Quote:
Originally Posted by oldtamiyaphile
This is exactly what I was getting at. "Peak" is really a misleading term and actually depends on the resolution of the meter being used. A meter that samples at 1000Hz will record a much higher "Peak" than one that samples at 100Hz. Electronic devices have 5, 10, 20 second etc current ratings.
IMO, these high peak values are for such a short amount of time that small LiFe packs are quite capable of handling them. I have one of those 1/5 scale R/C buggies that I converted to electric power it runs the same LiFe cells as my 1:1 Fiat and draws 'peak' currents of 7500W (measured by the onboard data logger) and this happens dozens of times per charge.
That's over 400A  |
Good points.
The peaks are still good to know even if they are just ballpark figures and only for a brief moment. Batteries are still rated in burst draw, and for my small 4.2Ah pack, that figure is 168A. I don't think starting my car is good for the battery given this rating. LaserSaber blew the same pack by trying to jump start his lawnmower.
Regardless, my main concern isn't discharge due to starting, but the charge current from the alternator, especially in sub-zero conditions. My battery is rated at only 8.4 A charge at normal temperatures. An alternator would easily exceed this after sitting for a while and then starting a car.
Ultimately I plan to keep the ultra capacitor in the engine bay for starting the vehicle, and relocate the LiFePO4 battery to inside cabin. This will help regulate battery temperature and make it easy to take it indoors to balance charge. Eventually I want to do an alternator kill switch and charge the battery from the grid.
Quote:
Originally Posted by Enki
To measure the total consumption, just use the farad rating of your bank combined with start voltage and end voltage.
For instance, if you have a 100 farad bank, and the voltage when started has dropped 5 volts, you've used 500 amps to start the car.
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I started with about 13v in my 350 F series capacitor bank (58.3F series capacitance). After starting, I hit a minimum voltage of 9v. So, I used 233 amp seconds in just under 2 seconds of cranking the starter.