# Question about coasting



## Mad_Scientist (Jun 10, 2008)

I'm new to this forum and have a general question.

I'm interested in direct drive, but don't want to give up the ability to extend range by coasting when possible. I have been trying this some lately with my ICE (like the "hypermileage" guys) and have improved my mileage.

In an EV with a manual transmission and clutch, you can push in the clutch and assure that you have no drag from the motor. But I like the idea of having no transmission and no clutch (for better efficiency).

With a series wound DC motor and direct drive, am I correct in thinking that when I take my foot completely off the accelerator there would be virtually no resistance from the motor? That is, it would spin freely and not slow me down, so I could coast as far as possible? The other question is, are there series wound DC motors available that would work adequately for direct drive. I'm thinking that about 55 mph comfortable running speed (top speed would probably have to be a little higher) would be good enough for my purposes.


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## John (Sep 11, 2007)

I don’t think the pulse and coast method of driving would net you much gain in an EV. With an ICE part throttle efficiency is less than full throttle efficiency so with pulse and coast you're using engine power with a closer to a fully open throttle where the engine develops power more efficiently. In an EV particularly one with flooded lead acid batteries high amperage drains reduce battery efficiency so I believe steady would be best. Does anyone else have any thoughts on this? Coasting down from speed rather than using the brakes would how ever gain you some.


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## Manntis (May 22, 2008)

Mad_Scientist said:


> I'm new to this forum and have a general question.
> 
> I'm interested in direct drive, but don't want to give up the ability to extend range by coasting when possible. I have been trying this some lately with my ICE (like the "hypermileage" guys) and have improved my mileage.
> 
> ...


Remember that in an ICE, engine drag includes the crankshaft sloshing through oil, piston rings rubbing cylinder walls, and valves closed on every 2nd rise of a given piston. There's a lot of friction and compression going on trying to slow down the engine.

an electric motor, OTOH, is a balanced shaft turning on bearings on either end.


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## VDubber (Jun 2, 2008)

An electric motor will present almost no engine drag, it basically acts as a flywheel when not powered (besides the minor drag of the brushes + fan).

Whether it would give you more range is based on so many variables (controller efficiency at various PWM levels, RPM of motor, etc.) that it would be interesting to see some real-world data from EV drivers.

The OP never said anything about "pulse & coast" (which I never thought was a good idea because it stresses a drive train and shortens it life), only coasting. I love coasting, I do it ever chance I get - not for economy (which is a nice side effect), but because of something my grandfather told me when I was young and thought engine braking was cool:



> Tsk... transmissions make VERY expensive brakes, ya know


The uber-coasting ability of EVs is one thing that drew me to them.


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## John (Sep 11, 2007)

VDubber said:


> The OP never said anything about "pulse & coast" (which I never thought was a good idea because it stresses a drive train and shortens it life), only coasting.


I know it is a bit of a leap but when he mentioned "like hypermilage guys" do in his ICE car, I put 2 and 2 togeather. Coasting to a stop instead of using the brakes would definately yeld good returns in an EV even beter than regenerative braking, pulse and coast no. In an EV it would be beter to drive in a manner that kept the amps low by using the vehicles momentum and maintaining steady amps rather than speed unless of course you have batteries with a super low Peukert's effect.


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## VDubber (Jun 2, 2008)

I totally agree. To fight Peukert's Law, one must use a light foot.

Many stateside boobs (i.e. typical US drivers) seemed to have learning a rather peculiar way of driving from their parents (who must have abnormally high blood pressure, or very low IQs): 

They mash the throttle at a green light, accelerating at 50% power to 10 over the speed limit - which of course locates them about half a block from the next (currently red) light. This requires them to mash the brakes and sit and idle until the light changes to green. Rinse, lather and repeat.

This behavior must be the single biggest useless waste of fuel I have ever seen in my life, especially when done on a mass scale. The only time I use more then the first 10% of my throttle and brake pedal is when I am forced to by another driver, or are going up/down a hill. IMHO this is called being a skillfull driver - anticipating the road ahead of you and adjusting accordingly. 

Idiots that mash pedals and throw their cars around like that should have their licenses revoked for causing such a public menace. And don't get me started about that assinign phrase "the natural speed of traffic"... like there is anything even remotely *natural* about cars or traffic.


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## Mad_Scientist (Jun 10, 2008)

Thanks for all the replies. This is very helpful.

