Just for the record:
power is rated in watts,
power = volts x amps

from some website somewhere:

Electric Power is the rate at which Energy is spent, or P = E/T. Since the Units of Energy are Joules,

the Units of Power are Joules/second or Watts where 1W = 1J/s.


Writing out the whole equation we get P= (Q*V)/T, but since Q/T is the definition for current (Current is the charge flowing per unit time) we have that P = I*V which is the Basic Power Formula.

otherwise i'd have to agree with what you said phunk...

I think phunk is not disputing that Power is measured in the unit of Watts [possibly not explaned the best], rather that batteries these days have a rating in "Amps" ie the amount of current the battery can deliver. Same goes for alternators, they have an Amp rating. As you can more or less state that 12v is a given [I know it can vary up and down slightly] and that the "Amps" is the value that determines the power delivered / drawn.

At the end of the day, I can not see how that a battery can have enough power to crank the engine and at the same time not supply enough power to an ECU.....

If the ECU is playing up, surely it would be the circuit between the battery and ECU or the ECU itself.

I think phunk is not disputing that Power is measured in the unit of Watts [possibly not explaned the best], rather that batteries these days have a rating in "Amps" ie the amount of current the battery can deliver. Same goes for alternators, they have an Amp rating. As you can more or less state that 12v is a given [I know it can vary up and down slightly] and that the "Amps" is the value that determines the power delivered / drawn.

At the end of the day, I can not see how that a battery can have enough power to crank the engine and at the same time not supply enough power to an ECU.....

If the ECU is playing up, surely it would be the circuit between the battery and ECU or the ECU itself.

im sorry if my undereducated termanology is confusing you, but my point that i am trying to put forward is that:

for example,
you have a 12v motor and you aply 12v to it and it spins around really fast. with the same motor you apply 9v to it and spinns relatively slower.( this part im not sure on but) if the the motor is using less voltage, would it be drawing less current or would that not affect it as the motor is rated at 12v.

if that makes any sense read on

ok, with the ecu, it requires 12v+/- to fuction properly and if it has a voltage drop to low and things arent working properly, it would swich itself off so that it doesnt do itself any harm and inside the cabine an orange light( in most cases) would shine brightly and a little 'cheak engine' symbol would appear

with my car i narrowed the problem to a faulty battery and when i changed it the car magically worked again

ok, this is what i was taught at skool:

p(power) =volts
i(current) = amps
r(resistance) = ohms

watts is the power consumtion of electricity

for example, a 70watt light bolbwould use 70watts of electricty every hour or something allong those lines

non rechargeable battery are labled in volts, as for a size AA battery it clearly says 1.5volts( as i have one in my hand right now) and for the rechargeable batterys of the same size, they are labled in milliamper hours

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the motor would spin slower than normal. in the case of a starter motor this probably isn't enough to start the car.

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most certainly not. power is measured in watts. this is equal to volts times amps.

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a rechargeable battery is usually 1.2 Volts. This is because the chemicals the battery is made out of are different to the ones used in the 1.5 volt non rechargeable batteries.

the milliamp hours part refers to how long the battery can provide a certain amount of amps. The voltage stays at 1.2 volts though.

A 500 milliamp-hour battery could produce 5 milliamps for 100 hours, or 10 milliamps for 50 hours, or 25 milliamps for 20 hours, or (theoretically) 500 milliamps for 1 hour, or even 1,000 milliamps for 30 minutes.

have a look at how stuff works - batteries

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Exactly - Watts is power used.
In this topic we are talking about a batteries power capacity.
We dont say a battery is "*"watts
We say a battery is "*"volts with "*"ampere hour capacity.

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A motor with a load on it will draw current. A 12volt battery with only 9volts is a flat battery and doesnt have enough output current to turn a motor with a load.

As for your magical car - take it to Ripley's and you might get on TV.

if p(power) = watts , then what is volts the unit of.... can u please tell me coz this is starting to get confusing

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a rechargeable battery is usually 1.2 Volts. This is because the chemicals the battery is made out of are different to the ones used in the 1.5 volt non rechargeable batteries.

the milliamp hours part refers to how long the battery can provide a certain amount of amps. The voltage stays at 1.2 volts though.

A 500 milliamp-hour battery could produce 5 milliamps for 100 hours, or 10 milliamps for 50 hours, or 25 milliamps for 20 hours, or (theoretically) 500 milliamps for 1 hour, or even 1,000 milliamps for 30 minutes.
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ok i really dont give a damn about batterys i was just stating the difference in ratings between rechargable and non-rechargable batterys

and with the hypathetical situation with the 12v motor when aplying 9v to it is not a flattened 12v battery( otherwise i would have stated it), it is just 9v. there is no need to complicate the situation

Volts = Potential Difference.
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Since we are taking of a car with a starting problem and you are the one saying it needs a new battery - this is what we use for variables.
A starter motor and a 12 volt battery.
Complicating it would be to say a 12volt motor and a 9volt battery - reason being is we dont know the variables of either of these. Both 12volt motors and 9volt batteries come with numerous specifications.

Lets just end this discussion and stop dragging it out. If you can add anything to the topic of the thread, do so. If you want to learn about electrics - do it elsewhere.

yes i agree, this thread is getting to side tracked

any, back to the topic

razor, if ur still there, cheak to see if you still have fuel presure once the motor has stalled. to do that take a fuel line off at the fuel rail and crank it over, if fuel stil squirts out fine then the cause for your motor stalling isnt a blockage in the fuel line

otherwise thats all that i can contribute