Inverters Solar and Batteries

Can-Am has been installing solar panel and inverter systems since 1984. Over that time, we have developed a reliable, relatively simple system which we have installed hundreds of times.  

A few terms to explain: 

For some electricity is easier to think of as water in a plumbing system. 

Voltage is the amount of force in an electrical circuit. (water pressure).

• 12-volt system: (what your car operates on) operates all necessary systems in your trailer. 
• 120-volt system: (what’s in your house) In a trailer it operates the wall outlets, microwave, Air Conditioning.

Converter: (Every trailer has one) Converts 120-volt power to 12-volt power to charge the batteries and operate the 12-volt systems in the trailer when your plugged into shore power.

Inverter: (Some trailers have them, can be added to any) The inverter changes 12-volt power to 120-volt power to be able to operate 120-volt items when dry camping. A tiny inverter can be plugged into a cigarette lighter plug to operate a TV or charge a computer. For larger loads like the microwaves, coffee makers, hair dryers etc. you need a larger built-in inverter. 

Amps: Is the flow rate of the power. 

Watts: is the volume of power being used or produced no matter what the voltage is (Gallons per minute).

Battery capacity: is measured in Amp Hours (water in a tank) in theory a 100 Amp hour battery can generate 100 amps for 1 hour. Or 10 amps for 10 hours. 

How Volts, Amps & Watts relate to each other:

The equation that relates these is Volts x Amps = Watts. If you have a 12-volt circuit running at 10 amps you’re using 120 watts. 

If it’s a 120-volt circuit running 10-amps, then you are using 1,200 Watts. 

If you’re using an inverter to run a 1500-watt coffee maker you need 12.5 amps of 120-volt power (12.5x120=1,500watts) to generate this from the inverter you need 125 amps of 12-volt power. 

Lithium vs Lead Acid Batteries:

With a lead acid battery, you can never actually use all its capacity.  The voltage gradually drops as the state of charge decreases to the point of being too low to be useable so in reality a 100 Amp Hour lead acid battery is around 55 amps useable. 

The advantage of a lithium battery is that you can use 100% of its capacity. So almost double the power from the same size box. Good ones last10 years vs 3-4 for a lead acid. They are lighter weight as well. 

The disadvantages of a lithium battery are it costs 8 times as much. They are more sensitive to temperature and charge voltages. If you don’t look after it then it is an expensive error. On some lower quality batteries there is an increased fire risk. The Discover Canada Batteries that we recommend are very high quality and we now have an extensive track record with them. https://www.youtube.com/watch?v=h5tdu-CGA0c 

Typical Power Usage Large Inverters:

Thinking of the coffee maker again if it is going to run for 15 minutes through the inverter using 125 Amps of 12 Volt it will need 31 amp hours of power from the battery. As well you decide to use the hair dryer for 10 minutes and the microwave for 10 you have now used about 100 Amp Hours (1,200 Watts) of power just to power the inverter. 

The 12-volt system (fridge lights fans etc.) averages 6 amps for 24 hours that’s another 144-Amp hours. If you’re running the furnace blower it can easily increase to 10.  

144 Amp Hours for 12 Volt use plus 100 Amps Hours for the Inverter gives a total of 244 Amp Hours of battery power needed. If you have a 200-Amp Hour Lithium battery you will obviously run out of power in less than a day. For this use we need to get some additional power into the battery.

Methods To Charge The battery. 

1. When traveling the tow vehicle charges the battery through the 7-way plug in the bumper around 15 amps. 
2. Today solar panels are very popular. 400 watts of solar should in theory provide 33 amps of charging current.  400Watts / 12Volts = 33.3Amps.  However, the most you will see is 18-20 amps on a typical sunny day. I guess the 400 watts is only achievable on the equator at noon. One other advantage of solar panels is that your battery is maintained when your unit is in storage.
3. There are methods to get charge from the tow vehicle. If you have lead acid batteries this can be as easy as using jumper cables between the tow vehicle and trailer batteries. If you let it sit for 20 minutes and then idle the motor for 15 in 3 cycles you will have a pair of batteries at 80%.  

If you have a Lithium battery, jumper cables are not an option as Lithium batteries      don’t play well with other batteries. What is possible is to install a 50-amp DC/DC charger using large #4 wire connected to an Anderson connector wired in under the hood of the tow vehicle and the other end wired into the trailer. With this you can drive up to the trailer and plug the two connectors together. Occasionally customers want the connector routed to the rear of the vehicle so they can charge 50-Amps while driving. This often can be done but because this connector is outside the vehicle it is not ideal for Canadian winters.

