Motor controller and battery output

All new at this. Planning to install a 36volt motor 20 amp controller in E-bike. Will there be any issues if I build a battery pack that is 36 volt 5P @ 50 amp and or 10P @100 amps? Does the 20 amp controller only provide 20 amps regardless that the battery build is over a 20 amps pack?

Thank you.

First off, you may be confusing amps, and amp hours. But for sure, the bigger your battery in amp hours, the less amps each cell has to put out, to supply your controller with 20 amps of current flowing. In addition, your pack may have a bms which limits amps to 40, or 60, or whatever, in case you hook it up to a very large amps controller at some time. In general, for a 20 amps controller, a 40 amps bms will be plenty. At first start, it will pull more than 20 amps for a brief time, and you don't want it shutting off before it can get going.

Your controller will max out at or near 20 amps after that first spike at starts, The motor will gladly suck more, but the job of the controller is to control that, limiting it to 20 amps. So it quickly ramps the amps back down to 20 or so. This is partly to limit speed, or power to legal limits, partly to make motor burn out less likely.

So yes, make the battery as big as possible, without making it too heavy and awkward to carry on the bike. 15 amp hours of 36v will still be pretty light and compact, but 20 ah of 36v can still be carried easy enough.


If you want huge range, then you need to carry a lot more, and in general, are best to consider cargo bike of some type, which is able to carry 30-40 pounds without handling poorly.

Hi Dan, Great information thank you for this.

Determining the battery's size, weight and mounting will be the challenge.

I am building my own pack with new cells and I am not going to put in a BMS at this time. I plan on monitoring with a cell meter with voltage alarm on this pack. The issue with a BMS I see is you don't know what it is doing or even working. I made a small 12 volt pack with a BMS just to check out the functionality of a BMS. Would love to see a activity light on a BMS telling me something. It is like driving a car without a dashboard. A perfect BMS would be able to send error codes.

Without a BMS, it would be important to have cells that would support a amp load that a more powerful controller would need without effectively destroying the cells. Sounds like the controller is the gate-keeper to limit power to the motor, but could also harm the cells if they were not properly sized for a higher amp hour controller. Also it appears the controller must be sized so it does not burn out the motor rating.

Look forward to more learnings in the forum.

Thank you.

Regards
Steve

Yes . A 15ah or 20ah pack is ez to use without bms smaller packs are harder on cells and range without anxiety. Ye s you can self monitor quality cells easier with less trouble. I did this for 5yrs same pack replaced sense wires 3 times. Always discount the rating of your cells.

:thumb:

stevecahill said:

A perfect BMS would be able to send error codes.

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I don't know the specifics, but there are some that do. There's a thread in the sale section, I think, about a Bluetooth BMS (by that title).

That said, I don't use a BMS on my bike or trike packs, I just make sure the pack is big enough of high enough quality cells and don't run it down too far, so it always stays balanced on it's own.

Sounds like the controller is the gate-keeper to limit power to the motor, but could also harm the cells if they were not properly sized for a higher amp hour controller.

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Controllers don't have amphours; taht's a measure of capacity. Batteries do.

Controllers limit current, and are commonly rated by the Amps of taht limit.

But otheriwse, yes, your statement is correc.t

Also it appears the controller must be sized so it does not burn out the motor rating.

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But it must also be sized to provide the current necessary at the voltage the system runs at to give the total watts (power) to drive the motor under the conditions you'll ride at (wind, hills, acceleration time, speed, etc).

I recommend checking out the http://ebikes.ca/simulator to learn more about the interactions of battery, motor, and controller, and your riding conditions and usage.

I visited http://ebikes.ca/simulator last week, so many selections, I was intimated, not ready to take this on, but will take another look.

Thank you for your input.