Question about 12V sockets not working

[Snomas]

I have two 12v plug in sockets on the dash of my Dutch Star and are only reading 11.1 Volts on my Volt meter. They will not run my brake monitor or TPMS monitor. My 4ea 6 volt coach batteries read 6.6 Volts. My Ford auto sockets measure 12.57 Volts and work the Monitors. What can cause this low voltage? Any thoughts appreciated.

[Snomas]

Doug of Carrolton was right. It was a partially blown 20 amp fuse in the fuse panel on top of the dash.
I called Newmar to locate which fuse covers the 12 sockets and then replaced it. Newmar's fuse diagrams don't list which circuit the 12V sockets are on! Thanks Doug!

[lanerd]

Thanks John...I never knew that. Good info to know.

Ron

[wa8yxm]

lanerd wrote:

dougrainer wrote:
=or partially blown fuse. Doug

Really? A "partially" blown fuse??? With all due respect, how is that even possible?

Think of how a fuse is made.. You have a thin wire usually inside a glass, ceramic or plastic case.. It takes TIME for the fuse to blow (In fact you can look up how much) fast acting fuses blow faster. Slow blow can hand in there for a couple seconds.

now... Imagine that the short only exists for 1/2 the amount of time it takes for the fuse to blow... It is only HALF melted.

(This is highly overly simplified but the point is that it is just shy of blowing when the sort is cleared or power is removed.

Page 2: that is not the O/P's problem however, he has a bad connection,, very bad if the voltmeter is enough to load it down a volt.

[dougrainer]

Snomas wrote:
I have the coach plugged in to the 120V house. The coach batteries are reading 14V and charging now. I will find the fuse. I checked the wires direct @ the back of the plugs and still get 11 Volts.

2 places the fuse is located
1. At the Shore Cord compartment on the back wall where the solenoids are. This is also where the Dash Radio fuse is located.
2. The fuse compartment in front of the LF tire. Doug

[Snomas]

I have the coach plugged in to the 120V house. The coach batteries are reading 14V and charging now. I will find the fuse. I checked the wires direct @ the back of the plugs and still get 11 Volts.

[dougrainer]

lanerd wrote:

dougrainer wrote:
=or partially blown fuse. Doug

Really? A "partially" blown fuse??? With all due respect, how is that even possible?

Snomas...try attaching a separate piece of wire to the ground side of the 12v socket and ground it to the metal frame somewhere. Bet you will read the same or a fraction less that what the batteries read.

Good luck

Ron

Don't know "how" it happens. But I have seen it numerous times. The tungsten in the fuse "melts" but there is a charred sliver left and is enough to cause a voltmeter to read less than the supply voltage. When I get that reading, I then check the voltage on both sides of the fuse. I find that on the HOT side of the fuse I get the normal 12.8 to 13.6 volts and then that less than 12 on the "cold" side of the fuse. Doug

[lanerd]

dougrainer wrote:
=or partially blown fuse. Doug

Really? A "partially" blown fuse??? With all due respect, how is that even possible?

Snomas...try attaching a separate piece of wire to the ground side of the 12v socket and ground it to the metal frame somewhere. Bet you will read the same or a fraction less that what the batteries read.

Good luck

Ron

[dougrainer]

Newmar Dutch Star the front dash 12 volt plugs are usually connected to the COACH battery system and not the Chassis battery system. See if the 11.1 matches the coach battery voltage. A Defective ATC fuse can cause that type of low voltage when the main supply is indeed over 12.8 volts. If you plug in a 12 volt appliance, it will not work but the voltmeter will read the bleed thru the defective or partially blown fuse. Doug

[fourmat]

Also they have a habit of corroding at the power point in center disconnect power and clean

[Dick_A]

I would suggest looking for a bad ground connection from the 12 volt socket. A poor ground connection will allow some current flow thus the voltage reading. However, when a larger load is placed on the circuit, the high resistance will cause the voltage to drop.