Electric Bikes - 24v Vs. 36v

Ok guys...help me out here...I see and hear alot of people using a 36v system. It appears to be more popular as compared to the 24v....Why is that? More speed? I think (correct me if I'm wrong) given the same ah, the cost is more expensive for 36v batteries weather it be a sla or LiFePo4...correct?

For a new guy like me who would like a cheap entrance into an e-bike experience why shouldn't I go with a 24v system with sla battery and then, at a later date, up-grade to a LiFePo4 battery? Would I be disappointed with a 24v system? Also is it difficult to swap out batteries from sla to LiFePo4, weather it be 24v or 36v?

Finally does a 250 watt bl motor work as efficiently as say a 600 bl? Is that a consideration to be looked at also when deciding which system to use?

Thanks!

Ok guys...help me out here...I see and hear alot of people using a 36v system. It appears to be more popular as compared to the 24v....Why is that? More speed? I think (correct me if I'm wrong) given the same ah, the cost is more expensive for 36v batteries weather it be a sla or LiFePo4...correct?

see below


For a new guy like me who would like a cheap entrance into an e-bike experience why shouldn't I go with a 24v system with sla battery and then, at a later date, up-grade to a LiFePo4 battery? Would I be disappointed with a 24v system? Also is it difficult to swap out batteries from sla to LiFePo4, weather it be 24v or 36v?

It totally depends on the system. It's a mistake to assume that the voltage alone tells you anything about the system's behavior. For a particular motor, higher voltage almost always means higher top speed, but it's possible to design excellent e-bike motors for use at 6 volts or 200 volts.

The number of watts determines the power of a motor, and watts equal amps times volts. (so two different motors may behave exactly the same when one is rated as 24volts30amps and another is 36volts20amps; both are 720 watts.)

A typical 250 watt brushless motor probably won't do what you want if more than one of these things is true:

you want to go up hills without pedaling
you want to go up hills that would be very difficult for you to ride up without a motor
you want to go faster than 20mph
you want to go faster than 12mph without pedaling
you are heavier than ~ 160 pounds
you want your e-bike to feel more kind of like a moped/motorcycle in terms of power

A 600 watt motor is sufficient for most e-bike users, unless what you really want is something that rides like a light motorcycle, or carries a very heavy rider up a very steep hill.


Finally does a 250 watt bl motor work as efficiently as say a 600 bl? Is that a consideration to be looked at also when deciding which system to use?

Your efficiency will depend on whether your motor is suited to the task at hand. A motor that is too powerful waste a lot of energy spinning its own magnets/electromagnets past each other. A motor that is under-powered will waste energy if, when you run it at full throttle, it is still not able to reach its range of ideal operating speeds (at least ~50% of the speed that the motor turns with the wheel off the ground). Ideally you'll have a motor that will be running at about 80% of its maximum no-load (wheel off ground) speed most of the time.

Cerewa was very thorough and accurate in his post. Yes a 36v battery will cost more than the 24v, and the 250watt motor will not be great for going up hills. But you live in Kansas and there aren't that many hills so a 24v battery mated to a 250watt motor might be sufficient for you. It won't feel very powerful, it will just feel like that a very strong tail-wind is helping push you forward all the time. ;)

Yes a 36v battery will cost more than the 24v

... a 36v battery with the same number of amp hours as a 24v battery usually costs about 50% more.

But it also stores 50% more energy (meaning 50% more range [miles] or 50% more power [ watts ]).

Ok...now my question has become...say I go for a 36v with say a 600w bl motor, would it be safe to say that a SLA battery pack with 36v w/12ah would have about 1/2 the life span of a LiFePo4 set up with the same numbers? Or would it be even less?

I guess I'm asking which set-up is the biggest bang (best value) for the buck?

Also are most dealers on e-bay reputable?...or do you guys know someone you'd suggest that is forth right (honest)? Like most...I'm not a big fan of getting ripped off, even more so when dealing in areas that I'm not well versed. Seems alot of this "stuff" is coming from China...trustworthy?

