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T O P I C    R E V I E W
nerdmobile Posted - 02/01/2013 : 07:41:32
Just got done installing a 500 watt assist hub motor on my recumbent trike / velomobile. I am using 4 12 volt SLA batteries in series for power. These are 7AH batteries, so can I assume that the power output would be 7A X 48 volts = 336 watts sustainable for 1 hour. Does this translate to 336 / 500 = .67 or roughly 40 minutes of full power? Or since the maximum output is 336 watts does this mean I can only get 336/500 = 67% of the electric motor's maximum power sustainable for one hour. I plan using the motor assist only for hills, but I'd like to know approximate range before embarking on a long ride. Also, as far as these sealed lead acid batteries are concerned, is it better to run them down to nothing and recharge, or recharge after every use, regardless of how much the batteries have left. Thanks for any info.

jeff garrett
9   L A T E S T    R E P L I E S    (Newest First)
chi6er Posted - 04/17/2013 : 15:36:04
Jeff;

I used SLA for my 1st ebike for about a year. You are right, easy to charge, one plug no worries, low maint. Why did I go to Lifepo4 then to LIPO? Well, other than getting a little more power and less weight by half, there a good chance of burning your house down, mixup the red and black wires by not paying attention and get a real bright arc of light, spend a couple hundred on charger and power supply, worry about puffy cells, have cells balance and all that good stuff.

Jerry
nerdmobile Posted - 04/15/2013 : 20:37:49
That's nice to know, but thanks to many of you guys, I have gotten the hang of my sealed lead acid batteries. Yes, they're kinda heavy, but they're simple, dependable, predictable, and inexpensive. I got this range thing down finally, and on a recent 48 mile ride, only used 25% of my charge. And a full charge only costs 4 cents of electricity!

jeff garrett
chi6er Posted - 04/11/2013 : 20:57:07
If you buy from Hobby King USA warehouse(a chinese company) two Turniqy 6s 5a Lipo batteries, you get 48v 5a for $88. four 6s batteries will give you 48v 10a for $176. six 6s batteries will give you 48v 15a $264. Only setback is you need to get a Lipo charger around, a BC168 will set you about $80.

http://www.hobbyking.com/hobbyking/store/__9176__Turnigy_5000mAh_6S_20C_Lipo_Pack.html

dealing with a chinese company is not all that bad, there are crooks out there, just got to watch out. the chinese dominate the Electric bike industry, think they sold 32 million ebikes last year. Not too much out there can touch their power and speed and price. even though the Cromotor from Czech republic has a brute motor.
nerdmobile Posted - 02/04/2013 : 06:37:17
Well I overestimated my range a bit. I did a 15 mile loop in a hilly area in my town. I could maintain 16 mph on the flats with no assist, and used enough electrical assist to keep 16 mph on the uphill sections, some pretty steep. I stopped at every stop sign and every red light, and used assist to get back up to speed. I never dropped down into lower gears, in fact, I rarely shifted at all. By the time I got home, I still had some juice left, but not full power. The 7ah sla batteries were cheap, about $66 for 4 including shipping. They weigh 22 lbs total. I can buy four 10ah sla's for $88 which will give me 1/3 more range, but weigh 36 lbs. 10a LiPo's weigh about 1/3, or about 12 lb, have 10 times as many charging cycles, but cost about $600 for 4, which can't justify right now. My goal is to be able to ride to work and back, a 40 mile round trip, which include a 1000 ft climb and many hills. I can keep a charger at work.

jeff garrett
nerdmobile Posted - 02/02/2013 : 06:27:47
For me and my velo, 15 mph is a comfortable pace. On level ground, I can do this all day with no assist. Adding enough assist to maintain this pace on gradual grades and hills is my goal. I think I can get a 40 mile loop out of a full charge, I don't know, I'll have to experiment to find out.

jeff garrett
OpusthePoet Posted - 02/02/2013 : 00:23:22
Also there is something known as Puekert's effect where the harder you draw on a battery the less you can draw out of it by an exponential relationship, and SLA has the worst Puekert's ratio of any of the commercially available chemistries. Lipo has the best with insane levels of current draw (60C! Current 60 times the Ah rating of the battery) resulting in Ah recoveries only a fraction of a percent lower than the C/20 rate (current 1/20 the Ah rating of the battery) that SLA are rated at. Legs have the same problem, you might have 150 mile legs at 15 MPH on the level (10 Hr at 100W or 1KWh) but only about 2 minutes climbing at 600W (20Wh).

Opus

My gas is up to $0.99 a burrito, $5.99 for premium and I'm only getting 10 miles to the regular burrito. Dang $0.99 burritos are smaller now.
jjackstone Posted - 02/01/2013 : 21:19:55
One thing to remember. If you continuously run the battery completely empty, you will shorten its life substantially. Lead acid is normally good for no more than a couple hundred full drains as I recall. Generally try to use no more than 80% of maximum charge. There are a variety of battery monitors out there that can tell you your energy usage. I used the Drain Brain which I believe is now called the Cycle Analyst. Still works after six years although I don't ride the electric much anymore. There is a huge amount of E-bike and battery info over at Endless-Sphere.

JJ
nerdmobile Posted - 02/01/2013 : 20:07:44
Hey JJ, thanks for the info. So when my tank has 336 watt hours, I could use 336 watts in one hour or 34 watts an hour for ten hours. It's kinda like an airplane, takes everthing you got to get up to altitude, then dial back the throttle and cruise. I live on the top of a hill so no matter where I ride, the last part of my ride is always an uphill slog. On level ground once I exceed about 15 mph, the aero advantage seems to offset the weight penalty. It takes very little electric assist to get from 15 to 25 mph. I just need to figure out when there's enough juice in the tank to get me backup the hill home. But it'll be fun finding out.

jeff garrett
jjackstone Posted - 02/01/2013 : 10:53:46
The 336 Watts is not the maximum instantaneous output. The 336 Watts x 1 hour = approximately 336Whrs available in your tank. You will not be running the motor at full capacity (500+Watts) most of the time just like you don't run a car at 100 mph most of the time. You will eventually need to figure out you average Watt-hour usage per mile to determine your maximum range. That will also depend on the route you take and how much electric assist you use.

I had a 150 Whr tank that would take me 5 miles at 18mph(on level roads) and no pedalling and leave about a quarter tank left in my battery. Helping the motor by pedalling as much as possible extends the range greatly. I often went 12 to 15 miles on a tank with just a mild pedalling input. Other than cruising at high speed the most energy usage is from a stop. Pedalling from a start saves a lot in energy usage.

Good luck with your build.


JJ

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