all the 17A i see are for 250-350 watt motors
mine is a 500
this is what i got
This 25amp controller will boost your bike to the next level of performance and you'll gain more power, acceleration and torque for climbing hills.
electrobikeworld.com
One of the wife's bikes (500w motor) has had a KT-17a in it for a year or so now, and it's fine. It came out prior to the 22a/25a controller so that's what I used.
Here's the math. If we use 50 volts as the average voltage from your 48v battery during the life of a charge, and we have a controller with 17a max available, that leaves us with 850 watts capacity (50x17=850). IMHO, that's actually a pretty good match for a 500 watt motor.
Consider the 25a controller using that same 50v battery, and you have 1250w capacity - for your 500w motor. Overkill? You bet! To get PAS 1 power down where you most likely want it with the 25a controller (75-150 watts or so) you are going to be cutting the available amperage WAY back - so you would never use a lot of that 25a capacity (that you worked so hard to stuff in that bike).
Here's where the rubber hits the road. Either of these 2 controllers will supply plenty of power for the 500w motor. Both are able to supply way more power than the 500 is rated for. IF/WHEN either of these is run at wide open throttle, stuff (motor, controller,wiring) is going to start warming up quickly. Extended wide open, say for more than a couple of minutes, is going to get things hot enough where you may let the smoke of of something. Crossing a busy road, climbing a short hill, catching up with a riding buddy, anything short term like that, you're fine at full power. The 500 is pretty peppy on that kind of power. The deal is though, you WILL have to use your head when it comes to how long you are using max power - no matter which controller you go with.
That's one issue. The second is, is the 17a small enough to be of any help, or is it STILL too big?
Either controller is going to civilize that bike. There's no concern there.... -Al