RV 12 volt System not Working [Troubleshooting]

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If your 12-volt system is NOT working, the first thing you need to look for is a blown fuse inside your DC panel. Also, there is a fuse (or fuses) on the converter itself and they could be blown. A depleted battery could also cause a problem if your 12-volt system is not working.

The vast majority of gadgets in your RV are powered by a DC power supply and that includes lights, LP leak detectors, fans, 12-volt refrigerators, pumps, slide-out, etc. DC current is a type of electricity that moves in one direction only (unlike AC, which alternates directions) and it comes from your 12-volt batteries or the converter.

An RV’s 12-volt system allows you to use your lights and appliances without needing to be connected to the power grid. Although the 12v system in an RV is not too complicated, there are still few key components to pay attention to.

They include:

• Fuses and breakers
• The battery
• Charging system
  

Here is a complete wiring diagram of your RV:

Feel free to download a schematic and wiring diagrams in PDF.

Before we jump directly into troubleshooting, it’s a good idea for you to think of a situation that could have led to the power trouble with your 12-volt system. You can yourself the following questions:

• When was the last time your appliance worked properly? What has changed since then? If any of your appliances shorted or you overloaded your DC circuit, look for a blown fuse. If your 120-volt appliances are not working as well on the shore power, look for trouble with the mains connection.

• Did you get a new converter or inverter-charger by any chance? If you triggered reverse polarity on that device by accident, look for a blown fuse (external) and replace it. If the fuse is internal, take your device to a specialist.

• Did you get a new battery set? Is it connected properly? Check your battery connection and all wires. Never hesitate to consult with a specialist if you are having trouble. Connecting battery banks in parallel should be done by a professional only.

• Did you leave your appliance running for an extended period of time and forgot about it? If your battery is not set up to cut the power if it gets to 50%, there is a chance that you killed it.

• Do you have a “parasitic” device that is draining your battery without you being aware? These little guys can really drain your battery over time and when you need it the most, there will be nothing left…

• Are any of your appliances at the end of their useful life? Any batteries that need replacement? Time to go shopping!

Now, let’s troubleshoot!

Fuses and breakers

Fuses are located in the 12-volt electrical panel. If you know exactly what is not working (a slide-out, pump, or lights, for example), you can try replacing that particular fuse and see if it solves your problem.

In case your whole 12-volt system is not working, then you will have to take your multimeter out and test individual fuses. Before you start doing any manipulations with fuses, it’s also a good idea to:

Check the switches and breakers that disconnect power from batteries for various reasons.

1. Battery disconnect switch

Coming out of long-term storage, there is a chance that you simply disconnected your batteries and this is why your 12-volt system is not working! There are two types of battery disconnect switches and they are:

1. Manual
2. Automatic

Manual switches could be located anywhere from being right on the battery to someplace hidden, but conveniently accessible for you. If at some point you disconnected the battery in order to preserve its charge, you will need to flip or turn the switch back to the ON position.

It could be a simple switch like this:

… or something a little more complicated.

Your battery disconnect switch could also be automatic. The battery will automatically get disconnected when it gets to a certain voltage (so it doesn’t get damaged).

The main point behind this device is that non-essential loads will be disconnected before they get a chance to completely discharge your battery and therefore damage it. This device also disconnects your sensitive loads if overvoltage occurs.

Victron Battery Disconnect (paid link), for example, can be programmed to engage and disengage at different voltages through a LED display (external link to Victron website) or an app. In this case, all you have to do is reset it.

2. Fuse boxes (or holders)

Now, let’s dig into a fusebox and look for a blown fuse! It can be installed anywhere, but it’s usually next to circuit breakers or a battery.

It is just a box with a bunch of wires connected to blade fuses and looks like this:

Distribution centers look like this:

If you know which specific circuit is not working, then all you have to do is replace a fuse. If you don’t know, you can test fuses individually with a multimeter.

3. Mini circuit breakers

There could also be a resettable circuit breaker connected to your batteries. If it was triggered, all you have to do is find a button on the side and reset it:

 

Here is an interesting video on how to find this switch:

There is also an automatic variation of the switch in case you get tired of resetting it all the time (like a guy in a video below):

Type I breakers are automatic and will keep on cycling ON and OFF until you disconnect the load and type II are automatic also, but it will “wait” for the load to be disconnected before kicking in again.

3. Inline blade fuse

It is also possible that your RV is equipped with some wire (on inline) fuses that could be installed on any of the wires:

It is a little tricky to find it, and you can do so by testing wire connections with a multimeter. These are usually simple blade fuses.

