LIVING WITH SOLAR AND A BIG BATTERY PACK
We added solar panels and redid the electrical system of the old coach, our 19 year old Foretravel. The up date was prompted by two factors. One, we were about to embark on a six month odyssey and second we wanted the option of operating the micro wave and coffee pot without firing off the generator. The question was, is it worth it?
This was more than just adding a couple of solar panels to the roof and some wiring. A good system will include:
- Solar panels
- A voltage regulator for the solar input
- A converter/inverter/charger
- A control panel for the converter/inverter/charger
- A decent sized battery pack
The system provided us from RV Solar Electric in Phoenix AZ included two solar panels rated at 160 watts, a Magnum 2000 watt converter/inverter/charger, the control panels and the 12 volt wiring. For the battery pack there was six Trojan T 105 batteries sitting in my golf cart that would only be sitting at home while we were on our trip. They ended up in a battery bank that also included an 8-D series heavy duty truck battery raising the battery capacity for the house side of the system from 250 amp hours to 1000 amp hours.
This means that we can draw one amp for 1000 hours or 1000 amps for one hour or any combination in between before the batteries are run down to a point that they will not safely operate the equipment. That is about 9.6 volts. The lower the voltage gets in a system, the higher the amperage draw is to operate a unit. It is the flow of amperage through a circuit that creates heat and increases the chance of an electrical fire.
INVERTER/CONVERTER/CHARGER
The heart of the unit is the Magnum inverter/converter/charger. The unit has three distinct functions:
- First, it will take 12 volt direct current and turn it into 120 volt alternating current.
- Second, it will charge your batteries with first a fast or bulk charge rate of up to 100 amps, and then drop off to a float charge that will keep the batteries fully charged.
- And third it will take 120 volts, either from shore power or the generator, and provide 12 volts to maintain the batteries and support all of the 12 volt loads in your coach. A good inverter/converter/charger will have automatic switching that will kick in when running the generator or plugging into shore power.
WATTS, VOLTS, AND AMPS
Volts is the electrical pressure in a system, just like the PSI in a hydraulic system. Volts is the push. Amps is the flow of electricity in the system and is like gallons per minute flow in a hydraulic system. Watts is a unit of measure that is volts times amps. Lets just say that the electric toaster on your kitchen counter is rated at 500 watts of power needed to operate. If you divide the watts, 500, by the voltage, 120, you find that the toaster will draw 4.1 amps. In electricity if we are going to draw 500 watts out of one end then we must put 500 watts into the other end. There is a small operating loss but not enough to bother with for these calculations. So, on the 12 volt side again divide the 500 by 12 volts and it comes out to 41.6 amps going in.
In the inverter mode it will run any 120 volt unit that has a current draw of less than 2,000 watts. That equals about 16 amps.
On top of this the solar system will add to the charge rate when ever the solar gain is high enough to raise the voltage above other charging inputs.
DOES IT WORK THAT WAY?
On this trip we just finished 4 days of dry camping in a row as our Thousand trails membership is the 14/7 plan. That means 14 days in a TT park and 7 days out of the system. We did not economize on the use of electricity using the coffee maker and microwave as needed. We watched TV and ran lights and both furnaces at night as the temperatures are in the 40’s overnight. The solar panels are rated at 160 watts under ideal conditions. This 4 days of dry camping occurred in the Sequim Washington area and the conditions were less than ideal. The sun was low in the southern sky and the days were 30% cloud covered. Instead of getting an output of 13 amps from the solar we were lucky to get 5 amps and for only 7 hours a day. That figured to 140 amp hours of power from the solar for the four days which covered the complete needs of the two furnaces, or about an hour of micro wave time, or any combinations, but you get the point. In case you are wondering what happened to the other three days, well we sat those out in Tall Chiefs Resort in Fall City, WA. waiting for flood waters to recede so that we could get to Sequim, but that is another story.
In this latitude this size solar will act to help lengthen the time that you can dry camp but will not comfortably solely support the coach without really conserving use. The thing that appears to be important at this point is to have enough battery capacity to support your system.
After the four days of boondocking, it took a combination, of first three hours of driving and two and a half hours of battery charging with the coach plugged into shore power to bring the batteries back up to snuff. This would have been the equal of five and one half hours of generator time.
How does that compare to the old system that had no solar and only one 8-D battery to support the coach and a 45 amp converter? Before the new system we would have run the generator two hours in the morning to make breakfast and charge batteries and two to three hours at evening meal time to make diner and watch TV making sure that the batteries were up in case we needed heat during the night. That adds up to four to five hours of generator time a day compared now to one and one quarter hours a day average.
On the road we keep the inverter on full time providing 120 volts in the coach keeping the lap top running with Streets & Trips, charging Lucy’s camera batteries, and running the refrigerator on electricity instead of. We switch over to propane when we stop for the night. The alternator on the engine supplies the current needs and provide us with fully charged batteries when we stop for the night, usually around 4 PM.
Even with the limited sun the system has worked and cut our generator use by at least 60%. And at 3 bucks a gallon for propane, run the numbers, it works. Not counting the convenience of coffee without the noise. While it is true that the system, as configured, will not support the entire load and keep the batteries charged but it is better than what we had.
This has been our experience in the northern part of the country in late fall when the sun is low on the horizon and we are approaching the shortest day of the year. After we leave the Seattle area we are heading south and we will keep the log going to see how the system works when we get more sunlight.
Brad