Adding Regen to DC? Not for range...

8009 Views 29 Replies 12 Participants Last post by Overlander23, Jul 7, 2010

ewdysar

Discussion Starter · Jun 30, 2010

I live in the foothills of SoCal and I notice that while I drive any of my ICE vehicles, auto or stick, I use downshifting to control my speed. I do this for traffic or hills. Since I am seriously considering a DC electric conversion, I would like some resistance from the drivetrain when operating under zero throttle. I would use the transmission to select the amount of drag, lower gears for more deceleration, just the same as the ICE vehicles. My intended pack voltage will probably be 156V (48 lithium cells). I know that a controller will be needed to prevent overcharging, the max regen (charging) voltage should be no higher than 168V - 170V.

Since I typically care about efficiency, I don't want to just drag the brakes all the way downhill or approaching a traffic signal (I don't do that today in my Suburban, Fit, Insight or 914-V8). So for the sake of driveability, how can I get the conversion to feel more like a regular car? I'm not impressed with the AC systems that are available today, none seem to match the power of a WarP9 for a similar weight.

I've spent a day reading way too many threads that barely touch on the subject (please don't mention perpetual motion) and the only practical advice that I mined from all that has been the guy with the S-10 that rewound his own alternator. I was hoping that I could buy most of the components necessary to build a similar finished product. I'm not looking for a kit, just some sources for the major components. I'm also open to alternative strategies. Anybody else headed down this path before?

Thanks,
Eric

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ewdysar

Discussion Starter · #4 · Jun 30, 2010

So let's say I chose the rewound alternator solution. Are there ones available on the market or do I have to wind my own? Since it appears that the "high power" alternators' voltage varies with RPM, is there an off-the-shelf controller that can take the raw alternator output with fluctuating voltage and output my desired 168V? Are perm magnet alternators the only way to get to our kinds of voltages? If so, adding a clutch like Wayne's S-10 configuration seems mandatory.

Adding an A/C drive does sound like a way to get the best of both worlds, but cost was one of the factors pushing me towards D/C. I guess that if they were coordinated correctly, both motors could be smaller... Hmmm.... Still seems expensive....

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ewdysar

Discussion Starter · #5 · Jun 30, 2010

TX_Dj said:
If you care more about the braking effect than the regen charging function, plug braking may be your answer. Also called dynamic braking, it's very similar in effect to regen, but instead of putting that energy back into the pack, you burn it off as heat in a resistor bank.

Not easily done with a series DC motor for the same reasons regen isn't easily done, so you'd still need some offboard generation device that can be "switch" into the mix to give you the braking effects. Then you're also carrying lots of extra weight to support that system, so your range goes down as well.

So long as your brakes can stay cool enough going down those hills so as not to fade and lose braking efficacy, I'd say just use the brakes unless you're willing to go all the way to build a proper regen system; otherwise it doesn't make sense to carry any additional weight to support the effect.

Yeah, I can see that weight is coming back into play. I beginning to think that your last paragraph may be what we're stuck with until better A/C systems become available.

Back in the mid 1990's while I worked for Disney, a friend won Frank Wells' electric Fiero in a rideshare drawing. I helped him refresh the car and worked on a number of other EV's. At that time, I decided that for me, the FLA batteries were too big of a performance/range hit for how I expect a car to work. Fast forward to today, and I'm converting my 30' sailboat to electric with a 48V system and a TS 160Ah battery pack. With a battery pack that weighs less than half as much, a conversion is looking more viable.

AC Propulsion was building some solid systems back in the 1990's, I would have figured that they would be more available by now. Oh well....

Eric

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ewdysar

Discussion Starter · #7 · Jul 1, 2010

DavidDymaxion said:
You could get a sepex DC motor and sepex controller http://www.kellycontroller.com/kdc1260324v-120v600aseparate-excited-with-regen-p-418.html . I have no personal experience with Kelly, so that is not a recommendation for or against them.

I'm doing a diy controller for my sepex motor -- regen down hills is very nice. Strong regens seem to have the side benefit of keeping the batteries balanced.

So where can I find Sepex motors? Is there a system available that is of similar performance to a WarP9 with a 750A controller? All I can find is the D&D 6.7" that seems max out around 84V, or Kostov's, where the only high voltage model is the 268mm model. Are there Sepex controllers available that run to 144-156V?

Thanks,
Eric

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ewdysar

Discussion Starter · #12 · Jul 1, 2010

DavidDymaxion said:
I'm not aware of any current sepex controller that goes higher than the Kelly 120 V. I think the max Curtis one is 96 V.

If you want an off-the-shelf sepex solution, it looks like you have to either go lower power, or go multiple motors (might as well go AC in that case).

That's one of the reasons I'm doing my own controller!

Ok, so what sepex motor are your running?

Eric

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ewdysar

Discussion Starter · #14 · Jul 1, 2010

Georgia Tech said:
I am not running ANY motor at the moment... I have a BIG sep Ex motor just sitting in my Garage.

I have read some SERIOUS debates and posts on here on the importance of interpoles for High voltage Sep Ex systems... It seems the consincous is that a Sep Ex system with out interpoles can be run at about 72 volts max...

What kind of "BIG sep Ex motor"? Like I said ealier, the only Sep Ex motor specs that I've seen rated to 144V is the Kostov 268mm. I'm just trying to figure out what options actually exist...

Eric

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ewdysar

Discussion Starter · #17 · Jul 1, 2010

Tesseract said:
The Kostov SepEx motor looks to be an excellent size even for relatively heavy conversions. Too bad making a SepEx controller that can work with a variety of motors is such a P.I.T.A. ...

As for a really "Big" SepEx motor... how about this 13" GE monster which is going to be added to our dyno real soon:

Cool, though I might have to beef up the suspension in the Metro...

Eric

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ewdysar

Discussion Starter · #27 · Jul 6, 2010

Tesseract said:
My take is that this isn't terribly practical for two reasons:

1. The average automotive alternator is ~1kW in size and about 50% efficient (typical "claw pole" design) and that power capability applies no matter what voltage you re-wind it for. This means you can develop a maximum of about 2kW of braking power with the average alternator.

2. 2kW of braking power, alone, can decelerate a 1000kg vehicle from 60mph to 0 in about 138 seconds. My guess is you would barely notice the difference between that rate of deceleration and simply coasting.

That raises an interesting question, how much decelerative hp comes from a regular 4 cylinder engine at zero throttle? In my experience, not that much, certainly way less than our Insight in it's regen mode. Since 2 minutes sounds about right for my car to coast down from 60mph on level ground in neutral, 2kW added to the regular coasting drag may be close to what a ICE adds (subtracts?), i.e. slowing down twice as fast.

That said, after evaluating how much braking would actually be needed during my regular commute without engine decel (shifting into neutral every time I lifted my foot off the throttle), I find that I had over-estimated the amount of braking that a regular DC conversion would require. So unless the regen for driveability solution is both cheap and easy, it won't make it onto the build list.

Eric

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