# AC vs DC for long-range EV



## Duncan (Dec 8, 2008)

The amount you get back from re-gen depends on many factors
The most important is the amount you use the brakes

If you are on "rolling" terrain and you just drive then you will see zero benefit from re-gen

So on your route - do you use the brakes a lot? - if you do you may see from 5 to 10% from regen

Most of us tend not to use the brakes that much - so we would gain very little


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## McRat (Jul 10, 2012)

You have to do the cost math.

Yes, AC regen will increase your range. But AC systems are more $ per HP than brush motors.

In the long run, all the OEM's are running AC induction, AC magnet, or Brushless DC.

Sidebar - It's pretty cool to have Max Regen when you lift the gas. It feels like chopping the throttle on a 11:1 compression big block. You do most your driving without ever hitting the brake pedal.


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## onegreenev (May 18, 2012)

I think it may depend also upon what you intend to build. Some smaller vehicles that can hold a lot of cells should do fine with the HPEVS AC systems available. Much more affordable and they come with warranty on parts for at least some time. I drive a Leaf all the time and always on the hwy and almost never use the regen for gaining any useful range. It really only gets you a little in return but will surely save your brakes. The AC system is also good because you don't have the brush dust issue and commutator issues and they will stay cleaner. They offer higher safer rpm limits than DC motors. Some DC motors can do some good rpms but most don't do much better than 5200 rpm. If you go DC then be sure you have a killer disk brake system installed. You will need it. You don't need regen and like was said if you live on hilly up and down roads and you can make use of the coasting abilities regen may not net you much of anything. Thats ok. AC systems are also quieter too. 

Pete


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## vocalnick (Aug 5, 2013)

Hi folks,

Thanks for the replies thus far - it's all food for thought.

I paid specific attention to my braking on my commute this morning, and there's not a lot of it! Most of the downhill sections level off gradually and I end up coasting, but not having to brake. There is a winding section immediately as I leave home, but presumably regen will be pretty pointless there as I should have a full charge.

So that puts paid to that!

I'm still tossing up the other benefits - I've heard AC can be more efficient? But perhaps I'd get better results using DC and spending more on a larger battery pack?

I was hoping there would be an objective truth - "Oh, for highway range, you want X" but it seems like there are lot of little pros and cons which have to be weighed up. I just don't want to get into the build then realise I should have zigged rather than zagged.


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## EcoReality (Mar 10, 2014)

Is your "specific attention" being done from an ICE car?

If so, consider that whenever you're "coasting" in an ICE car you'll be regenerating with an AC system.

When DC systems "coast," it's like pushing in the clutch or putting it in neutral. There is *no* engine braking at all.


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## vocalnick (Aug 5, 2013)

EcoReality said:


> Is your "specific attention" being done from an ICE car?
> 
> If so, consider that whenever you're "coasting" in an ICE car you'll be regenerating with an AC system.
> 
> When DC systems "coast," it's like pushing in the clutch or putting it in neutral. There is *no* engine braking at all.


It was an ICE car, but I'm not doing any significant engine braking (in fact I'll often shift to neutral and genuinely coast to save fuel). If I just take the foot off the pedal and let the engine braking take effect I end up slowing down too much.

That said, I want this vehicle to be pretty versatile, and this isn't the ONLY road I use. And you bring up a good point - regen isn't just about charging, it also provides something more akin to that "normal" car behaviour of engine braking. 

My instincts are saying AC, but I don't just want to throw money at it if it's not going to be of significant benefit.


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## Duncan (Dec 8, 2008)

vocalnick said:


> _I've heard AC can be more efficient? _


Not really - I gather that even if the motor is a tadger more efficient the controller is a bit less efficient so it all evens out

AC is the way of the future - just now it's too expensive

_ consider that whenever you're "coasting" in an ICE car you'll be regenerating with an AC system._


Nonsense - re-genning is like engine braking -
In a IC car you normally "coast" with a small amount of throttle - so it is similar to a DC system with no throttle


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## vocalnick (Aug 5, 2013)

Duncan said:


> Not really - I gather that even if the motor is a tadger more efficient the controller is a bit less efficient so it all evens out
> 
> AC is the way of the future - just now it's too expensive


Based on the costs I'm seeing in Australia is is more, but not a huge amount more in the context of the overall cost (much of which will be batteries)

HPEVS AC-51 motor/controller kit is AU$6150.

Netgain Warp 9 is AU$2395, Soliton JR is AU$2175, so a total of AU$4570.

So around 25% less for DC. But in the context of the overall build cost, it's relatively small. I'm willing to pay if it's worthwhile.


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## Duncan (Dec 8, 2008)

_HPEVS AC-51 motor/controller kit is AU$6150.

Netgain Warp 9 is AU$2395, Soliton JR is AU$2175, so a total of AU$4570.

_But you are comparing a wimpy system with a powerful one 50 Hp v 200 Hp

A better comparison could be 
Hitachi 11 inch motor - NZ$100 + OpenRevolt controller - NZ$600 total - NZ$700


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## vocalnick (Aug 5, 2013)

Duncan said:


> But you are comparing a wimpy system with a powerful one 50 Hp v 200 Hp
> 
> A better comparison could be
> Hitachi 11 inch motor - NZ$100 + OpenRevolt controller - NZ$600 total - NZ$700


Ah OK. Here's where my lack of knowledge kicks in to confuse things! I was just going by the evworks price/product list.

A motor for $100? Did you mean $1000?

And thanks for drawing my attention to the OpenRevolt. I solder like a 5-year old, but I play in a band with a fellow who's an electronics engineer by profession and will probably accept payment in beer, so that adds another option to the table.


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## Duncan (Dec 8, 2008)

_A motor for $100? Did you mean $1000?

_Nope I paid $100 for my motor - it had just been rebuilt when the forklift it came out of was scrapped off

There is a thread on using forklift motors, well worth a read

There are "Purpose built DC motors" but the only differences anybody has been able to point out to me have been a nice coat of paint and...,
Advanced brush timing - which is an easy DIY fix

(Did I mention I'm a Scotsman - living in Southland where the natives "encourage thrift")


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## vocalnick (Aug 5, 2013)

Duncan said:


> Nope I paid $100 for my motor - it had just been rebuilt when the forklift it came out of was scrapped off


Aaahhh OK. That makes more sense. I will find and read the forklift motor thread. But let's face it - just because you found an immaculate motor for $100 doesn't mean that I'm going to be able to. 

I did actually do some investigation into scrapped forklifts, and I've not found anything thus far. I'm in Tasmania, which makes NZ look like a bustling hive of activity, so I suspect my salvage opportunities are going to be a little slimmer.



> (Did I mention I'm a Scotsman - living in Southland where the natives "encourage thrift")


I'm very much for thrift, but I'm also playing a long game. Regardless of whether I go for AC or DC, I think the bulk of the cost will be in the batteries. So I want to find the most efficient motor/controller combo.


