lifepo4/speed

Just wondering if the lifepo4 give 's more speed say if you have a 36v 9ah sla and a 36v 20ah lifepo4 will the lifepo4 have more top end speed??? Right now I run 48v 9ah sla and my bike does 24+ with full charge so I disconnected one batt to give me 36v and I ran at 18mph, so for cost I thought I might go 36v 20ah lifepo4 and was curious if my speed would then indeed be 18mph ??? I believe I could live with that as my work is 13mi away and with the lifepo4 I could go wide open the whole way and not worry about enough "gas in the tank"

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I get a tiny bit more speed out of my battery from Li Ping, but since it's inexpensive lifepo4, it seems to put out a few less amps than sla. After about 2 miles and voltage sag begins to show in sla's , then the lifepo4 is much much faster. Since the lifepo4 charges to a higher initial voltage, it starts out a tad faster than the lead, but the lifepo4 doesn't ever fall below 40v so toward the very end of a totally discharged pack, I still have pretty good speed. Only the last mile before cutout is really very slow.

One way lifepo4 can increase your speed is that it is lighter, allowing 48v to be carried easier. So if you are running 36 now, a 48 lifepo4 will be a big improvement. If you buy too small a battery, the amps the battery can supply will be small, and that will make the lifepo4 slower than lead. Either a 36v 20 ah or a 48v 20 ah will have plenty of range for you to make your commute one way with lots of juice to spare, extending your battery lifespan. The 48 may go both ways depending on your motor and controller.

dogman said:

One way lifepo4 can increase your speed is that it is lighter, allowing 48v to be carried easier

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How light something is really only affects acceleration, everything else being equal(Like cross-sectional area). However, I'm actually lying. What's accurate is that it only *noticeably* affects acceleration but it might affect your top-speed by .1% or something, but you won't notice that and neither will the average bike speedometer. The reason is because weight alone doesn't effect wind-resistance, the thing that limits an e-bike's top-speed. However, more weight will cause more surface-area contact on the tire touching the road which will increase the amount of "rolling resistance", but a 10-pound increase on a 240 pound rig would only increase rolling resistance by around 4% and rolling resistance makes up less than 10% of total resistance with an average e-bike's top speed(Even less so as speed increases as rolling resistance is linear to velocity whereas "wind resistance" is quadratic.).

Should have said, can carry 48 volts easier than the 36 volts sla you are used to. The implied increase was for increasing the voltage. The original poster was allready at 48v, so that doesn't really apply to him. I found 48v sla impossibly heavy to carry except in my trike, which proceeded to break a lot of spokes. Sometimes I should just type a few more words to be more clear. The lighter weight did really increase my top speed up big hills, but otherwise, no noticeable increase. I think acceleration from a stop was better with sla's , because of the type of cells in a duct tape battery.

The main difference in speed with lifepo4 is that the speed you start out at will last many miles. My sla's would be fast for only about a mile, then slow to about 4mph slower for several miles, and by the time you used 70% very slow. Lifepo4 doesn't slow much untill about 90% discharged, and then it just goes from 20 mph to 0 in about 1/2 mile.

I definately noticed a speed improvement in several ways. I was at 48V 12AH SLAs and I was averaging about 20mph for my 13.9 mile commute. My top (fresh off the charger speed) was about 25mph but I could only do that for a few miles. I also have this huge hill near the end of my commute and I could barely do 7mph up that hill. This made my commute about 40minutes. The biggest issue was I had to really throttle back to avoid zapping the batteries completely before I got to work. I had to walk the bike up the hill several times pushing >40lbs of lead. That really sucked.

When I went to Ping LIFEPO4, my average speed went up to around 23mph. I could really hold the top end speed of 25-27 with no problem (about 400watts of continous power), but I did get some really warm batteries doing that. I was using about 5.6-6.0AH to get to work each day. Climbing that big hill was done at about 9-10mph. My commutes regularly took about 35minutes. Sometime I'd hit the LVC while climbing the big hill.

Finally, I upgraded to a 48V 10AH BMI pack. That battery is insanely more powerful. Now, I really do hold the throttle wide open all the way and never worry about voltage sag or overheating. The packs a couple pounds heavier than the ping pack (about 22lbs) much much lighther than lead. I average more than 27mph on my commutes now and can make it in 30minutes! My top speed on the flats is about 30mph. Climbing the big hill is now done at full throttle (the controller limits me to 20amps) and at a speed of > 12mph. I've actually seen locals gasp as I fly up the hill :lol: I'm thinking about upgrading to a faster motor because now I use only about 50% of the batteries capacity on my commute. I figure a faster motor could use more power and add even more speed. BTW, anyone got suggestions on a faster more power motor and controller than my currend WE BL-36 that could give more speed at a cost of more current?

My 14.5 mile commute took 55 minuites on the downhill leg on the sla's, and now it takes 45 on the lifepo4. So yeah, even without much increase in top speed, the average speed is up a lot. That last mile, on the last watt of the sla's was slooooow.