One last issue, if I go with SLA can I change it out, down the road, with a LiFePo4 w/o difficulty?

Thanks!

Yeah this guy cerewa is an expert on these ebikes i always appreciate his very useful input on all t ahese topics he seem to know it all (Big shout out to Cerewa! :thumb:) Okay imo the best way to get into the ebike world would be to buy a Ezip(about $300) and get a lifepo4 from ebay-people like ping batteries i heard were trustworthy. Ive been checking out sellers and prices out there and there is a guy on ebay screen name "Volgood" who has excellent prices on these batteries but dont know how safe it would be to buy from him but i suppose if u use paypal u should be fine.

My first experiment is going to add a 6v - 7ah sla battery to my currie pack to get my bike up to 17-20mph without any assist from me.Its the cheapest,lightest and most easy to do-for a quick burst.oiThen i think im gonna buy a lifepo4 battery from "Volgood" (24v-15ah) for under 200 bucks!!

The "Duct Tape" batteries from China on e-bay are advertised as LiFePO4, but they are inevitably LiCO or LiMn if you are lucky. They are not as good at producing high current levels, but they cost half as much and they are better than SLAs.

Also, the motor output power will not exceed the input power no matter how high they are rated. The max input power is the pack voltage V times the max controller current A, and the max output power is V x A x E, where E is the efficiency.

The "Duct Tape" batteries from China on e-bay are advertised as LiFePO4, but they are inevitably LiCO or LiMn if you are lucky. They are not as good at producing high current levels, but they cost half as much and they are better than SLAs.

I agree and am certain that many of those companies could easily be cheating us because sometimes their prices are extremely low. Ebay is an extremely competitive field and seeing such a wide range in prices is a sign that something is not normal.

At least we have a one trusted name on ebay (pingping227 (http://myworld.ebay.com/pingping227/)). Across several message boards, everybody seems to be satisfied with their work... for me personally it's also because somebody looked into their construction and they use the prismatic pouch cells that make the pack the lightest and smallest possible. The few people who have had issues with their packs have had their issues taken care of by ping under the warranty so communication is present as well.

Even Green Cycles (http://www.green-cycles.com/battery.htm) (located in southern california, not china, lol) take the ping packs, create an acrylic enclosure with the power plug/charging ports built into it and sell them for just a little bit higher than the raw-ping pack, but it looks like a much nicer finished looking battery pack. :love: If one doesn't care to figure out how to wire-up their raw battery pack or doesn't like the look of duct tape, I would say this would be a good deal too.
http://www.green-cycles.com/images/battery/AcrylicWeb_th.jpg http://www.green-cycles.com/images/battery/SideWeb_th.jpg (http://www.green-cycles.com/images/battery/SideWeb.jpg)

just a remind, maybe couldnot calculate the power by voltage x current, say 36v/20ah is 720w, this will be decided by the motor efficiency, most bl motor's efficiency ranges from 60% to 80%, by the peak power the efficiency is normally 60%--70%, so the actual power is only 720w x 0.6 (or 0.7) =400w--500w.

Another point is the max current your controller could handle, it makes no sense to use a battery with bigger max current than that of the controller.

The advantage of LIFEPO4 is very obvious.

OK, now I've got a question for you guys with the knowledge. Will a bigger volt system with bigger wattage (36 V Bionx kit vs 24 V Bionx kit) give me more torque?

I've been struggling with the start up from a dead stop and with the grinding up the hills. My knees are officially late stage arthritic. I'm OK with the smooth pedaling. I'm just suffering in the push-hard moments. Will more Volts and higher wattage help with this?

by a same current 36v powered motor will give you more torque than 24v motor does, if this 2 motor are with same technology & structure.

It all comes down on your riding experiance..the terrain..
the weight of the rider added to the weight of the BIKE..
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I have a 24-volt Scooter..at 500-watts is quite able..
I walk it up hills..
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I'm moving toward a 48-volt system..I want to build my own from scratch..
I want a 1000-watt Motor..
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Use your 24-volt..but make the move UP..
on your NEXT--EV.