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## Duncan (Dec 8, 2008)

_I'm in Tasmania, which makes NZ look like a bustling hive of activity, so I suspect my salvage opportunities are going to be a little slimmer._

I'm in Southland - a long way from the "bustling" North Island!
Electric forklifts are used in a lot of food processing plants - I suggest you try and find who repairs forklifts in your area 
Then visit them and ask about scrap bits,
the motors seem to last forever and are only worth scrap metal value

_So I want to find the most efficient motor/controller combo. _
There isn't anything in it for efficiency 
I expect AC to be the best deal in about 5 years - so if you have a cheap motor and controller you won't mind changing it if/when something better becomes available


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## vocalnick (Aug 5, 2013)

Duncan said:


> I'm in Southland - a long way from the "bustling" North Island!


I'd better stop or we'll end up doing the four yorkshiremen sketch 



> I suggest you try and find who repairs forklifts in your area
> Then visit them and ask about scrap bits,
> the motors seem to last forever and are only worth scrap metal value


I guess it can't hurt 

As I said up front, I'm looking for highway performance - do you have any experience using salvage motors in that context?


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## Yabert (Feb 7, 2010)

vocalnick said:


> HPEVS AC-51 motor/controller kit is AU$6150.
> Netgain Warp 9 is AU$2395, Soliton JR is AU$2175, so a total of AU$4570.


You compare a 65Kw system to a 100+Kw system.
If you consider a used forklift motor and a Zeva controller the cost difference can be huge.
Consider 11" forklift motor for long highway drive...


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## vocalnick (Aug 5, 2013)

Yabert said:


> You compare a 65Kw system to a 100+Kw system.
> If you consider a used forklift motor and a Zeva controller the cost difference can be huge.
> Consider 11" forklift motor for long highway drive...


Yeah, I've obviously confused things a bit by comparing two very different motor/controller combos. My bad.

I'll have a look around for salvage and see what comes up. As Duncan said above, if I can get DC cheaply now, I can always upgrade to AC later.


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## EcoReality (Mar 10, 2014)

vocalnick said:


> I solder like a 5-year old, but I play in a band with a fellow who's an electronics engineer...


Run! Hide! You want an electronics _*technician*_, not an engineer!

Engineers _think_ they can solder, 'cause they've built a few prototypes. But you want someone who does it eight hours a day.

(Duck! Incoming flames from all the engineers on this thread!)


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## vocalnick (Aug 5, 2013)

EcoReality said:


> Run! Hide! You want an electronics _*technician*_, not an engineer!
> 
> Engineers _think_ they can solder, 'cause they've built a few prototypes. But you want someone who does it eight hours a day.
> 
> (Duck! Incoming flames from all the engineers on this thread!)


Hah!

I'm probably using the wrong nomenclature. He knows his stuff


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## vocalnick (Aug 5, 2013)

OK, dragging this back up the page for a moment - I've got the DC version of my build pretty much hypothesised out, but I want to take another look at this AC idea before I lock anything in.

Traffic was a lot heavier this morning than it was when I did my drive the other day, and I noticed I was doing a LOT of downhill stop-start toward the end of the drive in to town (where some regen would be useful, as opposed to early in that trip). But more than the battery advantages, I also realised how nice it is to have a means of slowing the vehicle OTHER than the brakes. I've had brakes fail on me before, and with the terrain around here, that would be really scary in a car that can only accelerate or coast. This was already brought up earlier in the thread, but it's starting to hit home a bit. Besides, I _like_ the feel of engine braking!


I've also plotted out the elevation map for my commute on Google Earth (image attached) and it does make me reconsider the regen potential of that route...

So I'm looking at the HPEVS systems again. I realise they're a bit lower powered, but from what I'm reading they're still not exactly slouchy, and I'm not building a racer.

No real questions (although I'd be keen to see if the elevation profile prompts any more thoughts), mainly just updating the thread if anyone happens to search it later with the same query


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## EcoReality (Mar 10, 2014)

Cool! How did you obtain that plot? (Please tell me it was simple, and not a matter of mousing the route and logging the numbers into Excel... 

Although I'm resigned to DC (due to cost), I'm increasingly thinking about using the rear shaft to run a big alternator for regen braking. There's a fairly detailed thread around where the guy used an air-conditioner clutch to mechanically turn an alternator on or off.

I've got a huge 3kW Neville-Leece alternator that came out of a firetruck or ambulance or something. It should slow things down noticeably, no? Plus it would be good to dump 3kW back into the batteries, if only for a moment.


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## vocalnick (Aug 5, 2013)

EcoReality said:


> Cool! How did you obtain that plot? (Please tell me it was simple, and not a matter of mousing the route and logging the numbers into Excel...


Haha, I DID actually start doing that, and got to the bottom of my road (about 5.5km) and got fed up. Then a bit of googling and it turns out it's stupidly easy. You just do a normal "Get Directions" search on Google Earth, then click "save route to My Places". Voila! Your route is saved to your "My Places" list as a path.



> Although I'm resigned to DC (due to cost), I'm increasingly thinking about using the rear shaft to run a big alternator for regen braking. There's a fairly detailed thread around where the guy used an air-conditioner clutch to mechanically turn an alternator on or off.


That sounds interesting - I hadn't considered that sort of option... I have a bit of lead time on this project, and _hopefully_ a nice contract coming up toward the end of the year which will help to bankroll the whole thing, but I'm all for saving money just the same! 

The HPEVS systems are appealing to me mainly because of the "it just works" factor. This is my first project of this magnitude, so the more stuff I can get off the shelf, the less margin for me screwing things up...


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## EcoReality (Mar 10, 2014)

vocalnick said:


> The HPEVS systems are appealing to me mainly because of the "it just works" factor. This is my first project of this magnitude, so the more stuff I can get off the shelf, the less margin for me screwing things up...


Ah, that's where we differ. I'm not happy unless I've managed to strand myself by the side of the road because of doing something stupid... 

Case in point: my "donor vehicle" became available when I salvaged an oil tank with about 30 gallons of old heater oil in it -- and I decided to pour it into my diesel Vanagon's tank. It was full of rust, causing me to change the fuel filter every 10 miles or so... :-(


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## Duncan (Dec 8, 2008)

EcoReality said:


> Ah, that's where we differ. I'm not happy unless I've managed to strand myself by the side of the road because of doing something stupid...
> (


Unfortunately I resemble that remark


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## dedlast (Aug 17, 2013)

vocalnick said:


> Haha, I DID actually start doing that, and got to the bottom of my road (about 5.5km) and got fed up. Then a bit of googling and it turns out it's stupidly easy. You just do a normal "Get Directions" search on Google Earth, then click "save route to My Places". Voila! Your route is saved to your "My Places" list as a path.


DeLorme's Earthmate program has that feature built in. It's a bit more expensive than Google Earth, though...

Bill


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## Yabert (Feb 7, 2010)

Free: Ride with GPS


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## bwjunkie (Jul 31, 2013)

EcoReality said:


> I'm increasingly thinking about using the rear shaft to run a big alternator for regen braking.


This is what I was thinking about as well, but something that can engage and disengage on demand. Maybe a prototype could simply charge the 12v system.


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## EcoReality (Mar 10, 2014)

bwjunkie said:


> This is what I was thinking about as well, but something that can engage and disengage on demand. Maybe a prototype could simply charge the 12v system.


The one I saw used an air conditioner compressor clutch, which engages via a 12V solenoid. I don't know if he used explicit control, or ran the solenoid from the brake light switch. Seemed pretty slick, although a no-load alternator won't have much more load than a disengaged clutch -- a set of bearings and some rotating mass. (And yea, belt flex and slip.)


