How to calculate the change in watts if input voltage is changed?

[90cummins]

I have an electric heater space heater with (3) 2.5kw heating elements rated at 7.5kw at 208v that I use for load testing generators. It also has a 208v fan motor that uses 0.6amp.
I would like to calculate the actual load (watts) due to the increased voltage. Various generators operate between 220v and 240v loaded.
I just mated a new L70 Yanmar to a 5000watt head and I want to do an accurate fuel consumption comparison between this diesel and comparable gas units.
I would like a formula so I can accurately calculate loads?
Thanks
90cummins

 

[dave1949]

The basic formula is:

watts = volts x amps

and

volts = amps x resistance

 

[BrandonR]

In the heater coils resistance rises as current increases so we don't have enough information to calculate this. You need to use a meter to measure the current (amps) and voltage then it's simple math.

 

[90cummins]

Thanks for the quick reply;
I'll try to measure the watts/amps on 1 leg using my kilowatt meter.
90cummins

 

[Midniteoyl]

The basic formula is:

watts = volts x amps

and

volts = amps x resistance

In the Navy we learned for power.. P=Power, E=volts, I=currant... So, that power formula was easy as ... PIE

 

[Paul N]

Here's a list of all the formula's you'll be needing.

 

[dave1949]

For the algebraically challenged, like me :laughing:, we were taught the old finger on the circle trick:

E
-------
I R

I = E/R
R = E/I
E = IxR

I wonder if the power factor varies enough between the various generators to make a significant difference?

 

[techman]

In the heater coils resistance rises as current increases so we don't have enough information to calculate this. You need to use a meter to measure the current (amps) and voltage then it's simple math.

Actually in a heater, the resistance is stable with current or temperature. Nichrome, the most common metal used in the resistance wire for heaters only changes resistance by 1% from room temp to 2000 deg F. So if you know the wattage at a given voltage, ohms law can be used to calculate any other value for a given voltage.

In contrast, tungsten used in light bulbs changes its resistance dramatically with temperature. The resistance increases about 0.25% per deg F. Lamps have a high inrush current due to the low cold resistance, but when hot the resistance increases to the "rated" value for the wattage. This is a reason thet many lamps fail at turn on, due to the high current surge and the thermal shock.

paul

 

[k0ua]

Actually in a heater, the resistance is stable with current or temperature. Nichrome, the most common metal used in the resistance wire for heaters only changes resistance by 1% from room temp to 2000 deg F. So if you know the wattage at a given voltage, ohms law can be used to calculate any other value for a given voltage.

In contrast, tungsten used in light bulbs changes its resistance dramatically with temperature. The resistance increases about 0.25% per deg F. Lamps have a high inrush current due to the low cold resistance, but when hot the resistance increases to the "rated" value for the wattage. This is a reason thet many lamps fail at turn on, due to the high current surge and the thermal shock.

paul

Thank you... I learn something new everyday... who says you can't teach an old dog?

 

[buickanddeere]

Heat drops to 75.1% when 240V device is operated on 208V.