If an instantaneous current of 140A lasts only a few seconds, there should be no problem. The BMS has two different overcurrent protection settings. One allows the current to peak for a few brief seconds and then cuts off the power; the other will shut off almost immediately when a short circuit (a large current surge) is detected.
If you haven’t purchased a BMS yet, I’d recommend the 120A BMS for a little more safety. In my opinion, the price difference is so small that I would rather buy the 120A BMS than the 100A BMS.
- Whether or not to get a larger BMS: First, you should take a close look at the specs and capacity of your Ultra 100A BMS. Verify that it can handle loads as high as 140A momentarily. If the BMS does not have enough capacity, you may need to consider upgrading to a larger capacity BMS.
- Whether to bypass the BMS: If the BMS is unable to handle high loads, you may want to consider bypassing the BMS in some cases and connecting the load directly to the battery pack. This can be accomplished by adding a switchable connection or relay to separate the load from the BMS when needed.
MORE: How to test the BMS or charging system of an e-bike?