# Electrical calculations

Discussion in 'Tech/Mech General' started by Mike B, Dec 20, 2014.

1. ### Mike BFunster

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Where V = Volts - Voltage
I = Amps - Currant
R = Ohms - Resistance

The illustration shows a simple way to remember the three formulae.

From the middle pyramid, we can deduce that I = V/R (i.e. that current flow increases with

increased voltage but reduces with increased resistance).

Where E = Volts - Voltage
I = Amps - Currant
R = Ohms - Resistance
W = Watts - Wattage

You can calculate the amount of power if you know two of the three electrical values – voltage, current and resistance.

See the formulae in the wheel (E, like V, is used to indicate voltage).

e.g. I = W/E or E/R

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2. ### jdk62Funster

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The only formula I can ever remember is:

IVy watts is a powerful girl.....

3. ### GellyneckFunsterLife Member

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SMA is no a bad formula!

4. ### Minxy GirlFunsterLife Member

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5. ### Peter A ForbesFunster

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I have always used E rather than V for volts, all the formulae I remember and use have that notation.

In most daily usage you only need the basics to work out loadings, and in AC calculations Watts = VA X pf or (Volts X Amps) X power factor.

You shouldn't technically use Watts for AC loads unless their power factor is Unity or 1, ie: purely resistive loads.

Peter

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7. ### irnbruFunsterLife Member

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Looks pretty confusing for me.

8. ### Minxy GirlFunsterLife Member

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If you think of it as one of the following you won't go far wrong as a basis to then do other calculations:
• the first two items, amps and volts, appear earlier in the alphabet than watts, so remember to multiply the first two to get the last ...

• another way, always remembering it's a multiplication you're doing ... just scratch your head and think ... 'Watts the answer', ie A x V = W

9. ### GeordiesFunster

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Or the true electricians way, if the fuse blows, put in a bigger fuse.

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10. ### olleyFunster

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My old maths teacher at college, said don't remember formulas, remember answers, like 100c is 212f, play around with 9/5 or 5/9 +or- 32 till it works out right. 250volts at 4amps is 1000watts.

Ian

11. ### laurieashFunster

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So if I put my 2000w electric fire on for 24 hours at 8.7 pence per kwh
how much would it cost me?

12. ### scotjimlandFunsterLife Member

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2kw x 24hrs x 8.7p = 417.6p

13. ### Minxy GirlFunsterLife Member

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.... unless it had a thermostat and cut out when it reached temperature ...

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14. ### Wildman

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a better duvet is a lot cheaper

15. ### Minxy GirlFunsterLife Member

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A hoodie and bedsocks works well as does a nice hot dog on your feet!

16. ### Wildman

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nah can't stand stale bread and fried onions on my feet

17. ### Minxy GirlFunsterLife Member

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Neither can I ... so I have one of these ... although when she lets out one of her farts it smells like hot dogs!

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18. ### GizmoukFunster

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I'll stick with power calc and cable sizing Apps ta

19. ### laurieashFunster

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So of I reduce to 1000w It would be half of that

20. ### tonyidleFunster

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That's just cheating - she's gorgeous!