# DC verses AC



## Caps18 (Jun 8, 2008)

I don't have much time to write this right now, but I wanted to ask you guys about the basics about why going with an AC motor would be better than the DC one? Is it regen? Is it less maintenance? Is it more efficient/powerful? Does it cost more?

http://blog.evtv.me/store/proddetail.php?prod=AC50Kit

Compared to the Warp 9 let's say.


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## Ampster (Oct 6, 2012)

I am going to use an AC motor in my next conversion because I want regen. I recently purchased a RAV4 EV which also uses an AC motor. In the end it boils down to a personal choice based on your priorities and preferences.


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## Ivansgarage (Sep 3, 2011)

Caps18 said:


> I don't have much time to write this right now, but I wanted to ask you guys about the basics about why going with an AC motor would be better than the DC one? Is it regen? Is it less maintenance? Is it more efficient/powerful? Does it cost more?
> 
> http://blog.evtv.me/store/proddetail.php?prod=AC50Kit
> 
> Compared to the Warp 9 let's say.


 
Here we go again and again ect ...............................


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## Ziggythewiz (May 16, 2010)

Yes, Yes, No, Yes.


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## frodus (Apr 12, 2008)

Go to Search at the top, and type in "AC versus DC", you get quite a few results:
http://www.diyelectriccar.com/forums/search.php?searchid=574660

Sometimes when searching for short terms, like AC or DC, google is better. You can go to google and type:
site:www.diyelectriccar.com "AC vs DC"

Like this:
http://lmgtfy.com/?q=site%3Awww.diyelectriccar.com+%22AC+vs+DC%22

Basically, it's been brought up a ton, and been discussed quite a bit.

Good luck.


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## Qer (May 7, 2008)

Ziggythewiz said:


> Yes, Yes, No, Yes.


I think I'd rather say "Yes, Maybe, No, Yes", but what do I know...


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## Jan (Oct 5, 2009)

And I think, it's very simple: AC wins on all points over DC, except one: money. If you want the max power burst possible for your budget, go DC.


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## Tesseract (Sep 27, 2008)

This is one of the most tired and rancorous debates in EVdom.

I am the hardware design engineer for Evnetics so I won't even pretend to be neutral. As far as I am concerned, AC makes no sense at all for the DIY market. It's cutting edge technology for a market that is, shall we say, exceptionally "price sensitive"... 

What the AC vs. DC debate really boils down to in the end is regen braking and brush wear. How much more are you willing to pay to get the former and lose the latter?

For example, the Curtis 1238-7501 + AC-50 kit delivers 73.6KVA peak (we'll treat KVA as kW, though that's being overly generous) and costs $4600 (or $62.50/kW). The "leading description*" DC system with a WarP-9 motor can do 115kW (192V and 600A at the motor) and costs about $3900 (or $33.90 per kW).

The DC system is almost half the cost per kW delivered. But let's say you don't care about the power difference and are only interested in reducing energy usage. No problem, just compare the energy consumption with the help of regen vs. without it then see how many miles you have to drive to pay for the $700 difference in the two systems.

It has been widely reported here and elsewhere that regen braking returns, on average, about 5% of the pack's energy. Let's be generous and double that to 10%.

If the typical EV requires 333Wh to go 1 mile then you can drive 3 miles on 1kW-hr. Electricity in Tampa, FL costs $0.10 per kWh so the cost per mile is ~3.33 cents. Being extra generous, we'll say that regen saves 10% of that cost per mile, or 0.33 cents. You have to drive approximately 212,000 miles to save enough on electricity to pay for the "savings" provided by regen.

Maybe it extends the amount of time you can go before buying brake pads. I dunno. My Nissan Frontier truck went 80k miles before I replaced the pads, and they still had plenty of life left when I did it, but let's say you can save 1 brake pad replacement over the life of the car. What's that worth, $300? Okay, now you only have to drive 121,000 miles for the AC system to break (brake?) even.

This is nothing but math, and the math doesn't work in AC's favor. But I understand that there are legitimate intangible reasons for wanting AC, like you prefer the "engine braking" feel of regen, and there are legitimate tangible reasons, like not having to worry about brush dust and wear. I can't argue with any of those reasons because they are legitimate and/or subjective, and who am I to tell you how a car ought to drive? If your rationale for choosing AC is that it reduces energy consumption then can I perhaps also interest you in some fine Florida real estate I have for sale? 

That said, I am not so blinded by remorseless logic that I can't see this is a debate I am slowly but surely losing. If people are willing to pay twice as much per kW for an AC system then who am I to deny them the privilege (or myself the extra profit)??? 


* - two points to whomever remembers the phrase, "leading description cold remedy"...


