Newsgroups: sci.engr.electrical.compliance Subject: Re: DC Power Adaptor "wall wart", Fire Hazard Design Question References: <[email protected]> [email protected] writes: > DC Power Adaptor "wall wart", Fire Hazard Design Question > > If a DC adaptor rated at 1 amp is used to power a fan that is rated at > 1.8 amp, does this create a fire hazard issue, or merely an issue of > early power supply failure, or both? You definately get the issue od early power supply failure. Dependign on the design of the power supply and the enviroment it is located you have more or less fire hazard. A properly designed power supply shoud just get too hot and the thermal shut down fuze (or other protection circuitry) should blow. In cail it fails (not properly designed, damaged), there is a real fire hazard. > To be more specific, are DC adaptors made to be safe against this > possible mis-application? thermal protection, etc? They should be designed for this in mind. Practically all modern DC adaptors I have seen have included a thermal protection and/or other protection means. Typically the transformer in the power supply has a built-in therman protector in line with the transformer primary, if transformer gets too hot it blows. There are also adaptors that use fuse protection (on transformer primary and/or secondary) or have been built as short-circuit proof (some form of built-in overcurrent protection that limits current available from output to value safe for the adapter in case of overload or short-circuit). > Or would the > adaptor overheat to the point of possible combustion, with resultant > possible fire? A properly designed modern adapters the possibility of this to happen shoudl be pretty small. But even with protection there is at least a slight possibility of that to happen (no protection circuit is 100% effective always). If the adapter is very old, this could be built with less protection that some modern units (the regulators could have been not so strict on this ad they are nowadays in many countries). I have seen cases where the DC adapter has heated so much that part of the plastic case has melted, bad smell/smoke has came out. If your power supply is protected only by fuses, no internal overheating protection in transformer, then if you replace the protective fuses with larger than specified fuze, the risk of fire in case of overload is very real. Few times higher than specified fuze size combined with heavy overload, and the transformer can easily become smoking hot... It is matter of luck if you see flames or transformer primary failure first (primary cut open stops heating, fullshort circuit in primary burns the fuse on the mains panel thus stopping more heating). -- Tomi Engdahl (http://www.iki.fi/then/) Take a look at my electronics web links and documents at http://www.epanorama.net/
