Oms law

[Vipar]

Well I think that’s what it is called.

I have just bought a halogen heater 400w 800w at present I pay 16.5 ppkw. So how much will it cost me to run it for 1 hour? How do I work out how many amps it will draw is it
240 divide by 800 =3amp?
As you can see I can’t get my head around electricity.

 

[hilldweller]

Close enough.

 

[David and Sally]

Volts x amps = watts

240v x 4 amps = 1000 watts (roughly)

800w / 240v = 3.33 amps

800w for an hour is 0.8 kwh * 16.5 = 13.2pp hour

 

[kevenh]

ohms law is for current, volts and resistance.
You want the power formula :?

Watts / Volts / Amps / Ohms calculator
Watts (W) - volts (V) - amps (A) - ohms (Ω) calculator.

Calculates power / voltage / current / resistance.

Enter 2 values to get the other values and press the Calculate button:

Resistance (R):
	ohms (Ω) kiloohms (kΩ) megaohms (MΩ)
Current (I):
	microamps (μA) milliamps (mA) amps (A) kiloamps (kA) megaamps (MA)
Voltage (V):
	microvolts (μV) millivolts (mV) volts (V) kilovolts (kV) megavolts (MV)
Power (P):
	microwatts (μW) milliwatts (mW) watts (W) kilowatts (kW) megawatts (MW)
Calculate Reset

Ohms calculations
The resistance R in ohms (Ω) is equal to the voltage V in volts (V) divided by the current I in amps (A):

The resistance R in ohms (Ω) is equal to the squared voltage V in volts (V) divided by the power P in watts (W):

The resistance R in ohms (Ω) is equal to the power P in watts (W) divided by the squared current I in amps (A):

Amps calculations
The current I in amps (A) is equal to the voltage V in volts (V) divided by the resistance R in ohms (Ω):

The current I in amps (A) is equal to the power P in watts (W) divided by the voltage V in volts (V):

The current I in amps (A) is equal to the square root of the power P in watts (W) divided by the resistance R in ohms (Ω):

Volts calculations
The voltage V in volts (V) is equal to the current I in amps (A) times the resistance R in ohms (Ω):

The voltage V in volts (V) is equal to the power P in watts (W) divided by the current I in amps (A):

The voltage V in volts (V) is equal to the square root of the power P in watts (W) times the resistance R in ohms (Ω):

Watts calculation
The power P in watts (W) is equal to the voltage V in volts (V) times the current I in amps (A):

The power P in watts (W) is equal to the squared voltage V in volts (V) divided by the resistance R in ohms (Ω):

The power P in watts (W) is equal to the squared current I in amps (A) times the resistance R in ohms (Ω):

 

[kevenh]

Oh!! Out of habit I posted DC formula.
You may want to factor in the average power value for an AC application
Like described here

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[Vipar]

Thanks I will write it down.
This is my first lesson on trying to learn about the silent killer.

 

[Vipar]

I need to play around with a meter. I really only want to play with DC as I need to learn so that I can find faults and check if I am draining the leisure batteries to quickly or by more than 50% as quoted in another post.

 

[DBK]

You only need to do one calculation.

You are paying 16.5p for 1000W for one hour.

So the cost of running an 800W device continuously for one hour is:

16.5 times 800 divided by 1000.

Which is 13.2p.

It may cost less if the device has a thermostat and cuts out once the room is up to temperature.

 

[Vipar]

I intend to use it on hup as it is free, because my other half is a cold morsel. But I just wondered what it would cost, if I used it at home to warm the van before setting off in the winter.
If I have an item that I don’t know the values only that it is 12v how do I find out the amps it draws?

 

[David and Sally]

is 12v how do I find out the amps it draws?

Watts / 12 = amps
60 watts / 12v = 5 amps

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[hilldweller]

Well I think that’s what it is called.

Since everyone, it seems, likes to score points in here. Why not me.

Ohm's law deals with resistance/voltage/current calculations - not watts.

Watt's Law ( not a well used term ) is about power which is measured in watts in honour of the Scottish engineer James Watt better known for his steam power. This is what you were asking about, power. By coincidence the 800W you quoted is very close to 1 horse power.

746W is the same as that mysterious horse that hauls our MHs.

It can get very much more complicated if anyone wants to score points with Joules. Mr James Joule.

All these British names that helped kick off the industrial revolution, we have to ponder, we had the brains so where did it all go wrong ?

 

[Vipar]

How can I save this post so that I can refer to it later or better still print it ?

Thanks for all those who replied. Sorry kevenh got a bit lost on the diagrams I am a hands on guy. Give me the tools and tell/show me what to do and I will be ok. Nowadays I tend to write everything down in idiots/dummies guide usually phonetically

 

[kevenh]

Bookmark it? The icon middle of the three top right.

Then look in your profile area for saved bookmarks

EDIT: tested. You easiest find saved bookmarks clicking on your name from the top line of options ^^.
Then choose the bookmark tab

 

[Lenny HB]

Since everyone, it seems, likes to score points in here. Why not me.

Ohm's law deals with resistance/voltage/current calculations - not watts.