I was mainly referring to coasting to a stop, and coasting down hills. The info about pulse and coast not being useful for EVs also was helpful, though.

Another question: Are other types of DC motors also "free-wheeling"? I mentioned series wound, but I think there are also shunt wound and permanent magnets. It seemed to me that with the permanent magnets the motor might act like a generator when you are slowing down; this would create drag.

Also, what about AC? Is it the case that regenerative breaking will happen with AC anytime you take your foot off the accellerator? Or is there a way to "free wheel" and coast when you want to, and do regen when you want to? 

Thanks.


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## mattW (Sep 14, 2007)

If the controller doesn't complete the circuit with the motor, not current will flow and therefore no generator drag. Most controllers will have a button/pot to initiate regen, otherwise you will just coast. Although some EVers set up their acceleration/regen on the same peddle so to coast you'd have to find the sweet spot between forwards/regen to coast.


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## Mad_Scientist (Jun 10, 2008)

Just a follow-up to my last question:

If regen happens as a matter of course with AC when you take your foot off the accelerator, a way to avoid it and coast when desired would be to have a clutch that you could push in when you don't want to regen, but is there another way?


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## VDubber (Jun 2, 2008)

The controller controls it. So to avoid it the best path is to have the controller set to only regen when the brake peddle is pushed.

Many sepex/PM DC controllers can read a pot attacthed to the brake peddle and enable/vary regen based on how much you use the brake. They would coast just fine.

For AC controllers, it would likely be similar. It's just a setting or parameter that can be adjusted to your preferences by the installer or retailer. I once read about a AC controller that had a 'dead zone' on the throttle peddle where it would not supply power or regen. So to coast, you simply cracked the throttle ever so slightly. Personally I would rather have a 'dead zone' on the brake pedal that enabled regen without any brakes, so if I lightly pushed the brakes I would be grabbing ALL the energy available.


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## adric22 (Jan 17, 2008)

I just started driving my gas car again for the first time in a long time because I'm upgrading some stuff on my EV and it is out of commission. One of the first things I noticed is that when I go down hills the engine creates this huge drag on the vehicle that I'm not used to. I never really noticed back when I used to drive a gas car all the time. 

To answer the original question - Yes, an EV coasts down a hill just as if the car were in neutral. In fact, an old habbit of mine in a gas car was to put the car in 1st gear when parking because the engine will prevent the car from accidently moving if you don't pull up on the hand-bake hard enough. Kind of pointless in an EV as the electric motor will provide no such braking.

I don't have regenerative braking on my car since it is a series-wound motor. But one thing I've noticed is that it really isn't that neccessary for hills. I just let the car reach whatever speed is natural on the downhill slope (even if it exceeds the speed limit) knowing that this extra momentum will help me climb the next hill. Whereas my gas car's engine drags so much down the hill that I barely gain any speed at all and have to use the engine for climbing the next one.


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## Zer0 (May 9, 2008)

I've thought about the regen vs coasting periodically too. One thing that I considered, and the way I would personally set it up, is that regen would happen on lift throttle just like engine braking in an ICE vehicle. In a direct drive situation, I would put a dead pedal where the clutch used to be with a switch on top that was hooked to a main contactor and would act as an "electronic clutch". This is assuming, like mad scientist did, that the electric motor would offer no resistance if no current was going in or out of it.

Just a thought I had, don't know if it's viable or not, open to criticisms and comments.


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## Manntis (May 22, 2008)

Mad_Scientist said:


> Just a follow-up to my last question:
> 
> If regen happens as a matter of course with AC when you take your foot off the accelerator, a way to avoid it and coast when desired would be to have a clutch that you could push in when you don't want to regen, but is there another way?


mine has a switch that allows you to set max regen, no regen (for coasting), or a blend. (the same switch is what lets me select reverse, changing direction of the motor rather than shifting a gear)


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## ga2500ev (Apr 20, 2008)

I was doing some hypermiling coasting in my 5 speed ICE Corolla today. I found that on the surburban Atlanta hills that I only needed to apply the gas pedal about 1/2 the time.

I was also think that both regen and coasting are useful. I was talking to my son today about how a car could be configured so that tapping the brake pedal would activate regen without actually activating the brakes.