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## tomofreno (Mar 3, 2009)

vocalnick said:


> OK, dragging this back up the page for a moment - I've got the DC version of my build pretty much hypothesised out, but I want to take another look at this AC idea before I lock anything in.
> 
> Traffic was a lot heavier this morning than it was when I did my drive the other day, and I noticed I was doing a LOT of downhill stop-start toward the end of the drive in to town (where some regen would be useful, as opposed to early in that trip). But more than the battery advantages, I also realised how nice it is to have a means of slowing the vehicle OTHER than the brakes. I've had brakes fail on me before, and with the terrain around here, that would be really scary in a car that can only accelerate or coast. This was already brought up earlier in the thread, but it's starting to hit home a bit. Besides, I _like_ the feel of engine braking!
> 
> ...


Cool! Thanks for the info on how to generate that profile!
There is a graph with some data on my car in this post which may give you some idea of what you might get with regen on your commute: 
http://www.diyelectriccar.com/forums/showpost.php?p=366384&postcount=20

I also just added a post with some calculations to the regenerative braking section in the wiki.

You will be more limited in peak power with the HPEVS systems as you say. Depends on your priorities. Energy efficiency is way up there in mine, rapid acceleration is more important to others. At present, the latter is much less expensive to achieve with DC as several have mentioned.


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## lithiumlogic (Aug 24, 2011)

Most people i suspect would get a longer range if they just spent the amount saved on a cheaper dc motor on more batteries, since regen is minimal on highway driving. The only time that might apply is if you don't have a high horsepower requirement (since the lower performance AC kits cost not too different to the DC ones, its just that the DC is more powerful) or your car is already full of batteries anyway and you could not physically add more regardless of budget.

I had an idea that might give an advantage to AC in winter conditions.

Basically, to harvest the heat off the controller and possibly the motor as well and use it to heat the cabin. 

With DC this would not be possible, because the controller is highly efficient and gives off little waste heat, most of the losses are in the commutator of the motor, but you can't use air that has passed through the motor to heat the cabin because it is full of ozone and brush dust.

With AC, most of the heat loss is in the controller, so the air coming off the controller heatsink should be warm and clean, and if you collect air coming off the motor cooling vents as well, since there are no brushes that should be breathable too.

The objection everyone states to this is that the heatsink cannot be allowed to get hot enough to make a good heat source.

I'd say that's only true if you're pulling in outside air at north american winter temperatures and blowing it across the heatsink with a non-variable fan.

If you take large volumes of air from the cabin and push it over the heatsink then feed it back into the cabin again, it will get warmer with every pass. So long as the heatsink is warmer than cabin temperature you will get heat.

Now, the next objection is that the windows will fog. To which i'd say you'd use an adjustable amount of fresh air for the heatsink/motor cooling to combat condensation and also give a semblance of temperature control (otherwise the cabin is going to turn into a sauna with 3kw waste heat being dumped at highway speeds). You could back this up with a ceramic heater fo r scenarios where waste heat isn't enough (cold urban journey, or recirc open)


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## EcoReality (Mar 10, 2014)

lithiumlogic said:


> regen is minimal on highway driving


Let me guess: you're from the midwest, right? 

I grew up in "flatland," but I think the _best_ use of regen is in hilly terrain -- better than "stop-n-go" traffic, where your need to stop is generally sudden enough to _have to_ use the friction brake.

Many cities are in valleys, and many commuters live in neighbouring valleys, so they have to go up to a pass and down again. About 90% of my driving is going to be up a 10% grade for a few hundred feet of elevation gain, then down a 7% grade back to sea level.

Another common pattern is people living up in view areas and commuting down to a city. This doesn't favour regen so much, unless you can charge your car at work instead of at the very beginning of your richest regen source.


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## vocalnick (Aug 5, 2013)

I've been reading back & forth & all over on this.

One of the things that I'm keen to do is build a bullet-proof EV. Something that anybody can get in & drive without special training/orientation.

After reading this thread I'm leaning HEAVILY toward AC.

Sure, off-throttle regen will make coasting more touchy, but I can always shift to neutral to coast just like I do now with the ICE.


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## EcoReality (Mar 10, 2014)

vocalnick said:


> One of the things that I'm keen to do is build a bullet-proof EV. Something that anybody can get in & drive without special training/orientation.
> 
> After reading this thread I'm leaning HEAVILY toward AC.


There's no reason to leave the clutch installed, for either DC or AC.

That thread has changed my mind about leaving the clutch in. It's coming out! The tranny is loose enough that I can carefully run through the gears without a clutch.


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## EVfun (Mar 14, 2010)

Yes, I prefer AC/DC on a long trip. Its important to stay awake.


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## onegreenev (May 18, 2012)

> Something that anybody can get in & drive without special training/orientation.


Go drive an EV that has a transmission but no clutch and see how easy it is to shift fast. I find that most of the time I don't need to shift real fast but I do find I need to shift faster than a clutch less would allow. I don't just leave it in one gear. I do use my transmission. 

You may want to rethink that decision. Yes, you can do the shifting without the clutch but not fast. If someone else drives the car and they are used to a clutch it may be an issue. Not an issue with what you were wanting. If your doing to save weight then I'd say remove something else. That clutch is a pretty nice thing to keep. All my builds have retained the clutch. If you forget and try to jam the shift you can damage the internals of the transmission. It is important with a low voltage system to leverage the transmission and the transmission was designed with a clutch. Yes, I am aware that the electric motor is not like the pulsing gas engine but it is sure nice to do some quick shifting when jamming through town in heavy traffic. I fully utilize the power of the transmission. Just something to think about.

Pete


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## lithiumlogic (Aug 24, 2011)

The "hard" part about driving a stick shift (if you're just wanting to get around safely) is avoiding stalling by not slipping the clutch enough when pulling away.

This is not a consideration on an electric motor. You can select the gear, let the clutch out and then pull away, if it makes life easier at junctions. You cannot stall.

You can also find yourself in too high a gear with engine rpm dropping below idle (causing the idle governor to jam the throttle open to try maintain rpm when you may not want to accelerate right now, and the whole car to start shuddering) and find yourself forced to make a gearchange during a high workload time. 

Again, not a problem on an EV with smooth running down to 0 rpm and no idle governor bumping you forward.

Another issue a novice driver may find themselves needing to accelerate through a junction but being in too high a gear. Less likely in an EV since max torque is delivered down to 0 rpm.

Then there are the myriad of finesse factors which are easier with the EV - worrying about the engine vibrating because the revs are too low and the load too high, or of it racing loudly due to you slipping the clutch too much or being slow with an upshift.


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## dougingraham (Jul 26, 2011)

EcoReality said:


> There's no reason to leave the clutch installed, for either DC or AC.
> 
> That thread has changed my mind about leaving the clutch in. It's coming out! The tranny is loose enough that I can carefully run through the gears without a clutch.


You cannot go clutchless and use coast down regen of an AC system. There is simply not enough energy stored in the rotor and when in neutral the motor stops turning immediately so you never see a speed match. I supposed you could put a button on the stick that would let you disable to regen for when you are shifting.

