Hi all, can somebody tell me what this equates to in mAH: 48v10.4 AH lithium ion battery
It is an e-bike battery. I bought an external (130w) power bank that is 27,000 mAH. It has AC output so I’m trying to figure out how much it could recharge the bike battery. An online calculator told me the bike battery is only 10400 mAH which seems wrong considering the bike battery is far bigger and heavier than my power bank.
yes, 10.4 Ah is 10400 mAh.
here’s the thing- when you parallel cells, you add their capacities (in Ah) but the voltage stays the same. when you put cells in series, you add their voltages but the capacity stays the same. e.g. two 3.7v, 5 Ah cells in parallel will be 3.7 volts, 10 Ah. in series, they’ll be 7.2 volts, 5 Ah.
the bike’s battery probably has the cells arranged such that they get higher voltage at the cost of capacity.
Cool, thanks! It seems the bike can function while plugged…so I can charge while riding to extend my range in theory. If the power bank is 130 watts and the bike motor 350 watts, does that mean battery will recharge at 1/3 the speed of at the normal bike battery depletes? Or is that not relevant.
It’s relevant, but still not complete.
You’ve told us that the battery bank can charge the bicycle at 130W, but you haven’t told us how long it can do that. 6 minutes? 60 minutes? 60 seconds?
You can estimate how good the battery bank is by comparing it to the weight of the bicycle batteries: if it’s the same kind of battery and weighs 1/3 as much, your first estimate is that it will last less than 1/3 as much (less than because of losses).
Or we can estimate if you tell us the battery-bank (internal) battery voltage.
It’s important to remember that Amps are the unit of current, not of power, and so amp-hours are a unit of charge, not of energy, which is what you actually care about in this context. The unit of energy (for this purpose) is watt-hour, which is calculated by multiplying the amp-hours by the voltage. So, your 48V, 10.4AH bike battery contains just shy of 500WH of energy (48*10.4=499.2)
I don’t know exactly what power bank you have, but googling 130W 27000mAH power bank brought me to this, which states it has 99.9WH of capacity. For something like this that can output several different voltages, stating the capacity in mAH is a bit misleading, since 99.9 watt-hours of energy equates to a wildly different amount of amp-hours of charge at different voltages. In this case, 99.9WH / 27 AH = 3.7 volts. On the one hand, this is entirely accurate, the operating voltage of a single lithium-polymer cell (or several in parallel) is ~3.7V. On the other hand, it’s totally misleading, in that none of the outputs the power bank have are 3.7V, so the amount of mAH of charge you get out of its 99.9 WH of energy will always be less than 27,000.
So, in any case, that power bank, with 99.9WH of capacity, would be able to charge your bike battery about 20% of the way (actually a bit less due to various losses, like Melbourne said). In the case of charging while riding, assuming perfect efficiency, (which you can’t get), drawing 130W from a 99.9WH battery bank would discharge it in 99.9/130 = 0.77 hours, assuming your charger can also handle 130W.
Even more loss – in ‘charging while riding’, the e-bike is carrying the extra weight of the charging bank, as well as the bike itself + you. The extra weight will further decrease the efficiency of the e-bike charging.
Interesting, and yes the power bank you linked to is correct.
Silophant has the correct answer. Ignoring losses, the power bank contains one-fifth of the energy of the bike battery so theoretically it would charge it by 20%.
I would add that I use this type of battery, inverter and charger stuff all the time and IME a realistic loss when charging the bike battery with the power bank is about one-third. So in practice using realistic assumptions it would charge it by two-thirds of that, or 13%.
500 W-hr? Holy smokes (hope not), that is one powerful bike battery. I need to look into one of these.