Regenerative Breaking

I was wondering about this issue...I have a 3-phase Mars ("brushless Etek") motor with a Sevcon Millipak SBPM controller that I will be using in my vehicle with a 36V system. Sevcon says the controller has regen, but I can't find much in the controller manual to indicate how this is actually accomplished. The wiring diagram shows how to wire in a forward/reverse switch, and I thought I might as well have a reverse gear on my scooter since it would be so simple.

Given what I've read in the other posts in this thread, I'm reluctant to throw it into reverse while moving forward. I would hate to fry my battery, BMS, or anything else (though I suspect the main fuse might prevent this from happening).

Does anyone know how to enable the regen capabilities of a Millipak controller, or is it just automatic?

Thanks,
Jake

Boy, I can see why new ppl to EV's can get so confused when starting out. There are alot of opinions mixed in before explaining the basic electronic principles behind what happens in regen (power generation) as what the original poster really needed. [Where's Fechter when you need him. He was usually around to straighten out the messes.]

Every motor can be a generator especially PM brushed DC motors. And this goes back to the basic principle of every dynamo - that any time an inductor coil passes through a magnetic field it will create a current and voltage. This current and voltage happens to be in the opposite direction (or negative voltage) from the original motor current direction - i.e. it runs backwards. You can see this very clearly if you have an oscilloscope (aka an o-scope). What as o-scope does is shows voltage performance over a length of time to create a waveform. Luckily with computers this can be done now with a voltmeter hooked in a realtime display program so it does not have to be another piece of equipment to buy. When you do hook one up to an o-scope and run a PMDC motor as a generator, you will find that a saw tooth pattern will be created not a true DC straight-line. In fact this line pattern will be dependant upon the RPM of the generator and the timing of the brushes on the commutator.

CONTINUED>>>

What does all this mean for an application in the EV world? This means even when coasting a back voltage will be created to the controller. A GOOD controller will be able to handle this back voltage (negative voltage). This can be done several ways. Usually, a good controller has the mosfets that have a high enough resistance to counter this voltage (like a diode) and it dissipates as heat. OR, A controller with regen will take this opposite voltage and feed it back to the batteries. OR a separate DC regulator (sometimes variable) is switched via relay to the batteries which involves disconnecting the controller and running the circuit "backwards" or "reverse" to the original motor direction. (GEE didnt you just say that?)

The problem you will encounter with regen (besides the proper way to charge the batts) is determining how much braking force is needed. Hopefully it is adjustable like in the Vectrix.

NOW for the other arguments whether the validity of regen - that topic will be for each operator to decide per the driving situation, but hopefully it is at least available to everyone. It is the old argument of coasting vs. regen. My stance on this - Everyone in the EV world argues about % in some form and this one topic ppl will spit out % from thin air both for and against regen. Its pretty simple to me...at least have REGEN available for the rider/driver because not every driving situation is the same and there are different driving needs. Can you travel a good distance without using power from the batteries and treat the vehicle like a rollercoaster or soapbox derby car? - YES. Can you add energy and life to batteries when you do have to stop? - YES. But at least have it available.

I was wondering about this issue...I have a 3-phase Mars ("brushless Etek") motor with a Sevcon Millipak SBPM controller that I will be using in my vehicle with a 36V system. Sevcon says the controller has regen, but I can't find much in the controller manual to indicate how this is actually accomplished. The wiring diagram shows how to wire in a forward/reverse switch, and I thought I might as well have a reverse gear on my scooter since it would be so simple.

Given what I've read in the other posts in this thread, I'm reluctant to throw it into reverse while moving forward. I would hate to fry my battery, BMS, or anything else (though I suspect the main fuse might prevent this from happening).

Does anyone know how to enable the regen capabilities of a Millipak controller, or is it just automatic?

Thanks,
Jake

I have not used that controller and motor combination yet so I could be wrong. According to the pdf on the electricross site. http://electricross.com/Downloads/Millipak%20PMAC%20User%20Manual%20April%202006.pdf

pg 19 shows the various settings and pins of your controller. does it come with an interface cable and program so that you can select the setting from your comp? normally, an ac controller has so many different combos that it becomes necessary to allow the user to decide it from preset programs. once you decide that then go to the section in the manual for regen.

EVEN after my long discertation even I screwed that up...Now I am gonna have to add disinformation BAD INFO to my rep. I forgot that power generation will still follow the original path of rotation. But switching the output will allow it to back to the batts....SORRY ABOUT THAT.

