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Battery Packs - How to decode V, AH, and WH?


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Hello Everyone.

Please bear with me and excuse my ignorance.

So I was told that my wheel came with a 132 WH battery.  

But the sticker on the back of the battery pack looks like this.

I was also told it uses genuine Samsung Batteries, is that true?

So what is it?



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in the left upper corner you have the brand... SA/22P...

Samsung 22P ...with 2150mah...sometimes announced with 2200mah!

this type has a max Amp draw of 10amp continuos!

as you have only a ONE pack configuration...with 16s1p...(16seriells1parallel)....the complete used power and conplete Amp draw goes on this one pack...so if your motor on steep hills draws for example 15 Amp...the batteries are really under stress and can barely deliver that...and perhaps then shut off!

one bigger batteries you have 2 (or more) of 16seriells pack in parallel...which would mean in the 15Amp example each pack has only to deliver 7,5Amp!

thats why bigger batteries are not only for more miles! They are a real saftey feature!

132wh is (my 2cents) much to less for a proper usage...get some steep hills and the batteries are overstressed and empty much faster as you might think....

this type has a nominal 10amp draw...but this is not even recommed on this batterie...its a lot better for low draws with max 2 amp....

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V stands for Volts (the unit) or Voltage, voltage being a measure of "electric potential" (or potential difference, as it's usually measured between two points). In the case of batteries, the voltage reported is usually the so-called "nominal" voltage. I'm not actually 100% sure how the nominal value is decided upon, but it would seem like usually it's the average voltage of the battery between being fully charged and fully discharged (which depends on battery chemistry, like NiMH, Lithium-Ion and whatever).

For most lithium-chemistries, the nominal voltage lies between 3.6V and 3.7V per cell and for LiFePo4 it's around 3.2V per cell. Fully charged, typical lithium-ions (those that have nominal voltage around 3.6-3.7V) go up to 4.2V per cell (and some even up to 4.35V per cell), and fully discharged they drop below 3.0V per cell (usually 3.0V seems to be the typical "cut-off" after which the voltage plummets very fast even with lower loads).

So, in your sticker it says "Input: DC 67.2V". That means that the battery is to be charged with (up to) 67.2V direct current (DC) voltage. As with most wheels, this one is also a "typical" 16S (16 cells in series) -battery pack. The 67.2V -value is got when 16 cells are put in series, and each of them has a maximum voltage of 4.2 volts:

16 * 4.2V = 67.2V

A stands for Amperes (the unit) or amps for short. It's a measure of electric current. But when it comes to batteries, the typical value reported is expressed in Ah, which means Ampere-hours. As a simple example, if you have a battery of 1Ah, discharging it from full with a current of one ampere, it will be discharged in one hour (1Ah / 1A = 1h). Discharge the same battery with a current of 2 amperes, it will be discharged in half an hour (1Ah / 2A = 0.5h), etc. You get the idea. Amperehours are used to measure the capacity or charge the battery holds.

Also, your sticker says "Capacity: 60V / 2.2Ah". The 60V value is the (rounded) nominal voltage. Technically, it's somewhere between 57.6 and 59.2V (3.6V * 16 = 57.6V, 3.7V * 16 = 59.2V). The 2.2Ah value is the cell capacity. Each cell holds 2.2 amperehours (Ah) worth of charge.

When the cells are put in series, their voltages add up one after another: 3.7V, 7.4V, 11.1V, 14.8V... 59.2V (after 16th cell, with nominal 3.7V per cell). However, their charges are not summed together then. If the cells would be placed in parallel, the total voltage would be the same as a single cell (3.7V nominal), but the amperehours would be summed, creating a battery with 3.7V nominal voltage and 16 * 2.2Ah = 35.2Ah of capacity.

A more "useful" (depending on the situation ;)) measure of capacity is watthours (Wh). Watt is a unit of power, but when talking about watthours, it works similarly as amperehours: With 100Wh battery, drawing a constant power of 100 watts will discharge the battery in about one hour. 200W of power, half an hour etc. The amount of watthours a battery holds is usually calculated by multiplying the nominal voltage (typically the rounded 60V value) with the capacity:  60V * 2.2Ah = 132VAh. Since "power equals voltage times current" => P = U*I, and the units happen to be watts (power), volts (voltage) and amperes (current), you get W = V*A. Typical mathematical notation is to leave out the multiplication signs (so amperehours is actually amperes times hours), so you get W = VA. And then, 132VAh = 132Wh. And that's where the 132Wh value for the battery capacity comes from.

Hope that made any sense, do ask if something isn't clear.

EDIT: About the "usefulness" of the watthours; a typical cellphone battery can be something like 3000mAh (3.0Ah). That sounds like a lot, if you compare that to the (physically) much, much larger unicycle battery holds "only" 2.2Ah. But the amperehours -value doesn't take the voltage into account. The cellphone battery has a nominal voltage of only 3.7V. So it holds about 3.7V * 3.0Ah = 11.1Wh, whereas the unicycle battery again has 60V * 2.2Ah = 132Wh ;)  People look "too much" just at the amperehours, leading to situations like thinking that getting a 20000mAh (20Ah) powerbank (that puts out something like 5V, so it can't be even used to charge a wheel) they can ride a hundred kilometers with their wheels... :P 

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