What is the best motor for regen braking?

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twist
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What is the best motor for regen braking?

Post by twist » Jan 03, 2018 8:22 am

Hi everybody and happy new year,

this year I planing a 10000km ebike tour from Spain to Sweden (and back) and will be modifing my bike a lot.
2016 I already did a 5000km ebike tour from UK to Spain with a Surly Big Dummy (https://www.instagram.com/opendocumentary/) with a BBSHD and after around 3000km the controller broke. So I had to bike around 400km without motor (till I got a replacement BBS2) with a total weight of maybe around 150-200kg (most of the luggage is camera gear) and that close to the alps.

So for this tour I will be changing a few things:
300w Solar Power
At least one brushless hub motor (for using regen a lot)

My main goal would be to use regen a lot because on the other tour I was really bushing the breaks to the limit and I want to have 2 motors so that I have one as backup.

So what would be the best motor for regen?
Better 48V or 52V setup?
I don't have to go fast with my setup! I have to go far :)

I will be going with the Phaserunner (http://www.ebikes.ca/shop/electric-bicy ... unner.html) as a Controller.

Was thinking of going with the GrinHub (http://www.ebikes.ca/shop/electric-bicy ... ub-sl.html) but not sure if that one is strong enought for my weight (because of Bearing Size and Life) and it is also killing my budget :)
But what version would be better for regen (12.5 or 10.5 or 8 rpm/V) ?
Or what about the MXUS Rear Hub MotorMX3006RC (http://www.ebikes.ca/shop/electric-bicy ... 006rc.html) ?
Or is there a better option for efficency + regen?

Maybe I will be keeping the BBSHD but not sure.

Thanks for your help!
Chris
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dogman dan
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Re: What is the best motor for regen braking?

Post by dogman dan » Jan 03, 2018 10:25 am

Well, the best motor for regen power on braking will be a big one. More magnet, more resistance when in regen.

But my touring experience says that even smaller DD motors, like the 9c, or even cheaper clones will still give you at least enough additional braking to get down the big mountains with out scorching your regular brakes. I live in the south end of the rockies, and have ridden some big mountains loaded for touring.

I would lean towards a front motor though, because you are loading up the rear wheel with a lot of torque already. Sometimes a mid drive will twist the freewheel right off the motor cover. Your bike is fine for a front DD motor, so go with the larger crystalyte motor in a front version. To avoid drag from the dd, run the front motor all the time, and then goose it to higher speeds up the big hills with the mid drive helping. Climb at 15 mph, and all will be well with DD motor heating.

On the other hand, if you do plan to run mostly on the mid drive, then you want the 9c type motor, because it's known to have a very low cogging resistance. You won't want the big magnets unless you power them 100% of the time.

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Re: What is the best motor for regen braking?

Post by amberwolf » Jan 03, 2018 2:27 pm

The "best" motor for regen may also be the worst motor for efficient riding, because it may have more resistance to turning with no power applied (because it generates a higher voltage at the same speed as a different motor, inducing a higher current in the windings, creating more drag).

You also have to have a controller capable of dealing with the regen currents needed, for the lengths of time needed, without overheating or exceeding it's voltage ratings. I don't know what the Phaserunner's capabilities are in this.

And one with variable-level-braking, because it sucks to have really powerful regen that is only on/off. :( You can get used to it and learn how and when to use it, but it takes a while, and may result in some crashes while learning on a bike (less likely on a trike). THe Phaserunner does have variable braking available, AFAIK.


The battery also has to be able to handle the incoming regen currents, too. Since you're charging it with regen, you'd be best to find a battery that has a BMS that charges and discharges thru the same port, so the BMS cna protect the battery from overcharge, and from too high a charge current.

Regen won't work very well when the batteyr is at or near full charge--the BMS *should* disconnect the battery from the system when regen starts to overcharge it, but this means you now no longer have power to the bike *and* you have no braking other than mechanical, so if you are depending on that regen braking at that moment, or right after braking you needed power to accelerate, you're screwed. You can choose to never have the battery near full, never charging it to the top, to leave room for regen charging, but this means having to have a battery that is just that much bigger and heavier to do the same job as if you were fully charging it, just to get the same range out of it.


For the best range and efficiency I'd go with a non-regen motor, like a geared hub or middrive, and just have more than one brake on each wheel, if just the one brake on each is already very good but simply not enough. If you already have disc brakes, add rim brakes. If you already have rim brakes, add disc or drum or roller brakes at the hub. Or add a second set of rim brakes on the other side of the fork / stays like I did on the front of SB Cruiser. Carry extra pads for them if you wear thru them quickly.


