Regen

General Discussion about electric bicycles.
euro2g   1 µW

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Regen

Post by euro2g » Dec 05 2019 12:55am

It's a question about Regen, I would like to add a second hub motor to the front. Is it possible and if so to make it produce good amounts of Regen current back into the cells while it isn't under throttle? Any suggestions would help me achieve my final goal. My need is for maximum distance traveled for a trip through the Oregon coast. I am an avid cyclist and do acknowledge that I will be using alot of my own assistance. Thanks alot guys

obcd   10 W

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Re: Regen

Post by obcd » Dec 05 2019 9:31am

Wouldn't an extra motor and controller add extra weight to the e-bike lowering it's efficiency?
There is a topic about regen stating that the average gain is 10% You can get peaks of 20%
If you think about continously recharging the battery during the ride, you could as well lower the power of the motor.
Regen is basically only happening when you hit one of the brakes. Otherwise cycling without or with little assistance would become real difficult.
Regen is also only usefull if you ride down a lot of slopes. Using the brakes on a flat surface won't gain you much energy.

Most geared hub motors have a freewheel option so you don't have to drag the motor resistance with you when it's no longer giving assistance. Such can't be used for regen.

AHicks   100 W

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Re: Regen

Post by AHicks » Dec 05 2019 9:45am

Speaking from my own experience, the average hub drive using an average controller, will be hard pressed to provide 5% let alone 10.

That's NOT to say higher regen rates are not possible. But I think they are highly unlikely using a direct drive hub. Regen is way more about braking power when used at speeds over maybe 15mph. Any slower and I doubt you'll be able to notice the regen is even activated.

If talking about something like a GMAC hub, now we are talking about some serious regen. Enough where you can expect to see much higher percentages.

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E-HP   100 kW

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Re: Regen

Post by E-HP » Dec 05 2019 9:48am

euro2g wrote:
Dec 05 2019 12:55am
It's a question about Regen, I would like to add a second hub motor to the front. Is it possible and if so to make it produce good amounts of Regen current back into the cells while it isn't under throttle? Any suggestions would help me achieve my final goal. My need is for maximum distance traveled for a trip through the Oregon coast. I am an avid cyclist and do acknowledge that I will be using alot of my own assistance. Thanks alot guys
This idea will decrease your range significantly.
PS. don't get me wrong. i think it's a worthwhile experiment to see the resulting data. my guess is 25%-30% decrease in range.

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danielrlee   10 kW

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Re: Regen

Post by danielrlee » Dec 05 2019 10:09am


Putting the fact that it's a bad idea aside for a moment, if you're only planning on using the second motor for regen while coasting, why not just use the existing motor?
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donn   1 kW

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Re: Regen

Post by donn » Dec 05 2019 10:40am

danielrlee wrote:
Dec 05 2019 10:09am
why not just use the existing motor?
Might not have it - geared hub, crank drive ... But the 2nd hub idea is uncomfortably close to "perpetual motion."

It has been a long time since I went out on a long multi-day trip, but I've wondered how I'd make it work with my motor setup. Extra battery, for sure, maybe some kind of foldable solar panel, but there's still a lot that could go wrong, and I guess in the end, I'd leave it behind and go on my human powered bicycle.

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Re: Regen

Post by miro13car » Dec 05 2019 11:42am

so you have geared motor on the back, right?
in your place I would rather change all drive to DD motor on the back wheel and regen with proper controller would not be a problem
I ride DD motor 3-phase , FOC cotroller ..
and guess what?
Cycle Analist do not lie.
my average as CA shows is 15% return from regen braking.
and why many forget? regen saves brake pads, brake discs
why to stupidly grind pads, rims and discs on downhills?
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john61ct   100 MW

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Re: Regen

Post by john61ct » Dec 05 2019 12:48pm

I plan to do this, but because I need the regen-braking for the braking functionality, not for gaining any energy efficiency.

Heavy tandem / cargo rig, steep and long mountain descents where regular brakes used for continuous dragging wear out quickly and can fail from overheating.

And need multiple motors anyway for the ascent side.

Seems like a bad idea for your use case though.

euro2g   1 µW

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Re: Regen

Post by euro2g » Dec 05 2019 7:44pm

Some of the comments could probably be left out, if my post was read completely "I" asked for suggestions! Money is not a problem at all. Self made. Good investments when I was young. I am however frugal, I have a big family.
I do want quality products. I've only ever purchased products from (ebikes.ca) Eliza at Grin gets me my purchases very quick.

I want suggestions! I am running the Phase runner, I'm using Hohm Tech life cells at 60v (16s7p), DD-fst rear motor. Hopefully this can help with my original inquiry. Thanks

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E-HP   100 kW

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Re: Regen

Post by E-HP » Dec 05 2019 8:14pm

euro2g wrote:
Dec 05 2019 7:44pm

I want suggestions! I am running the Phase runner, I'm using Hohm Tech life cells at 60v (16s7p), DD-fst rear motor. Hopefully this can help with my original inquiry. Thanks
Fundamentally, you're asking for suggestions on how to change the laws of physics, so it may be difficult to provide what you're looking for. Just use your existing DD motor for regen, which will recoup some of your energy.

