A 30-amp BMS on A123 batteries is kind of like tying an anchor on a fine thoroughbred race horse. Is your 30-amp BMS is capable of higher bursts. If so, just get the 48v/40amp Crystallyte controller that is designed to go with that motor. A lot of people recommend the Lyen controllers, but I'm always seeing posts on here where people can't get them to work right with sensorless motors. There are a few vendors on here that sell Crystalyte designed specifically for your motor. I know Maxwell65 will give you a decent price on a sensorless controller. See his thread on here for how to order one: http://endless-sphere.com/forums/viewtopic.php?f=31&t=26500
I actually have the 12 FET 4110 MOSFET Generation 2 sensorless controller LYEN edition that is a perfect fit for both the Crystalyte HS3540 and HT3525 motors for up to 100V. This is a very new controller that I have yet got a chance to advertise in the forum. This is a second generation sensorless with both sensorless built into the main MCU chip instead of two separate processors for faster speed and features.
This guy was running at 18S lipo and later at 22S lipo. See here:
http://endless-sphere.com/forums/viewtopic.php?f=1&t=27585&p=411697#p411697
Another customer from France made a couple of videos with his HS3540 at 72V:
[youtube]oZn6ep1avYU[/youtube]
[youtube]dumowkcuELQ[/youtube]
In fact, I have received a comment from a French customer on the video above:
Sent: Sun Jun 19, 2011 10:05 am
From: pchen92
To: Lyen
I set the controller to higher amp and it makes a huuuuuge difference at low speed. Now I just have to accelerate from a dead stop or 5km/h to wheelie like crazy
RE the 30 amps, lame it may be, but it is one way to keep from constanly melting down motors. You can screw up fast at 3000+ watts. Just depends on your particular needs. More watts, run the batts down faster. If you still have enough range great. If you don't, not so great.
30 amps = lame? damn man I gotta turn off the ca and let this controller/motor have the full 50A. ive been riding round at 25 - 30 to break in the batts/get an idea of range, heat and power and I thought THAT was fun. all you boys running 80+a are crazy. And if I wasnt woried about burning my motor Im pretty sure I'd be too
One thing that you should take into consideration is if you are using a cycle analyst or not. The new Crystalyte controllers have no place to get a speed signal so if you want to get a speed reading you need a cycle analyst with a speed sensor. For that reason I would go with a Lyen controller.