regen on electric bikes

[tomasguit]

Hi, i would like to ask a question that is bothering me a lot..
Is it true that if you want to have regen on your bike the motor will be making resistance even when its off and how big is this resistance? Is there any way to avoid it, for example why not use synchronous motor with electromagnet (rotor excited??) im not sure how it is called in english. It would be great if you can adjust the strenght of braking by excitation of electromagnet. Is it possible for such small motors to have electromagnets in it? Or is there another way how switch of motor if you dont need it and just cruise without resistance?

 

[striider]

Regen functionality uses the permanent magnets in the motor to generate current (small amount) back into the battery upon braking. Usually, it is only enabled when the brake levers are engaged, which signals the controller to enable regen. There is no increased resistance from the hub, other than "cogging", as long as you are not on the brakes. The Adaptto controllers have the most aggressive and adjustable regen, which is what I think you you are talking about.

 

[dogman dan]

I think he is talking about cogging though.

For most well built direct drive motors, cogging at 5 mph is hard to even detect. You do feel something, but that is mostly just the weight of the motor, 15-25 pounds depending on the motor.

But as you increase speed, that cogging is felt, and the more speed the more it's resisting. It's very difficult to pedal a dd motor to 20 mph compared to a geared motor. Really fit guys can do it, and may even enjoy the extra resistance for the exercise. And, this extra resistance as speed builds up can come in very handy on a big long hill, like descending a real mountain, on a bike with no regen enabled.

But happily, if you need to ride motor off to make extreme range, there is an incredibly easy solution. Ride with just a tiny tickle of power. Crack the throttle a hair, and you can ride with 50w being drawn. At that rate, you could pedal for two hours and use only 100 watt hours. This is a tiny fraction of a larger battery, like a 1000wh 48v 20 ah pack. So don't fret about using a DD motor to ride very long ranges. If you want to really stretch it, just ride at very low power. If you ride with just a moderate assist of 200w the whole ride, you will get 5 hours of ride time from a 1000wh pack. At about 15 mph, that means 75 miles of range.

 

[tomasguit]

Thanks a lot for answer!! Do you have personal experience with it?? Would it be for example possible to set zero possition of throttle to some minimal power where you dont notice any resistance or it is more complicated and depends on certain speed?

 

[MadRhino]

Typically, those who want to pedal without resistance are using geared hubs. With a DD you always have some spinning resistance from the motor magnets, best is when unplugged.

Regen is another story. The more regen current produced, the more spinning resistance. That is making a very good braking assistance, on bad surfaces especially. I use powerful regen with an independant switch close to my brake lever, as emergency braking assistance. Many are using regen to brake all the time, with a switched brake lever.

 

[dogman dan]

I have a ton of experience, on road, off road, commuting, hauling cargo, trekking, racing. And I live in the mountains. I can ride ten miles from my house, and do a 2000 ft climb. So not a whole lot I haven't done, except a tadpole trike.

Oh yeah, not knocking regen for additional braking at all. I found coasting took me farther after a big hill than the power I'd get from regen. But if there is a stop sign at the bottom of that hill, why not grab a few wh back with a regen stop? Regen is great for saving your brakes for less need to adjust or replace pads.

Regen does require superb torque arms, I stopped using it on the bike I had it on, simply because my torque arms on that bike were not so great. I kept having to re tighten my axle nut, and got tired of it. I'd love a more variable regen, like a 3 way switch on it or adjustable pot. But that wasn't an option on the stuff I have right now.

To get to that perfect sweet spot, eliminating cogging while not using up much additional power, you really need something besides a bare throttle. Displays with 5 power choices work great, and lots of kits have that now. Level one is like literally no more than 50w on the E-bikekit brand. Also good, just a three way switch. I'm not sure if level one is quite so low with those. And even with either one of those throttle limiters, nothing beats a cycleanalyst, or other watt meter. Even a stand alone CA will allow you to see when you are pulling 20w and when it's 75. If you need the range that desperately, you can ride along staring at the CA and keeping it low.

