Batteries amperage: is it for capacity or for accleration or none?

[ebikebob]

Hi，


When it comes to real world applications to ebike batteries, when I look at a 48 V 12 A battery vs a 36 V 20A battery for example, (I know the latter may not exist) how would they perform differently given the same motor?

I read online that Amps corresponds to capacity, yet someone else said Amps corresponds to acceleration. And Volts translates to overall maximum speed. And V * A would determine overall range?

 

[AHicks]

I would add-
Amps = amount of potential power available
Ah = amp hours = how long that power will last.

 

[Bruce Arnold]

Acceleration has more to do with voltage. You get better acceleration when your battery is charged up because that's when the voltage is highest. Amperage has more to do with range. You'll have more volts for more distance if you have more amps.

So, for instance, a 52 V battery will have better acceleration over more of its charge than a 48 V battery. A 19 amp-hour battery will have higher voltage longer than a 13 Ah battery.

Just one more example: a 48 V battery which has dropped down to 47 volts would have the same level of performance on the same bike as if you put a 52 V battery on it that had also dropped down to 47 V, because they're both putting out the same voltage. A 19 Ah battery at 47 V will maintain that level longer than a 13 Ah battery at 47 V, because it has more capacity.

I hope I have succeeded in thoroughly confusing you. LOL.

 

[Alex M]

Hi，


When it comes to real world applications to ebike batteries, when I look at a 48 V 12 A battery vs a 36 V 20A battery for example, (I know the latter may not exist) how would they perform differently given the same motor?

I read online that Amps corresponds to capacity, yet someone else said Amps corresponds to acceleration. And Volts translates to overall maximum speed. And V * A would determine overall range?

You should get your ducks in row before moving any further, because you are confusing the units.
Current: A
Voltage: V
Wattage: W=A*V
Capacity: A*H=AH (amper-hours), or A*V*H=WH (watt-hours).


Battery is 48V*12AH (amper-hours), not 12A.

A is the current and correspond to acceleration.

V*A=W, this is power that motor can draw from battery, and has little to do with overall range, but has a lot to do with acceleration.

AH is battery capacity. Another way to measure capacity is A*V*H=WH, it is more informative than AH because it considers V of different batteries. Batteries 48V*10AH and 36V*13.3AH would have same capacity 480 WH and would (in theory) result in the same range at a given speed. Range depends on speed, among other things.

Volts in specs of the battery or motor doesn't really translate to overall maximum speed, it's just a nominal voltage, but batteries with higher nominal V usually can output higher V*A=W, and thus better accelerate.

There is also dependency btw battery remaining charge and its ability to output A - the fuller it is, the more A it can output and thus better accelerate. Incidentally, as battery discharges, its V drops, so the battery at the end of the trip would have lower V and thus, lower ability to accelerate.

 

[ebikebob]

Thanks this is very helpful. However one person said Amperage has more to do with range and another said amperage has more to do with acceleration. But I see how power is related to volts and amperage and how you need both to be high if you want speed and acceleration.

 

[Ebiker33]

Hi，


When it comes to real world applications to ebike batteries, when I look at a 48 V 12 A battery vs a 36 V 20A battery for example, (I know the latter may not exist) how would they perform differently given the same motor?

I read online that Amps corresponds to capacity, yet someone else said Amps corresponds to acceleration. And Volts translates to overall maximum speed. And V * A would determine overall range?

If I had to answer in one word I would say capacity, in the cordless power tool world if you are using the same voltage and the same type of cells (18650) Amp Hours only increases run time. 18V 3Ah verses 18V 9Ah for example, you might be able to use a tool with that battery all day where you would need to charge or use a second battery with the 3Ah version depending on the tool of coarse, lets say a circular saw.
If however you change the cell type to 21700 for example then you can get more power/acceleration even within the same voltage somebody made a home made battery with them and they said it was better.
A 18V 21700 6 Amp hour will have more power than a 18V 18650 9 Amp hour, but you will run it out faster, the run time is still less on the 6.

 

[Alex M]

However one person said Amperage has more to do with range and another said amperage has more to do with acceleration.

Hard to tell what they meant. Most likely the first person meant "ampere-hours" - battery capacity, and the other one meant "amperes" - current. People often confuse these terms.

Ampere-hours is only a proper measure of battery capacity (and thus - the range), if we compare 2 batteries of the same voltage, ex. 48V*10AH and 48V*20AH - the 2nd one will result in longer range. Again, it is not "amps" but "amp-hours".

You can't compare two batteries based on AH alone, for example 48V*10AH and 36V*13.3AH, because the 2nd one will NOT result in a longer range. Both of them have same capacity 480WH. Always convert to WH to avoid the confusion.

There is a relation between the drawn amperes (=current) and range, - and it is an INVERSE relation. When you draw lower current from the battery, you go slower and your battery charge lasts longer. Similar reasons are causing your car to have a better mileage at slower speed. Whether that first person really meant this scenario, I don't know but have some doubts because in this case people usually say that range increases at slower speed.

Doesn't really matter what those 2 people meant. If you want to know the truth, this page is it

 

[Explorer-1]

As Alex M says, best to use Wh rating to get a range estimate. As for acceleration I don't think anyone mentioned how important the controller is in this regard. So unfortunately I would ignore everything about acceleration in this thread. There is a critical controller, software, and motor windings to consider. Even if you are talking about different batteries on the same bike, the controller and software might limit the response.

 

[Ebiker33]

As Alex M says, best to use Wh rating to get a range estimate. As for acceleration I don't think anyone mentioned how important the controller is in this regard. So unfortunately I would ignore everything about acceleration in this thread. There is a critical controller, software, and motor windings to consider. Even if you are talking about different batteries on the same bike, the controller and software might limit the response.

That's so true, you could the best battery but only a 20 amp controller bottle necking the whole system because of government regulations, when both the battery and motor need a 30 amp controller to make that bike like it is suppose to.