Excessive voltage drop... time to deal with it

[RustyDave]

Good day everyone.
New to this forum but I'm on my 3rd travel trailer. I'm having some electrical issues and would love to solve this myself prior to calling someone out to deal with it at $150 an hour.
Last camping season we started to get the low voltage warning on the CO detector. Long story short, I took it to the rv place and they said everything was fine and that my batteries weren't charged enough. Charged them for a week and got the alarm again at 4 am dry camping on the second night. I have a 2000 generator and would keep it going for 4 hours daily and I'm very conservative with my power usage. I then purchased new 6v volt batteries and a new Safety Alert unit and the problem continued. Frustrated, I disconnected the CO alarm and bought a battery operated one from home depot (although it doesn't have the propane alarm). I've been using it that way this season but figure it's time to deal with this problem.
Now please excuse me if I don't describe this properly. I've been using this forum to try to trouble shoot but I need some further guidance.
I've plugged the trailer into shore power and I'm getting 13.5 volts at the batteries. They're generally sitting around 13v at this point so the charging unit is working. Also, when I put a load on the batteries, the voltage returns to a previous level after 30 minutes of rest. I've crossed off the batteries and the charging unit off as potential problems.
My overhead lights in the main part of the trailer have 4 sets of fixtures that hold 2 bulbs each (non LED). The odd time when I put the switch on for these they don't turn on for about 5 seconds. That problem is intermittent. I figure this might be the low voltage problem area so I've been focusing on that.
Today, I hooked up the voltmeter to run some test at that light switch. Voltage at the light switch on the battery side was 13.3 but as soon as I turned the switch on it dropped to 12.2 (2 of the 4 light fixtures were selected for this test, 2 bulbs each). I figure that's a significant drop and not even using all 4 fixtures. I decided to test each of the four fixtures separately and each time I turned them on I got a drop from about 13v to 12.46 on all four fixtures individually. Also the voltage seemed to be dropping about .01 every 10-15 seconds. Just out of curiosity I tested the voltage and turned on the bedroom light (separate switch from the other 4 fixtures but same kind of fixture) and it read 12.8 at the same testing location. So basically I'm seeing about a .45v drop for the same kind of fixture on the problem switch area.
So I'm getting good voltage coming to the light switch but when I turn it on with 1-4 of the fixtures attached to the switch I'm seeing big drops compared to the other fixtures in the unit.
I guess I'm looking for guidance from here. I will be switching to LED but I'd like to figure out why I'm getting this low voltage alarm first.
I have a 2011 KZ Spree 281BHS. We love the unit but this problem is driving me nuts.

[keymastr]

DC current has much larger line loss than AC so the longer the wire run is the more voltage drop you will see.

[Bigbird65]

To me that does not seem like an unusually large voltage drop for incandescent bulbs. LED bulbs will show a lot smaller drop.

[RustyDave]

Originally Posted by Bigbird65

To me that does not seem like an unusually large voltage drop for incandescent bulbs. LED bulbs will show a lot smaller drop.

Originally Posted by keymastr

DC current has much larger line loss than AC so the longer the wire run is the more voltage drop you will see.

Thanks guys but a couple of things.
The voltage drop is significantly higher on these fixtures (individually) than the bedroom one although the bedroom one (at the front) might have a little shorter wire run but not much.
Also, why would this switch sometimes delay in turning on the lights? This happens every once and a while. I flick the light switch and nothing happens for 5-10 seconds. Could this be a switch problem?

[2late]

Just because the physical distance from switch to fixture seems a little shorter. RV reality is there could be lots more wire going a shorter distance!
The intermittent switch delay could be a dirty switch, clean the contacts and check the connections for tightness.

[Skip426]

Multiple erratic electrical issues ; JMHO . Start at the batteries , and follow the power wire ALL THE WAY to the fuse/distribution panel ; some where ( usually in the first three feet of that wire ) either on the frame , or just inside the RV body you should find a whole 12 volt system, circuit breaker , that needs to be checked for poor wiring connections or internal defects .

When testing with a multi-meter , it's important to remember , it only takes mili amps to get a digital reading , the fuse & holder below , passed enough power to light up an LED display on my leveler panel and show battery voltage on a multi-meter , but wouldn't make a 12 volt test light glow.

[hillbilly3]

Check for corroded ground connections, the manufacture is probably using the frame as a return path. Start with the ground connection at the batteries. Corrosion can cause the issues you are having. The high resistance return path can manifest as a voltage drop, when the bad connection heats up, it expands, and makes a better connection, that is probably why the lights don't imediatly come on.

[RustyDave]

Originally Posted by hillbilly3

Check for corroded ground connections, the manufacture is probably using the frame as a return path. Start with the ground connection at the batteries. Corrosion can cause the issues you are having. The high resistance return path can manifest as a voltage drop, when the bad connection heats up, it expands, and makes a better connection, that is probably why the lights don't imediatly come on.

