Efficiency test on the X5

[Lowell]

Rode 28.4km this morning, max speed of only 65km/h, avg 35km/h. End result? 19.9 Wh/km. I'm sure if I used the DrainBrain speed and throttle limiters it could be even better, but when you have 5000+watts it's hard not to use them a few times... 8)

This should give me a theoretical maximum range around 90km if I was really patient.

 

[eP]

I see your average current is less than 25A so average torque is less than 24 Nm.
At that level and high speed you have high eff. better than 75%.

Low eff. problems arrising when you need over 50 Nm, especially at lower speeds (lower rpm).

If you want go below 10 wh/km and use high diameter rims for low rolling resistance you can get bad eff. at hilly area as you probably need much more torque if you are gearless.

When you are happy at 20 Wh/km you dont bother of rolling resistance, as your energy consumption depends on your air drag mostly.
So you can use small diameter rims and you dont need heavy torque even at high slope hills.
This way you are very happy at high eff. motor.
But it doesn't mind that all others are happy now too. (Especially when they are gearless at big rims )

 

[Lowell]

I went for a 43.5km cruise tonight, max speed 81km/h, average speed 44km/h. Did some sightseeing at the beach, fast turns, 1 burn out and a few wheelies. Averaged 35.9Wh/km.

Ideally I'd like a 5304 in a 20" wheel with 132V. That would give the best of everything. 160lbs thrust off the line, great efficiency at just about any speed, and around 91% at 60mph cruise. Lithium power of course... 8)

 

[eP]

I went for a 43.5km cruise tonight, max speed 81km/h, average speed 44km/h. Did some sightseeing at the beach, fast turns, 1 burn out and a few wheelies. Averaged 35.9Wh/km.

Lets look at these nubers again:

1) 28.4*19.9 = 565 Wh, 28.4/35 =0.8 h, 565/0.8 = 700 W, 35 km/h = 590 m/min, 20''rim = 1.6 m, 590/1.6 = 365 rpm at Kv = 10rpm/V 365 rmp => 36.5 V (working voltage )
lets assume 16 A av. current so 16A * 400 mohm =6.4 V (waste/heating voltage)
So lets check we assume right current: 700/(36.5+6.4) = 16 A so it is right average current for that case.
16A * 6.4 V = 100 W for heating loses
so you have 600 W of working power and eff. = 6/7 = 86%

2) the second case: 43.5*35.9 = 1600 W, 44km/h => 460 rpm => 46 V
lets assume 30A av. current and check them:
1600 / (46+30*.4) =1600/58 =27.6A, so assume 28A now:
1600/ (46+28*.4)=1600/57.2= 28A so it is correct now.

28*11.2 = 313.6 W and average eff. still better than 80%

But you have to keep in mind that real eff. will be lower as your speed varies from av. speed and we skip additional loses at simple calcs above.

Ideally I'd like a 5304 in a 20" wheel with 132V. That would give the best of everything. 160lbs thrust off the line, great efficiency at just about any speed, and around 91% at 60mph cruise. Lithium power of course... 8)

Try to cruise at 40 mph only at possible constant speed as much as you can keep(at flat road) and check your wh/km.
I'm sure your av. current will raise above 40A and yor eff. drop well below 80%.
So any voltage change can't keep your eff. at 90% level.

 

[Lowell]

At 40mph the current draw is only around 20 amps. 40 amps would be closer to 50mph.

 

[Stevil_Knevil]

Hi Lowell,

I would have to agree with your 5304 in 20" @ 132V analogy, fun.

So, what has been your best run -range wise- using the DB2?


Thanks,

-S

 

[eP]

At 40mph the current draw is only around 20 amps. 40 amps would be closer to 50mph.

So check your wh/km at 50mph.
And we will see what is your efficiency there.

I don't know your drag coef. so i would make wrong assumptions. But keep in mind that we talk - all the time - about motor current not the battery one.

So all the time as your motor current is far less than 50A ( battery current 30A at 60% duty - for example) the motor eff. is pretty well.
But when your motor current arise above 50A the eff. go down pretty fast and battery voltage increasing cannot change that. As cannot change physics laws also.

You see the same: 40mph -20A 50mph -40A but keep in mind that heat loses are proportional to square of current. So at 10 mph increase the loses arise FOUR times around.

Higher battery voltage can help you pump more cureent to motor at the same controler current limit.
But more current = worse eff. this way.

Wh/km tell you the truth.

 

[Lowell]

Hi Lowell,

I would have to agree with your 5304 in 20" @ 132V analogy, fun.

So, what has been your best run -range wise- using the DB2?


Thanks,

-S

45km is the longest distance I've ridden at one time, and around 35Wh/km. Average speed in the low 50's.