Amp options

[HughMorris]

Can anyone tell me if a higher amperage is better on a battery protection board. Some are advertised as 20 or 25A, but some are 45A. My battery will be 48V

 

[Nealh]

Be governed by the max current draw of the controller and the cell specs used, cells inside could deliver more current though demand is governed by the controller.
BMS protection is there to cope with current overload, generally 20- 25a is plenty for most controllers < 15 - 20a. Generally head room above the max controller current draw is recommended but you only need higher protection of 5 amps or so. Though rated 20 -25a continuous current loading, depending on the official specs most BMS can handle a higher peak value ( up to about double) for 20- 30 secs at a time.
Higher current rated BMS usually cost a bit more, the battery won't benefit from it unless you plan on going for more current draw.

 

[Andy-Mat]

Can anyone tell me if a higher amperage is better on a battery protection board. Some are advertised as 20 or 25A, but some are 45A. My battery will be 48V

It is important that the board is rated at a higher amps than your battery is capable of, this has little to do with just the voltage, as you appear to believe.
Whatever amps your can supply (this is a factor of the type and rating of the cells used, and how many have been placed in sets of series connected, parallel blocks).
The number of cells in series gives the voltage, the number in each in parallel give the current
There is generally a number somewhere on the battery that starts with the voltage, in your case 48.
With some numbers and letters, find that and put it here on your question.
You might want to review this Video to give you a better appreciation:-

The higher the current handling on the BMS board, the higher the cost.
So its a balance between cost and safety, if you like.
Usually, unless its very close to the possible high current of the battery, the next higher current value BMS board can be chosen.
Other than price, there is little difference, no real "gains" to be made with a board that can say handle twice the current, but a board rated at the same current or less than the battery can supply, will probably run hotter, and may break down earlier....
Maybe causing possible cell damage as well. Do not ever risk that.
Bike Controllers, in my limited experience, may have an electronic adjustment for maximum current (mine does), that is to extend the distance you can travel on one charge, or to allow a higher bike speed (more current), but with a reduced distance possible.
All of these are variables that some controllers can "control".
I hope this all makes sense for you.
regards
Andy

 

[vfr400]

Let's summarise that. there are four things that affect the power: Motor, xontroller BMS, battery cell-pack.
You start with a motor that can handle the power you want.
You get a controller that is rated for the power you want to run the motor at.
You get a battery that can provide the maximum current that your controller allows.

If you buy a ready-made battery with BMS, you only need to look at what its continuous current is. As a general rule you need a BMS rated 5A above your controller for currents up to 25A and 10A above your controller if your controller allows more than 25A.

 

[HughMorris]

Thanks for your replies guys .The battery I am about to build is 13 x 6. The cells are 3.7V. I'll go for the higher rated ampage as it's only a few pounds more . Thanks for the full explanation Andy.