So, how do we wire the motor to the batteries? Here’s area it starts accepting interesting.
The electronic gurus amongst you will by now be spouting phrases like ‘speed control through the pulse width modulation control of average motor current’ and stuff like that…but take a step back. Remember what was said aloft about best after-effects advancing from Keeping it Simple? (Oh, you skipped that bit – able-bodied go apprehend it again!)
There are two points to realise.
Firstly, a motor of the array that we’ve been anecdotic is basically a connected acceleration design. That is, back fed a specific voltage, it wants to circle at the one speed. Of course, as it is loaded down, it will circle added boring – but importantly, it will again additionally draw added accepted as it attempts to get aback to its ‘natural’ speed.
Secondly, in any practical electric bicycle, the natural speed of the bike (say, on the flat) will be way less than the speed limit – any speed limit!
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So let’s say that you’ve got the motor powered anon from the battery, application aloof an on/off about-face for control. The aftereffect of the accessible power, the gearing and aerodynamic and frictional drags is that back the motor is on, the bike campaign at (say) 20 km/h. No one in their appropriate apperception would appetite to go slower (and if you charge to, aloof about-face off the motor and pedal!), while back you ability a acropolis or run into a headwind and the bike slows, the motor will automatically draw added accepted and so advice you forth added strongly.
In effect, the motor self-regulates its accepted draw – demography added as added is needed, and abbreviation its burning as beneath ability is required. Hey, that’s accomplished – and all aloof done with an on/off switch!
But what about regenerative braking? Lots of electric bikes don’t use any form of regenerative braking, so in hilly areas they’re wasting plenty of power in heating the brakes - power which could otherwise be going back into the battery. So how do we make regen braking happen?
Regen braking occurs back the bike’s acceleration exceeds the ‘natural’ acceleration of the motor. In added words, if the bike commonly does 20 km/h on the collapsed and you go faster than that bottomward a hill, the motor automatically turns into a architect and the accepted flows aback into the battery, allowance to recharge it. But there’s a trick that can be employed to get regen occurring at much slower speeds: reduce the battery voltage that the generator sees!
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This diagram shows how it is done. Two batteries are acclimated with a bifold pole, bifold bandy (DPDT) about-face active to configure the batteries in either alternation or parallel. (A added about-face acts as an on/off control.) Let’s accept that they’re 12V batteries. When the batteries are configured in series, 24V is accessible at the motor. When the batteries are switched to parallel, 12V is available at the motor.
The natural speed of the electric bike in 24V mode might be 20 km/h, but in 12V mode it’s more likely to be just a quick walking pace. So aback you about-face to 12V approach aback rolling bottomward a hill, the motor tries to cull you aback to that apathetic speed. As a result, regen braking is very effective – in fact, in this example, the regen will work at all speeds down to a walking pace… at which point the 12V batteries again alpha active the bike forward.
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