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Does this exist? Regen braking for ebike & trailer.

Posted: Oct 28 2019 8:55pm
by Brian Walker
Hello All,

Is there a way to use regenerative braking to check downhill coast speeds at a fixed maximum for an ebike towing up to 70kg / 150lbs of weight in a small trailor?

I am legally blind and, although I can see well-enough to drive an ebike safely, I prefer not to coast at normal speeds downhill. I love in a hilly area and am searching for commute solutions. I was referred here byu the folks at who suggested you might have more experience with direct drive motors and regen braking. Clearly, I need a solution that would not involve normal brake mechanisms as they would wear out with constant applicaion under a load. Could a regen system be installed on the trailor to help spread the load rearward, as well?

I apologize in advance for being new to ebike mechanics and greatly appreciate any advice or suggestions you may wish to share.

Thank you!

Re: Does this exist?

Posted: Oct 28 2019 10:42pm
by john61ct
The general category is "drag braking", and prior to ebike issues, adult touring tandems had the same issues in landscapes with very long descents.

Yes hub motors are the tool of choice, and afaik DD type only, if any IGH models support regen I suspect their heat dissipation is up to the stresses of this use case.

I'm also very interested in this topic, for cargo bike usage in steep mountainous areas, total weight in the 4-500lb region.

Besides variable regen being a specialized topic area, another aspect is how to handle the heat dissipation when the battery bank is already full.

The answer I suspect being high-wattage resistors designed to shed a lot of heat, placed in the air flow but not where the rider will burn themselves.

I have not heard of constant-speed regulation being fully automated, do you really think that is critical to your use case?

Personally I'd be happy with a thumb/twist interface that made adjusting the regen level intuitive with familiarity.

Re: Does this exist?

Posted: Oct 28 2019 10:48pm
by john61ct
BTW a more specific thread title would be useful to attract a higher volume and quality of members contributing to the thread.

Maybe change it to something like

Variable regen solutions for drag braking down long descents


Re: Does this exist?

Posted: Oct 28 2019 11:39pm
by Brian Walker
Thanks for replying, john61ct!

I don't think the regen would need to be automated, just easily activated...

I shall start a new thread with a more descriptive heading, good idea.


Re: Does this exist?

Posted: Oct 29 2019 12:14am
by amberwolf
Why not just edit the first post of *this* thread to change it's title?

One solution to your issue is here:

If you already have a Cycle Analyst, you can try this
viewtopic.php?f=2&t=100125&p=1465913&hi ... A#p1465913
but it does require a controller like the Grinfineons or Phaserunner that have braking controlled by the throttle input between 0.0 and 0.8v. (or other programmable controllers that can be setup to do this)

I forget where it is, but there's at least one other downhill drag brake regen thread that has other solutions in it.

Re: Does this exist?

Posted: Oct 29 2019 1:10am
by Brian Walker
Thanks for these references & sorry for the duplicate thread...

Re: Does this exist? Regen braking for ebike & trailer.

Posted: Oct 29 2019 5:53am
by dustNbone
Implementing a speed controlled regen would be fairly simple with an Arduino, a regular old magnet/hall type speed sensor, and a controller that supports regen.

The most complicated part would be the user interface, assuming you wanted to be able to set the target speed on the fly. If you just wanted it fixed in the firmware then it's much simpler, just a momentary switch (click on click off, or click through several steps of regen strength if the controller supports variable regen), or toggle switch.

Nothing really complicated or expensive involved here. Just depends how far you want to go with it.

Re: Does this exist? Regen braking for ebike & trailer.

Posted: Oct 29 2019 7:53am
by dogman dan
Trailer brakes would be great, if the trailer was that heavy. But chances are, just regen on the bike itself will be enough. If you build a push trailer, then it could have regen brakes using its motor.

What you need is pretty simple. A direct drive rear motor on the bike, and a controller that allows regen.

When I ran regen, I preferred to be able to choose to use it, or not, when I used the regular brakes. So instead of brake handles with switches, I used regular brakes. Then I used a push button on the handlebars to activate the regen when I wanted it. Easy to grab a brake handle with fingers, and still stab the button with my thumb. I put the pushbutton on the left handlebar.

Ran that on a large cargo bike, that loaded with me and cargo, weighed 450 pounds. Regen was real nice, but in many cases, just the DD motor alone provided enough resistance to lower my speed and minimize the need for regular braking on long mountain descents. But I could see, so I could ride down at 30 mph. Regen slowed me to 5 mph, which might be perfect for you.

I don't think you will really need variable regen. You will just want to go down the hill with lots of regen on, slow and safe. But with a push button, you can pulse the regen on and off, as needed, easy.

Re: Does this exist? Regen braking for ebike & trailer.

Posted: Oct 29 2019 10:07am
by donn
It seems to me too that common on/off regen, as provided with inexpensive controllers, will do the job, but of course it depends on the details. Given the actual combined weight, typical descent grade, and desired speed, someone here probably knows from experience. One consistent speed across varying scenarios isn't going to happen, but you can certainly speed up if desired by alternating regen with free coasting.

Mine is set at a moderate level, as typical with on/off regen, on a moderately heavy rig, and it's a typical out-of-the-box setup with the regen controlled by the right brake lever switch. (Hence that switch also overrides throttle and cruise-control.) It's easy to get regen only with a light touch on the brake lever, or clamp down harder and add mechanical braking. Yesterday morning I noticed that my rear mechanical brake sounded kind of gritty, but I do need it all the time, to come to a full stop - single rate regen isn't very effective at slow speed.

Re: Does this exist? Regen braking for ebike & trailer.

Posted: Oct 30 2019 11:43am
by Brian Walker
Thank you all for such thorough input! I concur that variable regen may not be necessary (at least to begin with). I need to read up on the basic terms and mechanics of these systems. I've been in touch with GRIN ( and they seem to offer everything I'll need. An engineer on corrected my terminology: He pointed out that I should be using the term "dynamic braking" as opposed to "regen braking." Is there a significant difference?

Also, how is heat discipated from regen/dynamic braking motors if the batteries are fully charged?

Have you found e-trikes to be better for hauling trailors?

Thank you!

Re: Does this exist? Regen braking for ebike & trailer.

Posted: Oct 30 2019 12:43pm
by john61ct
Dynamic brakingĀ is the umbrella term.

Rheostatic is when no charging's going on, need to use big hot resistors instead. That will need to be a DIY kludge, never seen production gear do that in the ebike arena.

Regen technically only applies to the charging part, but that's the common term used for all of it for forum / googling purposes.

Re: Does this exist? Regen braking for ebike & trailer.

Posted: Oct 30 2019 2:52pm
by gogo
I have a folding bike with a 200W geared motor that has no mechanical motor freewheeling. The controller is set for permanent regen. When I close the throttle at speed it starts dragging and the same happens when I exceed top 'e-speed' at full throttle. Its quite an effective speed limiter and much appreciated because the tall handlebars bet bendy when braking from high speeds.

I wonder if the higher RPM of a geared motor is easier to control for this type of operation. Since heat is a much more limiting factor for geared than DD, it may be a moot matter.