4. For about the same cost as the DC/DC charger you can use a neat unit called a Car Generator. This is an inverter packaged for outdoor use that you can connect to an Anderson connector under the hood or with attached jumper cables. You plug the trailer’s 110-Volt cord into it and then charge the trailer battery using the converter. This gives 50-100 Amps of charging depending on the converter size and allows you to run 120-Volt items in the trailer. https://www.cargenerator.com/ One added benefit is you can use the car generator for backup power for your house.
5.  
6.  Add a generator to the trailer. A 2200 Watt Honda generally fits quite nicely between the LP tanks and the front of the body they lock down but can be removed for long term storage. When we install these, we usually run a dedicated cord to it connected through an automatic transfer switch, this way when you need power you just pull the cord. The added benefit of the generator is that you can run the AC or Convection portion of the microwave with it, neither of which is possible with batteries (unless you go to a massive battery bank). You can put the generator in the back of the tow vehicle or trailer storage compartment, but this involves getting the cord out and plugging it whenever you want to use it.  Having it mounted and wired in is very convenient. The only disadvantage is you need to carry a small gas container for refilling it. 

 

How much do I really need? 

Possibly none of it. One of our customers lived in their Airstream for 31 years and spent half the year dry camping in Provincial, State and National Parks. They had two lead acid batteries and a set of jumper cables but a propane fridge. 

If you go to full hookup sites and park the trailer at home, you don’t need any additional a couple of lead acid batteries will do for travel days. However often the nicest sites are the ones without power, so most people do some solar many do a battery upgrade. 

For the last 25 years or so the most common setup was 200 watts of solar with two lead acid batteries. For people not building in a large inverter this was all they needed. Now that we have changed to 12 Volt compressor refrigerators, 400 watts of solar power gives about the same results. 

If you have lead acid batteries, jumper cables are handy for those occasions when there is too much cloud cover for the solar to keep up. A 200-amp hour lithium will just about quadruple your reserve, but it is $2,000 more than the Lead Acid Batteries. Jumper cables are $35.00

Large Inverter Systems:

If you would like to be able to run larger loads on your inverter such as the Microwave or coffee makers (though a Moka Pot for French Press makes more sense for RV use) then a large invertor with 4 lead acid batteries or their equivalent is necessary generally along with a large amount of Solar charging.
What is fashionable today is to install an all-in-one system where the battery charger, inverter, 12-volt power and 110-Volt switching is done in one box. We don’t care for these systems, if that box dies your RV is dead in the water and there is no power anywhere. The other issue we have with these overly complex systems is that they change their design frequently. They have firmware and software which sounds trick but rarely do these companies have enough sales volume to do it properly. If the guy that designed leaves or forgets how he did then there is no repairing it in 5 years, for us remote after sale service is almost impossible.

  This system has several advantages:

1. each individual component is easy to replace by any electrician even if they have never seen an RV. 
2. The core 12 volt and 110 systems of the RV are undisturbed so there is almost always a way to get everything going. 
3. The battery can charge from 110 power, but the rest of the systems can operate off the Inverter. For example, you are plugged into someone’s outside garage outlet with minimal power or 200 feet of extension cord, you can be rather reckless with your 12 volt and inverter usage as the battery is constantly being charged but larger loads are powered by the clean power from the inverter. 
4. You can also update any single component if something better comes along. Customers who installed these systems 10 years ago can change only the relatively inexpensive converter to a lithium model if they change to lithium batteries.  

On the internet you will often run across people whose hobby is their solar system. They delight in seeing how much capacity and complexity they can add. They then in a very well-meaning way suggest all their systems to everyone else.  This is fine if you want it to be your hobby but if you just want reliable simple power consider following the KIS principal.   

Now you have likely noticed that some people have 6 or 800 watts of solar and huge battery banks for their systems, but does this make sense? If you are parked in a forest under substantial shade or in a northern climate, spring and fall when there is not a lot of sun and you’re running the furnace blower at the same time no amount of solar is going to keep up with your use. For many a second power option such as a form of generator is likely to be more convenient and cost effective. 

 

 

Cpap Machines:

Many need to power Cpap machines. The first thing to do is see if your machine has a 12-power cord available as that is more efficient that running through an inverter. If your machine has to be 100% reliable, we can add a dedicated battery just to operate it. That way if the furnace runs the batteries down over night the Cpap will have its dedicated power source. 

 

Conclusion:

We can help you decide what sort of system you need. Most systems are scalable so if you want to start with a 200-amp hour battery and 200 watts of solar you can always add to it down the road. That way you do not over buy for your usage. I hope this helps and feel free to call or visit with any questions.