From the manual that goodnslo references - the MilliPak appears to do four different types of regen braking - I believe you want the Footbraking option (a potentiometer tied to either the front or rear brake):

Footbraking can be initiated in one of two ways:
- Via an analogue input configured as a Footbrake Pot. Using a potentiometer allows the
operator to vary the amount of braking they want. See below.
- Via a digital input configured as a Footbrake switch. When the switch is active, the system
will brake at the footbrake level

What I don't know is what the voltage and current levels output by the controller are. So, you may need control circuitry between the MilliPak output and the batteries to prevent attempting to overcharge the batteries. Also, if you want to get maximum benefit from regen AND you find that the controller outputs more than you need THEN you need to capture that extra power (e.g. in a supercapacitor). To me that's why regen is not worth it - even if the smarts are in the controller then there are likely still extra components needed to implement it effectively. From what I've read, and I take goodnslo's point that the % are really rather arbitrary, I can't see the amount of energy recovered being worth that extra cost and complexity (this is all from the POV of a motorcycle - a city bus has a lot more potential for effective gains through regen).

So, think carefully about how to implement the complete regen system and what costs vs. what benefits you will get - like most things "the less you know the simpler it seems".

BTW, does anyone know why implementing regen for a series wound motor is more difficult than from a PM motor? If you look at kellycontrollers.com you will see that they offer regen on some controllers - but not the ones for series motors. Any idea why? Not that it matters much because I don't want regen anyway... ;-)

with the rotor and stator in series, the magnetic field of the stator collapses right when the rotor passes or builds up an inductive field. Its easier to have the stator and rotor parallel.

Let me try and clarify. I hope this can help.

If you are traveling forward and you switch the motor wires to make the EV go reverse than current will still flow in the same direction out of the batteries. As long as the current is flowing from + to - than the battery will be discharged.

You can do a bench test to prove what I'm saying. Take any small motor (a little hobby motor from radio shack for example) an amp meter, and a small battery. Run the motor. As you slow it down it will draw more and more current. When hold it stopped it will draw even more current. And when you rotate the motor in reverse you will actually be able to draw even more current than when the motor was stalled. This will result in a lot of heat and the battery being discharged really fast.

So how do you use the motor on the bench to charge the battery? The way to do this is to rotate the motor fast enough in the same direction that it would run when you connect it to the battery. Faster than it would run no-load, so that it generates a higher potential than the battery. If you do this you will see the amp meter go negative because now current is flowing in the opposite direction.

I know it's kind of confusing. But think of it this way. What happens when you connect two batteries like this:

+ => -
- => +

Can you see that both batteries will have current flowing in the direction of + to - ? You may know from experience that you'll get a big spark and both batteries will get hot and discharge quickly. Please DON'T do this, it's dangerous. Its just like connecting two batteries in series than shorting them out.

Now what happens when you connect two batteries of different potential like this:

+ => +
- => -

Can you see that the battery with the lower potential will have current flowing from - to + and will actually be charged?

Isn't it obvious that a motor rotating in the opposite direction to that which it would run when connected to the batteries will have a potential opposite that of the batteries? This is not what you want. You want a potential greater than that of the batteries.

That helps, and yes, it seems obvious now. So here's what I've learned:
1) Don't switch into reverse while moving forward.
2) I'll have to assume that the regen abilities of the Millipak controller are automatic, but even if there aren't any,
3) Regen for a motorcycle isn't worth much anyway.

Thanks!

Jake

Thank you Andrew that was far more accurate than anything that I attempted to explain.

Awhile ago( witnin the past 6 months ) read about a new all electric car develop by Audi using 4 motors one in each wheel , and NO BRAKES whatsoever , the article claim that brakes will no longer be required with well designed regeneration . the system would bring the car to safe and complete stop .
There was a mechanical parking brake on the car .
Like to believe that Audi is well along the technology knowledge curve so as not to go chase a worthless concept case like regeneration .
The limiting factor in regen and charging efficiency and/or current is again Impedance ( the much hated word that everyone know about and do not want to face ) if the thermal characteristic of the batteries is addressed then amazing thing can be done with charging and of course discharging .IT all started with .....IMPEDANCE .....HOW LOW IS IT ?

Yeah I saw the same with wheel motor car...I think something I linked to from here that was a mini cooper converted. The description stated that with the regenerative braking regular brakes were eliminated.

Now, perhaps USATracy, Andrew or somebody else can tell me their guess about this. I've asked before somewhere on the forum but no particular specific responses as I recall. You guys know from my posts that I have the XB600. It was very soon after I began riding it that I realized when I put on the front drum brake...something was happening to provide braking to the rear wheel....but then the rear wheel drum brake is the other brake lever than the front of course. So I knew the rear drum brake wasn't being actuated as well by pulling the front one. And just to be sure I watched when I applied the brake. To find out what was sort of happening I put the bike on centerstand,key switch on,I kneeled down by the rear wheel and reached up and pulled the front brake...then tried to turn the rear wheel. Sure enough it was very hard to turn. I could move it but only with alot of force. Release the brake and of course the wheel was free. So apparently when I actuate that front brake lever it is not only using the front drum brake to mechanically stop the front wheel but it is doing something to hold the back wheel from easily turning. My question...anybody have a guess or answer to what it's doing? I'd really like to understand how it works this way. It really makes for a good braking system. I use the back brake most of the time but when I really need a quick stop I use both the back AND the front and I'm getting single braking on the front and a "double" braking (mechanical drum, something electrical to the motor) on the back.