Up shifts take quite a bit longer because there is no drag slowing the motor down. Down shifts can be accomplished fairly quickly by goosing the throttle.

If you want a project you can build a speed matcher that knows what gear you are trying to go into, calculates the input shaft rpm based on current speed for that gear and forces the motor rpm to match what the input shaft needs to see. Then you could truly eliminate the clutch.

Best Wishes.


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## EcoReality (Mar 10, 2014)

onegreenev said:


> it is sure nice to do some quick shifting when jamming through town in heavy traffic


My EV will never be driven that way. I live on a rural island, and this vehicle is being specialized for two purposes: farmers market, and picking up guests at the ferry.

Still, I see that you're almost as likely to damage the motor by slipping it into neutral and revving as you are by pushing in the clutch and revving.

So moving on to ease of install.

Is a clutched adaptor easier to build than a clutchless one? I've been thinking a clutchless one would be easier, but now I realize that by leaving the clutch, all I have to do is make the electric motor look like a flywheel, which is probably simpler than making it look like a pilot spline.

Also, my application doesn't have a lot of room. I thought ditching the clutch would make for a shorter installation.

(Sorry to hijack this thread — feel free to point me to other threads that have covered this issue.)


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## lithiumlogic (Aug 24, 2011)

EcoReality said:


> My EV will never be driven that way. I live on a rural island, and this vehicle is being specialized for two purposes: farmers market, and picking up guests at the ferry.
> 
> Still, I see that you're almost as likely to damage the motor by slipping it into neutral and revving as you are by pushing in the clutch and revving.


Impossible on an AC - the controller has to turn the magnets on and off in sequence to produce rotation, so even with zero load the motor won't spin any faster than the controller allows it to. The software rev limiter kicks in at 8000 on the AC 50 which is about double where max power is, but i imagine it could spin an awful lot faster still without flying apart. No camshafts and valve gear to worry about like an ICE, in fact no reciprocating components at all.


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## EcoReality (Mar 10, 2014)

lithiumlogic said:


> Impossible on an AC - the controller has to turn the magnets on and off in sequence to produce rotation, so even with zero load the motor won't spin any faster than the controller allows it to.


A very good argument for AC! But I already have a DC motor and controller, so I can't afford to change horses in the middle of the stream.

I'll just have to train people how to drive it.


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## vocalnick (Aug 5, 2013)

EcoReality said:


> (Sorry to hijack this thread — feel free to point me to other threads that have covered this issue.)


I'm the original poster, and I'm happy with the divergence. I've pretty much covered off my original query, and I'm learning a lot following the subsequent discussion... carry on!


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## EVfun (Mar 14, 2010)

I built my EV Buggy without a clutch and a Datsun wagon with a clutch. I prefer clutchless. Shifting is a little slower, but it has never been enough to be a concern. I hear some transmissions don't do as well as others though. Here is a shop that offers both types. I haven't done any business with them as my clutchless coupler was made locally about 15 years ago.


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## EcoReality (Mar 10, 2014)

EcoReality said:


> Is a clutched adaptor easier to build than a clutchless one? ... I thought ditching the clutch would make for a shorter installation.


I found the "clutch vs clutchless" thread.


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## onegreenev (May 18, 2012)

EcoReality said:


> My EV will never be driven that way. I live on a rural island, and this vehicle is being specialized for two purposes: farmers market, and picking up guests at the ferry.
> 
> Still, I see that you're almost as likely to damage the motor by slipping it into neutral and revving as you are by pushing in the clutch and revving.
> 
> ...


Yes, there is always a chance but in reality if you know how to drive a stick then it usually won't be an issue. I will have an RPM limiter so if the controller is powering the motor I won't have to worry if I blip the throttle before I have the clutch fully engaged. My limiter works pretty good. 

No issue about hijacking. Happens all the time.


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## onegreenev (May 18, 2012)

Going clutch less can shorten the length and it may be a help. If your just lumbering along and really never needing to jet through traffic then clutch less should be fine. Be sure the transmission is in good mechanical condition.


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## dougingraham (Jul 26, 2011)

EcoReality said:


> Still, I see that you're almost as likely to damage the motor by slipping it into neutral and revving as you are by pushing in the clutch and revving.


I was worried about this a little bit when I first started driving my car. I have a DC Netgain Warp 9 with a Soliton 1 and a clutch with a lightweight flywheel. I have a tach sensor on the aux shaft and the Soliton 1 won't let it go over the 6k rpm setting. My greater fear was missing a downshift and forcing the motor beyond anything reasonable with the mass of the car. And this would be an issue for either type of motor. It turns out that I don't even think about this anymore. The car stays in third gear and reverse except when I am giving demos where I use second gear to take your breath away. I was told that Warfield spin test the armatures to 8000 rpm so I would have to be exceeding:

1st gear 38 mph
2nd gear 64 mph
3rd gear 99 mph
4th gear 141 mph
5th gear 186 mph

The 4th and 5th gear examples are only possible in some sort of James Bond universe where he drives the car out of the back of an airplane and lands on a vertical piece of the Toyota Corolla joyride commercial set. And even then it seems unlikely the aerodynamics of the car would let you reach those speeds in freefall.

Clutch less it is not going to happen. You would put it in neutral and mat the throttle pedal and wait and wait and wait and wait some more and keep on waiting and it would take a long time and you would realize what had happened and let off the throttle and put the shift selector in the position for the gear you really wanted. With a clutch you would start to release and you would hear the motor rev up to an insane speed like you have never heard before and the tires would most likely lose traction and you would step back on the clutch and wonder what you just did. But probably no damage. It is the same issue as was there with the ICE and blowing up the ICE almost never happens. If it happened that often we would have a lot of interesting rollers to convert.


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## lithiumlogic (Aug 24, 2011)

Is that any more likely to happen to an EV than an ICE?

Yes perhaps because the motor has less inertia and lower drag, it will be physically easier to select a wrong gear. No because the motor should handle overspeed much better than an ICE with conrods, camshafts and timing belts.

It's the sort of thing I used to worry about before I learned to drive.

Then when I started taking lessons, i found that it's almost impossible even if you tried. Even with the clutch in, the synchromesh or something baulks when you try selecting a gear that would take the engine over the redline - for example when going from 2nd to 3rd. There's no way to accidentally select 1st because if you push the stick too far leftwards (first) the huge resistance naturally diverts the lever where it should go. In twenty years of driving a manual i've never accidentally selected a gear that is too low. 

I have, several times, gone too high. Eg. from 2nd to 5th when i wanted 3rd, because in this direction the gearbox won't try and stop you.

I think it's because slushboxes dominate in NA people get hung up on this sort of thing.

For me i can only imagine an electric motor with manual box and clutch being almost as easy to drive as a full auto.

Yes, you physically have to move the lever and change gear, but not as often as on an ICE because it pulls so much better down low and makes so much less noise up high. And the hardest thing, slipping clutch so you make a smooth start (not bringing the pedal up too fast and getting a lurcher, not too slow and racing the engine and making unecessary clutch wear) is gone.

Stop at the red light, then downshift to whatever gear you want to pull away in - have it ready while the light is still red. Then when it changes, just press the accelerator and leave the clutch alone.


