Friday, January 18, 2013

Charger Efficiency

Here is an illustration of the dramatic effect that charging efficiency has affected the Electric Booger over time:
Any modern charger will be a PWM charger, so it usually isn't an issue in a "normal" EV conversion. But when a guy like me decides he needs to cheap out and buy "hardware store type" chargers, the difference is amazing.

For those wondering about this fancy graph, has a great feature to help keep track of your fuel mileage. All you have to do is register on the forum and then add a vehicle to your "garage" to start keeping track.

I finally got a chance to register at the forum. I introduced myself with a whole bunch of pictures of the eBooger conversion just to see what the reaction was. It was kind of funny - mostly "wows" and "that's kind of neat" type stuff. One guy said the original 1.6L is such a gas sipper that I am probably paying more for electricity now. Right. I attempted to teach him about to virtues of EV efficiency.

Other than that, it's mostly just drive -> charge -> repeat these days. I am already starting to wonder what my next one will be. I really want to convert a motorcycle.....


  1. Great ingenious conversion! What's the max current the Kelly field controller has to handle?

  2. Thanks for your kind words!
    I have the Kelly controller set to 50A max when the armature current is at 450A. Since this is 50% of what this controller is capable of, I have not seen it go into thermal cutback yet. Plus it eases my concerns about reliability, since Kelly controllers do not have the greatest track record.

  3. Have you had a chance to actually measure the max field current?

  4. Yes. I measured it with a remote ammeter in order to set up the Kelly controller. 50A max is a good balance of starting off torque and top RPM. If I want I can decrease the field current to give me more motor speed, but I lose torque. Also, I am not sure how high I can go on field current because I cannot find the specs for my motor, so I am sticking with 50A max just to be safe.

    1. And what was the actual current over the motor RPM range? 50 amps seems pretty high for your sized motor. I know it's usually only for a short interval, but in a locked rotor incident or a steep incline start, I wonder if it could be a problem.

    2. Field current is proportional to armature current. Since I cannot afford a proper Curtis sepex motor controller ($1500 after the smoke clears) I do it this way. It makes my sepex motor act exactly like a series wound motor would. At zero RPM (from a stop), if armature current is 450A (which I have measured), field current is 50A. I have a minimum field current of 7A whenever the key switch is on. This is to avoid the possibility of armature current without field current present, which is very bad for the brushes.

      According to the folks at, 50A is most likely the 20 minute rating for a motor like mine. Remember that on a steep incline start, it is the armature (more specifically, brushes/commutator) that can be damaged from over-current, not the field. Giving the field 50A without powering the armature does no harm to a sepex motor.