Of course figuring out regen on the cheap is tough. The article in the wiki about regen talks about how to get it to work for series wound motors. It does have some complexity. I was wondering about the utility of attaching a PM DC generator to the opposite end shaft of dual shaft traction motor via a magnetic clutch. Regen occurs when you engage the clutch.

Just an idle though.

ga2500ev


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## JRP3 (Mar 7, 2008)

ga2500ev said:


> Of course figuring out regen on the cheap is tough. The article in the wiki about regen talks about how to get it to work for series wound motors. It does have some complexity. I was wondering about the utility of attaching a PM DC generator to the opposite end shaft of dual shaft traction motor via a magnetic clutch. Regen occurs when you engage the clutch.
> 
> Just an idle though.
> 
> ga2500ev


Someone did this with a high output alternator, hooked up to a brake switch, which engaged the magnetic clutch and powered up the field, generating power and slowing the vehicle. (Roland Wiench ? on the EVDL I think.)


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## Manntis (May 22, 2008)

ga2500ev said:


> Of course figuring out regen on the cheap is tough. The article in the wiki about regen talks about how to get it to work for series wound motors. It does have some complexity. I was wondering about the utility of attaching a PM DC generator to the opposite end shaft of dual shaft traction motor via a magnetic clutch. Regen occurs when you engage the clutch.
> 
> Just an idle though.
> 
> ga2500ev


cheaper and easier to install a regen mode switch, and use the motor - or choose to not use the motor - for regen. Fewer moving parts, too


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## VDubber (Jun 2, 2008)

JRP3 said:


> Someone did this with a high output alternator, hooked up to a brake switch, which engaged the magnetic clutch and powered up the field, generating power and slowing the vehicle. (Roland Wiench ? on the EVDL I think.)


Reverend Gadget did the PM generator thing in a Triumph Spitfire:










Seems like alot of work for just a little more range. How much range would you gain by replacing the cost and weight of the gen with more batteries?

Roland's approach seems pretty effective. But remember what he is driving - one honking massive El-Camino with alot of lead aboard. The benefit one can get out of regen is directly related to your vehicle's weight.

The lighter your vehicle, the less it makes sense. It's much easier to conserve (as in conservation of motion) your energy then to recapture it IMHO.


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## JRP3 (Mar 7, 2008)

I agree. Unless you are doing an AC system which has regen built in I doubt it's worth the extra effort.


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## mattW (Sep 14, 2007)

VDubber said:


> The lighter your vehicle, the less it makes sense. It's much easier to conserve (as in conservation of motion) your energy then to recapture it IMHO.


Why would the size of your vehicle make any difference at all? You are just recovering a set percentage of the energy it took to accelerate, heavy vehicles use more and so recover more but I should get just as much or a range extension on my motorbike as he does on his camino. I figure if you ever use your brake pedal then its worth at least considering regen, coasting is better when you can, but I coast as much as I can in my normal car and I wish for regen plenty of times every trip.


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## JRP3 (Mar 7, 2008)

Yes I guess you are correct. So the question would be is the extra cost, weight, complexity of creating regen for a DC system worth the extra 10% or so gain? 5 miles added onto a 50 mile range doesn't seem worth it to me, especially when you could get that with extra batteries and have better performance all around.


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## ga2500ev (Apr 20, 2008)

JRP3 said:


> Yes I guess you are correct. So the question would be is the extra cost, weight, complexity of creating regen for a DC system worth the extra 10% or so gain? 5 miles added onto a 50 mile range doesn't seem worth it to me, especially when you could get that with extra batteries and have better performance all around.


Range is a critical parameter for EV usage. Increasing range by 10% is very helpful.

There is a point where adding extra batteries becomes tough due to weight and placement.

ga2500ev


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## VDubber (Jun 2, 2008)

mattW said:


> Why would the size of your vehicle make any difference at all? You are just recovering a set percentage of the energy it took to accelerate, heavy vehicles use more and so recover more but I should get just as much or a range extension on my motorbike as he does on his camino. I figure if you ever use your brake pedal then its worth at least considering regen, coasting is better when you can, but I coast as much as I can in my normal car and I wish for regen plenty of times every trip.


You are assuming a completely flat road. If you live somewhere flat, you will not see much range extension using regen versus just driving more sensibly and not accelerating so fast... plus you might live longer. Now if you like to jackrabbit your car around town, then yeah, regen might get you a noticeable range extension.

