Trouble shooting DC Electrical problems - Fiberglass RV


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Old 12-05-2016, 12:48 PM   #1
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Name: Daniel
Trailer: UHAUL CT-13
Texas
Posts: 15
Trouble shooting DC Electrical problems

Hi all,

I'm new to this forum and to the world of travel trailers. I just bought my first trailer, a UHAUL ct-13 and I am trying to diagnose my electrical problems. I've been reading alot, but still pretty over my head. Anyways here is where I've gotten.

First, when plugged into AC power, the 110V outlet works, but none of the house appliances work which makes me think the converter is shot.

Second, I put in a new deep cycle battery (tested with analogue multimeter reads fully charged 13v), but still none of the house appliances work. I then checked the fuses and replaced one that was blown, still nothing. With the battery plugged in, I checked the voltage going to the fuse box and the voltage from where the wires are attached to the fuse box for each circuit and got a voltage reading (around 8-10v). Is that low? Should it be 12? So that makes me think there is power going out to the appliances, but still nothing works. Could be that each one of the circuits has bad wiring, but the likelihood of that seems slim? Also strange, I left one fuse for the vent fan out and got voltage readings from the other circuits, but when I put a 20 amp fuse (it requires a 6 amp fuse I think just didn't have one), I got no readings from the other circuits at all....completely stumped.

Any ways sorry for the long posts. Any thoughts out there?
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Old 12-05-2016, 02:57 PM   #2
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Name: Steve
Trailer: Casita 17 ft DLX SD & 21 ft SOB
NW Wisconsin
Posts: 3,584
First thing , the standard receptacles in your trailer are 120 VAC.
The lights in your trailer are 12 VDC. The 12 VDC system in your trailer is separate from the 120 VAC system . In other words your 120 VAC receptacles can work and your 12 VDC appliances may not or your 12 VDC may work and your 120 VAC may or may not .
Your 12 VDC circuits should work whether you are connected to shore power or not.
If you have 13 VDC at the battery , you should have 13 VDC at the converter / fuse terminals , if the battery is properly connected.
Is the battery properly connected , correct polarity , terminal connection tight , fuse between battery and converter / DC fuses good ?
With the battery disconnected and the trailer connected to 120 VAC shore power is the converter putting out approx 13 VDC.
The 12 VDC loads in your trailer should work off the battery or the converter ( Assuming you have a converter)
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Old 12-05-2016, 06:44 PM   #3
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Name: bob
Trailer: 1984 u-haul ct13; 1996 Casita 17 Spirit Deluxe; 1946 Modernistic teardrop
New York
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Does your trailer have the original orange box power converter. If so, it may be bad. Ours would drain the battery. I replaced it with a modern converter that has a smart charger for charging the battery, a dozen 12 volt circuits, and space for some 110 breakers.
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Old 12-05-2016, 08:48 PM   #4
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Name: Byron
Trailer: 2006 Scamp 13' towed with a 2005 Dodge Dakota 4.7l Magnum W/full tow package (over kill)
Oregon
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Safety rule no. 1. If you don't understand electricity and wiring, take it to somebody that does.
Safety rule no. 2. See No. 1
Safety rule no 3. See no. 1

Just because 12 VDC won't shock you doesn't mean it's perfectly safe to mess with. See Safety run no. 1.
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Old 12-05-2016, 09:22 PM   #5
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Name: Daniel
Trailer: UHAUL CT-13
Texas
Posts: 15
Thanks for all the advice and words of caution. I didn't know much about wiring until about two days ago, but I'm learning and moving slowly.

First thing, my trailer does have the original red converter box with Uhaul printed on the cover. My guess is that it is dead because none of the DC appliances run when plugged into shore power. That being said, I haven't checked it out with the multimeter yet and will do so tomorrow. I plan on charging the battery with solar, so really I don't really care about the converter for now.

Upon tightening the connections at the battery, I found I did have 12v of power at the fuse terminals and all the fuses are good, so I know there is power going out of the fuse box. I guess the next thing is to move further down the line and see where the power stops.

