> Four tired lead acid starter batteries aren't going to give > much range with a brushed motor, keep that in mind too. I don't know how far > you want it to go, but I can't imagine that setup being good for more than > 5-10 miles TOPS, and you'll be charging for a long time with it.
Well, let's math it out. A lead acid will have somewhere around 1200 watt-hours of energy each. So, 4800 watts hours is what I'm looking at if I use 4. An electric bike at highway speeds is pulling, oh, 120 watt-hours per mile? Half what an electric car is? 4800/120 = 40 miles, absolute best case scenario at 60mph. Let's doublecheck that with some gas math. It takes about a 9hp gas engine to hold 60mph on a bike. 750 watts per horsepower so 6750 watts. I only have 4800 watt-hours so I definitely can't sustain it for an hour, only 71% of an hour. Which is 42 minutes at a mile per minute. Pretty much bang on. 40-ish miles. If I'm trying to pull that out quickly, lead acids are going to begin to chemically choke out and only get half that, they'll be gasping in 20 minutes. It's not an energy or efficiency loss, it's a chemical and time limitation (let them sit for 10 hours and the other half will reappear). So, probably 20 miles on the highway. My typical driving is probably half city and half highway, so, city driving will be about double that range, plus some extra because I won't hit chemical limitations. I'd love to have a 50 mile range at 45mph but I doubt I'll get it. I burn out on projects easily, biting off more than I can chew so for this, "done is better than perfect." My goal is to start having fun on it ASAP and just go from there. If I can't get to the next nearest town, oh well, it'll be good enough for around town. A brushed motor is going to be a few percent differently efficient than a brushless (10%?) but meh. I can get a brushed motor cheap or free, a cheap brushless does not exist. I can get lead acids for functionally free ($10 at the junkyard, worth $10 in scrap when they're done)... can't get lithiums for free. Well, I might able to, but I'd rather put them on other projects. I have a line on salvaged ones. I have 80 lbs of lithiums in moderate condition, I just don't want to even bother building a pack out of them when I can grab lead acids off the shelf and never have to worry about theft or damaging them. > My own conversion plan uses LEAF battery modules, I have them laid out in > four blocks of 4 that I can connect in series to keep current demands down. Ehn, it's a single digit percentage difference in efficiency to run higher voltage and lower current. Power is power. It tends to just make sense to be in series for most motors and that's really what you're designing to. You can't cheat physics and become extraordinarily better ranged by trading off amps for volts. > BMS, good sine wave brushless controller, I'm hoping to see a good 70 miles > highway range so I can commute to the office and back on a charge. If you want more range, ditch the active BMS. Keep a charger-based BMS or just manually balance once per season. It's not anywhere near as big a deal as anyone makes it. The fact that the batteries are in series means that the same amount of current MUST flow through them, so other than temperature and manufacturing distances, they won't drift apart. -- You received this message because you are subscribed to the Google Groups "Nighthawk Motorcycle Lovers!" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at https://groups.google.com/group/nighthawk_lovers. For more options, visit https://groups.google.com/d/optout.
