Dynamo Regenerative Braking?

With a 4 diodes bridge you can use both alternances and thus double you energy harvest.

The problem is that the voltage developed will be depending on the speed (or the RPM)

So as the bike slows down, the power generated will be lower and lower as will be the drop in frequency.

The better way (may be) is to used controlled converters so that effectively the voltage is maintained (by controlling the switching). As you know that the charging of your batteries do need almost constant voltage

hi i've just came across to this forum while in search for the answers to the similar project. you mentioned about using controlled converters to maintain the voltage. is it possible if you are able to explain that bit and where can i get or make such device to correct similar problem too. thanks :)

If you are using a PM DC or brushless-DC motor to move the bike, I believe you will get the best regen braking energy recovery IF the drive controller itself uses the motor to recover that energy.

If you choose to continue with your current idea, use a full wave bridge rectifier on the circuit sketch.

My understanding of this is probably less than most of the people posting here think. I am assuming that a bridge rectifier is something more like this than my drawing:

My motor is a permanent magnet brushed motor...900watts. My controller is a 40a 24v rated PWM based motor controller. I use 2 18ah 12V AGM batteries wired in series power the bike. So you're saying that I would need to use the motor itself along with a different controller to handle the regen braking. The motor I am using is hooked up to a freewheeling chain drive system. In other words...when I am not running the motor, I have freewheel clutches allowing the chains to pass freely over the still shaft.

Similar function, but the diode bridge I'm referring to (4 diodes) only needs the single transformer winding (no center tap required) shown on your original sketch.

The free-wheeling linkage won't allow the motor to act as a brake. You would need to redesign the mechanics and purchase a controller($$) that can perform regenerative braking. This will probably NOT be worth the effort and cost.

As others have pointed out, you will need a generator/alternator that is at least half as powerful as your motor to get any reasonable braking effort and energy recovery. Even under ideal conditions, 10-15% energy recovery would be outstanding. Expect LESS!

It is important to understand that MOST of the energy is used to push aside AIR and to overcome mechanical drag. The kinetic energy (that may be recovered by regen) is always the smallest part of this particular energy equation.

I would be proud to have put together something similar to your current design. It looks good and appears to work well considering the bike size and the components use. I would be reluctant to perform such radical surgery on this project since IMHO it has reached its limit.

My "suggestion" is to keep Ebike 1.0 as-is and start a new project ... call it Ebike 2.0?

Plan for larger motor and matching regen controller, more & larger batteries, and maybe spring($$) for a few (ultracapacitors) to buffer the batteries from the regen current.


Best wishes!

Yeah I think this design is about at it's limit as well. The major limit is the bike frame itself. It was not designed to handle the rider weight (200lb in my case) plus 42 pounds of battery motor etc. If I wanted to add more batteries I would want to do a parallel system like so:

...and have some kind of battery monitoring system in place to keep the batteries in balance. I know || systems can be troublesome but I believe it is worth the effort to set up such a system because it reduces amperage draw on each pair. I think that will prolong the life and provide the power I want without destroying the batteries with high-amperage draw. I also think that having 4 12ah SLAs giving me 24 ah of capacity will keep me from dipping into the battery state of charge more than %50...which will help prolong their life also. I'm not saving any money on gas if my batteries are costing me $500 a year...

PS- I actually should have mentioned the project's title: "HI-V" meaning "hydrocarbon independent vehicle."

Regen in DC motors usally involves Step-UP DC/DC switching conversion and then current control at power rates possibly higher than continuous motor rate and up to the charge rate your batt can handle. Depending on your dynamo type you can Step-Up at AC, (inefficient at low Hz) then rectify and control current at DC for braking, or rectify first and treat as above. If you don't Step-Up you can regen brake only at non practical high speeds

A more effective arrangement would be to use the drive motor for regen, using a controller designed for that purpose. Even with such a controller, regen doesn't do wonders, with range extension of perhaps 10%. Adding mass and a little extra friction during driving, along with an inefficient system, could end up as a net loss.

The amount of regen has to be adjustable to work at high speeds and low, so the circuitry is not all that simple. You would need a much much larger hub dyno for effective braking. Typically, regen occurs at up to half of the peak output of the drive motor, so if an e-bike has a 500 watt (peak) drive motor, regen could be up to about 250 watts -- almost 100 times the output of the hub dyno you linked to.

You might check Kelly controllers. I think they make regen controllers small enough for an ebike.

Thanks for the input, even a 10% range extension would be good. So essentially I want to find a high output hub motor and find a controller that would support the regen braking. If I were to just simply pipe the energy back into the batteries it could destroy them, yes?

Also for the reason mentioned above I can't exactly use my drive motor to support regen....I would have to add a hub motor and that would probably increase the bike weight by about 15%. Not exactly optimal for this build. Perhaps for the next bike...

Its an addiction, designing stuff like this...isn't it? :) The pic shows where the drive motor is mounted. You've seen it before I believe...and thanks again for dropping in to take a look!

dequinox: a 3 watts generator wouldn't provide much braking. perry

I've decided to altogether abandon the idea of regen braking for this project... thanks for the input everyone!

Pardon me but you said " have a diode or series of diodes to convert the current to ac" Huh?? Are you serious? CONVER THE CURRENT TO AC.

Better review basic electricity 101 before proceeding further with your project.

If you actually read my previous posts you may have been able to determine I am indeed intelligent enough to know that from the dynamo I'd be converting AC to DC. Next time try not to trip so very epically over a simple typo.

your cheapest setup would prob be to leave the bike as is, except put a trailer behind it for your braking system. rig up an alternator or generator on the tires. when braking is needed, close the circuit to send power load to the batteries. when not charging/braking, the gen should have very little resistance. If the resistance is too great, just rig a lever to remove the gens rotor from the tires. set it up like the old weedeater powered bikes were built, insted of a two cycle motor mounted on the rear wheel, mount your gen head. big wheel with small shaft size should get you some juice to the batts. also, if you can find or build a constant voltage circuit, this would keep the right voltage going from about 3-20 volts, leveled at 12 volts. I think these circuits are used in some battery powered florescent lights, because by the time the batt runs out, it is very low, and the voltage must be kept fairly constant, to keep the bulbs lit.