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E-HP   100 kW

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Re: Regen

Post by E-HP » Dec 05 2019 8:24pm

AHicks wrote:
Dec 05 2019 9:45am
Speaking from my own experience, the average hub drive using an average controller, will be hard pressed to provide 5% let alone 10.
I've noticed that the higher regen is set to (better braking), the less power goes to the battery, since it ends up stopping the bike before much is produced. The lower settings give significantly more back to the battery.

AHicks   100 W

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Re: Regen

Post by AHicks » Dec 05 2019 8:28pm

That may be, but the amount actually making it back in to the battery is negligible.

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E-HP   100 kW

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Re: Regen

Post by E-HP » Dec 05 2019 8:41pm

AHicks wrote:
Dec 05 2019 8:28pm
That may be, but the amount actually making it back in to the battery is negligible.
May depend on terrain. I repeated some tests on a hill by my house. 1 mile descent, 700ft drop, 15-17% grade for the steeper sections; 1v-1.5V increase in pack voltage after letting the battery settle (2V immediately after stopping, waiting a few minutes for the voltage to settle). I normally run my pack between 57v down to 47v, so 1V-1.5V is around 10%-15%.

AHicks   100 W

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Re: Regen

Post by AHicks » Dec 05 2019 8:57pm

How did you get back up to the top of the hill?

I'm thing of regen vs. no regen on a 10 mile ride I guess. How much effect the regen will have on a battery after a 10 mile run, vs. no regen. I have little doubt your down hill run was able to do as claimed. The reality is though, you can't just figure the down hill parts of a run.

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MAXIMUM_AMPS   10 mW

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Re: Regen

Post by MAXIMUM_AMPS » Dec 05 2019 9:07pm

euro2g wrote:
Dec 05 2019 7:44pm
Some of the comments could probably be left out, if my post was read completely "I" asked for suggestions! Money is not a problem at all. Self made. Good investments when I was young. I am however frugal, I have a big family.
I do want quality products. I've only ever purchased products from (ebikes.ca) Eliza at Grin gets me my purchases very quick.

I want suggestions! I am running the Phase runner, I'm using Hohm Tech life cells at 60v (16s7p), DD-fst rear motor. Hopefully this can help with my original inquiry. Thanks
Fast-wind motors don't put out a lot of regen power. Consider swapping the motor with a lower Kv like a Crystalyte H3525.

I'm gonna work you through the math here:

Say your motor has a Kv of 10RPM/V. You can use the reciprocal of that to calculate 1/10th of a volt across the windings per RPM. So if your wheel is spinning at 300RPM, you will see 30V across the windings. By comparison, a motor with a 6RPM/V winding will put out nearly double the voltage. 50V.

The controller does some circuitry magic to boost the voltage up to 70V or so to charge your battery. Below I've linked the best/simplest explanation for a beginner, the specifics are different for 3-phase ebike motors, but the base concept is the same.

https://electronics.stackexchange.com/a/459766

With a higher voltage out of the motor, the "duty cycle" of the SW2 switch is lower, meaning you can recover a lot more power at the same wheel RPM. The circuit/motor is essentially "working less hard" to charge the battery. In addition, the lower Kv motor winding has more inductance, due to having more turns, so the voltage conversion strategy the controller uses is even more efficient, resulting in even less power wasted in SW2.

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E-HP   100 kW

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Re: Regen

Post by E-HP » Dec 05 2019 9:12pm

AHicks wrote:How did you get back up to the top of the hill?

I'm thing of regen vs. no regen on a 10 mile ride I guess. How much effect the regen will have on a battery after a 10 mile run, vs. no regen. I have little doubt your down hill run was able to do as claimed. The reality is though, you can't just figure the down hill parts of a run.
I figure since almost all my riding is on hills, so anything I get back in regen is better than nothing.
I noticed that there are a high percentage of hybrid cars owned by people in my neighborhood and more near the top of the ridge, probably for the same reason. No sense in wasting that energy after using so much climbing the hills.


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donn   1 kW

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Re: Regen

Post by donn » Dec 05 2019 9:22pm

miro13car wrote:
Dec 05 2019 11:42am
and guess what?
Cycle Analist do not lie.
my average as CA shows is 15% return from regen braking.
Actually, CA sort of does lie. It gives you the straight consumption numbers, so you can do the math yourself, but when it calculates the percentage, it's Wr/(Wf - Wr), where Wf is what goes to the motor, Wr is what comes back in regen, and thus Wf - Wr is what has to be supplied by the battery. So if you had a fantastically efficient motor that recovered every watt of potential energy on the downhill, your percentage would be infinite, instead of 100%. It should be Wr/Wf. Someone else pointed this out to me here, hope I didn't mess it up (did you have any idea how good a "paloma" style margarita is with mezcal instead of tequila? It's real good.)