And you said it yourself - it's a percentage, but of energy expended, not range. Since a heavy vehicle uses a higher total energy to accelerate at the same rate of a light vehicle, it would see more range extension over NOT having regen. 

A lighter vehicle uses less of it's pack's total energy to accelerate, so there is not alot of energy to get back (it's fundamentally more efficient without regen). A heavier vehicle uses more of it's pack total energy to accelerate, so there is more to get back (because you wasted more without regen).

You see this same effect with ICE cars/trucks. Heavier vehicles have a greater difference between their city/highway mileage then lighter ones. They are more wasteful when constantly accelerating/braking. A heavy truck might need 4x the power to accelerate versus just cruise, where a light car might only need 2x the power. 

In summary, without regen you are wasting more energy in a heavy vehicle then in a light vehicle. So your benefit from regen versus no regen would be greater.


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## VDubber (Jun 2, 2008)

On a related note, I did just see this:



EVDL said:


> I am now in the process of removing the Lithium boost pack. It did add only 2.3ah but did extend the range of the truck by more than 2.3 ah should have (6.5 miles more with careful driving).I think the drain on the 26ah hawkers was a lot lower thus allowing more to come out. The single string of altairs provided most of the takeoff power and then at cruising speed the altairs were charged by the hawkers.


This is kinda cool. Extending your range by using a hybrid battery pack seems to perhaps work well. A 2-3Ah string of lithiums would only be around 10lbs with BMS...


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## ElectriCar (Jun 15, 2008)

What regen controller do you DC guys use/recommend? I'm inclined to the Zapi H3 at this time. It's 24-144V up to 1000A and is programmable also.


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## JRP3 (Mar 7, 2008)

Last I knew there were a lot of failures with Zapi controllers. Most brushed DC motors don't bother with regen controllers since brushed DC doesn't do regen very well.


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## VDubber (Jun 2, 2008)

JRP3 said:


> ...Most brushed DC motors don't bother with regen controllers since brushed DC doesn't do regen very well.


You mean *DC series motors*, right?

DC PM, shunt, and sepex motors handle regen just fine - and they are all brushed motors... but that does not apply to car conversion because they don't make 'em the right size these days.

Now for motorcycles, an Alltrax PM or sepex setup would be a inexpensive, effective way to get regen. With brushes no less!


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## JRP3 (Mar 7, 2008)

Yes of course, I should be more precise with my terminology.


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## ElectriCar (Jun 15, 2008)

I'm going to have regen come H or HW if possible. I'm building this thing because my commute is 7 miles of red lights and turns and I do lot of city driving, nearly daily.

I know it's a waste of money if you're driving mostly long hauls but that's not my thing. I've got a Biodiesel powered F250 for that and heavy hauling. I figure with this thing I'll save close to or more than $3G/year. I go all the time! 

I had figured $2500 a year but my biodiesel supplier just went up from $3 to $3.75 a gallon! If I were paying $5 as most around here are, it would pay for itself probably in under two years!

Do none of you regen DC??? The sep-ex motors (shunt wound DC motors) I've seen are all <100V. I'd rather go high voltage as the wiring is smaller (read cheaper and lighter weight) for a given HP. 

1000A at 72V could be done at 500A at 144V!. Half the weight in wire. Less weight = free HP! Lower current is cheaper to maintain as the contactors can be smaller as well. 

Or that's my reasoning as an EV newb anyway...


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## JRP3 (Mar 7, 2008)

On the other hand high voltage means more batteries which means more connections, which means more wires, so it may even out as far as cable weight. More thinner cables or fewer thicker cables. I would think cables are such a small percentage of vehicle weight it wouldn't make much difference anyway. I think your range requirements are more important than driving style as far as regen is concerned. If you only need 20-30 mile daily range that's pretty easy to get even with lead, so the extra cost of regen doesn't seem worth the few extra miles you might get with it. If you really want regen and have a small vehicle you might look into the Solectria AC24, but you'll be spending around $5-$6k with controller as opposed to $3-$4k for a DC 9inch plus Curtis 1221.


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## ElectriCar (Jun 15, 2008)

Oh guy, I love the 6 wheeler! I wanted one of those the first time I saw one! How close are you to dip testing it?


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## JRP3 (Mar 7, 2008)

I'm hoping to get it running this weekend, but my stream is a little low so I don't think I'll be able to fully float it. That might be a good thing since I'm not sure how low it will float with all the battery weight   Should be alright though.


