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MidcoastMike posted 08-22-2009 02:42 PM ET (US)   Profile for MidcoastMike   Send Email to MidcoastMike  
I don't know too much about electrical systems.

One of my aux switches controls both the GPS and VHF. I normally don't keep my VHF on, but I keep my GPS on always. The other day I noticed that the aux switch was really hot to the touch while the VHF was on at the same time as the GPS. I turned off the VHF.

On of my other switches controls the nav lights. Today I was replacing my port nav light bulb. When I popped the new bulb into place, I was surprised at how hot to the touch the bulb got almost immediately. I screwed the nav light cover back on, and the metal cover itself quickly got really hot to the touch too.

I assume neither of these issues are good signs. Is this one related problem or two? What should I do? Thanks!


davej14 posted 08-22-2009 07:04 PM ET (US)     Profile for davej14  Send Email to davej14     
It is not unusual for a bulb to get hot, over 90% of an incandescent bulbs energy makes heat. Check the contacts in the light socket and if they are clean I wouldn't worry about it.

The switch is another matter. The two loads you describe are not very high. I would not expect the switch to get hot. Generally this is an indication of corrosion of the contacts. If the contact resistance increases then there will be excessive power loss in the switch. Another possibility is that the connections to the switch are loose or corroded. I would inspect the connections first, if they look OK then you should probably replace the switch. Another consequence of high resistance contacts is that you will drop some voltage across them. If they are bad enough, then the voltage to your equipment may fall below operating specifications.

MidcoastMike posted 08-22-2009 08:57 PM ET (US)     Profile for MidcoastMike  Send Email to MidcoastMike     
Thanks for the insights Dave - much appreciated - I will check it out.
jimh posted 08-23-2009 09:23 AM ET (US)     Profile for jimh  Send Email to jimh     
The filament of an incandescent light bulb is heated to several thousand degrees. As mentioned most of the electrical energy is converted to heat, not light. It is completely normal that an incandescent light bulb feel very warm to the touch, and often so warm as to cause a burn.

It is not a good idea to touch the surface of incandescent light bulbs with your fingers, not so much for the health of your fingers, but for the health of the light bulb. Touching the glass bulb of an incandescent light bulb with your fingers will leave some oil residue. This oil will become heated and may become hot enough to burn. This is not too much a concern in 15-watt bulbs, but in compact and high-wattage bulbs contact with the glass bulb should be avoided. Use tissue paper to install the light bulb. And, whatever you do, do not apply dielectric grease to the glass envelope.

jimh posted 08-23-2009 09:29 AM ET (US)     Profile for jimh  Send Email to jimh     
When replacing electric light bulbs in navigation lamp fixtures, be certain that the replacement bulb is the proper wattage. It is quite common that the same size bulb and same socket are made in light bulbs of many different wattage. If a replacement bulb with a larger wattage than the original is used, too much heat may be generated. This is particularly important for owners of older classic Boston Whaler boats, where the navigation lamp fixtures often contain plastic lenses which cannot be easily replaced.

Electrical switches should never feel warm as a result of current flow through them. If an electrical switch develops resistance in its contact mechanism, heat will be generated. Usually heat causes further increase in resistance, causing more voltage drop and more heat. Investigate any switch which shows temperature rise above ambient when current flows through it.

MidcoastMike posted 08-23-2009 10:12 AM ET (US)     Profile for MidcoastMike  Send Email to MidcoastMike     
I replaced the nav light bulbs with an identical 12V10W Ancor festoon end bulbs. I hear you regarding touching the bulb and leaving residue - it was a brief contact by accident. I am going to have the switch wiring checked out over the winter. Thanks very much for your feedback folks!
pglein posted 08-25-2009 03:18 PM ET (US)     Profile for pglein  Send Email to pglein     
I would do two things:

First, check that the circuit for the GPS and VHF is protected by a circuit breaker or fuse, and that the amperage is appropriate. If the amperage of the fuse/breaker is too high for the wiring in the circuit, it could be allowing too much current to pass. But this would require two things to be the case in order to see the switch get hot; the draw from the two devices would have to be rather high, and the rating for the switch would have to be VERY low. My guess is that this is not the case.

More likely, as was suggested, the switch is corroded. I would simply replace it rather than "investigate". It is a $5 part that can be replaced in about five minutes. Check that the wiring connections on the back are not corroded, and replace the wiring terminations as necessary.

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