Battery amps

paintboy

Pedelecer
Nov 14, 2020
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Hi, had a few questions answered so thanks for that.
I understand the fundamentals of battery building but here's another one that l want to grasp.
An 18650 cell for example has a spec of 3000mah and a continuous discharge of say 10. So if it's made into a pack of 5p it becomes a 15ah battery with continuous discharge of 50 amps?
If that's correct, the pack will last an hour at 15 amps? My point is on an ebike, at what riding would it pull the 50 amps?
 

Nealh

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Aug 7, 2014
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Cells amp rating is tricky although rated for 10a it will not last long running at 10a and life will be shortened, the max amp rating is a short burst rating. Generally one should be looking at a max 60/70% of the call amp rating or follow the battery spec guidance. If a manufacturer rated a cell at 10a but only gives it a continuous 2c rating then one would only run it max at 6a. 1c is 1% of the mah rating so a 3000mah cell rated at 1c is 3a.

The Sam 25r is 2500mah and the spec's give it an 8c rating which is 20a but one can run it at 25a for a very short burst.
 

Nealh

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If that's correct, the pack will last an hour at 15 amps? My point is on an ebike, at what riding would it pull the 50 amps?
It won't unless the controller has a max 50 amp current rating and the battery BMS allowed this.
With any battery build, regarding current draw (amps) one should allow approx. a 30% head room or more on the current draw of the battery so that the controller cannot draw more.

If one wanted to draw 50a then one would use 20/25a cells and more then 5p.

My Swizzbee has a 24v 200a 40.7ah rated setup and I only get around 55 - 60miles range from it, the controller draws on average 16a continuous but I have seen 34a on the wattmeter displayed. It is enough for me to ride to the seaside and back on a nice day.
 
Last edited:

paintboy

Pedelecer
Nov 14, 2020
51
0
Cells amp rating is tricky although rated for 10a it will not last long running at 10a and life will be shortened, the max amp rating is a short burst rating. Generally one should be looking at a max 60/70% of the call amp rating or follow the battery spec guidance. If a manufacturer rated a cell at 10a but only gives it a continuous 2c rating then one would only run it max at 6a. 1c is 1% of the mah rating so a 3000mah cell rated at 1c is 3a.

The Sam 25r is 2500mah and the spec's give it an 8c rating which is 20a but one can run it at 25a for a very short burst.
Hi nealh, thanks for reading. So like a car, the battery pack would draw most current on climbs, starting off etc? What amps would it draw flat out? Impossible to say?
 

soundwave

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May 23, 2015
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with a mid drive bafang bike you can change the power and speed settings via the programme cable but top speed will be limited to the controllers power or you will just blow it up.

so you can speed along going 50mph but you wont get very far range wise.


he has a giant batt in a back pack.
 

Nealh

Esteemed Pedelecer
Aug 7, 2014
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Yes most current is at low speed so can be on starting or climbing. Invariably one needs to fit a watt or coulomb meter to gauge current usage.
 

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