Voltage drop when halogen deck lights on and motor not running

Bustedknuckle84

Chief Petty Officer
Joined
Sep 29, 2010
Messages
421
I have the main power wire going to a 4 way distribution thing that has the glass fuses.It distributes power to the radio,stereo, and halogen deck lights(one in the front one for the back).

Problem: When I flip the switch for to turn on the deck lights the voltage drops to 8v's for the entire boat. Havent tested at the battery yet but the even boat battery teleflex gauge reads 8 volts. as soon as the switch is off back up to 12 v. with the motor running it doesnt give me as much as a problem. this happens with the motor off.

Questions:
If the 8v's stop at one side(power side)of the glass fuses and doesnt pass through the fuse, what could that mean?
is this a ground problem? or could it be to small of a gauge wire for the lights?
 

smoedog

Petty Officer 1st Class
Joined
Mar 25, 2012
Messages
238
Re: Voltage drop when halogen deck lights on and motor not running

My boat had the same problem. I have a fuse panel that powers every thing on my boat, docking lights, radio, nav and mooring lights, as well as interior lights. With my radio on, if i turned the docking lights on the radio would die and lights would dim due to the voltage drop.

Investigated and found my fuse panel was being fed by a 14g wire, with an inline 30amp fuse lol.

I would find what is actually feeding your main fuse panel, and then what is feeding your lights. I would go with at least an 8 guage, 6 gauge perferable depending on how much your powering, feeding your fuse panel and then at least a 10 gauge feeding your lights.

If you have good wiring, start looking at grounds and connections, such as terminals and splices. any loose or broken wires or corrosion will cause your resistance to go up and voltage drops to increase.

When I rewire my toon next year any splices are going to be solder sleeve splices
 

UncleWillie

Captain
Joined
Oct 18, 2011
Messages
3,995
Re: Voltage drop when halogen deck lights on and motor not running

A text book example of Ohms law at work.

The Wire from battery to the fuse block is too small for the job at hand.
When drawing high current the resistance of the wire drops 4 volts.
12 volts at the battery 8 volts at the other end by the fuse block.

According to The Table....
For a 30 amp run of less than 18 feet at 12 volts you will need at least 6 gauge wire to keep the losses under 5%. (0.6v)
And at least 10 gauge at any length.
 
Top