DC Power Issue

Hi, I’m having a problem with DC power in my trailer. The short version is that when I turn on enough lights or appliances, the power goes off to everything. Everything works fine on shore power.

The long version: I have a 2018 little guy max trailer with a 100 watt solar panel. We bought it used early this year and the battery worked fine for the first trip (but we didn’t use much power at any one time, so it may have been a problem from the start). Here is what I have done so far to try and find the problem:

First, I replaced the battery, although it tested fine at the store. The new battery is a 100 amp-hr deep cycle wet lead acid type.

I covered the solar panels to try and isolate the problem, then:

With shore power disconnected: battery shows 12.9V. I can run most of the lights and as I turn each of them on sequentially, I can see the voltage drop at the DC fuse panel with each set of lights until the power shuts off entirely. It doesn’t matter which sequence I use to turn them off, once I have enough turned on, everything shuts off. I then turn every switch back off and plug into shore power briefly which resets everything. I can also cause the power to shut off by just using the water pump without any lights since the water pump has a higher current draw.

With shore power disconnected: battery shows 12.9V and DC fuse panel is 12.6 V.

With shore power connected: battery shows 14.6V and DC fuse panel is 13.6 V.

With shore power disconnected and solar panels uncovered in full light: battery shows 14.5V

So I conclude wiring from solar panels to battery is ok and wiring from battery to DC fuse panel is ok.

From another post, I read about a DC circuit breaker near the battery. I found it and it appears to be an automatically resetting type. Since it is between the battery and the fuse panel, I'm guessing it is ok but is there a way to test it?

Any ideas on what the problem might be or what I can check next?

Any help/advice is appreciated, I thought this would be simple but it has me stumped.

26 Replies

SolanaJohn
Explorer
Oct 08, 2019
Problem fixed! The ground wire had a bad connection somewhere. I never discovered where exactly, but I replaced the wire. This trailer has a wire from the negative battery terminal all the way to a buss bar next to the power converter. There is a separate wire from the buss bar to the trailer chassis. I replaced the (battery to buss bar) wire and everything works fine now.
I also cleaned up the chassis ground even though it looked good.
Thank you for all the detailed responses - big help!
JRscooby
Explorer II
Sep 23, 2019
I bet the OP needs to check all the grounds. Electricity likes to be where it is at. If it can't see a way back it ain't going anywhere.
23hotrodr
Explorer
Sep 23, 2019
Be sure to clean and retighten your negative cables. Especially take care with the frame connection. Generally, make sure all connections are clean and tight including terminal to wire connections. Good luck!
opnspaces
Navigator III
Sep 22, 2019
I sent you a PM,

Ultimately you might want to break this down into two separate trouble shooting issues. Start by focusing on the original equipment in the RV:
Cover solar and disconnect solar charge controller wiring. Make it as if there was never any solar.
Disconnect all negative terminals of the batteries.
Unplug shore power.
Take a picture of all the fuses in the fuse panel.
Pull all the fuses out and figure out how to open up the fuse panel.
Once open replace all the fuses and find where the wires come from the batteries to the panel.
Hook up the batteries and take voltage readings at (battery, circuit breaker posts, any fuse you can find in the line,the connections and reverse polarity fuses at the use panel.

I'm assuming all is working at this point. If so leave the system unplugged.
Turn on the lights until the system goes dark.
Measure voltage at the fuse panel.
Measure voltage at the circuit breaker.
Measure voltage at the battery.

Somewhere in the path between the batteries and the board in the power center you will find the power suddenly stops.
Sam_Spade
Explorer
Sep 22, 2019
SolanaJohn wrote:
SolanaJohn wrote:

Controller panel shows 12.7V
Turn on lights sequentially until all lights fail.
Turn off all light switches. Switch on lights (none light).
Return all light switches to off position.
Across battery 12.8V
Battery - to fuse + : 12.8V

Thanks, I did this already

Not really.

