problems with one particular formula.

[Tom]

Hi all


I’m in the middle of my level 3 and having problems with one particular formula.

The question is: 1.5Kw heater with a resistance of 0.5 ohms. What is the current drawn?


Can anyone help me with the formula and some examples please?


Thanks


Tom

 

[wade88]

Hi Tom,

You need to find the square root of the sum of watts divided by resistance. So in this instance, watts - 1500, divided by 0.5 = 3000

Then find the square root of 3000 and that is the Amps, in this case 54.77.

Hope that helps mate

 

[Adam W]

I tried that, 54.77A for a 1.5kW heater doesn't sound quite right though...

 

[wade88]

No i know its a very odd result however thats the answer so i guess thats all he needs.

 

[MarkieSparkie]

Agree with wade 54.77A, it's a high current mate because the supply voltage is low (approx 27V).

 

[malcolmsanford]

as the voltage is not know it may well indeed draw 54.77 amps

√P/R is the right ohms law formula

 

[Richard Burns]

A 1.5kW heater would have a resistance of 35ohms. A resistance of 5ohms would be a 10.5 kW heater. on a 230V system.
But other than that the calculations are correct.

 

[wade88]

Yea exactly mate, 27.3850 volts

 

[wade88]

This is what you need Tom. Print a copy off and keep it in your tool kit

 

[telectrix]

looked at simply, P=VI, as we don't know V, then by ohms law, V=IR, so, substitute IR for V, you get P = Isq. xR.

so Isq. = P/R = 1500/0.5 = 3000. so I =sq.rt. 3000 = 54.77A. now we can find V ( V=IR ) so V = 54.77 x 0.5 = 27.386V

( i never had a pie chart )

 

[platty1005]

The formula quoted in previous posts are all correct the answer is somewhat suspect. Go back and read the question again maybe you have the values wrong.
Basic formula
Volts = Amps x Resistance (Impedance) or V = I x R, V = I x Z
This basic ohms law formula is used in BS7671
also Watts = Volts x Amps or P = V x I
Watts also = amps x amps x resistance = I x I x R = I[SUP]2 [/SUP]R
In exams you will not be able to take in a pie chart so memorize these 3 basic formula the rest you can work out from these
V = I x R
P = I x V
P = I[SUP]2 [/SUP]R

 

[pmac10]

if you have an Android smartphone, download an app called PIRE wheel, then you can carry Wade88's pie chart in your pocket, it'll even do your calculations for you, and no i'm not on commission.