If you really need the regen, motors with a wide stator and magnet rotor should provide more braking (and acceleration) than a narrower stator/rotor all other things being equal. But they will be heavier.


Different turn counts (windings) of the same motor will also give different regen levels, for the same battery voltage, because at the same speed the (IIRC) higher turn count will produce a higher voltage than a lower turn count.

YOu can't directly compare different motors with different turn counts, though--you'd have to see what each one does under the same conditions. http://ebikes.ca/simulator can be used to see acceleration with different configurations and motors, which will imply the braking (deceleration) under the same conditions, as long as the controller allows it.

twist
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Re: What is the best motor for regen braking?

Post by twist » Jan 03, 2018 4:48 pm

Thank you for the help!

After looking at the MOTOR SIMULATOR from Grin and reading your advice I think the 9c+ Front 2707 (http://www.ebikes.ca/m2707fd.html) would be a good choise for me and keeping the BBSHD but with the Phaserunner as a controller.

I will be also thinking about adding maybe one or two V-Brake to my Disc-Brakes. :)

Is there also a version with 8 turns of the 9c+?
Grin doesn't have it in stock ... any other stores?

Thanks,
Chris

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dogman dan
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Re: What is the best motor for regen braking?

Post by dogman dan » Jan 04, 2018 9:18 am

E-Bikekit, where I used to work sells a 9 turn version of a very similar motor. Its the "trike motor" on the website. Comes only in the front version. (They used to stock it in rear, but don't at this time)

It will be more suitable for use at lower speeds, with a 48v speed of about 20 mph, and less of course, loaded down hard. But the lower rpm motor would be capable of getting up hills without overheating, at closer to 12 mph than 15 mph. So better for long grinds up a mountain with the load. I don't think it will regen less than a faster version. However, it will reach a point not in regen, just cogging, that limits your speed on downhills. Lower rpm motors reach strong cogging at a lower rpm. So that 9 turn motor limits your speed just coasting, more than a 7 turn motor. The faster the rpm, the more a dd motor cogs and resists, even if not in regen. Resists much more in regen though.

You might find that just that effect alone, may enable you to use up your brakes less. Personally, I run a large crystalyte motor on my cargo bike, and it limits my speed enough on down hills that I no longer bother with regen. I can hit about 35 mph max. When I want a bit of help braking, I just get off the throttle. When I need to coast, I just give a tiny crack of throttle, and the cogging vanishes. Just one of the things that can be cool about a DD motor.

It will of course need the help of the mid drive, to get up big mountains with big loads, and not overheat. ( the trike motor I mean) Just keep it going 12-15 mph up those hills by adding enough mid drive power to get it done.

800w continuous from each motor should do it, based on my riding in the rockies with a loaded cargo bike. 400-600w plenty on the flats, so just run the front motor then.

twist
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Re: What is the best motor for regen braking?

Post by twist » Jan 05, 2018 3:09 am

Thank you for your great input!

I now ordered the 9c+ Front 2707 and the Phaserunner and hope that non of my motors break on this tour :)

I was in contact with Justin from Grin and he tryed to explain to me the difference between the 9c+ 2707 and 9c+ 2706 when running with the Phaserunner and he said the only difference is that
one is wound with a KV of 10.5 rpm/V and the other ~9.1 rpm/V.
The 2707 also doesn't have more torque at lower speeds and that was what I was thinking?!

Justin:
The motor efficiency's are also identical, changing the winding does not change the efficiency of the setup, it just changes the phase current needed for a given torque, and correspondinlgy the pack voltage needed for a given top speed. But the battery currents and battery power will be identical for the same riding conditions.
I just don't want to bother Justin anymore :)
But can somebody explain me again the difference?
I can go faster with the 2706 and thats it?
So where are the benefits of the 2707?
What influence has the Phaserunner on the torque?

Would be great if somebody could shine a light for me :)

Cheers,
Chris

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dogman dan
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Re: What is the best motor for regen braking?

Post by dogman dan » Jan 05, 2018 8:58 am

I don't understand motors near like Justin. But he is right, the slower motor will pull exactly the same at 0 rpm, same torque.

However,, and this is where I get my ass jumped here, as you go from 0 to 10 mph, I think there is a big difference. And its not what you might think. As a motor gets closer to its max rpm, back EMF increases, casuing the motor to pull less hard. This happens sooner, or at least at slower rpm, with the slower motor. So some will claim the fast motor pulls harder. And indeed, you will see it pull more watts longer with a wattmeter. So the fast motor pulls more torque longer? Yes, sort of. Watts does not measure torque, and the fast motor will make more heat till it gets up to speed. So what is really happening?

