Help with electrical questions.

Discussion in 'Electric Bicycles' started by motorbikemike45, Aug 15, 2010.

  1. I'm looking at an e-bike kit and I have some questions. In the kit I'm considering, the rear hub wheel offered is used with either a 36v(750w) or a 48v(1000w) battery pack. Since The 48v 1000w appeals to me for the slight performance increase(20mph at 36v vs. 26mph at 48v), how can a motor be used at two voltages? Wouldn't putting 48v into a 36v motor cause it to run hot and shorten it's life significantly?

    Next question concerns the battery pack. Which is better for longer range and higher torque for climbing the occasional fairly steep but short hill? Choices are, LiFeP04 36v 9.5ah, LiFeP04 36v 10ah prismatic, or a LiFep04 48v 9.5ah. Just what is "prismatic" all about?
    Last edited: Aug 15, 2010

  2. wineboyrider

    wineboyrider New Member

    Yes, the motor will get warmer/hotter at higher voltage. But, how hot it actually gets depends on how hard, long, fast, and uphill you run it. You can put a temperature probe next to the motor and get an idea of how warm your motor is. I would opt for the 48v unless you want to travel longer distances than I would go for the 36v (cooler running and you can go further).
  3. wheelbender6

    wheelbender6 Well-Known Member

    Good questions. The rated watts of a motor is a measure of how much heat it can handle. Generally, the higher the rated watts, the thicker the filaments of wire within.
    There is an "intro to batteries" somewhere on the site that explains all this stuff.

    SLA (Sealed lead acid) batteries are cheaper, but last only a couple of years. If you discharge them too deeply, they never recover full strength. They are very heavy. They need to be charged regularly, whether you ride or not, or they never recover full strength. They can take six hours to fully charge.

    I don't recommend NiCad. You must fully deplete them before charging. Failure to do so will cause it to build up memory - it never recovers full strength. NiCad is OK if your bike pedals well and you don't mind some exertion.

    The higher tech batteries (LiFeP04, NiMH, etc) are light, charge quickly, and can be charged twice as many times as SLA (Double the lifetime). They cost twice as much as SLA too.

    For example, you can get three 12v/20ah SLA deep cycle batteries shipped to you for under $200.
    A 36v/20ah LiFePo4 battery pack from Ping will cost over twice that, and Ping is about the best available.
    Cheapie LiFePo4 battery packs are about half way in between for cost, but are not as well made.

    For a first build, I would probably go with SLA. When they wear out, you will have a lot of experience and can decide if you had rather get a high tech battery pack.
  4. I've heard both good and bad things about hub motors. Light, maintenance free, balanced, ease of installation/removal if you buy the wheel already laced to the hub, good for pedaling if you can install a rear cassette (I'm more interested in rear drive), and simplicity. Then on the other hand, little torque at low speeds or when climbing hills, poor acceleration, high current draw due to single speed, burn out is common due to high current draw, etc.

    I like the smaller motor that mounts under the frame behind the crank and has a planetary gear reduction as it drives the bike chain and you can use the bike's rear gears to multiply torque. The drawback for this unit is the very thin case around the planetary gear case that cracks easily. I would also be concerned about the low mount due to water (splash or driving through deep puddles) getting into the motor.

    The info on batteries is most helpful and I appreciate the help. Now any help with motors would also be helpful. I'm sorry to burden ya'll with my ignorance in the electric bike field. I know a bit about gas engined bikes, but my knowledge of electrics is woefully inadequate. I'm guessing I'll go with the SLAs until I gain knowledge. Good advice there. Putting a gas genset in a trailer for long trips would solve any problems with range. My last gas bike, a RS 35 on a GEBE drive, was stolen and I may replace it with electric since I can keep it in my living room without freaking out the fire marshals.
  5. wineboyrider

    wineboyrider New Member

    The watt rating is also relevant to your voltage. In other words a nine continent direct drive motor is rated at 500 watts at 36 v and 750 watts at 48 volts. I would go with a 9 continent kit either from or
    Trust me I have several ebikes and this is one sturdy motor. Like I said if you want to go long distances go for 36v or if you have short trips like 4 or 5 miles one way than go 48 and enjoy the ride. When you get a chance you need to check out lifepo4 batteries at
    SLA's good to start out with, but you'll want to upgrade eventually if you keep riding.
  6. wineboyrider

    wineboyrider New Member

    The two voltage is question is simple. It just depends on how much voltage your controller can handle. The e-bike kit controller can handle even more voltage if you know how to beef it up. But, you'll like it plenty at 48v for a while.
  7. wineboyrider

    wineboyrider New Member

    I have a cyclone kit a currie mountain trailz a geared hub motor and a direct drive motor bicycle. And the direct drive is my daily driver as it has the least maintenance problems. When you go through the gears you have a lot more maintenance issues.