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## EVfun (Mar 14, 2010)

Yes, over-revving is more likely to happen with a DC motor EV. If you coast over the maximum speed in a gear there is no ever increasing motor drag trying to hold you back. If you are blipping the throttle to match rpm for downshifting (or with the clutch pedal depressed) it is worth noting that the motor revs up insanely fast. The throttle only needs a tap, as quick as you could punch the throttle to the floor and release it the motor will be near redline.


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## Ausemoto (Jun 6, 2014)

Why all the talk of using the transmission still? Its a huge waste of the main thing that is going to cause the guy trouble with reaching his targets on a long range car. Energy.

As pretty much all conversions sit in 1 gear 99% of the time why would you want to keep the 10-20% losses of a transmission just for the odd chance that it might be slightly easier to change gear? Just gear the car for 140km/h and you will still manage to have enough power to get the car moving faster then most other vehicles on the road.

Also no one seems to be mentioning BLDC, to me the easiest way to build his car up with the range he is desiering would be to use a twin motor setup to allow for the peak power levels for acceleration of 100kw, been BLDC he will be able to use regen and hopefully the motors he sources will have a high efficiancy. The motors Ripperton used in his Mira conversion would be a great idea. You could build the drive system using some standard drive shafts into a central retainer, have the motors running parallel to the drive shafts will a belt/chain drive connecting them to allow for gearing changes to get the desired top speed.

For batteries I would recommend packing them along the base of the car similar to the Tesla S, just make sure the bottom plate of the battery pack is relatively thick and strong  BMS system for a car i am really liking the Zeva system. Not cheap but very worth it as the batteries are the most expensive part of the car. 40S and some Kelly controllers and it will be a fun long range EV.
http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=57291


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## Duncan (Dec 8, 2008)

_Why all the talk of using the transmission still? Its a huge waste of the main thing that is going to cause the guy trouble with reaching his targets on a long range car. Energy.

As pretty much all conversions sit in 1 gear 99% of the time why would you want to keep the 10-20% losses of a transmission just for the odd chance that it might be slightly easier to change gear? Just gear the car for 140km/h and you will still manage to have enough power to get the car moving faster then most other vehicles on the road._

Where do you get 10 - 20%???

A manual transmission has losses in the 2 - 4 % range - or less


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## Ausemoto (Jun 6, 2014)

Sorry maybe my % are abit of a exaggeration but the 10% will not be far off when you start talking about a almost 20yr old car that probably was not maintained to the best standard.

2-4% would be just the gears themselves in a good modern transmission. Then you start talking loading friction and oil movement etc. Modern manuals maybe <4% in specific situations. How many OEM electric vehicles use transmissions?


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## dougingraham (Jul 26, 2011)

Ausemoto said:


> How many OEM electric vehicles use transmissions?


I can't think of any. They do however have a gear reduction and that is chosen quite carefully, something that is rather more difficult for us as DIY to do. So keeping the transmission allows us to use a less powerful motor that has a lot lower RPM limit and take advantage of the torque amplification of the transmission. The transmission can get us close to the ideal gear for a single gear system. In my case the 4th gear is just a little too tall to use for everything. Even with 1000 amps on a WarP 9 a 3.909 final drive does not get the acceleration I would feel comfortable with. The top speed is adequate at just under 100 mph. Third gear is better but not quite what I want for taking off from lights. Top speed in third is about 68 mph and it has a final drive ratio of 5.598. To be comfortable with that would require both more torque and a higher RPM limit with a wider torque band. 2nd gear is very powerful delivering almost 1/2 g of acceleration but only up to 32 mph and the redline speed is 45 mph (8.67 final ratio).

So to go single ratio you need a high torque and high revving motor with a carefully selected single reduction ratio.


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## bwjunkie (Jul 31, 2013)

Ausemoto said:


> As pretty much all conversions sit in 1 gear 99% of the time why would you want to keep the 10-20% losses of a transmission just for the odd chance that it might be slightly easier to change gear?


My DC motor has a powerband just like a gas motor. I understand the transmissions primary job is to manage powerband. And going in reverse.

But I'll just assume for a min you are correct:
I guess it would be nice if you explain the route a typical $9k (4k after credits) DC conversion guy like myself could have gone to magically replace the transmission.

What do I hook my two axles to? How do I get into reverse?
How do I mate my wheels to a motor that likes to spin at 3k RPM?
And do it without increasing the price more than another 1k?

josh


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## rochesterricer (Jan 5, 2011)

Ausemoto said:


> How many OEM electric vehicles use transmissions?


Brammo Empulse is the only one I can think of, besides plug in hybrids.


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## frodus (Apr 12, 2008)

rochesterricer said:


> Brammo Empulse is the only one I can think of, besides plug in hybrids.


And it's a blast! Just rode mine to work this morning. Does help put it into the power band of the motor a bit, but 6-speeds might be overkill.


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## Duncan (Dec 8, 2008)

Ausemoto said:


> Sorry maybe my % are abit of a exaggeration but the 10% will not be far off when you start talking about a almost 20yr old car that probably was not maintained to the best standard.
> 
> 2-4% would be just the gears themselves in a good modern transmission. Then you start talking loading friction and oil movement etc. Modern manuals maybe <4% in specific situations. How many OEM electric vehicles use transmissions?


10% is far too high - just think of the heat dissipation that would involve

All OE electric vehicles use a transmission - as in a way of gearing the motor to wheel rpm and driving two wheels

What they don't use is a multiple speed transmission - because with high speed motors and a decent amount of torque they don't need to

If you use a manual gearbox
You are carrying extra weight
The gears that are not being used are spinning away under no load

These do give some losses - but tiny 2 - 4 % - probably LESS on an old well worn in manual gearbox


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## Ausemoto (Jun 6, 2014)

> Remarking on transmission efficiency in a paper on advanced technology vehicle modeling, Edward Nam of the U.S. EPA states
> 
> Manual transmissions range in efficiency from 87-99%. Automatic transmissions range 85 – 95% when locked, but can drop to 60 - 85% unlocked. An overall 1.5% improvement in transmission efficiency could correspond to a 0.1 km/L increase in fuel economy Greenbaum, et al., 1994; Kluger, et al., 1995; Bishop, et al., 1996. Manual transmissions have similar efficiencies to continuously variable transmissions (CVT), so can be seen as equivalent to advanced transmissions.
> 
> Vehicles whose drivetrains run off of motors do not require complex transmissions employing gear shifts. These motor driven vehicles usually only require a single gear due to the large operating range of motors. Single gear transmissions naturally tend to be very efficient and are assumed to be 95% efficient in this report.


So I guess your right, manual transmissions can be really efficient. 99% sounds more then just abit impossible for a multi-gear transmission but EPA says its so. 

I am suggesting the use of BLDC motors *http://en.wikipedia.org/wiki/Brushless_DC_electric_motor *rather then the simple Brushed motors, Ripperton has just used one on his mira conversion that is working quite well. They are compact and very power dense. 

Hopefully there is enough room for a pair of the motors to be running across the engine bay facing each other. As explained briefly before build up a simple mounting box for the drive shafts to mount into, the motors would sit parallel to them using a belt drive to connect a single motor to each drive shaft.

Calculating max speed is not hard with some simple maths, if you manage to get it wrong change the pulleys slightly to get the speed you are after. 