But if you do have a CA, you can do better than that, and plan your ride from the first foot. When I need 80 mile range, I know exactly what the wh/mi average number is, that I will need to make it to the next town. No plugs, no water, no help between towns out here. So as I leave the house, I can do some simple math, and then go ok, I need 25wh/mi for this trip. Or whatever.
Then about halfway, I can make adjustment. Oops, it was windy, I'm halfway and doing 28 wh/mi. No worry, slow down by 2mph, and I'll soon be back on my number, knowing I'll make it.

This way, I work, but not harder than I have to. Plenty of work going 80 miles, even if the average is 250w of assist most of the ride.

 

[Cephalotus]

But as you increase speed, that cogging is felt, and the more speed the more it's resisting. It's very difficult to pedal a dd motor to 20 mph compared to a geared motor. Really fit guys can do it, and may even enjoy the extra resistance for the exercise. And, this extra resistance as speed builds up can come in very handy on a big long hill, like descending a real mountain, on a bike with no regen enabled...

Depends on the motor type.

Cogging on my BionX PL and SL Motors (with their built in 48V 30A controllers) is comparable to a hub dynamo (+with lights active), so at 20mph the resistence is somewhere between 5W to 10W (estimation!), this is not nothing, but will cost you maybe less than 0,5km/h in speed. To me this is acceptable.

I have no experience with more heavyweight / powerful DD motors...

 

[Dave Sloan]

With a new DD motor on a bike it appears that there is resistance. This is probably not due to the brake regen but that the bearings are still tight. After about 1500 miles on my bike I noticed less resistance when coasting. My controller was programmed for regen when I first got the bike and I found it useful when going down gravel hills. It did not increase the battery life by any appreciable amount and I eventually disabled it in the controller. I would rate regen in a controllers usefulness at about one out of ten. Loose bearings will give more mileage as it consumes between 10 to 20 watts depending on speed = I have measured it on my 500w E-bikekit hub. I even thought that it may be wearing out so I bought a backup second. Well 6500 miles later it is still smooth with even less resistance - I have replaced alot of other pieces - including one spoke at 700 miles. My take on regen is that it is better to get used to the regular brakes for control purposes and work on other ways to get the bike efficient. And if people ask - which they often ignorantly do - does it have regen = say yes : just do not tell them that it is turned off.

 

[wesnewell]

Hmm... I've got about 15K miles on the bike I ride most and i wouldn't go without regen braking. The resistance is minimal and can be brought to zero by setting the throttle level to the speed you want and then pedaling up to the no load speed of the motor. This will also extend the range of battery considerably. And while regen braking doesn't recharge your battery a lot, it certainly makes braking a lot easier and stronger. I've never worn out my brake pads since using it.

 

[rsilvers]

Hmm... I've got about 15K miles on the bike I ride most and i wouldn't go without regen braking. The resistance is minimal and can be brought to zero by setting the throttle level to the speed you want and then pedaling up to the no load speed of the motor. This will also extend the range of battery considerably. And while regen braking doesn't recharge your battery a lot, it certainly makes braking a lot easier and stronger. I've never worn out my brake pads since using it.

Does someone know how many extra watts you need to pedal a DD bike that is out of power and you unplug the battery vs a bike with a geared-hub for a given speed?

 

[Cephalotus]

typically my regen rate is around 10-20%, but can be has high as 30% if you use modest motor power in a hilly terrain. Brake wear is down by around 80-90%

On my speed pedelec (45km/h) regen rate is only 3-5% and brake wear may be reduced by just 50-70%...

I like regen a lot, but many DD+ controller systems can't do it well.

 

[Cephalotus]

Does someone know how many extra watts you need to pedal a DD bike that is out of power and you unplug the battery vs a bike with a geared-hub for a given speed?

Depends on the speed. On my BionX bikes I would say the DD takes 5-10W at 30kph, less at lower speeds, more at higher speeds.

As a rule of thumbs it will cost you maybe 0.5 km/h in speed.

There are DD system witch much higher resistance.

Resistance of gear hubs depends on the hub and your pedal power, but not on the speed. It could cost maybe 5%, so if you pedal with 200W it would cost you 10W compared to a new or well serviced chain drive train in an efficient gear...