When you reach the point where the lights fail, STOP....and do not move any switches or change anything else while you check for where there IS voltage and where there is NONE.
You MUST LEAVE everything in exactly the same situation as the moment it failed.
opnspaces
Navigator III
Sep 22, 2019
SolanaJohn wrote:
I ran through all the voltage checks again:

Shore power off (no power to trailer)

Solar panels not covered/full sun.
Solar controller panel reads error (can’t detect a battery)
Across battery: 12.8V
Battery - to fuse + : 12.8V
Battery - to CB near battery: both sides 12.8V

So power is not getting from solar panels to the batteries. My first step is to check with a meter anywhere I can access between the panels and the batteries. Somewhere along the line you will poke that positive probe and it will come back with a zero reading. If the point you are testing is out in the elements try to find a way to test without poking a hole in the wiring.

Cover solar panels

Solar controller panel goes blank
Across battery: 12.75V Sounds like some power (.5v) is possibly trickling to battery from solar. Or the battery is just normally bleeding off excess charge. You could verify by uncovering the solar and see if the voltage goes back up to 12.8.
Battery - to fuse + : 12.75V
Battery - to CB near battery: both sides 12.75V

Plug in shore power (solar panels still covered)
Solar controller panel indicates 13.7V (no indication that battery is being charged)
Across battery: 12.77V
Battery - to fuse + : 12.77V Shore power plugged in and no charge to battery? I would pull the front off the fuse panel and start doing voltage readings. You should be able to find the wires coming from the batteries to the panel and see what power you have there.

Solar panels not covered/full sun.
Solar controller reads charging up to “13.8V / Full” Solar charger is being fooled by the shore power and thinks the batteries are charged when in fact is still doesn't even see a battery in the system.

Unplug shore power
Across battery: 13.58V
Battery - to fuse + : 13.58V
This is a bit confusing to me. A minute ago the batteries were at 12.77 when the shore power was putting out 13.7. Are you saying the battery reading jumped up as soon as you unplugged shore power? If so I would start to suspect the solar controller to be glitchy.

Cover Solar panels
Across battery: 12.9V
Battery - to fuse +: 12.9V
Controller panel shows 12.7V

Turn on lights sequentially until all lights fail.
Turn off all light switches. Switch on lights (none light).
Return all light switches to off position.
Across battery 12.8V
Battery - to fuse + : 12.8V
Next steps/any ideas?
wa8yxm
Explorer III
Sep 21, 2019
I am fond of saying many RVers have a few screws loose.. Turns out we have a few loose nuts in the RV world as well.. No do not be offended.

The screws I refer to are the ones in the power distribution panel that hold the wires.. one of mine took over 3 full turns before I was happy with it.. No wonder the A/C connected to it worked part time (Works great now)

The nuts... Well that was another RVer and they were in his 12 volt system.

Check all connections. Clean battery connections.
time2roll
Nomad
Sep 21, 2019
SolanaJohn wrote:
Thanks, I did this already and since battery is over 12 volts (12.8) that means an open circuit? OK, but since battery to fuse is also 12.8 volts then does that imply open circuit is between fuse and lights?
Yes. Keep checking until you find some device or connection with 12.8 on one side and near zero on the other.
SolanaJohn
Explorer
Sep 21, 2019
SolanaJohn wrote:

Controller panel shows 12.7V
Turn on lights sequentially until all lights fail.
Turn off all light switches. Switch on lights (none light).
Return all light switches to off position.
Across battery 12.8V
Battery - to fuse + : 12.8V

Thanks, I did this already and since battery is over 12 volts (12.8) that means an open circuit? OK, but since battery to fuse is also 12.8 volts then does that imply open circuit is between fuse and lights?
time2roll
Nomad
Sep 21, 2019
Load it up until power cuts off as originally stated. Then with everything failing to work check your battery voltage. If you have battery voltage above 12 then find the open connection. If battery voltage is dropping then have the batteries checked.