wattage and amps on 36v controller for a 1000W motor

[void7775]

hi. i have a 1000W motor, and a 36v 20ah battery. i would like to buy a 36v controller so that i don't sell my battery to replace it with a 48v. i have the option to buy a controller which is 36v 18amps max (the seller says it's 360w), and the second seller has a controller of 36v and maximum 25amps(and he says it's 900w rated at:12A).
1.the first seller actually has 36*18=648W?
2.the second seller actually has 36*25 or 36*12?
3. which one should i get in order to use the most of my battery and how much approximate percent will it use from it?
4.is it a bad idea to buy 36v and i should just sell my 36v battery and get a 48v 15ah battery?
thanks

 

[dogman dan]

A 36v 20 ah battery should be able to easily handle a 25 amps max controller. I would choose the 18 amps only if you know the battery is weak and old, or you never want to leave a stop sign fast, and have few hills. Your battery, unless its very poor, should handle 20 amps continuous ok. That would be if you climb big hills, or ride very fast.

As for real world amps, lets say you cruise 20 mph on the flat, in a little bit of wind. That's 600w, And you will pull about 15-16 amps continuous. That will be exactly the same no matter what controller you pick. Slow down, and 12 amps, and so on. If you ride full throttle, you should still be in the 20-22 amps ball park, even into some wind.

So what I'm saying here, is if you want to go farther on the same battery, slow down. Run at 12 amps, 400w. That should still get you 15-18 mph, but its amazing how much farther you go using 25-30% less watts, but only 2-3 mph slower. A watt meter on the bike is essential, for maximum distance rides. But just keeping the speedo under 20 will do, and work wonders for your distances. At 15 mph or less, you should have close to 40 miles range.

But get a big enough hill, or just leaving stop signs, the 25 amps controller will get you all 25 amps briefly as you start, and will be much nicer to ride IMO. If you had a 10 ah pack, I'd then say get the 18 amps max controller.

 

[pullin-gs]

Yes, go big on the controller. It will not only sink the current, but it will probably do it more efficiently (less resistance due to additional drive MOSFETs).

 

[void7775]

it's not an old battery. i will go with 25a. thanks.