Does Watt's law work in reverse?

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sofarsogood

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I just got a usb tester that is supposed to record how much mAh was used to recharge a battery. I'm hoping to use it to see how many mAh I used to vaporize a given amount of liquid at my setting and/or how much mAh i use in a typical day. I should be able to recharge during the day and get the numbers I'm looking for so long as the tester is always between the power supply and the recharging battery. the tester has non volitile memory that retains mAh until it's reset with a button. https://www.amazon.com/gp/product/B00J3JSEG6/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1

If I run the battery down to the end won't it take more mAh to recharge than if I'm regularly topping off the charge. It takes more amps to supply a given amount of watts as volts decline so would the total mAh recorded to fully recharge a battery be more than the mAh needed to top off the battery because it takes less mAh to increase the charge of a battery with higher volts than lower? Watt's law in reverse?

61W5M7uIHfL._SL1200_.jpg
 

sofarsogood

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In total the mAh charged should be the same in both cases, if I understand your question correctly.

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It takes more amps to produce watts as voltage declines so if I'm using a freshly charged battery through the day and topping off the charge every few hours I believe the mAh meter will show fewer mAh used than if I only start the recharge at the end of the day when voltage of the battery is lower. i put the question here to see if someone knows better than me.
 

KenD

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It takes more amps to produce watts as voltage declines so if I'm using a freshly charged battery through the day and topping off the charge every few hours I believe the mAh meter will show fewer mAh used than if I only start the recharge at the end of the day when voltage of the battery is lower. i put the question here to see if someone knows better than me.
The battery can only hold so much though. More mAh would mean that the capacity would be larger if topping up during the day. There might be a slight difference but I doubt it would be significant.

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Barkuti

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sofarsogood's concerns make a lot of sense. Seems people tends to usually focus in “Ah” as a measure of the available energy in a battery and tend to use such figure to compare between different units, but this is incorrect. W = V × I, and thus the available energy in a battery is equally dependent on the shape/distribution of its voltage curves.

1kaoia.jpg


It can be clearly seen that, while an NCR18650B may have ≈¼ extra capacity versus an ICR18650-26F, notice how this extra capacity is located on the lower end of the battery discharge curve spectrum, and that is not to say its voltage tends to be a little lower (mainly at the lower discharge rates). Thus, the overall extra energy an NCR18650B may provide over an ICR18650-26F may only reach about 20% (quick guesstimation, of course).

So yes, better focus in measuring “Wh”.
Take a look a this gadget on my wishlist:

HTB1OJnnPXXXXXX8XFXXq6xXFXXXN.jpg


USB tester DC current meters ammeter digital voltmeter amperimetro voltage meters amp volt detector power bank charger wattmeter-in Voltage Meters from Home Improvement on Aliexpress.com | Alibaba Group
Pretty good looking for the price. Measures in watts/hour.
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Cheers
051.gif

P.D.: by the way, HKJ tested one of those devices from ETORCH => Test/review of USB meter: USB OLED display tester J7-4T | BudgetLightForum.com (seem good).
 
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sofarsogood

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Oct 12, 2014
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sofarsogood's concerns make a lot of sense. Seems people tends to usually focus in “Ah” as a measure of the available energy in a battery and tend to use such figure to compare between different units, but this is incorrect. W = V × I, and thus the available energy in a battery is equally dependent on the shape/distribution of its voltage curves.

1kaoia.jpg


It can be clearly seen that, while an NCR18650B may have ≈¼ extra capacity versus an ICR18650-26F, notice how this extra capacity is located on the lower end of the battery discharge curve spectrum, and that is not to say its voltage tends to be a little lower (mainly at the lower discharge rates). Thus, the overall extra energy an NCR18650B may provide over an ICR18650-26F may only reach about 20% (quick guesstimation, of course).

So yes, better focus in measuring “Wh”.
Take a look a this gadget on my wishlist:

HTB1OJnnPXXXXXX8XFXXq6xXFXXXN.jpg


USB tester DC current meters ammeter digital voltmeter amperimetro voltage meters amp volt detector power bank charger wattmeter-in Voltage Meters from Home Improvement on Aliexpress.com | Alibaba Group
Pretty good looking for the price. Measures in watts/hour.
075.gif


Cheers
051.gif
Thanks. The numbers that interest me are how much capacity remains in a particular battery and how much energy, whether it's amps or watts, does it take me to vaporize an ml of liquid. I've got my vape to a point where i can puff all day and get it done with a single LG HG2. I want some more precision.
 
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