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Georgen
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Joined: 13/09/2011
Location: Australia
Posts: 462

Posted: 03:55am 03 Apr 2012

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Loaded my Nokia mobile phone (still had 2 bars charge) and ALDI meter showed 0.007 kWh
That�s on 240V side.

17Ah Battery dropped from just under 13V down to 12.7 or even 12.6V
Suppose my 12V DC to 240V AC inverter got warm and meter took some power too.

But does it all add up?

And how do I convert AC 240V kWh-ours to 12V DC Ah-ours.

George

Tinker

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Joined: 07/11/2007
Location: Australia
Posts: 1904

Posted: 03:04pm 03 Apr 2012

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A 'nominal' 12V battery may show 13V at the terminals if it just been disconnected from a charger. Let it sit unloaded for a few hours and measure again, if the meter then reads 12.7V or 12.6V the battery is fully charged.

KWh (the 'h' stands for hours so delete your "-ours" as it is incorrect) is a measure of energy consumed.
Ah is usually a measure of battery capacity or battery charge, the former is quoted at a low discharge current.
For example 17Ah may mean 0.85A for 20 hours but not 17A for one hour - you get less with the higher discharge. However, if you drain *all* the charge from your battery its life span will be greatly diminished. As a rule, never discharge lower than 50% of the capacity - this means you need an Ah rating of at least twice of what you drain from the battery before recharging.

You can't easily convert what you ask as Watts = Volts x Amps not Volts x Ah.
KW = Watt x 1000, 1 KWh = 1000W for one hour, 500W for two hours etc.

Klaus

Georgen
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Joined: 13/09/2011
Location: Australia
Posts: 462

Posted: 10:23pm 03 Apr 2012

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Tinker,
Thank you very much, appreciate your willingness to help me.

Suppose I wrongly assume that 1kWh is chunk of energy that for example costs $0.25

So if my mobile phone used up 0.007kWh it costed me less than 0.2 cents

I thought that I can calculate how many kWh's, or what portion of kWh I can have from my 17Ah battery.
(I charged phone using charger plugged to 300W inverter connected to 12V battery)

George

Tinker

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Joined: 07/11/2007
Location: Australia
Posts: 1904

Posted: 02:08pm 04 Apr 2012

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Georgen said Tinker,
Thank you very much, appreciate your willingness to help me.

- You are welcome. -

I thought that I can calculate how many kWh's, or what portion of kWh I can have from my 17Ah battery.
(I charged phone using charger plugged to 300W inverter connected to 12V battery)

You *can* calculate that. Simply connect an Ampmeter in series with one lead from your inverter input to the battery - it does not matter if its the pos or the neg lead but you *must* get the polarity of the meter leads right if its an analog (pointer) type ampmeter or it will bend the pointer backwards

. Digital meters just give a negative reading if its the wrong way round BTW.

Do not try to measure the 240V side, its misleading and dangerous - you are, after all, interested in the power drawn from the battery.

Then plug in your phone charger and measure the Amps the inverter (& phone charger) draws from the battery. If you have another meter measure the battery Volts at the same time.
Then multiply this Amp (or mA) reading by the Volts reading, giving you Watts.
It won't be Kw BTW

but if you must know that then divide the Watts by 1000.
The figure obtained, if consumed for one hour, is your Wh (or KWh) that you were interested in.

Klaus

Georgen
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Joined: 13/09/2011
Location: Australia
Posts: 462

Posted: 05:10am 05 Apr 2012

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Thank you again.

George

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