Hello, if I am writing in the wrong section then please move it. I heard that watts can be counted by multiplying volts * amps (12x420) and I came up with 5kW and 40W. Is this correct? Did I misrepresent something? Will it really pull that much?

First of all, it's 5040W not toto something you wrote. Other than that, I think it said 420Ah not 420A. That's the difference!

Approximately can, I understand that you substituted the allowable instantaneous battery discharge current. 12V x 420A = 5040 W or 5.04 kW

It depends on whether the capacity or max inrush current was specified. A battery will only give you so many watts for a few minutes.

420A is the stated maximum inrush current that the battery can give out for a while.

@aviva1 You're thinking right. More is described here:

Hi. On a continuous basis (about 1h), a NEW and fully charged battery of 55Ah can give off power of about 500-550W. In a string of 10-15sec it can indeed give out about 2kW.

For a few/some seconds yes. I think not .

These 5kW will pull for a short while. (I'm not talking about discharging the battery here). In practice some... 2kW. Look: A car alternator has a power output sometimes over 1kW. What does this energy receive besides the battery (charging)? Lighting- 600W. The on-board computer- 75W. The engine ignition is also quite a lot. Plus various other dupes.

With minutes I would be cautious, the maximum power will quickly start to drop. Practically there will never be 5kW because with a 420A load the battery will not hold 12V.

You have a picture because, to me, those 420 are amps

Without the photo, it is also clear that A and not Ah . Has anyone come across a 420Ah battery? There are but 400Ah and rather not automotive .

I don't have such knowledge on the subject to understand something from it I already got the answer to the question and the topic to close. Everyone will of course get a helped .

Calculating Car Battery Wattage: Understanding Volts, Amps, and Kilowatts

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#1 14717618 24 May 2015 18:19

aviva1 aviva1

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Post #1
14717618 24 May 2015 18:19

Hello, if I am writing in the wrong section then please move it. I heard that watts can be counted by multiplying volts * amps (12x420) and I came up with 5kW and 40W. Is this correct? Did I misrepresent something? Will it really pull that much?
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#2 14717637 24 May 2015 18:26

Anonymous Anonymous

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Post #2
14717637 24 May 2015 18:26

aviva1 wrote:
I came up with 5kW and 40W
First of all, it's 5040W not toto something you wrote. Other than that, I think it said 420Ah not 420A. That's the difference!
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#3 14717642 24 May 2015 18:28

vodiczka vodiczka

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Post #3
14717642 24 May 2015 18:28

aviva1 wrote:
I heard that watts can be counted by multiplying volts * amps (12x420)
Approximately can, I understand that you substituted the allowable instantaneous battery discharge current.
aviva1 wrote:
I came up with 5kW and 40W. Is this correct? Did I misrepresent something?
12V x 420A = 5040 W or 5.04 kW
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#4 14717649 24 May 2015 18:31

Tommy82 Tommy82

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Post #4
14717649 24 May 2015 18:31

It depends on whether the capacity or max inrush current was specified.

A battery will only give you "so many watts" for a few minutes.
#5 14717651 24 May 2015 18:33

vodiczka vodiczka

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Post #5
14717651 24 May 2015 18:33

aviva1 wrote:
It will really pull that much?
For a few/some seconds yes.
Kraniec_Internetów wrote:
Otherwise I think it says 420Ah not 420A.
I think not .
#6 14717653 24 May 2015 18:34

Anonymous Anonymous

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Post #6
14717653 24 May 2015 18:34

These 5kW will pull for a short while. (I'm not talking about discharging the battery here). In practice some... 2kW. Look: A car alternator has a power output sometimes over 1kW. What does this energy receive besides the battery (charging)? Lighting- 600W. The on-board computer- 75W. The engine ignition is also quite a lot. Plus various other dupes.
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#7 14717661 24 May 2015 18:36

vodiczka vodiczka

Level 43

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Post #7
14717661 24 May 2015 18:36

Tommy82 wrote:
The battery will only give you "so many watts" for a few minutes.
With minutes I would be cautious, the maximum power will quickly start to drop. Practically there will never be 5kW because with a 420A load the battery will not hold 12V.
#8 14717669 24 May 2015 18:40

aviva1 aviva1

Level 9

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Post #8
14717669 24 May 2015 18:40

You have a picture because, to me, those 420 are amps
#9 14717677 24 May 2015 18:43

vodiczka vodiczka

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Post #9
14717677 24 May 2015 18:43

Without the photo, it is also clear that A and not Ah . Has anyone come across a 420Ah battery?
There are but 400Ah and rather not automotive .
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#10 14717687 24 May 2015 18:46

janek1815 janek1815

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Post #10
14717687 24 May 2015 18:46

420A is the stated maximum inrush current that the battery can give out for a while.
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#11 14717716 24 May 2015 19:00

freebsd freebsd

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Post #11
14717716 24 May 2015 19:00

@aviva1 You're thinking right. More is described here: https://www.elektroda.pl/rtvforum/topic2027258.html
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#12 14717733 24 May 2015 19:04

slawussj slawussj

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Post #12
14717733 24 May 2015 19:04

Hi. On a continuous basis (about 1h), a NEW and fully charged battery of 55Ah
can give off power of about 500-550W. In a string of 10-15sec it can indeed give out about 2kW.
#13 14717805 24 May 2015 19:26

aviva1 aviva1

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Post #13
14717805 24 May 2015 19:26

freebsd wrote:
@aviva1 Well thought. More is described here: https://www.elektroda.pl/rtvforum/topic2027258.html

I don't have such knowledge on the subject to understand something from it

I already got the answer to the question and the topic to close. Everyone will of course get a "helped" .
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Topic summary

The discussion centers on calculating car battery wattage using the formula watts = volts x amps. A user initially calculated 5kW based on a 12V and 420A input, but responses clarified that the correct calculation yields 5040W (or 5.04 kW) if 420A is indeed the maximum inrush current. However, it was noted that a battery can only sustain high wattage for a short duration, and practical continuous output is significantly lower, around 500-550W for a 55Ah battery. The importance of distinguishing between amps (A) and amp-hours (Ah) was emphasized, as well as the limitations of battery discharge under load.
Summary generated by the language model.