Comments below. Please bear with my ignorance... :) -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Joe Smalley Sent: Friday, September 27, 2002 9:19 PM To: [EMAIL PROTECTED] Subject: Re: How much power am I losing?
1. Measure the resistance of the motor at zero RPM (zero backEMF). This can be with a variable current power supply by applying a fixed current and measuring the voltage across the motor. Resistance is volts/amps. This wiring resistance is the fixed resistance of the motor. All losses in the wiring resistance show up as thermal losses in the motor. Do you mean I should find/get an adjustable power supply type thing from Radio Shack and connect it directly to the motor, and then use my multimeter to measure the voltage as the motor runs at a specific number of amps? 2. Measure the current <through the motor> on a second by second basis during a test drive. This can be done with an emeter connected to a laptop in the car. I take it this would be separate from my current E-meter/Link10, since that measures battery amps, not motor amps. Do I need another instrument, or can I use my multimeter? 3. Square each amp reading and multiply by the motor wiring resistance to get the number of watts being dissipated in the wiring resistance each second during the test. Note: This is a second by second current average instead of a cycle by cycle power average so the real losses are actually larger than the indicated losses if the current ripple is a large percentage of the average current value. If the duty cycle is large and the frequency is relatively high, the ripple is small compared to the average value and this method gives reasonable results. 4. Sum up the watts being wasted each second of the test and divide by 3600 (seconds in an hour) to get the number of watt hours being wasted. 5. Divide this number by the number of miles driven to get the number of watt hours per mile being wasted in the motor. 6. Read the <battery kilowatt hours> consumed by the car during the test drive off an emeter reading <battery> current. 7. Divide the kilowatt hours consumed by the car during the test drive by the number of miles driven to get the number of kilowatt hours consumed by the car during the test drive. 8. Divide the resulting number in step 5 by the resulting number in step 7 and multiply by 100 to get the percent power being wasted in the motor. If you do this with different driving styles, you will get different percentages. If you drive with lots of motor current (low RPM), the percentage will be larger that if you use lots of RPM and very little motor current. Joe Smalley Rural Kitsap County WA Fiesta 48 volts NEDRA 48 volt street conversion record holder [EMAIL PROTECTED] ----- Original Message ----- From: "Mark Dodrill" <[EMAIL PROTECTED]> To: "EV List" <[EMAIL PROTECTED]> Sent: Friday, September 27, 2002 4:59 PM Subject: How much power am I losing? > Since my Optima YT's are rolling along just fine (about 1k miles on them > now), I want to turn my attention to increasing overall efficiency, to reduce > my Amp/Hrs per mile. I'll be looking into front end alignment, LRR tires, > etc, but I suspect my motor is where I'm losing the most. > > Since it is a 6.7" ADC (a bit small for my car), I suspect that I'm having > a lot of electricity turned into heating up the motor instead of having > the motor run faster (since I'm at the upper end of the power/torque it > will do). I'm wondering how I can measure this loss. If I were to measure > the air temp going into the motor and the temp leaving the motor, with a > fan of a fixed CFM blowing air through the motor (in a sealed manner), can > I use that information to figure out how many BTUs or Watts of heat are > being generated? > > Any ideas on how to proceed on quantifying this would be appreciated. > > Mark Dodrill >