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## LiquidForce (Jul 9, 2008)

Mad_Scientist said:


> The other question is, are there series wound DC motors available that would work adequately for direct drive.


 
I'm new here as well and read through this post but did not see this question answered.

Are there any that would work as direct drive and if so is there a weight limit before it becomes necessary to go with a gearbox?


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## JRP3 (Mar 7, 2008)

NetGain has the TransWarp series of motors that have a drive shaft yoke on the end and are designed for direct drive. They are more expensive than the non yoked version of the same motor but you don't have to make a trans adapter.


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## Andrew Carson (Jul 7, 2008)

If you set up a switch on the brake pedal so that it activated your regen braking, and then had another switch on the accelerator pedal to disengage the regen, then you could have the idea that you want, just a thought though. enjoy



ga2500ev said:


> I was doing some hypermiling coasting in my 5 speed ICE Corolla today. I found that on the surburban Atlanta hills that I only needed to apply the gas pedal about 1/2 the time.
> 
> I was also think that both regen and coasting are useful. I was talking to my son today about how a car could be configured so that tapping the brake pedal would activate regen without actually activating the brakes.
> 
> ...


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## DVR (Apr 10, 2008)

JRP3 said:


> my stream is a little low ..................  Should be alright though.


Hmmmm.......Sound like prostate trouble.


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## Astronomer (Aug 7, 2008)

Coasting is something I've given some thought to. When going downhill, it would be nice (and much safer) to have something besides just the brakes to control speed. Even moderate inclines, if long enough, can smoke your brakes if you don't use the engine for braking, and this is even more true when you fill the car with 1000 pounds of lead. And if you're lucky enough to have an EV that can climb a mountain pass, don't even think about coming back down without regen braking.

What I've considered doing is having a conventional 12VDC accessory circuit with an alternator and a battery, with the alternator driven by the traction motor through a magnetic clutch. The clutch would be engaged only during braking, so the 12V battery would be recharged only when slowing the vehicle down. 

I know a lot of you have come out against attaching an alternator/generator to the traction motor to power the 12VDC circuit, and I completely agree to the extent that you shouldn't sacrifice mechanical power for any purpose other than driving the wheels. But do your objections extend to using such a setup only during braking?

I'm looking to gain the advantages of coasting (efficiency), with the advantages of “engine braking” to ease the (now) enormous burden on the brakes. 

I understand the weight issues, but I'm not looking to extend the range through regen braking, so the arguments of “a battery of the same weight would be more better” don't really apply. Adding another traction battery instead wouldn't really accomplish what I'm trying to do. I'm just trying to come up with a a robust 12VDC circuit alternative to a DC/DC converter that also increases safety during deceleration. (And, yes, I understand that charging only during braking isn't likely to maintain the 12V battery, and it will need nightly recharging, just like the traction battery.) Additionally, the system would be mostly free, since I already have the alternator and battery. I just need to cobble it together with a magnetic clutch and a switch.


And speaking of the switch, it _would_ be nice to be able to engage the regen without engaging the brakes. What do you think of having two, stepped return springs on the accelerator pedal – one weak, one strong – so the first half-inch of travel requires very little force, and pushing the pedal beyond that point would require noticeably greater (and more familiar) force. With no force on the accelerator pedal at all, regen would be engaged. Push the pedal just a half-inch to the first “detent”, and you would be coasting with no brakes, no regen, and no power to the motor. Push beyond this detent, and you would be sending power to the motor. I rather like this scheme because it doesn't involve the brake pedal, so you can engage regen without the brakes, and you get positive feedback from the accelerator pedal which “mode” you're in.


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## JRP3 (Mar 7, 2008)

I think you'll need more than just a regular alternator and one battery to slow the vehicle down. You'll need someplace to put all that charge and the traction pack can take a lot more than a single 12 volt battery, and a high output alternator to load the vehicle and slow it down.


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## CNCRouterman (May 5, 2008)

Let's see how much regen energy you can get with the alternator assembly.

A 12V alternator, with a 90 amp capacity would yield 1090 watts, ignoring efficiency losses, which would improve braking (it would take more than 1090 watts going into the system to generate 1090 watts out). I guess you have to determine if ~1090 watts of braking is sufficient for your purposes, and of course, you have to evaluate rpm matching, and you can probably overdrive that alternator quite a bit to yield much more than the 1090 watts. The proposed alternator hookup will be a relatively small braking "motor", however, something (1090 watts) is still more than nothing!

