Today I just got back from a nice bike trip with my daughter, to the Triad Electric Vehicles Association meeting, in Burlington, NC. I was invited to their monthly meeting to give a presentation about Lithium batteries and battery management systems, since some of the members are starting to contemplate moving away from lead acid batteries. In fact, two of the members have recently commissioned us to build custom packs for their EV’s.
We rode over there on my electrified Surly Big Dummy, with an eZee electric kit on front. We had 3 different LiFePo4 battery packs (48V x 10 amp hour (Ah), 2 x 36V x 10 amp hour, totaling about 1200 watt hours, which equals a 100 watt lightb
ulb running for 12 hours). I didn’t really expect to use that much battery power on the 33-mile each way ride, but I brought them for show and tell (and glad I did). I also brought some BMS boards (designed by the folks on Endless Sphere), PSI cells, and more. We also had all our overnight gear. So the bike was well loaded with us and all our stuff. I estimate that the gross vehicle weight was close to 400 lbs with us included.
While a round-trip 65 mile bike ride may not sound like a big deal to some folks who ride their road bikes 60+ miles in a day, this was a ride with precious cargo on the back, and a fully loaded bike, on some sections of busy road. I planned the route using Bikely.com, which allows mapping out a route using Google maps. I tried to choose a lower-traffic route most of the way, but some high-traffic stretches were unavoidable (why don’t they put shoulders on the roads in this part of the USA????)
We started out mid Friday afternoon, hoping to make it there before the main rush hour traffic hit. As soon as we got on the road, there were some serious headwinds. The national weather service reports winds averaging 15mph, with gusts up to 43 mph – coming straight from the direction we were going. I was sooooo glad to have electric assist. That would have been a miserable ride without. At one point, I was going full throttle (using about 1,200 watts) and pedaling full tilt, on flat ground into the wind, and only going about 15 miles per hour. Without electric, that would have been about 6 miles per hour. There were also some nice hills, too (totaling about 1,200 feet of up and down). Without electric, and with that headwind, the trip would have easily taken at least 4 hours. Despite the winds, we made it there in 1hr 45 min, at an average speed of just under 18 mph. But we burned up way more energy than I planned – about 24 watt hours per mil
e. (i.e., four miles riding would equal a 100 watt light bulb running for an hour). I had planned on 20 watt hours per mile. Glad I had those extra batteries!
Jack, one of TEVA’s leaders, graciously hosted us for the evening and let us crash at his place. We had a nice dinner and after-dinner discussion about quantum mechanics, consciousness, God, and evolution (I am making slow progress on a book about these subjects). We also had the obligatory discussion of the current financial “crisis”. Anyway, to bed very late, and up somewhat early next morning to head out for the meeting.
So I’m not someone to get shy in front of groups of people, since I give scientific lectures fairly regularly (just gave one last Thursday to an audience of 40-50 people). But this group was a bit intimidating, because there was only one other woman present, and it was about 20 guys, who were obviously quite tech savvy. Well, after some introductions and whatnot, we got down to business and I started describing the ins and outs of Lithium Iron Phosphate (LiFePO4) batteries for electric vehicles. I talked about keeping cells healthy, the benefits and drawbacks of these batteries, and discussed some basic design elements for battery management systems (BMSs), the electronic systems that keep cells healthy. There was some good discussion and questions. Afterwards, we went out to the parking lot to check out the various EV’s there.
Here’s an interesting observation that one of my hosts made: I was one of only 2-3 people who actually used an electric vehicle to get there, and mine was a bicycle.
This was a very interesting observation, so I’m going to sidetrack for a second on that. Why didn’t more people drive their EV’s over there? I can only guess: I think the biggest reason is that of the various people I talked to, many people had lead-acid battery packs that weren’t performing too well anymore, or didn’t have sufficient range, or… etc. One guy mentioned a story about being out in his EV one day and getting stranded when the batteries ran out, and having to walk 3 miles. So here’s the interesting thing. If a bike battery runs out, you can still pedal the bike. Even my nearly 400 pound cargo bike, if I had to, I could pedal it that whole distance. But I think the bigger take-home message is this – the main impediment to people using their EV’s more often is the batteries. For a bike, the battery is relatively small, and hence (though not cheap), not nearly as expensive as for a car or truck-sized vehicle. So nowadays, many people use lithium or at least nickel batteries on bikes, whereas most electric cars of the hobbyist variety are still lead acid. One older gentleman even prodded me a bit because he said he had access to very cheap lead acids, so he didn’t see why it was worth buying lithium batteries. I understand that point of view, that in an ideal world lead acids can run for a very long time, so why pay (lots) extra for LiFePo4? But, being in the e-bike repair business, I have seen so many “dead” e-bikes simply because the batteries died, and people hate having to replace them every few years. And it gets worse when you put them in a series string to produce higher voltage. Aside from the longer life and lighter weight of lithium, there is the lower hassle factor. If you get a working system with a good BMS (very important), it should give many years of service without issues. I used lead acids for many years before I switched. But now that I’ve “seen the light,” it is hard to fathom ever switching back to the heavy, bulky (though cheap up front) lead acids.
But anyway, some people tried out my Big Dummy and had lots of fun. Then a bunch of the members headed off to the Earth Day fair in Greensboro, and we got headed back to Chapel Hill/Carrboro.
This time, the wind was at our backs, and still pretty strong. Sweeeeet! There were a bunch of times we were cruising along with just pedaling, no electric power at > 20 miles per hour, a good clip for a 400 lb cargo bike. We made the return trip in just under 1:30 hrs, averaging almost 19 miles per hour, and using about 16 watt hours per mile. After a nice stop at a friends’ house along the way, we got back home. And after just having biked 68 miles on a fully loaded cargo bike in 1.5 days, I wasn’t totally wiped out (I definitely got some exercise, but not to the point of being wiped).
Total stats for the trip:
-Average 18.4 miles per hour
– 67.85 miles
– 3:40 minutes riding time
– 19.9 watt hours per mile
– total energy used by bike, 1,350 watt hours (for perspective, a typical gasoline powered car would use this much energy to go about 4-7 miles). I probably burnt another 400-600 watt hours from leg power.
I was nicely surprised by how well most drivers treated us. There was only one situation that made me nervous, a stupid dude in an ancient camper truck passed us at the same time there was oncoming traffic, and only gave 6″ to spare. I don’t know what his deal was, but maybe his engine couldn’t handle slowing down on the somewhat steep uphill we were on, without stalling. Anyway, here’s a plug for rear-view mirrors: I knew the guy was cutting it close, and I was prepared to bail out onto the grass if he got any closer, long before he was upon us. I don’t know how any cyclist can stand riding without a rear-view mirror. I use mine constantly.
But anyway, most drivers gave us wide berth, and we had a really nice ride through the countryside of the piedmont.
3 cheers for human-electric hybrid vehicles!