Anyway, your percentage is still a lot higher than 5%, even calculated correctly (and mine too and I don't have any fancy controller), so I think your point stands, but the 15% is really 13% the way most people would see it [check my math.]

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Re: Regen

Post by AHicks » Dec 05 2019 9:54pm

E-HP wrote:
Dec 05 2019 9:12pm
AHicks wrote:How did you get back up to the top of the hill?

I'm thing of regen vs. no regen on a 10 mile ride I guess. How much effect the regen will have on a battery after a 10 mile run, vs. no regen. I have little doubt your down hill run was able to do as claimed. The reality is though, you can't just figure the down hill parts of a run.
I figure since almost all my riding is on hills, so anything I get back in regen is better than nothing.
I noticed that there are a high percentage of hybrid cars owned by people in my neighborhood and more near the top of the ridge, probably for the same reason. No sense in wasting that energy after using so much climbing the hills.


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No argument. I spend a lot of time (my winters) in a rolling coastal area. That's one of the reasons I went with a MAC recently, for the extra performance in the hills. I do miss the direct drive regen though.... GMAC has been on my mind a lot recently.... -Al

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Re: Regen

Post by miro13car » Dec 06 2019 7:31am

if you read from Cycle Analist display .
as we know CA display Forward Ah and Regen Ah .
with those AHs after my rides CA displays right %
maybe your definition of regen % is different
people posts before my post mentioned regen % , are they wrong?
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donn   1 kW

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Re: Regen

Post by donn » Dec 06 2019 1:23pm

miro13car wrote:
Dec 06 2019 7:31am
as we know CA display Forward Ah and Regen Ah .
with those AHs after my rides CA displays right %

OK, here's what I have right now, after a ride a few days ago with a heavy hand on the throttle:

(f - r) Ah: 1.994
(r) Regen Ah: 0.1784
(r/(f - r)) Regen 8.9%
(f) Forward Ah: 2.1730

... where by normal accounting (r/f) it should be Regen 8.2%

Like I said above, my definition of regen % is such that, if you get everything back when you go downhill, it's 100%, not "infinity".

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MadRhino   100 GW

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Re: Regen

Post by MadRhino » Dec 07 2019 1:57am

Adding a second motor for regen, would it be for energy economy or braking performance, will produce negative values. You will have shorter range, and longer braking distance.

Then, adding a second motor for better hill climbing performance is poor engineering because powering with only one bigger rear motor would make better performance and efficiency.

All this seem obvious to most of us ebike builders, but is repeatedly coming back in a thread once in a while. The ONLY good reason to power a bike with 2 motors is traction, because 2 powered wheels are giving a better grip, at the cost of extra weight, lesser efficiency, higher maintenance, and poor handling at higher speed.
Make it fool-proof, and I will make a better fool.
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dogman dan   100 GW

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Re: Regen

Post by dogman dan » Dec 07 2019 8:37am

It only takes about 100 miles of pedaling with heavy resistance to recharge a typical bike battery.. Or, you could just pedal 200 miles without regen on, for the same effort.

What you want is not regen. Get a planetary geared motor that won't resist while you pedal with it off. Then tow a relatively big trailer, big enough for a 100w solar panel. The panel will get you about 400 wh per day of extra range.

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Re: Regen

Post by john61ct » Dec 07 2019 9:26am


MadRhino wrote:adding a second motor for better hill climbing performance is poor engineering because powering with only one bigger rear motor would make better performance and efficiency.

All this seem obvious to most of us ebike builders, but is repeatedly coming back in a thread once in a while. The ONLY good reason to power a bike with 2 motors is traction
Assuming gearing.

If using DD hubs only, 2 motors will enable torque for loads that no single existing motor can handle.


donn   1 kW

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Re: Regen

Post by donn » Dec 07 2019 9:46am

dogman dan wrote:
Dec 07 2019 8:37am
What you want is not regen. Get a planetary geared motor that won't resist while you pedal with it off. Then tow a relatively big trailer, big enough for a 100w solar panel. The panel will get you about 400 wh per day of extra range.
That might be an interesting idea, particularly if you're already carrying enough to make a trailer load.

What do you think, though, about the story that if you feed the motor enough to overcome the core resistance, you'll come out way ahead at the end - i.e., regen is not just positive, it's a net positive counting core loss on a typical ride?

I wouldn't bet on a direct drive hub motor for touring, normally. It's the worst situation for an electric motor, so you'd want something that's less of an encumbrance when it stops being useful, and that isn't a direct drive hub. But that trailer might be enough to keep it in the game, too early in the morning to think about the math.

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Re: Regen

Post by niwrad » Dec 07 2019 8:34pm

I think the regen% on CA should be interpreted best as, 'how much larger battery I would have needed', i.e. if you recover 100% of your energy then you would have infinite range, which makes sense.

So if I run dry and had 15% regen, then without regen I would have only made it 85% of the way home, or I needed a 15% larger battery. Or if I didn't run dry, then I could use X% smaller battery for the same trip
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