watt usage battery recharger

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Hi all
I need to calculate the wattage required on a 12v/240v invertor to charge a
dewalt 2amp/hour battery from a dual battery system. Is the correct formula
W=VxI ??
Therefor would the power invertor required be 240v x 2.0 amps = 480 watt

Re: watt usage battery recharger

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you need to factor in the efficiency .

Re: watt usage battery recharger

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480 Watts sounds a bit high to charge a battery. You need to multiply
the battery current by the BATTERY voltage. Correct wattage is probably
around 24 watts or a bit higher, depending on the battery voltage.


Re: watt usage battery recharger

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If I understand you correctly, you want to convert 12v to 240v, then use
a 240v charger to charge a battery pack (not the battery pack that
you're converting to 240v)?  Is this correct?  And you want to know how
many watts the 12v to 240v invertor has to be able to output to do this
task?  And your battery is rated at 2Ah?

First of all, you need to know the charging rate.  Does your charger
have a sticker or manufacturers plate on it?  That may tell you what the
charging rate is.  Otherwise, how long does it take to charge a
completely flat battery?  That would also tell you how much power it's
putting into the battery, and therefore how much power it needs at 240v.

Let's say, for example, that your dewalt battery is 12v, and that the
charger is putting 1A into it (ie, it takes 2 to 2.5 hours to charge the
battery).  That means (in round figures) that the charger is supplying
12 watts (12v times 1A) to the battery.  The charger will be
inefficient, lets pick a figure of 75% or so, so call it 15 watts.
Round that up to 20w because it's always best to over-estimate.

If what you're trying to do is "size" your 12v to 240v invertor, then
basically anything you can buy will be suitable, since I think they
start at 60w or so.


Re: watt usage battery recharger

Thanks very much pete, thats exactly what my plan is. Thanks for the info,
i'll install the 150w invertor that i have and try it
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charge a

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