Farm Power & Machinery Management 3(2+1)

Lesson 13. Variable Costs

i) Repair and Maintenance Costs   

Repair and maintenance costs are considered as an essential and significant part of machinery ownership.  Occasional repairs and periodic maintenance are required to maintain a machine in good working order and ensure a high degree of reliability.  The more a machine is used, the greater is its need for repair.  The following factors necessitate the repairs in a machine:

• Routine wear

• Accidental breakage or damage 

• Operator’s   negligence, and

• Periodic overhauls

Repair costs consists of the expenditures incurred for the spare parts and the labour for repairs made in a shop or on the farm.  Repair costs vary from one geographical region to another because of the differences in machinery use, labour wages and prices of spares.  Repair costs increases with the age of a machine but tend to level off as a machine becomes older.  The accumulated repair and maintenance costs (TAR) at any point in a machine’s life can be estimated by using the following formulae (IS:9164 - 1979).

For four - wheeled and crawler tractors                                             TAR =   0.100 X^1.5            

For stationary power units and two-wheeled tractor                            TAR  =  0.120 X^1.5

For agricultural trailer                                                                       TAR  =  0.127 X^1.4 

For PTO-driven combine, seed drill and Sprayer                                TAR  =  0.159 X^1.4

For plough, planter, harrow, ridger and cultivator                                TAR  =  0.301 X^1.3

For seed cleaner                                                                               TAR  =  0.191 X^1.4

For self-propelled combine, dozer and scraper                                    TAR  =  0.096 X^1.4

Where,

TAR  = Total Cumulative repair and maintenance costs per year divided by the purchase price of the machine expressed as percentage

X      = 100 times the ratio of accumulated hours of use to wear out life

ii) Fuel and Oil Cost

With tractors and other powered farm equipment, the cost of fuel and oil must be included in the total machine charge.  Power required may be estimated as follows:

                                        D S

                        dbp   =    --------

                                        270

Where,

dbp  =  drawbar horse power, hp

D       =  draught, kg_f

S       =   speed, km/h

or

                                       D S

                        dbp  =    -------

                                       3.6

Where,

dbp  =  drawbar power, kW

D       =  draught, kN

Fuel consumption depends on the size of the power unit, load factor and operating conditions.  The actual consumption can be measured in the field or can be estimated by using the following equation (IS:9164 - 1979):

F  =  0.15 P

Where,

F  =  average diesel consumption, l/h

P  =  rated power, kW

or

F  =  0.25 P

Where,

F  =  average petrol consumption, l/h

P  =  rated power, kW

Fuel consumption can also be estimated by the following equation:

F  =  LCF   RHP   SFC/1000

Where,

F       =  fuel consumption, l/h

LCF  =  load coefficient factor for the operation

RHP  =  rated horsepower of the power source, hp (kW)

SFC  =  specific fuel consumption, ml/hp/h (ml/kW/h)

The values of LCF and SFC for different operations and power sources are given in Table 3.

Labour Charge:  The cost of operator and labour is calculated from the actual operator and labour charges paid in Rupees per day at the prevailing rates in that region.

Table 3: Values of LCF and SFC for different operations and power sources.

Power source	Type of work	LCF	SFC ml/kW/h	SFC ml/hp/h
Stationary diesel engine	-  Water lifting	0.6	300	220
	-  Threshing	0.7	300	220
Tractor	-  Light work e.g. transport, water     lifting etc.	0.4	285	210
	-  Medium work e.g. secondary           tillage, sowing,     inter-culture etc.	0.5	285	210
	-  Heavy work e.g. primary tillage,        Sheller, cane crusher, combine etc	0.6	285	210
Self-propelled combine	-	0.6	285	210
Small petrol engine	-  Spraying, dusting etc.	0.8	680	500

 Oil costs  =  0.20 x Fuel costs