This will be a very informative post about batteries and stuff. If you are not that technical or interested in the subject ( just like me), you might find it a little boring. Dirk has taught himself quite a bit while being on the road ( and I am proud as a unicorn haha). I am talking about the mechanical part of the RV. Something that I do not understand a lot of and also don’t wanna understand haha. Anyway for the rv beginners, this might be a very helpful post. Dirk is taking over now. Enjoy!
Before we hit the road, I realized that the batteries in our motorhome were at least 5 years old. While I called the dealer to inquire about the battery type (there was a sticker on the side of the batteries), I found out this type of battery has not been available for 5 years. After a test, during which I unplugged shore power (the cable you plug into your RV while stationary anywhere), the batteries seemed to drain very fast. By pressing the battery button on our “Jensen Data Center II”, I could check the battery status.
It told me “fair”, so I knew the batteries wouldn’t hold a charge long enough for us to be on the road. Since I felt the need to upgrade, but had no clue of what I was doing, I needed to do some research first to understand how things work.
Let’s start by explaining the electrical system in an RV:
The energy to run anything (lights, fridge etc) either comes from shore or generator at 120V AC or from your batteries at 12V DC. Typically your battery powers all lights, fans, sensors, water pumps, fridge, while all electrical outlets are powered from the 120V shore power or generator.
What does DC, AC, V and AH mean?
- A DC (direct current) circuit always has the same positive and negative leads. The current will always flow from one pole of the source (like a battery) to the other pole.
- An AC (alternating current) circuit has changing/alternating polarity (60x/second)
- V and ah can be easiest explained by a pressurized water tank with a faucet. The Voltage is equal to pressure and the amps are equal to the flow rate once the faucet is opened. The higher the voltage/pressure, the higher the flow rate/amps. If you look at amps over time, you are talking about ah (amp hours). Let’s say you have 20 amps of current over a period of one hour, then you will have consumed 20 amp hours.
- AH is a classification of the battery capacity (how much “water” would fit in there to be released again). The higher the AH, the longer you are able to use it without recharging.
There are much more details to explore, but let’s keep it this simple for now.
Basically you have two different power circuits that are not compatible with each other. Once you have depleted you battery to about 50% (you should not go lower than that), you will have to recharge it to the same level as it was full (ah=quantity). This is where 120V and 12V systems connect. Almost all RV’s have a device installed that will charge the battery. There are several options:
1. Converter/Charger
There are many different variations, but the basic principle is the same. The converter/charger will convert the 120V alternating current to 12V direct current that can feed all the 12V appliances (lights, fans, etc), and charge the battery at the same time
>> There are simple “old skool” chargers that will always charge the battery with the same amount of “pressure” (V) to get all the capacity back in there. This will work fine if you are full time connected to 120V, as these converters only charge with a low pressure of usually 13.6 V. Depending on your unit, this could mean you can charge at a rate of 3 amps. Assuming you have a battery that has 230AH ( 50% depleted like ours), you will need (230/2) / 3hrs = 38 hours to recharge it. If you are boondocking , you can easily consume between 30 and 100ah a day, which means a simple charger won’t work to recharge your batteries.
>> There are also more sophisticated “smart” chargers that charge the battery with a lot more pressure, resulting in way faster charging times. Depending on the type you buy, this will be somewhere between 14.6 and 15.1 V, at least for the first 80% (bulk charge) of charge. The fuller the battery gets, the lower the Voltage will be set by the charger. If the pressure would remain high (even if the battery was full), you would “overpressurize” the battery, which would ultimately destroy it. These chargers can feed the battery between 40 and 100 amps during the bulk charge. In the end, this means that you can charge a 130 ah battery bank within roughly 3-4 hours. Sounds already a lot better, right?
2. Inverter/Charger
This device will charge just like a smart charger, and will also invert the 12V DC to 120V AC. This means, that you could run everything out of your RV that requires a regular power plug from your battery as well. Inverters/chargers are typically classified by power output in Watts. Depending on your usage, you can choose the right sized inverter. If you already have a way of charging your batteries, you can buy a pure inverter , so that you still be able to use 120V appliances.
3. Alternator
While driving your Motorhome, the alternator of the engine ( a device that charges the motor battery) will also charge your house batteries. If you have a 5th wheel or trailer this might not be the case, as it depends on the wiring between the alternator and your trailer. Or the alternator can only senses the motor battery and does not provide enough power to recharge your 5th wheel/trailer. In our motorhome, we have seen a maximum of 65amps being absorbed by our battery at once. This can be a fairly effective way of charging your house batteries if you are on the road.
