ngant17 wrote: ↑
Jan 28, 2018 11:36 pm
I see you’re getting +22 watt-hours per mile, which jives pretty well with Luna Cycle’s standard 20 watt-hours/mile.
I have (2) 60v x 4Ah Li-ion batteries which is 480 watt/hrs. My latest test-run barely got me home with less than 10 mile range. So I’m really failing that standard by at least half.
I enjoy keeping it in a low gear ratio but I have a Shimano-Nexus 3-speed IGH sitting in a box ready to go on a rear bike wheel in a future project. Since I’ve been riding on a single-speed freewheel, do you think I would go further on these batteries with more gear selection?
So you only have one gear? If so, then yes, adding some gears might help. I basically use maybe three gears when riding. On for starting from a stop. One for medium cruising (20 mph or so) and another for faster cruising (25 mph or so). I'm not so sure an internal gear hub is the right way to go though. A freewheel and derailer are more efficient and probably more durable. And even a cheap five speed has the bonus of providing a seldom used "granny" gear for hills or other difficult situation.
Here are some some other thoughts. Others who know more about mid-drives might have some more useful insights.
1) Each of your packs is probably a 15s 2p 18650 pack. It really isn't a 60v pack. It's probably a 55.5v pack (15 x 3.7v). 3.7v is the approximate average voltage as a pack discharges from 4.2v per cell down to something around 3.4v per cell. I think Greenworks is taking a value of 4v cell and multiplying that by 15 to get the 60v. It's a marketing gimmick (note that they say 60v Max) that uses a voltage close to the peak cell charge voltage (usually 4.2v for 18650 lithium cells) instead of the average voltage. Your total capacity is probably closer to 440 watt hours. Maybe even less if the official charger doesn't charge to 4.2 volts/cell. I've found ads that spec. 216 watt hours/pack.
2) If my guess is right about the pack configuration, then you only have 2 cells in parallel for each pack. I'm assuming you are running both packs in parallel. If so, you only have four cells in parallel over which to spread the current draw. That's not very many and might be straining the cells and reducing efficiency. If your controller is actually pulling more than 750 watts, that could be a huge strain. Have you measured your peak current draw? If you are running one pack at a time and switching, thing are even worse. Do your packs get warm when you are riding?
I'm running seven 2p packs in parallel. My 1250 or so peak watts (35 peak amps) is being drawn across 14 total cells. That means each cell experiences significantly less stress (current draw). My packs never even get mildly warm. They aren't operating at optimal efficiency, but they aren't too far off from what the manufacturer's spec sheet uses for calculating capacity.
3) I don't know what kind of low voltage cut-off the BMS in these packs have. They might be very conservative in order to help the batteries have a long life. You might do a slow 10 watt or so drain test on one of these packs (I've used a couple halogen lamps) with a current measuring device attached and see what the actual pack capacity is.
4) I don't know how you are riding. Is it fast or slow? Do you accelerate really fast a lot? Are you pedaling a lot to help out, or letting the motor do all the work? How you ride matters.
Anyway, those are my thoughts. If you had four packs in parallel, I think your overall efficiency would improve.
FWIW, I did a long (40 mile)ride today with the idea to be miserly on power usage. I kept the PAS in 1 or 2 mode most of the time and kept my typical speed at 20 mph or less. I averaged about 13.5 watt hours/mile. Far better than I get with my faster and more aggressive riding on my commute. How you ride makes a bid difference.