Cost,
2x motors from kelly $1600 64kg 92% efficient
2x BLDC controllers $3400 15kg 144v600a
Engineering parts $2000 ~30kg Mounting box, bearings, belt, pulleys
Batteries 10kwh Lipo $5500 60kg Freaking ton of wiring. So worth it.

$12.5 without asking for discounts. Could probably get it down to $11k just on the discounts from Kelly for buying so much at once. So you would have a 100kw car with regen, higher efficiency, longer range and probably better power control then a Brushed motor system. And if you looked around some more it might be possible to go cheaper on the same parts just from different locations.

Keen to hear what type of system you have for $9k, really wish i could get a $5k payback  Sorry i kinda derailed the thread abit.


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## Duncan (Dec 8, 2008)

$8k for motors and controllers

Mine (DC) cost $700 - leaving more money for batteries
And I have 100Hp from mine


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## Ausemoto (Jun 6, 2014)

Impressive, $700 for motor inc controller?

You wouldn't mind telling me your best 0-60mph time, even a rough idea would be great? And a total weight for your car?


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## Duncan (Dec 8, 2008)

Hi

The Device feels between my Legacy (9.5 sec) and my wife's SLK (7 sec) in performance,
About 8 seconds to 60mph (100Kph) ????
It used to weigh 710Kg but I've added some cells 740Kg???

http://www.diyelectriccar.com/forum...-dubious-device-44370p2.html?highlight=duncan


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## Tesseract (Sep 27, 2008)

Ausemoto said:


> ...
> I am suggesting the use of BLDC motors* ... *rather then the simple Brushed motors, Ripperton has just used one on his mira conversion that is working quite well. They are compact and very power dense.....


I wonder about your (and his) definition of "working quite well"... Last I read, Ripperton's little Mira takes somewhere around 20 seconds to get to 100kph. No thanks - there are electric wheelchairs that accelerate faster than that...

BTW - brushed motors are actually more complex than BLDC or induction motors; it is the *controller* that is simpler for the brushed motor.


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## QuietCar (Jan 3, 2013)

After building cars with transmissions as well as direct drive, My brain tells me to go with the transmission. you would need a very special motor as well as a specific gear ratio to make direct-drive work. 

50% of your driving will be unloaded and with mulitiple passengers.
You will need around a 9:1 to a 12:1 gear ratio for direct drive to work.

Any hills, large loads or offroad use will also need a transmission.

QC


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## Ausemoto (Jun 6, 2014)

Seems i have a lot to learn, i did not notice that little bomb of 23sec to 100km. I guess i should have waited until i have my drive motors and controllers up and running before saying how good BLDC is. I ll still stay on the side of ditching the transmission and just using a appropriately sized motor.

QuietCar, with the cars with and without transmission did you use the same size/type cars? Am i barking up the wrong tree, was there much of a difference in mileage with no transmission vs having one.


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## QuietCar (Jan 3, 2013)

I have owned several EV's. Some were DC, some were AC. I have a fondness for both types. They both have their good points

In one of them, I got to try it with and without a transmission. 

In a DC car with a trans and 3.50 rear gears, it was quick and nimble out of the hole in low gear and after a shift, it would nicely accelerate up to traffic speeds. (First gear and third gear)

But when I got to a hill, the amps would rise and use current a lot.
If I dropped to first gear, it would hold 35 MPH with low current draw, but traffic would back up behind me. 

Second gear was a life saver in those conditions. (Also when there was more people in the car.) 45 MPH with a decent current draw.

The AC cars drove differently. They were softer out of the hole, but had a 
nicer RPM range, so I only needed 2 gears and used a lower rear axle ratio to take advantage of the extra top RPM. 

After a while I did some figuring and decided to lower my rear gear and 
just drive in high gear. It worked out so well that I eventually removed the transmission totally. This car weighed less than 2,500 LBS. 
I would not try direct drive over 2,500 Lbs.

Plus with my gearing, I was cruising at 2,599RPM most of the time. (under the field weakening base RPM where it had a lower current draw).

I had 5.13 rear gears and short tires.......letting that AC motor work in it's happy spot.

The AC/no trans was a wonderfully simple car to drive, but the DC car with a trans was slightly longer range and more adaptable to loads and terrain.

QC


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## arklan (Dec 10, 2012)

isnt mileage increased with a gearbox?
because ur not drawing so many amps out of the batteries at take off


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## samwichse (Jan 28, 2012)

Battery amps aren't equal to motor amps.


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## QuietCar (Jan 3, 2013)

> Battery amps aren't equal to motor amps.


I don't think anyone suggested they were.



> isnt mileage increased with a gearbox?


Yes, and for the same reason as on an ICE. It matches the motor's most efficient RPM to the load more easily.

Direct drive is just simpler to drive. You pay a penalty in wrong gearing at either low speed or higher speeds, how ever you gear the car. 

When geared for high speed, you pull extra amps while accelerating through the lower speed range. OR, geared for low speeds, you zip up to high speed easily and use a lot of throttle to cruise there. (Without a transmission)

With careful engineering and resources, it can be optimized somewhat.

QC


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## major (Apr 4, 2008)

arklan said:


> isnt mileage increased with a gearbox?
> because ur not drawing so many amps out of the batteries at take off


Probably not. If you travel the same speed, the battery current is nearly the same regardless of the gear ratio over a wide range of motor RPM. The losses in the transmission and additional mass of it could actually mean less range.


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## arklan (Dec 10, 2012)

one says yes and one says no
it seems to make sense to me that having a gearbox would increase range because ur not working the motor so hard, seeems logical to me but im no expert(tm)


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## major (Apr 4, 2008)

arklan said:


> one says yes and one says no
> it seems to make sense to me that having a gearbox would increase range because ur not working the motor so hard, seeems logical to me but im no expert(tm)


If you care to research the topic, there are numerous threads on this site discussing EV transmission use. There are also threads on the subject over on endless sphere and elmoto. It is a common topic right up there with the AC/DC thing


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## vocalnick (Aug 5, 2013)

Ausemoto said:


> Sorry i kinda derailed the thread abit.


Original poster here - I have no problems with a thread derail - it's been an interesting diversion, and it's still pretty much on-topic as far as I can see 

I'd love to ditch the transmission (less weight, less complex) but I'd kind of intuitively assumed that it probably wasn't a good idea based on the fact that almost nobody else does it... 

My project has been in stasis for a while, as my contract work went off its nut for a while so I had no spare time. Now things have settled down a bit, so I can start finally pulling out the ICE stuff and getting on with it.


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## onegreenev (May 18, 2012)

vocalnick said:


> Original poster here - I have no problems with a thread derail - it's been an interesting diversion, and it's still pretty much on-topic as far as I can see
> 
> I'd love to ditch the transmission (less weight, less complex) but I'd kind of intuitively assumed that it probably wasn't a good idea based on the fact that almost nobody else does it...
> 
> My project has been in stasis for a while, as my contract work went off its nut for a while so I had no spare time. Now things have settled down a bit, so I can start finally pulling out the ICE stuff and getting on with it.


I think if your planning any of the HPEVS systems you should consider keeping the transmission. It is there to take advantage of and being the HPEVS systems are considered low voltage (lower rpm) systems you will need to leverage the transmission to your advantage. Nice car. 

