Quote:
Originally Posted by redpoint5
There is a defect if you are experiencing that much capacity loss, either in the caps themselves, or in the balance circuitry employed. Even with constant light emitted from a crude LED and diode balance circuit, my caps go for months with just a volt or 2 of loss. Without the balance circuitry, they can go much longer.
The real issue, as you pointed out, is parasitic drain from the vehicles electronics. This should be measured before designing a battery replacement. Motorcycles are the perfect application because they are most sensitive to weight, and tend to have low parasitic draw. Combining with a small LiFePO4 battery will give the standby capacity needed.
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This is very much possible. Balance circuits are factory made, they employ a small IC with a power transistor and resistors. Alternator makes 14.2 volts engine hot, 14.4 volts engine warm, 14.6 volts engine cold. The maximum experienced were 14.8 volts, in freezing temps, just after engine start. This is measured at the OBDII port, not battery terminals.
Nippon supercaps are rated to 2.5 volts each normally (15V in series) and 2.7 volts maximum possible (16.2V). Fully assembled with the circuits, they are within a maximum 0.24V difference. Strongest at ~2.44V, weakest at ~2.20V. Circuit boards are designed to not allow a cap go above 2.5V. So the circuits may be dropped altogether to save energy.
Lithium batteries are barely usable at freezing temps. Even high tech Varley Lithium are rated by factory for no less than -10°C (14°F).
So the battery has to be a lead-acid for robustness. The cheap 10Ah AGM I've used had no issues in -5°C to -6°C. But gave up at -11°C. It drained to zero and could not hold a charge. Tried to jump start the car, supercaps charged a little and cranked for about 3 seconds. Battery still dead. Tried again to jump start, left the engine to run until the coolant reached normal running temps, stopped, voltage dropped at once to 9.2V and then slowly to zero. Most likely the battery, which had been for many months in the shop and had no manufacture date sticker, had been sulfated. And much too diluted electrolyte froze.
So the next step is a new, properly made and charged AGM from a reputable brand, no more than 4 kg in weight.