[vinod]

The e-rickshaws in India come with 1kW motors and have a curb weight of 350KG and regularly do 70-80kms using 48V/100Ah Lead acid batteries at 20-30kmph

Will it be safe to assume that if we replace the 1kW motor with 5kW, we should get the same range if we drive at similar speeds and everything else remaining the same?

 

[madderscience]

you will probably see similar range if yes you drive exactly the same way as before.

What is the reasoning behind the motor upgrade? If the reason is to get faster acceleration, then you might or might not see similar range (more accel takes more power of course, but you also get up to speed faster) If the reason is overheating or excess wear on the 1kw motors, that might be a sign they were undersized to begin with and a larger motor might actually give better range.

If the motor has a significantly different diameter or voltage rating than the original you might find top speed is different and you might need to adjust gear ratio (assuming it isn't a wheel motor) to get to optimal specs. If you have torque/rpm curves for the new motor you should be able to compute what the ideal gear ratio would be at a given speed.

Good luck.

 

[vinod]

Thanks for your inputs. The main reason is reduce wear on the motor and also ability for the vehicle to do high grade slopes. Also a sports mode option where the user can accelerate faster with complete knowledge that he might end up reducing his range significantly

 

[madderscience]

the large motor will probably be more efficient in hill climbing than the smaller one will. If the existing motor gets hot to the touch it is probably overloaded.

With lead acid batteries (especially flooded ones) they suffer from the "peukert effect" which is an observation that the faster you discharge them, the less overall energy you get. If the new motors are frequently used to get more power than the old could do, that will probably be the biggest source of range loss.

Not sure what the market penetration for OEM EVs is yet in your area, but in USA most people doing conversions these days use surplus Nissan Leaf cells. A stack of 14 nissan leaf or equivalent modules (2p7s) would give 130ah at 48v and weigh much less than the 8 6v golf cart batteries they replaced. In fact the weight reduction might be enough you no longer need the larger motor.

Good luck.

 

[kennybobby]

Would you be able to get a measurement of the current draw while moving at your average speed, ~25 kph ?

The lead acid battery is likely the limiting factor for power and performance--at full power your 1kW motor draws 21 Amps, but a 5kW will draw over 100 A, which your battery will not like...

 

[tomofreno]

1 kW is likely the constant power rating of the motor limited by overheating, not the peak power. So peak current would be higher than 21A, likely limited by the peak current of the motor controller at low motor rpm and by the low pack voltage at higher rpm due to back emf of the motor. The latter will be worsened by sagging of the pack voltage at higher currents and will likely limit the speed on hills.

You will need to know the current the motor now draws going up a given hill, the rated peak current of the controller, and how that compares to the peak current your 100Ah batteries can supply, in order to see if a larger motor will provide any benefit. It could be that the lower power motor doesn't have sufficient torque, but I think it more likely that the controller or batteries are the limitation.

If you have no current meter, but have an Ah meter you could get a rough estimate of current by driving up a hill at constant speed (the speed you approach at from the bottom, so no complication due to acceleration) and recording Ah reading at the top and bottom of the hill, taking the difference and dividing by the time taken to drive between the two points. You will need a long, steep hill to consume enough Ah to get sufficient sensitivity in the measurement, less so if the meter reads to the nearest tenth Ah. The vehicle may slow as you climb the hill, but that's ok, the discharge current will likely remain about constant at the peak the controller or batteries can supply.

The Peukert Effect mentioned decreases battery capacity at higher discharge currents. So for example the Trojan T-125 has 240Ah capacity at the 20 hour rate, but has only 195Ah at the 5 hour rate (4x the discharge current).

The larger motor will not cause a significant change in energy consumption if the vehicle is operated the same as with the current motor.