Interesting. Thank you. This intermittent problem with the lights coming on seems to be when I first turn them on. Also, would I not see these problems throughout the trailer if it was the ground connection closer to the battery? This only happens on the one set of lights on the ceiling. Might be a dumb question but could the ground connection for that circuit alone be loose or corroded? And where is the ground for that circuit generally? Fuse box, frame?

Thanks.

[cavie]

Originally Posted by RustyDave

Thanks guys but a couple of things.
The voltage drop is significantly higher on these fixtures (individually) than the bedroom one although the bedroom one (at the front) might have a little shorter wire run but not much.
Also, why would this switch sometimes delay in turning on the lights? This happens every once and a while. I flick the light switch and nothing happens for 5-10 seconds. Could this be a switch problem?

Yes, it can be bad contacts in the switch.

[hillbilly3]

Originally Posted by RustyDave

Interesting. Thank you. This intermittent problem with the lights coming on seems to be when I first turn them on. Also, would I not see these problems throughout the trailer if it was the ground connection closer to the battery? This only happens on the one set of lights on the ceiling. Might be a dumb question but could the ground connection for that circuit alone be loose or corroded? And where is the ground for that circuit generally? Fuse box, frame?

Thanks.

The battery connection is usually outside, so it is the first to corrode, so it needs to be checked regardless. If the the walls and ceiling are framed with metal, most likely the builder used the frame as a return path to save money on wire. The ground could be connected using a rivet of a self tapping screw, either could be loose.

[KanzKran]

If the switch is in the wall, pull it and put a jumper across it to see if the lights go bright. Or measure voltage drop across the switch when it’s on, especially when first turned on. Use alligator clips on the leads so you can pay attention to the meter.

Other causes include any splice or connection, including the ground connections as already mentioned. A poor connection may register full voltage with nearly no load (like with a DMM, also as already mentioned), but the connection can heat up and close when passing current, reducing the voltage drop. Did they use any of those cheap blue or brown Scotchlok connectors in your unit?

There’s a poor connection somewhere in there. You need to find it.

[Persistent]

I see a lot of good posts here. It is all good advice.
I agree most likely issues are tight connections and switch contacts.
My Kodiak Cub has a common buss. It is a square metal bar with a row of screw connections. Every 12 volt line returns to this buss. All the house wiring is 14 gage. Only the furnace has it’s own ground.
I would first look at how tight the screws are at the common buss and at the 12 volt fuse panel. You may have a 12 volt breaker panel, this is less common. I would do this because it is easy to access and a good starting point for more testing.
Next, determine which fuse supplies which lights and the propane detector wire. Turn light on. Pull fuse until you find the one.
Check voltage at the fuse on each side of the fuse while the circuit is under load. This is not likely the problem, but easy to do. If the battery tests 13 volts under load, the fuse panel connections should test about the same under load. Any voltage drop at the fuse should be very small.
14 gage wire is rated for 15 amps in 115 volt house wiring. That is designed to allow about 1.5% voltage drop in 50 feet (100 feet counting 50 feet out plus 50 feet back). So, 15 amps at 50 feet would lose a little more than 1.5 volts. Half the current would have half the voltage drop.
The difference in amp carrying ability between 115 volts AC and 12 volts DC is nothing. Amps are amps either way.
In automotive wiring, smaller gage wire is generally acceptable because of shorter distances involved. Voltage drop in some standards are set to 3%. However, 3% of 12 volts is 0.36 volts. I don’t know what 12 volt standard your TT manufacturer used.
Your lights are unlikely to be drawing 15 amps and the distance from battery to switch is unlikely to be 50 feet, so 1.1 volt drop would be unreasonably high. However, you need to measure the voltage at the battery and the voltage at the switch while the load remains constant (light is on).
Line voltage drop is the difference between source end, and load end voltage.
I recommend you check for loose connections where ever you have easy access. Next, carefully re-measure your line voltage drop by measuring at source and at load without changing load. I assume you are using a digital voltmeter.

[RustyDave]

Amazing answers. Thanks everyone. I’m going to start my focus on the ground connections because this I think would be the biggest culprit according to your answers.
I stopped by my RV today and found those connections. The first picture is the ground connection by the battery. Looks like it needs a change. The second is in the back by the fuse panel. The wire on the left was crazy stiff and when I unscrewed it, it has a fair amount of corrosion. Would the line on the right be the AC plug ground? Regardless, I think these all need to be changed out.
Im assuming I take these connectors to my local RV place for replacement?

[Persistent]

I can't tell from the pictures. Are they loose? External corrosion is normal. How far it penetrates into the connection is what matters. The battery terminal screw looks loose in the picture.

Test by getting some 12 volt current flowing and using a digital voltmeter from the frame to the battery terminal. You should find almost no voltage drop for 10 or 20 amps.

Your pictures show 12 volt grounds. There should be no alternating current grounds in your TT. There is an exception for certain generator configurations.