Thank you both. I'm starting to get a better understanding of the charging math.
The Empulse's spec sheet doesn't mention 3 kW, but maybe I should have divided the battery pack capacity (10.2 kWh) by the charging time (3.5 h) to yield 2.9 kW. Is that the correct formula?
From the value 3 kW, how does one calculate the maximum current that the on-board charger would accept? You're saying that the Clipper Creek, at 72 A, would not increase the speed of charging, so the on-board charger must have a limit below this. Dividing 2.9 kW by the battery pack's capacity of 117.6 V yields 24 A. Is that the correct formula for determining the maximum current draw of the charger?
That's the right idea for calculating the DC charge current.
The easiest way is to look at the
spec sheet (PDF), which states that the maximum AC current input is 14A.
Chargers convert AC input to the appropriate DC current/voltage to charge the battery safely, so referring to current/voltage must specify whether AC or DC. They can either be installed onboard the bike or offboard. An offboard charger - like CHAdeMO 50 kW or Tesla's Supercharger 135 kW - is typically larger than an onboard charger (if any; onboard chargers are typically removed for racing), and it can pair with or bypass the onboard charger to charge the EV battery directly.
Lithium-ion chargers typically have two phases of operation: a bulk constant-current charge, where the charging power will rise as the battery pack voltage increases; and a terminating constant-voltage charge, where the charging power tapers off as the batteries near their maximum charge. The charge is terminated when the constant-voltage charging current drops below a certain value. Cells are usually balanced at the top once fully charged, essentially by moving charge from one cell bank to another until their top voltage measurements are even.
The Empulse is 28 cell banks in series. Each cell maxes at 4.2 volts, so 117.6 is the maximum charge voltage for the battery pack. The particular model of charger used by the Empulse maxes at 25A DC output, so at 0% charge the DC output power will be around 3.2 V/cell * 28 cells * 25A = 2.2 kW, and 4.2 V/cell * 28 cells * 25A = 2.9 kW when it switches to constant current mode.
The Powercharger 3000 is 95% efficient at 100% output, so its maximum AC power draw is 3.05 kW. The charger accepts any AC voltage from 85 to 275V AC; at 230V AC it will draw 13.3A from the EVSE. Depending on the length and size of the cable run out to the EVSE and whether the EVSE is fed with 208 or 240V AC, the EVSE output voltage can be as low as 190V. In this case full charge power would require 16A, so the charger will reduce power towards the top of the constant-current charge.
Likewise, if the included 120V EVSE is used, then the charger will draw the maximum 14A for a AC charge power of 1.7 kW. When the charger is limited by a lower AC voltage input then the "constant" current charge phase will probably not be constant, but slowly drop as the cells fill.
If that's correct, then the high-amperage L2 is not going to make the Empulse charge faster but it will charge.
Correct.
Has Brammo announced plans to increase the charging speed in the future?
Nope. Keep in mind that the charger and its large heatsink (95% efficient means 5% of 3.1 kW gets turned into heat, 150 watts is 50% more than a 100 watt incandescent bulb) are heavy, bulky, and cost somewhere around $600-800. Brammo could add one or more chargers in parallel - and I think they do for the Empulse RR race bikes - to charge at up to 28A AC, which would charge the Empulse's 9.3 kWh pack from 20% to 80% charge in 1 hour.
It would be neat to see an Empulse touring kit with a faster charger but Brammo has not announced any plans.
