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Old 27-02-2016, 05:38   #1
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Watt Hour

If I have a 210ah 12v battery I get about 2520 watt hours. If I take two of these batteries and put them in series for 210ah at 24v do I still get 2520 watt hours or 5040 watt hours.
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Old 27-02-2016, 06:11   #2
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Re: Watt Hour

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Originally Posted by tuberider View Post
If I have a 210ah 12v battery I get about 2520 watt hours. If I take two of these batteries and put them in series for 210ah at 24v do I still get 2520 watt hours or 5040 watt hours.
To arrive at your solution you correctly multiplied 210Ah x 12V.

2 in parallel would be 420Ah x 12V.

2 in series would be 210Ah x 24V.

So, 5040Wh either way.

Ah at a given voltage is more often used to compare battery bank capacity though, if that matters to you.
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Old 27-02-2016, 06:12   #3
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Re: Watt Hour

Amps x Volts = Watts
210 X 24 = 5040

So you'd get 5040 watt hours. What you would expect from two batteries.
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Old 27-02-2016, 06:49   #4
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Re: Watt Hour

The above answers are correct.

However, remember that the rating of 210AH is at the 20-hour rate of discharge, i.e., 210/20 = 10.5 amps.

If the average discharge rate is less than 10.5 amps, then the available capacity increases.

Conversely, if the average discharge rate is more than 10.5 amps, then the available capacity diminishes.

The more the discharge varies from the 10.5A 20-hour rate, the more the available capacity increases or decreases.

Bill
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Old 27-02-2016, 08:32   #5
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Re: Watt Hour

Thank-you very much

Sent from my Nexus 7 using Cruisers Sailing Forum mobile app
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Old 27-02-2016, 15:43   #6
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Re: Watt Hour

That's the advantage of using watt-hrs...it doesn't matter what your voltage is. 2 batteries = 2 times the watt-hr

The problem is most DC systems are rated in amps. Obviously, you can convert to watts but as long as the entire system is at the same voltage, which it works fine and saves you a step in the calculations.

Now if you are working in amps and you compare 2 batteries wired for 12v vs 2 batteries wired for 24v, the 12v system will have twice the amp-hrs (assuming else is the same). Of course, the 24v device will draw fewer amps for the same amount of work.
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Old 28-02-2016, 13:31   #7
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Re: Watt Hour

Also, for actual usage, never discharge your batteries below 60% full charge, and I have been reminded that it is sufficient to call it just a watt because it's definition includes a time factor. So 210 amp/hours at 12 volts or 2520 watts. Nitpicker's corner.
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Old 28-02-2016, 15:28   #8
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Re: Watt Hour

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Originally Posted by dlymn View Post
Also, for actual usage, never discharge your batteries below 60% full charge, and I have been reminded that it is sufficient to call it just a watt because it's definition includes a time factor. So 210 amp/hours at 12 volts or 2520 watts. Nitpicker's corner.
AAAAHHHHHHH! Did you do this deliberately just to provoke my reaction?

A Watt does not contain a time factor, it an instantaneous measure of power, not energy. A Watt hour is a measure of energy. Please learn the difference.

210 Amp hours (not amp/hours) at 12 Volts is 2520 Watt hours.

Amps v Amp hours v Amps/Hr


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Old 28-02-2016, 15:46   #9
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Re: Watt Hour

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...I have been reminded that it is sufficient to call it just a watt...



...So 210 amp/hours at 12 volts or 2520 watts.


Your reminder needs to read this link and try to understand the arguments that show that he is wrong.

This link can't be posted too often...

http://www.cruisersforum.com/forums/...ml#post1933764
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Old 28-02-2016, 16:32   #10
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Re: Watt Hour

"I get about " Bear in mind that unless you are using a trivial load, like a ten watt light bulb, whatever you have connected will probably be sensitive to the loss of battery voltage as the amps are being drawn out of the battery.
Fresh new batteries are typically 12.8-12.6 volts, so using "12" volts is also a bit deceptive. A "12" volt battery starting at 12.6-12.7 volts (typical) will basically be dead at a point one volt lower. As the voltage drops, some loads won't care, others will grow dimmer (tungsten bulbs) and some, like electronics, may begin to misbehave or stop working.

So "watt hours" can be accurate--but still not tell you how much useable power you will get for any specific purpose. As a ballpark estimate, it still is perfectly good.
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