Topic: 1933 Light Circuit Fuse?


BigBlockFord    -- 08-03-2010 @ 10:17 AM
  I have an ongoing problem with the 20 amp fuse under the dash that keeps popping. It seems to occur when the headlamps, and directionals are on, and applying the brakes. I have been using SFC20 fuses, but just replaced that with an AGC20, and it seems to be ok. Is there a difference in these type fuses? Could just be a coincidence, or I may be missing something? (6 volt system with alternator)
Thanks


supereal    -- 08-03-2010 @ 11:10 AM
  A 20 amp fuse is too light to carry the headlights. A minimum of 30 amps capacity is needed, more if you are using halogens. If you figure that each headlight requires 50 watts, alone, for a total load of 100 watts, the current requirement is just over 17 amps for that part of the circuit. Add stoplights, etc, and you have overloaded the 20 amp fuse. If you convert to halogen headlights which use about 100 watts each, a 40 amp fuse is needed. Ohm's Law says that power, in watts, is produced by the product of current (amps) times voltage. At 6 volts, the current requirement is considerable. That is one reason manufacturers went to 12 volts, to reduce current and wire size, and there is a move today to go to 42 volt systems because of the heavy load of accessories in new vehicles.


BigBlockFord    -- 08-03-2010 @ 5:38 PM
  That's right, headlights were converted to Halogen as well as tail lights. Is the original style harness adequate for that kind on amperage flowing through it? I'll plan on getting some 40 amp fuses.
Thanks for the help.


TomO    -- 08-04-2010 @ 8:48 AM
  The standard wiring for your headlights is probably 14 gauge wire. At 12 volts this would be OK for the short run of the headlight wires, at 6 volts this would be marginal with the halogen lights.

To get a good idea of how well the wire is carrying the current, connect a voltmeter between the battery cable and the connection at the head light bulb. There should be less than a .1 volt reading with the lights on. If it is .5 or higher, there is enough circuit resistance to over heat connections.

Tom


supereal    -- 08-04-2010 @ 9:41 AM
  I installed halogen headlights in my 6 volt '47, and found they were less bright than the sealed beams they replaced. A quick check with my Amprobe told me the circuit was insufficient, made worse by the loss in the switch, dimmer, bullet connectors, and light (no pun) wire. I built a bypass unit that is operated by the original headlight wiring that places full battery voltage to the lights. Now, they are as bright as some modern cars without having to rewire the whole system.


EFV-8 Club Forum : https://www.earlyfordv8.org/forum
Topic: https://www.earlyfordv8.org/forum/viewmessages.cfm?Forum=18&Topic=1645