37 miles on 3 Fatpacks
No this wasnÃ¢â‚¬â„¢t an exercise in hypermiling just a normal Saturday afternoon ride; more on that later but first an update.
Since putting the ebike into service at the beginning of February I have been on 28 rides and logged 723 miles. Early this month I switched from using 3-12V/9Ah SLA batteries to a LiMn battery pack made up of three Bosch Fatpack 36V tool batteries. After constructing the pack sans all of extra parts I tore it apart and rebuilt it with the heavy rubber endcaps. I did this for added protection even though it added 11 ounces to the overall weight of the pack. Here it is in the SLA tote bag;
I have ridden 10 times with this battery pack and really like it. The most capacity is about 6.4Ah which I recorded one day when I ran the voltage all the way down to the LVC of the controller (31.5V) several miles from home. The voltage didnÃ¢â‚¬â„¢t just sag to that level as on previous rides, oh no I had drained it completely, well maybe 95% complete since the LVC is a bit high for lithium. Still when the voltage gets this low there is precious little left to give even if the controllerÃ¢â‚¬â„¢s LVC were marginally lower. I had no power whatsoever for the last few miles of a 33 mile ride which wouldnÃ¢â‚¬â„¢t have been so bad, the bike pedals fine with no assist, except I had bonked the same time as the battery. Apparently I hadnÃ¢â‚¬â„¢t filled up my
battery after the previous dayÃ¢â‚¬â„¢s ride. Oh well at least I found the batteryÃ¢â‚¬â„¢s limits.
I bought a LiPo charger on eBay, for $24 delivered, as soon as I constructed the Bosch battery pack but while waiting for that to arrive (from China) I used my SLA charger for the first half-dozen recharges. I monitored the charging process with a Watts-Up meter and pulled power when the battery got to where I wanted it. I charged it to 41.5V the first few times but then noticed that precious little juice was actually being put into the battery after 41.0V. IÃ¢â‚¬â„¢ve heard the standard Bosch charger charges to around 40.5V and this is probably the reason why, as is I suppose the desire for longevity which according to Doctorbass is greatly extended by not trying to get that last bit of energy into the cells. For standard LiPo that means 41.5V is better than 42.0V but apparently the cells in these Fatpacks like even a lower voltage. I ended up settling on 41.15V. I finally got the charger and here is a picture of it side by side with my SLA charger;
They not only look the same on the outside they have the same circuit board on the inside. One problem with the LiPo charger was that it came with a 250V Euro style ac plug. The seller sent me several emails asking about how I planned to use the charger and if I had any special connector requirements. I told him to leave the output leads bare, which he did, so I could install Anderson connectors but I never thought to tell him I wanted a 120vac North American style power plug on the thing. Luckily the rating plate states the charger works on 100-240vac, 50-60Hz so I found an old power cable and spliced it in. I then opened the unit and adjusted the output to my preferred setting. I monitored the first couple of charges to make sure it worked properly. The front LED goes from red to green at 41.09V at 0.16A and if I leave it connected for an hour or two itÃ¢â‚¬â„¢ll finally settle out at essentially zero current and 41.16V.
As for the Bafang motor itself I have had no problems. It still vibrates under load and no amount of spoke tightening seems to fix that so IÃ¢â‚¬â„¢m going to have to live with it.
I broke one spoke at 500 miles on the new pre-built rear wheel I bought to match the rim I used for the front motor/wheel. I found when replacing the spoke that the elbow length of the spokes they used were too long so the spokes didnÃ¢â‚¬â„¢t seat in the flange and this probably accounted for the early failure. I replaced not only the broken spoke but 8 others which exhibited the poor spoke head seating.
The 6.4Ah lithium battery and the little Bafang are a great combination thatÃ¢â‚¬â„¢s well suited for rides of 20 miles. Over this length if you want you can use full throttle and get some assist at 19+ mph due to the higher working voltage of the LiMn battery compared to the old SLAÃ¢â‚¬â„¢s which offered nothing at 18 mph. As stated earlier in this thread the top speed of the motor on the battery only went from 16.5mph on fresh SLAÃ¢â‚¬â„¢s to low 17Ã¢â‚¬â„¢s with the Bosch pack.
Ok back to todayÃ¢â‚¬â„¢s ride. ItÃ¢â‚¬â„¢s been quite a chilly April this year in Wisconsin with temps rising only into the 40Ã¢â‚¬â„¢s on most days. Today that (briefly) changed with temps in the mid 60Ã¢â‚¬â„¢s as I left to ride. The wind was brisk out of the southeast at 14mph and as I got near Lake Michigan I could definitely feel the cooling effect from the big lake. This was the first day I rode in shorts and a t-shirt, well two t-shirts actually, and it got pretty nippy with the lake breeze so I headed west. Just a few miles in it warmed up nicely. I continued on to the rolling countryside.
I got to one particularly rough road, I knew it was rough because they kindly posted a sign Ã¢â‚¬Å“rough roadÃ¢â‚¬Â, though so many of the roads around here are crappy this one would have to get in line for the rough road title. It was narrow however and on the left side of this crummy road I spied a brand spankinÃ¢â‚¬â„¢ new bike path (why are they always on the other side of the road?). Let me say right off I donÃ¢â‚¬â„¢t like most bike paths. I think many bike paths are less safe than riding on a roadway. I only wish they could build roads with at least a 3 foot paved shoulder on both sides and forget about many of these silly paths. Not all are bad mind you but most are poorly designed and just when you get on them they stop. Take the one I encountered yesterday; IÃ¢â‚¬â„¢m rolling along this country road and once again on my left I spot this new subdivision and this brand new bike path. The problem was as I rode along wondering if I should zip across to the path I noticed all of the streets the path crossed and at each one a little stop sign. I must have seen a half-dozen of these crossings and while I was also passing cross streets I was doing so on the main road with the right-of-way. To me each time a bike path crosses a road at a point a motorist is not expecting cross traffic the likelihood of an accident rises. Okay enough ragging on bike paths. Today the smooth goodness of the path beckoned to me just like the sound of the ice cream truck tune does to a youngster on a hot summer day. I found a driveway and hopped on her. Oh how lovely fresh asphalt feels I thought to myself. The curving path combined with a tailwind made the next mile cycling nirvana, but as with all good things it ended far too soon. Back to reality and time to head for home as the power was starting to get low.
The last hills before home made quick work of what was left in the Fatpacks and I was getting a little tired myself. In the end I had ridden 37.1 miles (59.4km), used 6.13Ah/225Wh with an average speed of 16.6 mph (26.6kmh). The 6.1Wh/mi (3.8Wh/km) used was lower than normal for me and speed slightly higher than normal for this distance but that has more to do with the weather than anything else. I ride better when IÃ¢â‚¬â„¢m not freezing my butt off and I imagine my aerodynamics are improved without a jacket and sweat pants flapping in the breeze. I estimate I used the throttle at least 80% of the time though itÃ¢â‚¬â„¢s almost always partial throttle. For recreational riding the combination of a low-power hub motor and lightweight battery on a decent riding bike canÃ¢â‚¬â„¢t be beat.
Oh yeah, when I got home I checked the weather from two websites and one reported 56F and the other 70F. I guess one must be near that ice cube of a lake