Pete


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## steven4601 (Nov 11, 2010)

dougingraham said:


> You cannot go clutchless and use coast down regen of an AC system. There is simply not enough energy stored in the rotor and when in neutral the motor stops turning immediately so you never see a speed match. I supposed you could put a button on the stick that would let you disable to regen for when you are shifting.
> 
> Up shifts take quite a bit longer because there is no drag slowing the motor down. Down shifts can be accomplished fairly quickly by goosing the throttle.
> 
> ...


Clutchless up shifting takes me about 2-3 seconds on a warmed up gearbox/motor bearings. A little slow indeed compared to clutched or dogbox shifting, but most of the time rest of traffic is many car lengths behind trying to catch up. I should post a crystal clear video perhaps how easy AC is with clutch less. 
The whole AC regen on zero throttle is a choice, not a hardware limitation. I choose zero regen on zero throttle. Coasting for miles is possible that way.


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## bjcouche (May 17, 2013)

Back to your original design goal of 100+ mile range... I'd recommend an AC system, possibly an HPEVS AC35 X 2. Or possibly just a single HPEVS motor option if your car is going to have a final weight of 2500lbs or less. 
From what I've seen, the folks with lead batteries do well with the DC motors. That fits well, cheap motor, cheap batteries. Obsolete battery technology, obsolete motor technology. I've heard from several people who upgrade their lead sleds to lithium and increase their drive time from 15 minutes to 60+ minutes. The problem is that by the end of the 60 minute commute the DC motors are super hot, well beyond their 30 minute time rating. After a few months of doing this the armature is destroyed and they buy a new motor.

Brian


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## Duncan (Dec 8, 2008)

bjcouche said:


> Back to your original design goal of 100+ mile range... I'd recommend an AC system, possibly an HPEVS AC35 X 2. Or possibly just a single HPEVS motor option if your car is going to have a final weight of 2500lbs or less.
> From what I've seen, the folks with lead batteries do well with the DC motors. That fits well, cheap motor, cheap batteries. Obsolete battery technology, obsolete motor technology. I've heard from several people who upgrade their lead sleds to lithium and increase their drive time from 15 minutes to 60+ minutes. The problem is that by the end of the 60 minute commute the DC motors are super hot, well beyond their 30 minute time rating. After a few months of doing this the armature is destroyed and they buy a new motor.
> 
> Brian


If you are using a teeny tiny motor - yes 
But I can cruise at 100kph (speed limit here) at less than the 1 hour current on my DC motor
AC is the way of the future
But my $700 DC system is more powerful than a $12,000 AC system
Which leaves a LOT more money for batteries


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## bwjunkie (Jul 31, 2013)

bjcouche said:


> . Obsolete battery technology, obsolete motor technology. I've heard from several people who upgrade their lead sleds to lithium and increase their drive time from 15 minutes to 60+ minutes. The problem is that by the end of the 60 minute commute the DC motors are super hot, well beyond their 30 minute time rating. After a few months of doing this the armature is destroyed and they buy a new motor.


Sounds like a popularity contest for motors when using the word "Obsolete" which has little definition, except "no longer produced or used" which is obviously not true. I'm prototyping anything I think might work, and it seems to me that is a good description for much of the EV world. It's a very good point on the heat issue, which I am examining now that I'm extending range on my DC system. How simple of a cooling system will do the job? We shall see. 
-josh


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## vocalnick (Aug 5, 2013)

Some people seem to have some very strongly held views on both sides. I try to cut through the ideology when I'm evaluating all the various tips and advice.

I hadn't considered the heat issue either, so that's another one to add to the list. It is hard to argue with DC's value proposition though...

Sigh... The real problem is I don't have the funds right now, so I have far too much time to think. If I'd already made a purchase I could just start looking for evidence to support my decision and "pick a team"


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## aeroscott (Jan 5, 2008)

On evtv Jack said his suv will overheat with 2 11" motors after about 1 hour. Big batteries can last long enough to get into heat problems for dc motors. Lot of heat in the commutators.


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## bwjunkie (Jul 31, 2013)

aeroscott said:


> On evtv Jack said his suv will overheat with 2 11" motors after about 1 hour. Big batteries can last long enough to get into heat problems for dc motors. Lot of heat in the commutators.


can you post a link, or do you know if he has since considered any cooling fins or tubs, etc?

-josh


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## aeroscott (Jan 5, 2008)

Google evtv in the last 2 or 3 episodes . blow as much air threw them as you can and don't overwork them. Cooling only works on the surfaces exposed to cooling.


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## bwjunkie (Jul 31, 2013)

aeroscott said:


> Google evtv in the last 2 or 3 episodes . blow as much air threw them as you can and don't overwork them. Cooling only works on the surfaces exposed to cooling.


okay thanks,
I'm wondering about increasing the surface area available for air to contact with.
-josh


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## aeroscott (Jan 5, 2008)

Big utility's use He or H2 gas cooling which is a much better thermal conductor then air and has less drag, but this requires a sealed system .
A easier fit for a ac system.


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## Duncan (Dec 8, 2008)

aeroscott said:


> On evtv Jack said his suv will overheat with 2 11" motors after about 1 hour. Big batteries can last long enough to get into heat problems for dc motors. Lot of heat in the commutators.



My 11 inch motor has a continuous rating of 208amps - so two would be 416amps
And that is a typical conservative forklift rating - without any extra cooling

I would expect a small amount of extra cooling to give at least a 20% improvement

Does jack really have a pack that is bigger than 600Ah on his SUV??


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## onegreenev (May 18, 2012)

Duncan said:


> My 11 inch motor has a continuous rating of 208amps - so two would be 416amps
> And that is a typical conservative forklift rating - without any extra cooling
> 
> I would expect a small amount of extra cooling to give at least a 20% improvement
> ...



I believe the cells in Jacks SUV are either 300ah or 400ah. Not 600ah. Given to him by Winston Battery Company as payment for advertising.


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## Hollie Maea (Dec 9, 2009)

Duncan said:


> My 11 inch motor has a continuous rating of 208amps - so two would be 416amps
> And that is a typical conservative forklift rating - without any extra cooling
> 
> I would expect a small amount of extra cooling to give at least a 20% improvement
> ...


Current rating is only half of the story--it determines copper losses. But the motor ratings assume that the voltage is at the (low) nameplate voltage--as is the case in the forklift. Jack is running his motors at much higher voltages--as is pretty much anyone who is trying to run a car at road speeds. Those higher voltages mean significantly more iron losses. So that's a second source of losses, and a second source of heating. That means you no longer can tolerate as much copper losses continuously.

Power is power. You can't use current (or voltage for that matter) by itself as shorthand for power. The bottom line is that at the end of the day, your motor is rated something like 12 horsepower. DC motors are great at blowing their ratings out of the water for short periods of time. But on the long term, you always will run up against that limit. And since DC motors produce their losses primarily in the rotor, there aren't good ways to cool them down. In the lead days, it didn't matter because you would run out of juice before they heated up completely. But it's an issue with today's ranges.


