**purpose of**

minimize the total cost of a system of autonomous power supply (EPS) at home over long periods of time.

considered a part of SAP meant:

- electric generator to the internal combustion engine;
- unit lead-acid batteries (battery);
- charger for charging the battery;
- inverter (inverter battery voltage in ~ 220Volt).

**Path achievement**

Reduce the time of the generator up to 3.5 hours per day.Maybe it can be somewhat faster, but there is a certain length of chemical processes in the lead-acid battery, and there is a limit on the temperature of the battery (40-45oS).

**Fuel costs generator**

For simplicity, the other operating costs of the generator does not believe - they are relatively small.

- Let the average consumption of the generator - 2 liters of fuel per hour.Let
- fuel cost - 20 rubles.per liter.
- Let the generators in the SAP open 7 hours a day.

Then the daily consumption of fuel will

If we can reduce the time of the generator to 3.5 hours per day, then there is only the savings on fuel - 500 thousand.rubles for 10 years.

**resource generator**

If the generator is running to 7 hours a day, his life - 2500 hours will be consumed within 1 year.With the cost of the generator auto-start 35 th. Rubles, for 10 years with one of their major repairs will have to replace items in the amount of 5 175 thousand. Rubles.

If we can reduce the time of the generator to 3.5 hours per day, then there is only the savings in the resource generators - 87tys.rubles for 10 years.And with the cost of fuel - 590tys.rub.for 10 years.

Why Andrew began reasoning 7 hours?This time, close to the most frequently used by people who do not carry out the calculation of economic efficiency of EPS.

**How is it possible to reduce the time of the generator?**

There is only one way - through accelerated charge high current battery capacity is large enough.

you have a problem - when you charge the battery current close to their limit, they start to warm up much, if overheated very quickly fail.Overheating of the battery greatly depends on the ambient temperature.

Some modern battery charging currents up to allow 0,2S (ie - 20% of the battery capacity figures in ampere-hours) - is, however, at ambient temperature - 20C.If the battery is discharged to a residual capacity of 30%, and the charging current 0,2S for 3.5 hours, then (when the battery charge efficiency = 70%) after 3.5 hours to get to the battery charge, equal to 80%.

Here's a graph of the voltage lead-acid batteries on the level of charge.By assumption, Andrew is right at 20 ° C and the battery disconnected from everything for a few hours.

However, at the same time, we use only 80-30 = 50% of the effective capacity of the battery, iethey should buy in capacity is 2 times larger than the theoretical value of energy consumption in the building.

**Why do you need to discharge the battery to 30% only, and not to zero, and to charge only up to 80% rather than 100%?**

discharge the battery to less than 30% is not recommended becausethey have, in this case, will be a sharp decrease in the resource.Pre-charge the battery from 80 to 100% is necessary to make small currents for many hours (at least 6 hours) that frequent use is absolutely unprofitable fuel and resource generator (see. Above).

**What are my options?**

- There are modern battery which (according to the manufacturer) are relatively resistant to systematic undercharging for example Challenger G12FT.Despite this, it is recommended at least once a month to conduct a full, 12-hour battery charge is good charger (starting with 0.1 C).
- Here you will read about the "economy (" push-pull ") system of autonomous power" that is absolutely devoid of this shortcoming, but "instead" requires additional, but payback on investment.

**On calculation of battery capacity**

To calculate the capacity of the battery Andrew brings some practical estimations for the hypothetical homes (80-150 square meters, heating and cooking food - no electricity).When permanent residence 3-4 people, if you do not do anything stupid, the average daily consumption of electricity in the winter can be up to 700W / hours (24-3,5) = 14,4kVt hour / hours.Given nedorazryada and undercharging, battery should have 28,8kVt / h.Ie- Battery with parameters 12Vh150Ach should be 16pcs.

**about calculating the cost of the battery**

If you take the battery type OpzS (and this is the most cost-effective battery), the price per share at 19 tr(Very roughly) will need to spend 19t.r. * 16pcs = 304tys.rub.With these characteristics of the discharge (30-80%) the number of charge-discharge cycles in this type of battery will be about 1600, ie4,4goda.When converted, for 10 years, the cost of the battery will be 304 x 10 / 4.4 = 690tys.rub.And with 7-hour (per day) of the generator would have to be in the amount of 590tys.rub.

"Lost" for 10 years: 690-590 = 100t.r.(Compare with the amount of losses at the generator 590t.r. !!!).

**On the choice of the charger (charger)**

memory - an important node in the SAPah sincethe correct battery charge depends on the duration of their life.It should be firm, and not less than 3 stage charging and should ensure that each battery charge current of at least 0,2S.It is also desirable to have a sufficient amount of adjustment for adjusting to different modes of operation.Well, of course, its output voltage must match the voltage of your battery unit (24 or 48 volts).12V for such a powerful system Andrew is not recommended.

Caution When charging batteries it is important not to overheat the battery, or they will quickly go out of order.

requires suppliers complete documentation on the battery (including TU) and act strictly according to the documents.

**On the choice of the inverter**

inverter is - a rather complicated and capricious system.It should be:

- brand,
- must have sufficient fixed and starting power,
- should be a sine wave output (and not meander or modified sine wave),
- must have service in your city,
- should naturallywork is from the tension that you build from their batteries,
- and will not prevent a very large number of customization options and functionality.

**On the choice of battery**

On the choice of lead-acid batteries for power supply systems can read - here.

Conclusion

Reduced daily working time generator 7 to give 3.5 hours for 10 years solid economic benefits for our example - about 490tys.rubles.

Note concluded

In this method should be applied qualified "balanced" system, becausein excess of the current battery charge (and most importantly - their temperature), they will quickly fail.If this type of battery will need a little time to increase the charge, it would probably be correct (all the same all have to be considered).

Forced cooling battery, such as a fan, greatly help to increase their service life (basement - an ideal place for the battery under any system, and for this method - especially).

Posted party forum "Home and Cottage" Andrei A.

Editor: Roman Adamov

problem

known that in the case of systematic undercharging of lead-acid batteries of their life is significantly reduced.