on expected body temperature.
Still well above boiling water.
My guess is that if you are in the "expected" design operating current range of the device, it's temperature will always be very high, well above 100C
Click on your link, and open up the data sheet. it shows resistance and temperature data.
Be concerned if the device is NOT to hot to touch after it is running with a decent load on the output!!!
Now, with very low load on the output, with input current in a few amp range, then yes, it may be pretty cool, at least cool enough to touch.
If the spec's had a resistance vs input current or temp vs input current graph it would be pretty easy to see what to expect for operating temperature.