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## Duncan (Dec 8, 2008)

_Current rating is only half of the story--it determines copper losses. But the motor ratings assume that the voltage is at the (low) nameplate voltage--as is the case in the forklift. Jack is running his motors at much higher voltages--as is pretty much anyone who is trying to run a car at road speeds. Those higher voltages mean significantly more iron losses. So that's a second source of losses, and a second source of heating. That means you no longer can tolerate as much copper losses continuously.

_On the other hand higher voltages mean higher rpms 
Which mean a lot more cooling air - with the standard on-shaft blowers
And that heat is NOT generated at the Com - which is normally the weak point


_your motor is rated something like 12 horsepower.

_True - and false - by keeping the same current and trebling the rpm you get 36Hp,

More heat to dissipate - maybe twice as much? with three times the air flow!

Two of these is 72Hp - more than enough for steady state highway speeds


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## Duncan (Dec 8, 2008)

I should ask Major this
If Hollie is correct then we should see failures from overheating inside the rotor windings,

I was under the impression that most failures were either "mechanical damage" or brush/com


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## Hollie Maea (Dec 9, 2009)

I think brush/com failures are common when motors are pushed to stratospheric levels for short periods of time. Windings overheating becomes an issue if too high power is sustained for a long time. There's a lot of thermal mass there, but at some point it heats up. Still, Major or Tessaract can correct me if I am wrong.

Keep in mind that the iron cores are basically the heat sink for the copper windings. If they are producing more heat due to the higher voltage, they won't be able to deal with the copper losses as well.

The bottom line is, if your current stays the same but your voltage increases from 50 to 150, your losses will triple unless your efficiency improves, which it won't. And all those losses must turn into heat. Yes, your self cooling will improve at higher RPMs, but not enough, I don't think.




> True - and false - by keeping the same current and trebling the rpm you get 36Hp,


That's the part I disagree with. Yes, increasing your voltage increases your RPM but you never get power for free. The 12hp continuous rating is all about how much heat the motor can handle/dissipate. You can't triple it just by increasing the voltage/RPM.


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## Tesseract (Sep 27, 2008)

Hollie Maea said:


> The bottom line is, if your current stays the same but your voltage increases from 50 to 150, your losses will triple unless your efficiency improves, which it won't...


Nah, tripling RPM will result in some increase in iron losses in the rotor of the DC motor (or the stator of the AC motor) but it won't be anywhere close to tripling. The vast majority of the losses in a well-made DC motor are resistive, which can be confirmed by looking at a graph of efficiency vs. RPM at a constant current.

The funny thing about motors is that no matter the type or construction they are all subject to the laws of physics. Generally speaking, that means their continuous power rating is directly proportional to their volume and mass (ie - the amount of iron and copper in them).

Why DC motors *appear* to be more fragile than, say, ACIMs is because they are routinely paired with controllers that far exceed their continuous power rating. This is done quite simply because one can - the series DC motor will continue delivering increasing amounts of power right up until the point it catastrophically fails, whereas the typical ACIM is limited to a peak power of around 3x its continuous rating, and beyond that output actually starts to fall (ie - past breakdown torque or a certain amount of field-weakening).

This is sharply illustrated by comparing two popular motor/controller combos where the motors are roughly similar in size/mass: the HPEVS AC-50 & Curtis system, which pairs up a ~50hp motor and a ~80hp inverter (ie - the controller is rated for 1.6x more power than the motor) versus a WarP-9 & Soliton1 system, in which the motor is rated for ~26hp at 72V/265A but can withstand 160V and 1000A for around 10 seconds (ie - 214hp, or ~8x more) and the controller, of course, can deliver that level of power indefinitely.

Now if you were to limit the controller in the DC system to only provide the same maximum power of ~80hp (say, 150V and 400A), you can pretty much rest assured that you'll never have to worry about brush replacement, comm flashover, overheating, etc., but then the value proposition of DC compared to AC is not so good anymore; let's face it, the one thing DC has going for it is gobs of peak power for cheap. 

Which kind of circles back to Jack's assertion that DC motors can't handle the kind of continuous power that a modern lithium battery pack can deliver. Well, duh... the HPEVs motor would be overheating, too, if paired with a controller that could deliver ~150hp continuously. So this is not an apples to apples comparison and, as per usual, his playing fast and loose with the "facts" results in conclusions that range from wildly inaccurate at best to disingenuous and self-serving at the worst. Remember, Jack is trying to sell a bunch of AC inverters (65, IIRC) that he bought at the Azure Dynamics auction back in November 2012... The fact that he has not yet sold them all tells you all you need to know about the size of this market.


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## major (Apr 4, 2008)

Tesseract said:


> Nah, tripling RPM will result in some increase in iron losses in the rotor of the DC motor (or the stator of the AC motor) but it won't be anywhere close to tripling. ........


Nice post, young Tess


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## Tesseract (Sep 27, 2008)

major said:


> Nice post, young Tess


File under: "Even the blind squirrel finds a nut now and then..."


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## Hollie Maea (Dec 9, 2009)

major said:


> Nice post, young Tess


So the forklift motors are most inefficient at their nominal college? They should work on that...


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## Tesseract (Sep 27, 2008)

Hollie Maea said:


> So the forklift motors are most inefficient at their nominal college? They should work on that...


That's one way of reading it. Power output goes up more than losses so efficiency in percentage terms goes up as well. However, for most motors losses do not increase as much as power output if just RPM is increased, so this is hardly a unique characteristic of series DC.


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## Hollie Maea (Dec 9, 2009)

Relax, I'm not bashing series DC machines. I just don't get why they would run at low voltage/RPM since that gives then lower efficiency. I don't see the downside of running at higher voltages, as is done by EVers.


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## major (Apr 4, 2008)

Hollie Maea said:


> Relax, I'm not bashing series DC machines. I just don't get why they would run at low voltage/RPM since that gives then lower efficiency. I don't see the downside of running at higher voltages, as is done by EVers.


OHSA and other agencies have a cutoff at 50 Volts. In Europe it is 80 V. So a lot of industrial and telecom equipments are 48 V or lower. You can run higher voltage, but have more stringent safety requirements for the machines and personnel. And that equates to cost


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## Hollie Maea (Dec 9, 2009)

Thanks, that explains it


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## bwjunkie (Jul 31, 2013)

re: DC (warp)

If I can keep the frame of the motor cool, will there still be a heat issue inside?
-josh


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## aeroscott (Jan 5, 2008)

Yes , coils in the frame and the armature (rotating part). Oil cooling is used but not in brush motors. There is a motor that has less heating in the
armature , switched reluctance motors. OEM's aren't even using them yet
except LTI( earth moving equipment)


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## major (Apr 4, 2008)

aeroscott said:


> Yes , coils in the frame and the armature (rotating part). Oil cooling is used but not in brush motors. There is a motor that has less heating in the
> armature , switched reluctance motors. OEM's aren't even using them yet
> except LTI( earth moving equipment)


Hi aero,

The rotor isn't necessarily the armature. It is with the DC commutator machines used for EVs. But in synchronous machines most often the armature is the stator and the field is the rotor, as in alternators and PM AC motors (including BLDC).

Typically the armature generates more heat than the field. The rotor in the PMAC and BLDC being permanent magnet produces very little heat. The rotor in the switched reluctance machine also produces very little heat as in next to nothing. It has been ages since I worked on SRD, but I believe the stator would be called the armature as it is a synchronous machine.


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