4. Solar Power
You can also charge your battery with solar power. Basically, you will have to add solar panels to the roof of your RV or get movable ones and connect them via a charge controller to the batteries. You can buy these as kits from $200 up. The advantage of solar is (obviously) that you do not have to hook up to anything or use any gas to run it. This is my preferred way of charging ( green energy), but also the one with the highest initial investment cost, especially if you are not going to install them yourself. Of course solar charging also depends on the sun, so if you’re living in a rainforest or area with minimum sun hours, this isn’t an option for you.
How do I know when my battery is charged/empty?
That is an excellent question. At the beginning, I pushed the button on my Jensen Data Center II, but later I switched to reading voltage of the batteries with a simple multimeter. How does this device works?
Basically, you attach the probes of your multimeter to the battery poles and get a reading. The chart to the left would tell you the state of charge. Unfortunately, this will not work on a day to day basis, because the voltage readings will be inaccurate as soon as the batteries have been either charged or discharged within a period of 24hrs. This means, you’d have to disconnect your battery for 24hrs before you can actually get an accurate reading. The method doesn’t really work for me.
There is another option of reading the specific gravity of a battery, but also therefor the battery would have to rest for a certain amount of time. Plus you would have to open the batteries, extract some liquid in a hydrometer etc. In my opinion this is not an option for everyday use.
Fortunately there are devices, so-called battery monitors, that are counting the energy flow (amp hours) in and out, so that you have an idea of where you are in terms of state of charge.
Battery Monitors
A battery monitor registers the voltage of a battery (we now know, that is not necessarily a reliable indicator) and it also measures the amount of amps going in and out of the battery. In order to work, it needs to have a shunt in one of the cables leading to or from the battery. The shunt routes all in and out-going energy through it, so that a reading can be done by the monitor unit. The shunt itself needs to be strong enough to withstand the amounts of amps (flow) going through it. I would recommend going anywhere above 100 amp rated shunts.
There are a few options available to use as battery monitors. When I started searching for these devices, I soon realized that they are fairly pricey and I was not sure if it would be worth spending this much on it. These two units are $ 150 +:
Victron BMV-700 Battery Monitor
TM-2030-A TriMetric Battery Monitor
DROK DC 0-120V 0-100A Digital Electricity Usage Monitor
What I like about this unit is first and foremost the price, and the fact that the functions are in line with two units mentioned above. One really great feature is that this display unit can receive data wirelessly ( it only needs a power supply from USB) and even if you disconnect the monitor, the data will be still collected and stored. You can also program the unit to direct a relay to start your generator if your batteries are depleted below a set level.
What did we do?
When I found out that our batteries were done, I measured the space in our battery compartment and started looking for golf cart deep cycle batteries (they seemed to give us the best bang for the buck). Golf cart batteries come in 6V, so you will have to buy two and connect them in series to get a 12V system. You will not gain twice the ah, only twice the voltage once connected in series. With these batteries we have 230 ah available. Considering that you can not go any lower than 40-50% of discharge, we have roughly 130ah we can consume before we need to charge.
Next, I installed a battery monitor system from DROK for only $30 to enable me to get all the battery info. It was fairly straight forward to install the shunt to the batteries, I just had to split the negative lead to place the shunt in-between:
Once this was done, everything seemed to be good until we hit the road……
While traveling, I realized that our built-in charger/converter did only charge at a rate of 3 amps. I did not notice this before, as we were stationary and hooked up full time. With an average consumption of 50ah/day while boondocking, this meant we either had to drive every second to third day for at least 3-4 hours to charge the batteries or have the generator running for about 40 hours, which is 1.5 days…..
There definitely had to change something! I ended up researching chargers that would be smart, cheap and charge fast. I narrowed it down to a PowerMax 55amp 3 stage converter/charger. Since our original converter/charger had an integrated fuse panel we had to get a stand-alone fuse panel. I also replaced the wires between converter and batteries with 6 gauge thick wire, since there would be more current flowing to and from the battery towards the converter
Lastly, I realized that it was kind of silly to have our generator running every time our laptop batteries were in need of charging. We ordered a standalone 1000W inverter from Amazon that also got wired straight up to the battery/shunt. Make sure the amps drawn by the inverter do not exceed the amp rating of your shunt or you have a potential fire hazard.
For me, this electrical system upgrade was a whole journey and I hope by exchanging my experiences, it will be a piece of cake for you 😉
Dirk