Its just hard for me to believe that all the circuits individually faulty, but then again the trailer seems to have sat around in disuse for some time. Also anyone know anything about all the minute circuitry in the lights. I just look at it and feel my brain exploding.
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Old 12-05-2016, 09:43 PM   #6
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Name: bob
Trailer: 1984 u-haul ct13; 1996 Casita 17 Spirit Deluxe; 1946 Modernistic teardrop
New York
Posts: 4,864
did you check for good connections and continuity on the negative side of the circuits. Before I replaced the converter I tossed the original and saved the fuse panel to operate lights off the battery. Used a battery charger to recharge the battery. Did not use 110 power at that time
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Old 12-06-2016, 05:12 AM   #7
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Name: Gerry
Trailer: 1979 Boler 1300 / 1991 Casita Freedom Deluxe
Maine
Posts: 1,579
Just a sugestion, Try takeing out one fuse at a time, for the 12 VDC and checking things out. You may have one appliance that is bad (ie bad motor in a fan).
Electricity can bite when on shore power so be careful.
#1 death of a Plumber is Electricution.... not drowning.
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Old 12-06-2016, 10:10 AM   #8
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Name: Daniel
Trailer: UHAUL CT-13
Texas
Posts: 15
Quote:
Originally Posted by Gerry View Post
Just a sugestion, Try takeing out one fuse at a time, for the 12 VDC and checking things out. You may have one appliance that is bad (ie bad motor in a fan).
Electricity can bite when on shore power so be careful.
#1 death of a Plumber is Electricution.... not drowning.
Not quite sure I understand. Could one bad appliance cause the other appliances to fail as well?
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Old 12-06-2016, 10:46 AM   #9
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Name: Steve
Trailer: Casita 17 ft DLX SD & 21 ft SOB
NW Wisconsin
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Make sure you have 12 VDC at the converter.
Pull the DC fuses making sure you note size and position
Turn on the DC loads in your trailer
Place voltmeter on DC volts.
Place one probe of the voltmeter on one side of DC fuses holder
Place other probe of the voltmeter on the other side of the DC fuse holder.
The meter should show approx 12 VDC
If the meter shows 12 VDC you have a complete circuit.
If the meter shows 0 VDC then the circuits are open
( Bad lamps , bad switches, broken / disconnected wires,
bad connections , no negative DC connection , bad lamps ETC
As Byron pointed out , if you lack the knowledge and are confused. ( Brain Exploding -- your words )
, it may be time to admit you are lost and find someone who understands the system .The wiring in a trailer is very basic and is not complicated .
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Old 12-06-2016, 11:53 AM   #10
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Name: Daniel
Trailer: UHAUL CT-13
Texas
Posts: 15
Quote:
Originally Posted by steve dunham View Post
Make sure you have 12 VDC at the converter.
Pull the DC fuses making sure you note size and position
Turn on the DC loads in your trailer
Place voltmeter on DC volts.
Place one probe of the voltmeter on one side of DC fuses holder
Place other probe of the voltmeter on the other side of the DC fuse holder.
The meter should show approx 12 VDC
If the meter shows 12 VDC you have a complete circuit.
If the meter shows 0 VDC then the circuits are open
( Bad lamps , bad switches, broken / disconnected wires,
bad connections , no negative DC connection , bad lamps ETC
As Byron pointed out , if you lack the knowledge and are confused. ( Brain Exploding -- your words )
, it may be time to admit you are lost and find someone who understands the system .The wiring in a trailer is very basic and is not complicated .
Haha, why is everyone telling me to give up?

I agree the wiring in the trailer is pretty basic, but to a newb it can be overwhelming. I'm stubborn though and am determined to figure this out (also I don't have the budget to pay an electrician).

Upside of this, is that I am beginning to get a pretty good grasp of the system, and by the end of this will hopefully be able to do basic fixes myself.

A small victory, I did manage to get one of my lights to work, and gosh that felt good! So since I am getting 12v coming out from the fuse box, I guess that the fault must be in each individual circuit (wiring, switch or appliance).

Also I got connectivity for the other light above the closet but no power. How can this be?
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Old 12-06-2016, 12:00 PM   #11
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Name: Gerry
Trailer: Triple E
British Columbia
Posts: 69
Check from the positive terminal of the battery back to the frame to ensure you have a good ground.If a good ground is not indicated check from the negative post of the battery to the frame to see that there is continuity. Then, check from the positive side of each appliance to ground to ensure you are getting 12/13 volts to each appliance. Then, check from the negative or ground side of each appliance to ensure you have continuity, and the ground wires are all intact. If all fuses are good, all positive connections are good, and all grounds are good, the battery should supply 12 volts to the appliances, even if the converter is dead. With the converter plugged in check for 110 volts into it. Then check for 12 volts out from it.The battery may have to be disconnected for this check, as battery power should feed through the converter circuits under normal circumstances.
In most cases only the lights, furnace, water pump, and any other 12 volt appliances all operate on 12 volts. Usually only the 110 volt outlet plugs will be 110 volts.
In most cases, if you have a good battery, the problem will be with a bad ground.
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Old 12-06-2016, 12:06 PM   #12
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Name: Steve
Trailer: Casita 17 ft DLX SD & 21 ft SOB
NW Wisconsin
Posts: 3,584
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Originally Posted by Daniel the Texan View Post
Haha, why is everyone telling me to give up?

I agree the wiring in the trailer is pretty basic, but to a newb it can be overwhelming. I'm stubborn though and am determined to figure this out (also I don't have the budget to pay an electrician).

Upside of this, is that I am beginning to get a pretty good grasp of the system, and by the end of this will hopefully be able to do basic fixes myself.

A small victory, I did manage to get one of my lights to work, and gosh that felt good! So since I am getting 12v coming out from the fuse box, I guess that the fault must be in each individual circuit (wiring, switch or appliance).

Also I got connectivity for the other light above the closet but no power. How can this be?
What is "connectivity "
I am a licensed electrician , have been for over 45 years.
I have tried to be of help as have many others.
At this point , I can see that I can be of no further help / use to you.
I wish you luck and hopefully success.
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Old 12-06-2016, 12:27 PM   #13
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Name: bob
Trailer: 1984 u-haul ct13; 1996 Casita 17 Spirit Deluxe; 1946 Modernistic teardrop
New York
Posts: 4,864
IF the wiring is original in your Uhaul (big if at this age of the trailer) there will be only one 110 receptacle and it will have a mini push button breaker on it. As I recall, the interior light wiring went back to a post on the fuse panel which was then connected to the battery, or to a post on the battery box that connected to the battery. The battery box should have a gasket on the top and be vented to the outside.
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Old 12-06-2016, 12:46 PM   #14
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Name: Daniel
Trailer: UHAUL CT-13
Texas
Posts: 15
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Originally Posted by steve dunham View Post
What is "connectivity "
I am a licensed electrician , have been for over 45 years.
I have tried to be of help as have many others.
At this point , I can see that I can be of no further help / use to you.
I wish you luck and hopefully success.
Sorry I meant continuity not connectivity. I will test the fuse connections like you advised when I get home. I really do appreciate you and everyone else for trying to help me and I hope I didn't give you the impression otherwise. Best.
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