Author Archive

26
Aug

Let the fun begin

Written by admin. Posted in Build Diary

OK, now that the BMS (battery management sys) is installed and working, I can finally go full throttle with a sense of confidence in the cell control. We learned early how quickly cells can be destroyed with such high currents involved. These cells are very robust when properly monitored/controlled, however.

So, let the serious fun begin:

Heads up about the noise level in the first video. Because of the auto gain mic input on the camera, it cranks up the gain from the lack of noise when nearby to the volume level that would match a four stroke, for example, in your audio playback.

 

24
Aug

Update

Written by admin. Posted in Motor Pull

We had to install this auto hoist for the sake of the Rav4EV upgrade project. This helps the project e-BMW tremendously.

Nearly the first thing we did was to yard out the old gas tank.

12
Aug

Data comparison

Written by admin. Posted in Build Diary

Here is the power and speed curve data of the electric e-MotoCRF250R Gen 1:

This is true SAE rear wheel power displayed.

Here is the quick comparison of rear wheel peak horsepower values:

CRF250X = 26 HP
e-MotoCRF250R Gen 1 = 33 HP
e-MotoCRF250R Gen2 = ~50HP (67HP @ engine out) – not dyno’ed yet

The torque is significantly higher in the electric that makes for excellent at off-the-line acceleration, so competing with gas bikes is now possible   

 The final weigh in with Gen1 prototype:  

CRF250X                 = 253 lbs  
e-MotoCRF250R   = 279 lbs
                                           —–
                                         26 lbs over

Well, with these outdated motors, it is more like the weight of the CRF450X … 

Despite this weight, you can clearly see the true acceleration from the dyno data. Considering the peak power from 25 to 30 MPH, this will truly be competitive on a tight track. 

We made a discovery after posting this dyno data and after our day on the track (see below): We later found all the fat copper lugs were getting so hot, it burned off the insulation around them. The thing that caught my eye was some dark color on one battery box cover that turned out to be charred FR4 material inside that was from a terminal bolt that was glowing red hot while full throttle. This is what happens if there is resistance in the current path and large currents flowing; power is dissipated (and wasted). No cells were hurt in the incident, FYI. 

So, because of that, the dyno data shows lower on the plot (above) than it actually is. Now that the resistive losses have been resolved, it will deliver more HP and now may exceed the 250X peak power, we will have to re-dyno to find out. Despite this wasted power, it performed very well on the track. Now it will perform even better and with more range than we reported below.

24
Jul

Close look at the box where modules will go

Written by admin. Posted in Battery Pack

Here is basic form of the structure that will hold the modules:

24
Jul

Things are looking up

Written by admin. Posted in Power Inverter

Things are looking up for the inverter SW design. There are multiple design efforts now going in parallel with this very capable power stage hardware.

This is one of those things that we did not plan to spend time engineering, but some times you have to take matters into you own hands… On the bright side, this forces us to thoroughly understand the optimization parameters of this critical element of the drive system that will certainly have big payback on future projects.

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