Some will, by seat of pants feel, swear the slow motor pulls harder. It does not at 0 rpm. but at say 80 rpm, it may waste less wattage at that moment, and actually feel like it pulls harder. Its not more torque, but if given equal watts, the slow motor does have less wasted watts at slower rpms. So this is why some say the slow motor is the high torque model. But,, because of back emf being different, its kind of impossible for the two motors to actually pull the same watts at a given rpm. Very hard to make a true statement at any rpm other than 0 rpm then. ( they should also pull equal, at equal rpm relative to the max though) The bottom line is basically this, if you will be riding at low speed enough of your ride, then a low rpm motor will waste less of your batteries watt hours than a fast rpm motor. But only at low speed and only if the load is high. If the load is low, like flat ground, the waste is less. And riding slower, of course tends to be more efficient simply because wind drag decreases.

And to confuse the issue even more, if you have a big motor, it accelerates so fast any differences like this become meaningless. The big motor simply blows past that inefficient rpm so quick its not costing you any heat, or lost watts. If your motor wind rpm is high, then more power solves a lot of the efficiency issues. Except for drag from faster riding of course.

Too many variables, my brain is about to explode now. :roll:

Why you want the slower motor is so you have a slower top speed, for whatever reason. For example, adult trikes need to stay below 15 mph, or you can't really steer them anymore. 8 turn, 9 turn, etc are slow in that type motor IMO.

Or, if you will be overloaded relative to your power, such as a 700w setup on a 400 pound bike with rider and or trailer. Then the slow motor will overheat slower, climb a steep hill longer without overheating, and work better than a 6 turn motor in a big wheel. The solution to all problems is a smaller wheel btw. When I wanted a lower power bike still able to tow a trailer up a serious mountain pass, I built this.
Finished cargo mixte..jpg
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This bike has the 9 continent type 500w rated rear motor, in the 9 turn version. Top speed 18 mph, but able to climb a three mile long 6% average grade at 400 pounds weight. Some of the benefit was the wind, but much more from the 20" wheel. At the top, the motor was warm, but not even close to hot. The weather, 105 F. No, not more torque at all, but able to tow a lot more weight up that mountain than the same motor, in 7 turn, in 26" wheel. That setup does make it to the top without melting the motor, but the motor is right at its limit at the top. One more mile would cook the motor with the 26" wheel.

This is why I say keep it moving 15 mph. With the 7 turn motor in 26" wheel you can climb more or less infinitely at that rpm, but less, as in the case with my test, (13 mph up the hill with 26" 7 turn motor and 400 pound weight) and you will hit a limit in length of climb. Rider only, and 300 pound total weight or less, no problem with the hill. Just a problem with only 1000w into a single hub motor, and 400 pounds.

With your mid drive and the 7 turn motor, you should easily be able to feed your bike 1500w continuous, and keep it up to 15 mph. With more power, you should not have any issues with the dd motor overheating.

Additionally, with the mid drive you can choose to climb only on the mid drive. Go slow as you want in the lowest gear, and just give the hub motor enough power to eliminate the drag, about 50w. You will need a watt meter on just the front motor of course, to know what is going on up there.

twist
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Re: What is the best motor for regen braking?

Post by twist » Jan 05, 2018 10:13 am

Thanks dogman dan for your infos!!! :D

Love that bike ... what kind of stand are you using? :)
On my last tour I broke 2 stands (https://www.instagram.com/opendocumentary/) :roll:

Now I'm still a bit confused but a little bit smarter :)

I have orderes 2 Cycle Analyst and 2 Phaserunner Controller and so I can messure and controll the power of the front and mid drive motor in the best way.

On my last trip (ca. 3100miles / 5000km) I just had the problem that the controller broke and I had no replacement. So I had to bike 250 miles / 400km without motor and that in a really hilly area. So with a weight of around 400 pound / 200kg I could not bike up the hills at all (maybe 2min and the I had to stop and push again). On the flats I was fine without the motor.

So this time I will be installing a 14 gear Rohloff internal hub in the back to have lower gears and install a front hub motor that should also be able to move everything (even when the mid drive brakes) up a hill. So I chose the 2707 for that task and for regen (to save on the brakes). Still not sure if it maters if I get the 2706 or 2707 but there are also not really that different :) for now the 2707 is on backorder :lol:

Cheers,
Chris

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