Excessive voltage drop... time to deal with it

[bobfrommaine]

Hi; As a retired marine mechanic, I offfer the following. 1) Make a 30 or 40' cable with allegator clips on both ends, 2) hook one end to the negative terminal of your batteries, hook the other to the black lead of your multimeter. Then measure from the hot terminal of your light switch to the lead to the negative terminal of your batery (I'll call it the negative terminal), then turn on your lights. Note the voltage with the lights on and off. If the voltage is the same, you have minimal resistance in the positive line. 3) Then hook the red (positive) of your multimeter to the GROUND of your light. There should be nearly zero volts. If it IS zero, the gnd to your batteries is good. Then hook the end of your long cable to the positive terinal of your batteries, again, measure the voltage at the positive side of your light switch, turn on the lights, the voltage should STILL be zero. If not, there is a resistive connection between the positive terminal and your switch. Such as: fuse, breaker, positive bus bar. Somewher between your batteries and the switch is a corroded (resistive) connection). The purpose of the measurements is to determine if there is a high resistance connection between the positive or negative terminal of your batteries and the load. Using the long jumper removes that resistive connectiion and accurately measures the voltage at the load. I have a 40' wire that I use and using that, I have found many, many corroded connections. This cable has saved me and my customers hunreds of dollars in investigation fees. The extension wire has no current flow (other than the minor resitance of the meter) and has found virtually all resistive connetions. Incandescent lights do draw a fair amount of current (up to 10A) and a resistive connection will cause a voltage drop. Your monitor may be (or not) hooked directly to the pos/negative buss wires, but the fact that it alarms indicates you have a drop somewhere and the long cheater wire should help you locate it.Describing this is a lot harder than it really is and if you use it, you WILLfind any resistive connections. If you find NO resistive connections, you have a battery problem (old batteries).
Bob 2014 Winnebago 37F Adventurer, Jeep toad.

[richard5933]

We struggled with a similar problem when we first got our coach. It's a 1974, and many of the wiring connects had just a hint of corrosion on them. Not enough to break the connection, but enough to lower the voltage a hair.

A can of DeOxit will be your friend as you go around the entire coach to unplug and clean every connector you can find, especially the ground terminals.

[McKannick]

Many electrical issues are just basic stuff that should have been addressed from the day the rig was assembled. But now that xx thousand miles of road time has been applied, the issues can become real.
One of the prime issues of many voltage problems is simply the lack of basic torque applied to the panel / converter / inverter or anywhere else electrical terminals are screwed down. Most of your required torque values are even handily printed on panels and components.
Watch the vid:

https://www.youtube.com/watch?v=zhg_x28bjK8

[WA7MLK]

Try a couple of ideas. (I'm an electrical engineer)

First, check to see that the battery is good. Monitor the voltage on the battery terminal to see if it is changing very much as the lights are turned on and off. Probe on the battery terminal and on the wire that clamps to the battery. If it is different, you may need to clean the clamp. If you are using lead-acid like I am, that can be an issue.
If the battery voltage is ok, proceed to the next step.
Second, if you have access to a clip-on ammeter, see how much current is flowing in both the on and off states for the lights. LED lights really do reduce the current and let your battery last longer. Hint hint
Third, switches and light fixtures in RVs are much poorer quality that residential ones. You may need to check the connections. Since 12 currents are higher than 110v currents, a little contact resistance can cause serious heat problems. Thus the burnt connectors that we earlier in this thread.
I would recommend against cleaning switches. Replace with new!
Last, you may have a bad connection because they often use crimps instead of better methods like screw terminals. It would take a point to point ohmmeter to track down the connection.
Apply ohms law to find out if a circuit resistance and voltage drop is reasonable.

[Cruncher]

I own a 2004 Newmar kountry star class a gas motorhome with a battery disconnect problem.Now recently I hooked my Rv into my house hydro I went to put the battery disconnect switch to store and nothing happened it was dead and there was no indicator light on.I put the switch in the use position and it worked fine.My house batteries are good and I/ve checked all of my fuses and circuit breakers at my fuse panel and they are good.All of my grounds are good.I have noticed when I hold the switch in the store position right down it works and then when I let go of it it goes dead.I have a fuse panel on my dash and all the fuses are good there to.So,is there anything else I can check.

[Piros1]

Originally Posted by 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?
Attachment 257310Attachment 257311

Lowe’s or Home Depot as well as any electrical supply house will have them. A lot of hardware stores also will have them.

