Recreational Vehicles & Mobile Homes Backup Power
You may think that you will have power all the time if you have a dual battery set-up where the auxiliary battery is charged along with the vehicle battery, and where you have some solar modules for when you stay put in one place for extended periods. But this may not be the case. Even when your power consumption is within an acceptable limit which had been accounted for in the design of the system, you may still unexpectedly find yourself short on power for any of a range of reasons:
1. The vehicle alternator is voltage limited such that the auxiliary battery never reaches full charge, particularly when the auxiliary battery is being cycled on a daily basis. This is not generally a problem for the vehicle battery as the only discharge is probably when you start the engine, after which the battery recharges when you are driving. The vehicle battery is thus generally close to full charge most of the time. Solar modules connected to your auxiliary battery bank via an appropriate regulator should allow the auxiliary battery to achieve full charge on a regular basis, as long as incoming power is allowed to exceed outgoing power by at least 15% (to allow for battery inefficiency).
2. It is very difficult to design an appropriate solar power system for a home with no fixed address. It is difficult enough when there is a fixed address, because even though you can get a fairly accurate average solar radiation value for each month of the year for that location, there is no guarantee that you won't have two months of predominantly overcast weather.
3. The standard practice of designing a solar system based on a given load profile is an inexact science at best. How can anyone say that he/she will use a particular light for 3 hours per night and watch TV for 2 hours per day. Anyone filling out the load profile form in order to have an appropriate solar power system designed, will use educated guesses at best or be totally misleading to avoid embarrassment at worst. Even though a person may volunteer that he/she watches TV for 2 hours per day, he/she may neglect to divulge that the TV is often left on as background noise or as a 'baby sitter'. The system design can never be more accurate than the information it was based on.
4. According to Murphy's Law, something will invariably go wrong, and usually when you least expect it. There can be any number of faults that could cause the battery to go flat. For all of the above reasons, it is good to have some kind of backup. So what is suitable for a backup to get the charge back into your battery bank? Keeping the engine idling or going for a long drive is not an acceptable option if you don't really need to go anywhere. Using a vehicle engine just to charge a battery and nothing else is not good fuel economy. This is where you need a small efficient motor (petrol, diesel or LPG) driving either a 230V AC or 12/24V DC generator.
The standard transformer style battery charger used to be quite inefficient (50% to 60% efficiency) and the generator to provide the power to such a battery charger needed to be able to produce four times as much power as the battery charger put into the battery (some of this to account for poor Power Factor).
There are two better options:
- Use a DC generator which is dedicated to be a battery charger and does not produce 230V AC at all.
- Use a quality Victron battery charger with efficiency rates around or above 80%.
If you need more information, please contact us.