Can you add a regen circuit

[mr.electric]

I wonder if you can add regen to a brushed 48v controller. I want to try a regen circuit that attaches to the brakes of an e-bike. I have a few of those chinese 48v controllers. Could I use two controllers one for regen brakes one for throttle?

 

[Leeps]

Theres no reason you couldnt add a regen circuit. Im pretty sure they dont make one, so youll have to make it. Its basically doing the reverse of what the motor controller does. The motor controller drops the battery voltage to whatever you want for the motor, the regen circuit boosts motor voltage to a voltage that can be used to charge the batteries.
The motor controller section in a motor controller doesnt have the right architecture for regen, it would have to be built seperately. The difference is really in the positioning of the mosfets and diodes, the logic section i believe could be reused. So you really could convert the motor controller into a regen controller. Be careful though if you hit the regen at the same time as the throttle you will let the smoke out.
Joe

 

[fechter]

I figured out a scheme to do this a while back. You need a small dc-dc converter to supply the regen controller. The dc-dc converter needs to have an isolated output so the controller voltage can go above the battery voltage.

As Joe points out, you also need a provision to prevent throttle and regen at the same time or you'll have smoke. Perhaps some kind of switch or relay on the throttle or controller logic power.

Regen works by shorting out the motor with a PWM. The freewheel diodes in the main contoller will circulate the current back to the batteries.

You could have the regen variable with a control or just switched on/off with the throttle left at a fixed setting.

 

[xyster]

That's great. I understand it much better now. Can we also copy all these great schematics to the schematics library?

 

[fechter]

That's great. I understand it much better now. Can we also copy all these great schematics to the schematics library?

OK, it's in there now.

 

[mr.electric]

thanks. I am going to try it. Is this better than installing a regen controller like an Altrax. I am tryng to make the regen proportional to the brake lever position. I know 4qed's have adjustable regen but they don't supply enough current for good motor power. I think altrax needs a pc hooked up to adjust regen.

I got this idea when I heard that the Lexus LS430H has all the regen braking in the rear because it is a rear drive car. I always thought that setting up proportional regen on an e-bike or scooter would be a waste of time because you are slowing the rear wheel not front wheel but now I want to try it.

 

[fechter]

You made me come up with an idea (danger alarm again)

By using a 3 phase bridge rectifier, you could circulate all the back EMF from a brushless motor into a cheap chinese controller and use that to brake switch the motor. The inductive kickback would be circulated back to the batteries by the FETs in the brushless controller.

A 3 phase bridge is just six diodes. They should be fairly cheap, and don't need to be real efficient.

What's ever cooler, is you could probably power the regen controller by using a charge pump diode, eliminating the need for a dc-dc converter. The charge pump might work for the brushed setup also (more thinking required).

You still need a way to control the regen amount and interlock the controllers so there's no way to have both on at the same time (instant smoke release).

 

[mr.electric]

Wow that looks like an efficient set up. A variable load DC- DC converter type device using cheap components. This would work to control MG1 on a Prius type system, I think.

 

[fechter]

Don't see why not. I think you can find monster sized 3phase diode bridges from some surplus places. The diode bridge will get pretty hot, so it will need a big heatsink.

After doing some thinking, I realized the charge pump would not work if you wanted to activate the regen at low speeds.

A dc-dc converter to power the regen controller would be much better. A really small one would work. A Vego controller, for example, draws about 100ma when working. I've seen some surplus ones for under $20.
For a 48v system, that $7 Lucent one from CandH sales would work if the brushed controller doesn't have a low voltage cutout.

If the brushed controller has a current limiter, it should still function in the regen mode, which might be a really good feature. If you have some speed built up and gave too much regen, something would probably blow.

A fuse in the regen circuit might be a good idea too.

 

[fechter]

After killing a few more brain cells, I figured out a way to make it work without a dc-dc converter and still work at low speeds.

For the brushed version, I don't see any way around the dc-dc.

 

[patrick_mahoney]

I took the time to draw up my idea.

Basically the brake connection - the same switch that disables the motor controller - drives an op-amp (probably inverting although I don't know how the switch is biased) which is biased to enable a set of FETs (or a relay...) to conduct. These drive through a fuse (although I'd probably move them to the other side of the FETs now that I'm writing this) into bridge rectifiers which drive out to a DC-DC voltage converter... although I'd put in some decent-sized capacitors and a zener diode to smooth out the DC-input, then drive this to either directly charge the batteries, or to drive a battery charging circuit.

I will more than admit that analog electronics is not something that I am adept at - but I spent a while thinking about it and this is my idea.

 

[fechter]

You could connect the bridge rectifiers directly to the motor all the time and have a single FET or relay switch right before the voltage converter. When the switch is open, there won't be any current in the rectifiers.

