EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: rdagger on July 09, 2018, 05:56:56 pm
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I bought an assortment of 5x20 fuses on eBay. I hooked up an 8A fuse to a 120VAC circuit and plugged in a 13A hair dryer. I ran it on high for about 2 minutes and the fuse didn’t blow. My meter read 12.9A.
They look like AC fuses. The fuse is stamped F8AL 250V. I know AC and DC fuses have different ratings. Could they be DC instead?
I guess I should have known better because the auction description described them as High Quality Fuze which seems applicable.
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Fuses have so-called I-squared-T curves, and depending on the ratings, some can withstand an overload for quite some time.
Google: I2t
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a fast blow 8A fuse will take way longer than 2 min to blow at 13A usually.
A fuse is designed to interupt serious overcurrent, not just a tiny overcurrent.
Look at the time-current chart for an 8A fuse in this datasheet as an example:
https://www.mouser.ca/datasheet/2/643/ds-CP-5sf-5sfp-series-1313110.pdf (https://www.mouser.ca/datasheet/2/643/ds-CP-5sf-5sfp-series-1313110.pdf)
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Fuses normally can survive like 1.3 - 2 times of the rated current for like a minute and a lot longer once you lower the current a bit. That multiplier usually is on the lower side for low current ratings and on high side for higher current ratings. Although I would not buy fuses from ebay, using safety devices from dodgy source is not smart. DC/AC does not matter for current they'll act. It matters for how high voltage and current they can break safely.
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Very helpful!
Thanks for taking the time to explain.