Not that any of you guys would think this....but let me clarify I do know that when one applies the brakes it cuts power to the motor...on any scooter I've had. THis is more than cutting power as I've described above.

Thanks to any of you guys who can help me understand how this is working.

Gushar

I'm new and I've been looking at which controler to buy. Some of them have a lot of wires, and when looking at the wiring diagram, I noticed that some brake levers have a switch to cut power as soon as you begin applying the brakes. This would prevent you from accidentally applying the brake and power to the motor at the same time. Perhaps it cogging or its aligned for regen mode?

http://www.popularmechanics.com/blogs/technology_news/4223118.html

I just read the recent Popular Science, and theres a $30 gadget hack where you open up a discarded electric screwdriver and replace the battery with capacitors from a camera flash unit. When I Googled it, I found Coleman is making a factory capacitor screwdriver for $99. Here's my thoughts and questions:

Lead/Acid batteries last longest when only drained 50%, and re-charged 10% of amps (yes?, a 10 AH battery should be charged at 1 amp? perhaps 2 amps for short periods?) So, it seems they can only absorb a small portion of the regen amps available on a downhill.

The capacitor screwdriver recharges in 90 seconds (could capacitors absorb ALL the regen amps produced?)

With the same volume of capacitor bank as the original NiCD battery, the screwdriver performed only half the number of "screw-drives", so, a chemical battery is still better volume-wise for the majority of power storage.

From this I have speculated that:

2 AH of capacitor storage can replace 1 AH of battery range, but you should only have as much capacitor as you could fill during an average downhill in your e-bike usage profile. It's my understanding that capacitors can be charged/drained ten-thousands of times.

This shouldn't be hard to verify or refute, but whats the best way to attach capacitors so they "charge first/drain first" to save on range and battery life?

Hi,

people interested in regenerative braking might be able to make some use of this video, so I put it here as well:

The video was recorded a while before my Vectrix died.

It shows the instruments of my Vectrix accelerating from zero to 100km/h, then decelerating with full regenerative throttle applied.

It's done with 111kg ballast on board, including the lot.

Add in the published weight of a Vectrix, use a stop-watch and you might be able to calculate a few things (if your physics and maths are less rusty than mine).

Interestingly, if you look at 0 - 80km/h, it appears to decelerate quicker than it accelerates!
From 0 - 100km/h and back this effect is even more pronounced.

It can sometimes be difficult to be sure if it is really completely flat, but it was close to flat.

The acceleration time I measured using this video lies smack-bang in the middle between the measurements obtained from other videos, which were done on a piece of road with a slight slope; and done in each direction. I believe that means that the road this video here was made on is very close to flat.
There was very little wind.

My Vectrix is currently still out of order, waiting for a thorough service and repair; the acceleration may be different for other bikes.

Mr. Mik, ............. Toyota Camry :(

Hi,
I've put some more info about real world regen braking effect here: http://visforvoltage.org/forum/2547-vectrix-reports

Mr. Mik

just saw a an interview with a sales guy on youtube about the vectrix.

Apparently in order to regenerate while slowing down using the vectrix you just put the bike into reverse and it slows down while pushing some of that energy back into the batteries..

My question is.. is it really that simple ?

if you placed a switch on your ebike to put the motor into reverse polarity while going down a hill.. would the energy be fed back into the batteries or would the controller stop it ?

What if you hooked up a bypass circuit that fed directly into the batteries via a voltage regulator whenever you switched the motor into reverse?

------------

If you have drive system without one-way clutches/bearings and you have a 4-quadrant (full-bridge) speed controller, then it will regen-brake. It works because all motors work as generators too. When accelerating or under load current flows from the controller into the motor. But when decelerating, current flows from the motor back into the controller (which in turn feeds current back into the battery). The controller automatically changes the voltage as required.

It's not the controller or motor reversing, it's the current that is reversing. If the controller is set to 50% speed, but the motor is actually running 60% speed, then current flows from the motor back into the battery and provides braking. You won't see this effect on many eBikes and scooters because of clutches or half-bridge controllers. But you do see it with machines without clutches (such as direct drive wheel motors) when used with a full-bridge controller.

Note - If there are one-way clutches then the wheel just free-wheels instead, no way to regen, even with a brushless motor. If the system is not designed for regen and you remove the one-way clutch its possible to blow the controller as the controller voltage will rise under hard braking. There has to be enough voltage margin in the caps and other components. I have seen 48V systems rise to over 60V in hard regen braking. Usually the controller can be programmed to have a separate current limit in regeneration and have a separate switch to turn regen on and off.