30A BMS vs 40A or 45A?

[rocketman58]

I have a 17.5Ah battery and am looking at getting a larger 20Ah battery. While both batteries use the same style holder and discharge plug, the older 17.5Ah battery has a 30A BMS. The newer 20Ah battery has either a 40A or 45A BMS.

Questions:

1. Since they both have the same battery carrier, can swap between the 17.5Ah battery in the new 20Ah?
2. Is my controller ok with a BMS of 40A or 45A? Controller is a 22A +/- 1A KT square wave controller mated to a 500w Bafang Geared hub drive?
3. Would I see any difference in performance of the battery or motor?

 

[E-HP]

I have a 17.5Ah battery and am looking at getting a larger 20Ah battery. While both batteries use the same style holder and discharge plug, the older 17.5Ah battery has a 30A BMS. The newer 20Ah battery has either a 40A or 45A BMS.

Questions:

1. Since they both have the same battery carrier, can swap between the 17.5Ah battery in the new 20Ah?
2. Is my controller ok with a BMS of 40A or 45A? Controller is a 22A +/- 1A KT square wave controller mated to a 500w Bafang Geared hub drive?
3. Would I see any difference in performance of the battery or motor?

The BMS doesn’t reveal anything about the capabilities of the battery. That is determined by the cells used in the pack, and their configuration (e.g. number of parallel groups), so Q2 & Q3 can’t be answered without more details about the packs.
Q1 would be yes, as long as it’s not a factory ebike with compatibility or integration issues. Q2, there isnt an issue with having a battery that can provide more current to the controller. Issues arise if it can’t provide sufficient current, mainly killing the battery pack. Q3 if the pack is more capable, the bike may have better performance on hills or while accelerating.

 

[rocketman58]

Both are shark type batteries with down tube carriers. Both use the same pin setup and XT60 discharge cable. The 17.5Ah came with the hub motor kit. It is generic, not proprietary. The 20Ah would be replacing the smaller 17.5Ah. I would like to be able to use the batteries interchangeably.

It sounds like the BMS manages the flow of electricity in/out of the battery. It also sounds like the controller will only draw as much as it is rated for. I wanted to be sure if the battery can deliver more Amps than the controller can use, that this is not a problem. Would this be like using faster RAM than your computer can use, but it does not harm the computer?

 

[E-HP]

Depends on your controller. Some controllers have a rating and a current limit that are the same (e.g. rated at 20A and limited to 20A), while others have a rating, but allow higher currents for shorter periods (e.g. rated at 20A, but can output or limited to 30A peak current). The former would prevent you from using the additional capability of the battery, while the latter would provide more performance when needed (and may rely more on the user to avoid abusing the throttle to prevent frying the controller).