Would you match rpms 1 to 1 or would you step up the rpms of the alternator such that both the traction motor and the alternator would red-line at the same time?


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## Astronomer (Aug 7, 2008)

> I think you'll need more than just a regular alternator and one battery to slow the vehicle down.


Yeah, I know. I appreciate what you're saying about how much better it would be to dump the energy into the traction battery, but I'm trying to kill two birds with one stone, here. So compromise is the word of the day. If all I wanted was regen deceleration, I just wouldn't bother with it in a DC system.


> The proposed alternator hookup will be a relatively small braking "motor", however, something (1090 watts) is still more than nothing!


Now you're talking!  Seriously, though, I'd be happy with ANY amount of deceleration as long as I end up with robust 12V power for my radio, wipers, and headlights. I just figured that since I already need 12V power, why not supplement it with a simple regen system using parts I already have?


> Would you match rpms 1 to 1 or would you step up the rpms of the alternator such that both the traction motor and the alternator would red-line at the same time?


That's not something I haven't thought through, yet, since I haven't actually done any calculations. I'd like to keep it as simple as possible, even to the point of running the alternator directly from the motor shaft. But I know that isn't likely to be optimal. But whatever I do, I want, as much as possible, to keep all the mechanical efficiency losses (belts, pulleys, stochastic sinusoidal replenerators, butfores, etc.) on the alternator side of the magnetic clutch so that there will be no price to pay during non-regen driving.

Also, if it turns out that the "regen mode" using a common 12V alternator doesn't slow the car down any more than sticking my hand out the window, then I might consider putting a switch on the dash that would engage the alternator at all times. I would then engage that switch for short night-time trips (say, to the grocery store) where using the headlights would drain the 12V circuit battery more than I'd like to.

Just my luck, though, I'd forget the switch is on the next morning when I'm rushing to the airport 25 miles away. 


Any opinions on my two-stage accelerator pedal switch thingy?


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## CNCRouterman (May 5, 2008)

I think it is a perfectly valid concept. Presumably you would set the throttle linkage such that you would not move the controller's throttle pot off zero through the regen travel, otherwise you would have to tell the controller to ignore values below some threshold.... etc. 

I had a Suzuki Sidekick for a while that had the overdrive enable/disable switch on the "T" shifter, which I find far superior to my Jeep's dash location. That may be worth considering for either the enable/disable mode, or for actual engagement, depending on your personal preference.


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## JRP3 (Mar 7, 2008)

CNCRouterman said:


> Let's see how much regen energy you can get with the alternator assembly.
> 
> A 12V alternator, with a 90 amp capacity would yield 1090 watts, ignoring efficiency losses, which would improve braking (it would take more than 1090 watts going into the system to generate 1090 watts out).


I've heard that most alternators are around 60% efficient, so potentially you'd have quite a bit more braking power, if you could actually get the full output. However, unless there is some sort of load on the system drawing all that amperage, you'll get substantially less out of it.
Maybe you could also rig up a switch that turns on the headlights and maybe a heating element when you hit regen, thereby giving more load?


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## JRP3 (Mar 7, 2008)

CNCRouterman said:


> I had a Suzuki Sidekick for a while that had the overdrive enable/disable switch on the "T" shifter, which I find far superior to my Jeep's dash location. That may be worth considering for either the enable/disable mode, or for actual engagement, depending on your personal preference.


I have the same setup on my RAV4 and often use the switch to turn off overdrive when going down a steep hill. It would feel quite natural to use the same button to turn on regen in an EV.


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## Coley (Jul 26, 2007)

Quote:
"Remember that in an ICE, engine drag includes the crankshaft sloshing through oil."

Wrong...your crank is well above the oil level. All it sees is mist.


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## Desjardins (Sep 23, 2008)

Mad_Scientist said:


> Another question: Are other types of DC motors also "free-wheeling"? I mentioned series wound, but I think there are also shunt wound and permanent magnets. It seemed to me that with the permanent magnets the motor might act like a generator when you are slowing down; this would create drag.


PM motors suffer from eddy current losses while coasting, that is the magnets make current in the moving laminations, that turns to heat. On a direct drive electric bicycle the effect is pretty much comparable to having one tire 1/2 flat, it sucks.


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