In my circuit, the cheapo controller acts as a voltage converter, but a properly designed circuit might be more efficient. It should be able to work with a wide range of input voltage, since the voltage will be a funciton of speed.

The charge controller part is a good idea. It would be possible to overcharge a battery if you started out with a full charge and went down a big hill.

The charge controller could simply open the switch and disable the regen if the battery voltage got too high.

 

[patrick_mahoney]

Thanks, Fetcher, I was waiting for the post that said "no, no, no... how could you ever think that would work?" I started off by thinking that I'd save money by using a DC-DC voltage converter instead of a brushed controller... but now I am not so sure... And I thought that you could better match with a battery charger. And I wasn't really thinking of SLA's - which tolerate overcharging moderately well... instead I was thinking of my lithium-ion batteries which do not.

Two things:
1. A Google search found this blog-like webpage about someone who implemented a regen circuit.
http://www.users.bigpond.com/solarbbq/regen/regen.htm

2. How do normal brushless controllers handle regen EMF currents? They must shunt them somewhere... don't they? If there is some form of resistor that takes the current... wouldn't a regen circuit need to disable this hypothetical resistor? Or am I missing something?

 

[fechter]

You're missing something.

The idea is the brushed controller briefly shorts out the motor windings, causing the magnetic field to build. When the switch opens, there's a big voltage spike that gets circulated back to the batteries by the body diodes in the main controller FETs. We don't want to dissipate the energy, we want to direct it back to the batteries. No resistors.

The cool part about this approach is you can control the amount of braking by adjusting the duty cycle on the regen controller. It will also be able to pump juice back into the batteries even at very low speeds without having to switch the configuration of the batteries.

On my Zappy, the regen current, and therefore the amount of braking force, was held constant by the limiter circuit. This made for nice, smooth braking anywhere from full speed all the way down to a crawl.

The circuit in the link is reconfiguring the batteries to a much lower voltage to allow regen. The problem with this approach is the faster you are going, the more current (and force) you get, and it completely quits braking at a reasonably high speed. There's also no current limiting, which might tend to rip the axle out if you hit the brakes at high speed.

 

[The7]

After killing a few more brain cells, I figured out a way to make it work without a dc-dc converter and still work at low speeds.
For the brushed version, I don't see any way around the dc-dc.

Assume the power FET is between B- and M- in the brushed controller similar to your version. And there are internal diodes in the power FETs.

The regenerative braking control circuit for a brushed motor is as shown.

Excuse me for using free-hand sketch.

 

[oatnet]

I am somewhat suprised to see all this interest in ebike Regen. I have not found the regen to be particularily productive on my TidalForce bikes; I did a few runs trying to maximize regen (much downhill and pedalling) but per my CA (CycleAnalyst) the power generated was not significant, and the power actually absorbed by the batteries was to be a fraction of that.

I do like the cruise control on the TF, when you exceed the set speed it uses regen to slow the bike down. I can set a speed, pedal hard against regen until I am tired, then let the bike pick up the slack.

Maybe the interest is more in braking than regen. However, the power yields should be enormous. If you have a 300lb human/bike combination travelling at 30mph, and you want to convert all of that momentum to electricity in 25' (guessing at bike braking range) or a second (guessing at braking time), you are going to have some pretty high amps coming out of regen. Wonder if you could 'flare' it into brake lights instead <grin>.

Also, to effectively use regen as braking, wouldn't you need some form of proportional control? The reed sensors on the TF are digital - on or off. I never added the xlyte (hall-sensor?) brake handles to my other bikes so I don't know if they are more proportional, but I suspect that the short range of the magnetic field makes them effectively digital too.

I believe the free-wheeling concept of the geared Puma's will be more energy effective than regen. Every time you coast, the drag of the hubmotor is sapping momentum that you have to use battery power to replenish next time you hit the throttle. If you coast as much as I do at the beach, I expect the waste from drag exceeds the potential gain from regen.

-JD

 

[xyster]

I believe the free-wheeling concept of the geared Puma's will be more energy effective than regen. Every time you coast, the drag of the hubmotor is sapping momentum that you have to use battery power to replenish next time you hit the throttle. If you coast as much as I do at the beach, I expect the waste from drag exceeds the potential gain from regen.

I agree. Regen is also harder on the drive parts. Brake pads are easier and cheaper to replace. I tried regen on my scooter. Did not like the effect it had on throttle control -- which was downright dangerous, and didn't allow me to remove my hand for repositioning. Energy re-capture seemed minimal at best. Even if the braking action had been better modulated, I'd still rather freewheel. Regen makes more sense for large vehicles in an urban setting, where the recapture is much greater due to increased momentum and stop-and-go driving.