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# Formulas

A note on Calculating cost per spot for a spot or projection welder

Electric Supply Volts = a
Current = b
Phase = c

Here a is supply volt either 230 or 415, b is line load shown by current meter,
c is phases of supply volt.
Now calculating KVA for above:

KVA = a*b*k/1000

Note: k = 1 for single and two phase supply and 1.73 for three phase supply

After it convert KVA to KW :
KW = KVA*pf(Power fector)

Note:- If you have not a power factor meter put a value from following table:

For step regulated machines
0.8 to 0.9

For Thyristorised control machines
0.8 to 0.9 at 100% power setting(Current)
0.7 to 0.8 at 75% power setting
0.5 to 0.6 at 50% power setting
0.3 to 0.4 at 25% power setting

Now apply cost formulla:

Rs = KW*time*unit price/3600

Here time is welding time in seconds and unit price is price to be paid for per unit consumption

e.g.:

supply = 415 volt, Current = 50 Ampere, Phase = 2, pf = 0.7 welding time = 0.2 sec
unit cost = assuming 3 Rs. per Unit

KVA= 415 x 50 x 1 / 1000 = 20.75
KW = 20.75 x 0.7 = 14.53
Cost = 14.53 x .2 x 3 / 3600 = .00242 Rs. or (2.5 Rs. per 1000 welds)

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