Watt's Law ( not a well used term ) is about power which is measured in watts in honour of the Scottish engineer James Watt better known for his steam power. This is what you were asking about, power. By coincidence the 800W you quoted is very close to 1 horse power.

746W is the same as that mysterious horse that hauls our MHs.

It can get very much more complicated if anyone wants to score points with Joules. Mr James Joule.

All these British names that helped kick off the industrial revolution, we have to ponder, we had the brains so where did it all go wrong ?

Just to be pedantic ohms law will only give you apparent power, true power calculations are a bit more complicated I seem to remember they involve J notation.

 

[kevenh]

Stealing your pedant's hat, Ohm's law is just resistance volts and current.

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[Vipar]

Thanks got bookmarks working save trolling through all the posts

 

[hilldweller]

Stealing your pedant's hat, Ohm's law is just resistance volts and current.

I told him that.

But it's futile. Resistance that is.

 

[hilldweller]

Thanks got bookmarks working save trolling through all the posts

It will take more than a bookmark to save you in this place.

 

[autorouter]

I have just bought a halogen heater 400w 800w at present I pay 16.5 ppkw. So how much will it cost me to run it for 1 hour? How do I work out how many amps it will draw is it
240 divide by 800 =3amp?
As you can see I can’t get my head around electricity.

Think of volts as how 'energetic' the flow of electric charge is.
12 volts means each amp carries 12 watts of power.
240 volts means each amp carries 240 watts of power.

800 watts at 240 volts requires 800/240 = 3.3 amps

Each amp of 240 volts carries 20 times more energy than an amp of 12 volts.

 

[autorouter]

I need to play around with a meter. I really only want to play with DC as I need to learn so that I can find faults and check if I am draining the leisure batteries to quickly or by more than 50% as quoted in another post.

If you are trying to measure current (amps) then a clamp meter is much easier to use than a standard multimeter.

To measure current with a standard multimeter, you have to break the circuit and insert the test probes so that the current flows through the meter. That can disturb the system so that the fault you are investigating can change.

To measure current with a clamp meter, simply open the clamp and clip it round the wire, insulation and everything. No wires, no need to disconnect anything. It measures current by sensing the magnetic field that the current generates.

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[autorouter]

All these British names that helped kick off the industrial revolution, we have to ponder, we had the brains so where did it all go wrong ?

Sorry to disillusion you, but it was a pan-european effort. Georg Ohm (German), Alessandro Volta (Italian), Andre-Marie Ampere (French), to name but three.

 

[Richard n Ann]

If I have an item that I don’t know the values only that it is 12v how do I find out the amps it draws?

You'd have to measure it's resistance with a multimeter, then work out how much current it would draw by using this bit of ohms law I=V/R ?

 

[Robin McHood]

If you are trying to measure current (amps) then a clamp meter is much easier to use than a standard multimeter.

To measure current with a standard multimeter, you have to break the circuit and insert the test probes so that the current flows through the meter. That can disturb the system so that the fault you are investigating can change.

To measure current with a clamp meter, simply open the clamp and clip it round the wire, insulation and everything. No wires, no need to disconnect anything. It measures current by sensing the magnetic field that the current generates.

To do that on DC you need a Hall effect clamp, a standard clamp won't do it, they only work on AC.

 

[Robin McHood]

While it is lovely to see people trying to help out, can I just point out that monkeying with electrics whether AC or DC, 12V or 220v when you don't know what you are doing and do not understand the concepts behind it can get you very quickly into serious trouble that can cause anything from burns through to fatality. Vipar 's question was a fairly simple one but no one answered with any form of caution on delving deeper. We have already had a thread on here relating to a battery isolator which taken at face value could have led to fire, serious damage and in the worst outcome death. Electrics are not to be trifled with, the 'silent killer' is an apt description. If you don't know, go to someone who is qualified and does know.

 

[Vipar]

312358305432 found this on eBay will it do the job?. I have no intention of touching AC

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[Robin McHood]

312358305432 found this on eBay will it do the job?. I have no intention of touching AC ⚰⚰⚰

I had a fire in RH caused by a previous owner's hidden mod to a DC circuit. Very fortunately it was quickly contained and only caused minor damage. If it hadn't that would have been a total loss...

 

[Robin McHood]

You'd have to measure it's resistance with a multimeter, then work out how much current it would draw by using this bit of ohms law I=V/R ?

Only applies to resistive circuits and not inductive or capacitive.

 

[hilldweller]

Sorry to disillusion you, but it was a pan-european effort. Georg Ohm (German), Alessandro Volta (Italian), Andre-Marie Ampere (French), to name but three.

We let them think they were helping. It is a well known fact, the British invented/discovered everything.

 

[autorouter]

We let them think they were helping. It is a well known fact, the British invented/discovered everything.

Yep, stands to reason, mate. It's a well-known fact that the Arabs invented nothing.

The number zero, I mean.

 

[hilldweller]

Yep, stands to reason, mate. It's a well-known fact that the Arabs invented nothing.

The number zero, I mean.

An Arab with a very Indian accent.

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