ANL & ANN fuses

ANL is another fuse that can be installed to protect the DC wires from sending too much current to your fuse panel. This is what it looks like:

These fuses get installed in a fuse holder. This is how it is installed:

Other DC fuses & holders

Other fuses and holders that you may want to look out for if you suspect a fuse problem:

• Mega fuse
• Class T fuse
• Terminal fuse

If you just got your RV and don’t know exactly what you have and consult a local electrician (see map below).

Battery troubleshooting

The purpose of a battery is to store electricity until you need to use it. There are two types of batteries that are commonly used as house batteries in the RV:

• Regular
• Deep cycle

You don’t want to use a cranking battery in your RV to run appliances!

It already has one cranking battery for the purpose of starting your engine and now you need a battery (or a battery bank) that will supply your mobile household with electricity while away from shore power. A deep cycle battery is usually preferred for this purpose.

Flooded (or Wet Cell), GEL, and AGM (or Absorbed Glass Mat) are the three most common types of deep cycle batteries. They are designed to be repeatedly depleted and can be discharged to about 80%, although 50% is commonly recommended by their manufacturer.

The chemistry of GEL, AGM, and Wet Cell batteries is all the same, but the plate architecture varies. There are also Lithium-ion batteries that are becoming quite popular among RVers.

Some flooded batteries can be either standard or maintenance-free (or sealed). This means that you really cannot add any water into these batteries, which basically damages them if overcharging takes place.

If you have one of those sealed batteries, ask yourself the following questions:

• Did you watch charge control really carefully?

• Was the battery disconnected promptly when charged?

• Is your converter-charger a good three-stage charging model?

Overcharging, undercharging, and deeply discharging are the three most common problems with regular (not deep-cycle) batteries. For example, if batteries were discharged over 50%, it is highly likely that you destroyed the battery.

It is not easy to watch what is happening to your batteries, this is why a good battery monitor is an important tool to have in your RV. The most popular model for RVers today is a Victron (paid link).

You can also use a multimeter to determine the condition of your 12-volt battery:

If you’re reading shows about  12.6-12.7 volts, then your battery is full.

Anything below 12-volts is about 50% depletion and needs to be recharged.

Now, let’s go over the battery problems:

• Depleted batteries. Unfortunately, if your batteries are fully depleted, they may not be able to retain a full charge any longer. You can still try to charge them with a powerful charger, but there is no guarantee that the charge will hold.
• Not fully charged batteries. Batteries need to be fully charged to perform best. Get a good charger and charge your batteries. Once again, if your battery is fully discharged, it is probably damaged and you need to get a new battery.
• Damaged or old batteries. Sorry, but your batteries will need to be replaced. Do NOT try to charge a damaged or old battery!
• Batteries with low electrolyte levels. Constant usage of a battery leads to some water evaporation and electrolyte level may get too low. Exposed plates in the battery cells could be another reason behind a damaged battery. If your battery is NOT sealed, replenish lost water with distilled.
• Dirty or loose battery connections. If you have the tools to tighten the connections, do so in a careful manner. If you don’t know what you are doing, consult a specialist! Battery connections could also be cleaned.
• Damaged battery cables. If battery cables are broken or cut in any way, they should be replaced.

How to know your battery’s % of discharge? You can refer to the following table:

Voltage	Discharge
12.7	0%
12.5	10%
12.42	20%
12.32	30%
12.20	40%
12.06	50%
11.9	60%
11.75	70%
11.58	80%
11.31	90%
10.5	100%

Battery charging system

If your 12-volt system is not working there could be a problem with the actual battery charging system.

Converter problem

The converter or inverter-charger (converter and inverter combined) is a vital part of your 12-volt RV electrical system. This is how your batteries get charged and AC (Alternating Current) gets converted to DC (Direct Current).

So why would an RV 12-volt system not work when plugged in?

• The converter may have a blown fuse. One or multiple converter fuses could be inside your converter or on the outside.
• Converter connections may be dirty or loose. Clean and tighten connections.
• Converter wires may be damaged. Visually inspect the wiring and ask for professional assistance if you find a problem.
• The converter may have an internal short. In this case, consult a specialist and replace the converter.

Power source problem

Once you figure out that everything is fine with your converter and a battery, it is a good idea to find why your battery is not getting charged.  You can use the following diagrams to find out at which section of your charging system you could have a problem:

Available in PDF version as well (schematics and wiring).

Check all the connections, wires, and fuses in between your main power source and the converter. If any of them are not letting energy through, your batteries will not charge and your DC appliances will not get power from the converter.

** A word of caution! If you don’t understand what you are doing, don’t do anything and consult a specialist!

Conclusion

If by this point you cannot figure out what the problem is, a professional electrician should be able to help you out (see map below for your local electrical service). This also applies if digging through mazes of wires is NOT your favorite type of vacation!

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