Controller seems to be dropping power- commom problem?

Discussion in 'Electric Bicycles' started by professor, Mar 9, 2010.

  1. professor

    professor Active Member

    On this bike, I went with the 450 w scooter motor, 500 w controller/twist grip throttle. After about a 1/2 mile the bike slows down gradually, even though the alternator output (right to the batterys) shows over 27 volts.
    If I roll the throttle back and quickly jam it on full, the bike surges ahead. But again, slows down.

    Today, I put the meter onto the output of the controller to the motor and I can see the voltage drop.

    Is there any likelyhood that the twist grip throttle is doing this or for sure it is the controller?

    I went with the controller rather than a simple on/ off switch, after not reading of much in the way of problems with them.
    The other bike is only 250 w and has quite a kick when the on/off switch is energized. I thought it would be good to lessen the (likely)more violent start on this bike by going "Normal".
    Any input before I rip these electronics out?

  2. ibdennyak

    ibdennyak Guest

    Interesting conundrum. I'm not familiar with the electronics in a brushed controller, but my 500 watt brushless hubmotor would do something similar. It would scurry up to about 20 and then stabilize at about 18. I was happy that it would move at all, so I just attributed it to something like a *governor* effect because some places state a top speed of 20 mph. Be interesting to see what results you come up with. In my case I could feel a definite surge of acceleration, and then a lull before it stabilized.
  3. AussieSteve

    AussieSteve Active Member

    Sounds like it might possibly be temperature-related. How warm/hot is the controller getting and does it have internal temperature protection? Might need a little more air flow.

    The twist-grip, (hall effect?), throttle will usually output 0-5V, so you should be able to test it with a DMM to ensure it's reaching maximum.
    Last edited: Mar 12, 2010
  4. professor

    professor Active Member

    Not likely to be temp related, was still in the 40 something dergees F here (spring IS coming ) and I only went for a mile or so.

    I am now thinking of a simple on/off switch.
  5. safe

    safe Active Member

    Cold batteries can deliver current at high levels for short periods, but then they "sag". The odds are that this will clear up when it gets up to about 60 degrees.

    I know on my own bike that temperature has a powerful effect on performance and higher temperature is always better.

    So it is temperature related in that it's too cold still.

    Electric vehicles are a terrible idea for cold climates.
    Last edited: Mar 12, 2010
  6. AussieSteve

    AussieSteve Active Member

    I forgot that you guys are at the other extreme right now - you're getting 40F while we're getting 40C.
    As safe said, that's pretty cold for batteries.

    I'd keep the controller. A simple on/off switch wouldn't allow you to 'idle' along slowly if you wanted to. That's one of the things that I love about my electric - I can tootle along at less than walking pace when shopping.

    A test with the on/off switch, though, would allow you to test the theory. See if it still slows after 1/2 mile or so.