[cavie]

Originally Posted by Cruncher

I own a 2004 Newmar kountry star class a gas motorhome with a battery disconnect problem.Now recently I hooked my Rv into my house hydro I went to put the battery disconnect switch to store and nothing happened it was dead and there was no indicator light on.I put the switch in the use position and it worked fine.My house batteries are good and I/ve checked all of my fuses and circuit breakers at my fuse panel and they are good.All of my grounds are good.I have noticed when I hold the switch in the store position right down it works and then when I let go of it it goes dead.I have a fuse panel on my dash and all the fuses are good there to.So,is there anything else I can check.

I suggest that you start your own post as this one has over 60 replies. Many people will not be back to read yours.

Your description seams to say it is working correctly. Store is off. In use is on.

[Persistent]

Originally Posted by Cruncher

I own a 2004 Newmar kountry star class a gas motorhome with a battery disconnect problem.Now recently I hooked my Rv into my house hydro I went to put the battery disconnect switch to store and nothing happened it was dead and there was no indicator light on.I put the switch in the use position and it worked fine.My house batteries are good and I/ve checked all of my fuses and circuit breakers at my fuse panel and they are good.All of my grounds are good.I have noticed when I hold the switch in the store position right down it works and then when I let go of it it goes dead.I have a fuse panel on my dash and all the fuses are good there to.So,is there anything else I can check.

Cruncher,
Please start a new thread. The OP for this thread may get confused if we try to post help for you here.
Paul Bristol

[Persistent]

For those of you who joined this thread recently and do not want to read the whole thread, here is a summary of the progress so far.

12 volt cables, connectors, breakers between the battery and the fuse panel have been tested, found to have some resistance, and replaced.


I think the battery has been replaced as a part of correcting the problem.

The branch circuit from the fuse panel to light switch to 4 incandescent light fixtures with two bulbs each has a voltage drop of 1.2 volts. This seems excessive and the search for the cause continues. The switch in this branch circuit has been replaced.

At least one other branch circuit also has excessive voltage drop.

Three methods of searching for unwanted resistance have been post. The OP is currently continuing to search. Please review the methods before repeating the same method.

This is a very long complicated thread. It is easy for the OP to become confused when repeat posts and unrelated posts are added. Please review the previous posts and use your best judgment when adding a post.

[RustyDave]

Thanks everyone. Persistent has been helping me all the way but I’ve learned a ton from all your posts.

I’m wondering if this has been solved. I’ve done the following. Replaced my negative cable from the junction box to battery. Replaced the positive cord from the junction to batt. This was an eye opener as I was able to pull one end of the cable out of the connector by hand because it was really corroded. I replaced the cb on that cable also. I also replaced a couple of ground connections on the RV. I’ve checked all the connections behind and around the panel including the bus bar. I was able to increase the voltage at the panel by .5v by doing all this.

So using a voltage drop calculator I’m wondering if these are normal readings now because I’m seeing these readings on my voltmeter. I haven’t switched to LED’s yet as I want to make sure this is solved first.

From the batt to the panel this is what the calculator gives me with 8 bulbs going:



And then from the panel to the switch:



These are the numbers I’m seeing on my multimeter.

[Spidertroop1]

Set screw wiring terminals exposed to the elements will inevitably have problems. Wires oxidize and the screws rust or otherwise corroded. This is a frequent cause of voltage drop especially in ground connections. A solution is to replace with soldered ring terminals. Then wire brush the chassis surface where the connection is to be made. Use new, clean bolts or screws, then spray paint to protect the connection.

[RustyDave]

The final step today was to put in LED bulbs.
I put them in, turned the lights on (8 bulbs) and had these readings. Batt 13, panel 12.88 and switch 12.77.

I think this has been figured out. Thank you everyone for your help. Much appreciated.

On to the next project. RV awning strip lights. [emoji108]

[KanzKran]

Originally Posted by RustyDave

These are the numbers I’m seeing on my multimeter.

I only checked the 12 gauge, because the NEC shows 2 ohms/1000 ft so it’s easy to remember, but the voltage drop I get is consistent with out and back on that branch circuit. At 120V, 13A is nothing on a short run like that, but with only 12V or so to work with, a volt or two is big.

Glad you got it worked out. LED lighting is marvelous for things like RVs and sailboats when living off the grid.

[LeisurePursuits]

Upgrade your charging system. Running you generator for 4 hours is way too long. Likely it is charging at a very slow rate.