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## Stiive (Nov 22, 2008)

Ziggythewiz said:


> Yes, Yes, No, Yes.


Yes, Yes, Yes, maybe.


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## Ivansgarage (Sep 3, 2011)

I wonder why big companys like these, use AC ????????
Maybe they know something the rest of us don't..

Tesla Motors AC
Toyota Scion xB converted by AC Propulsion
Think Nordic AC
Reva Electric Car AC
Nissan AC


I do like that title (chief electron herder)


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## Stiive (Nov 22, 2008)

Ivansgarage said:


> I wonder why big companys like these, use AC ????????
> Maybe they know something the rest of us don't..
> 
> Tesla Motors AC
> ...


+
Mitsubishi iMiev
GM Volt
All hybrids
Renault fluence
BMW mini E
Fisker Karmer
Audi etrons

Should we continue?

Infact i think the only OEM series DC EV was one of the Mahindra/Reva cars that also used lead acid. But then again, top gear proved a dining table was faster and safer than this car


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## PStechPaul (May 1, 2012)

Based on my knowledge and experience (more AC than DC), I would say:

1. Regen from AC may give 10% boost in efficiency and the familiar "feel" of compression braking in an ICE car.

2. Minimal maintenence of the ACIM is worth a lot to me. YMMV. 

3a. Efficiency of ACIM may be better than an equivalent DC brushed motor over a wider range of RPM and torque.

3b. The DC series wound motor has much higher PEAK torque than an ACIM of the same RATED power.

4. The commercial AC motor/controller kits are significantly more expensive based on PEAK power according to Tesseract, although they may be closer based on RATED Continuous power. But if you can use an industrial ACIM and VFD obtained used or surplus on eBay or elsewhere, the AC option will probably be cheaper (although salvaged forklift motors and controllers may be lowest cost - like the Forkenswift). 

What is BEST depends on your own criteria, which may involve your technical knowledge and experience, as well as your ability to make modifications and troubleshoot problems. If you need help, it seems the DIY EV community has much more experience with DC, so that may be the most important deciding factor.


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## sfk (Nov 18, 2010)

If maximum range is the desired goal, then AC is more efficient use of energy available. And if your commute includes stop/start traffic and hills, AC is better again.

I have a 160km round trip commute every day (90 miles) which includes some significant hill climbs and coasting on the downhill sides. I'd like to do the entire trip there and back in 1 charge if possible. From what I have learned so far AC is a better solution.

I'm not trying to save as much money as possible. DC is a cheaper option. But I can justify diverting my next few years worth of fuel bills into building an EV and have it pay for itself in 3-4 years and then go on to continuously save me money each year thereafter.

And I agree with the point raised previously: all the major car manufacturers designing EVs PEVs and Hybrids are going with AC systems. Why?


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## Duncan (Dec 8, 2008)

As Tesseract Said

AC is "Leading edge technology"

AC is best - the same way that a turboprop is better than old 1930's aircraft engine

But a Cessna has an old 1930's flat six engine 

And by exactly the same logic I am using DC - AC for DIY is either wimpy or expensive or both

If I was making hundreds or thousands of units AC would be better AND cheaper
Making one 
It's DC

SFC said 
_If maximum range is the desired goal, then AC is more efficient use of energy available. And if your commute includes stop/start traffic and hills, AC is better again._

Nonsense - _If maximum range is the desired goal, - _buy more batteries!
Re-Gen only scores if you are driving in cities - when range tends not to be important
Or if you drive like a hooligan_ - _careful driving gives most of the benefits of re-gen -- FREE


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## Stiive (Nov 22, 2008)

Duncan said:


> If I was making hundreds or thousands of units AC would be better AND cheaper
> Making one
> It's DC



I guarantee more AC motors are made daily than series DC. 
You can buy a used 7.5kw (10hp) AC induction motor for like $50 on ebay and then overclock it to 50kw+. Get two of those and your laughing.

But lets face it, people use DC cus the majority of other DIYers use DC, and therefore plenty of options for controllers and motors built especially for DIY have popped up. Mainly I guess because DC is so much easier to control and to get good power out of it - AC requires a bit more work. This has made DC cheap for DIY EV, and the controllers come with all the IO required for a vehicle - not like an industrial VFD for an AC motor.

I'd also agree series DC is better for average Joe doing a DIY EV conversion, but are we asking which is better? There's no contest IMO.


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## Tesseract (Sep 27, 2008)

Ivansgarage said:


> I wonder why big companys like these, use AC ????????
> Maybe they know something the rest of us don't.....


You already answered the question... they are BIG companies, and they have BIG piles of money to spend on R&D. Heck, Tesla was started with $7.5M of seed money from Elon Musk while Nissan spent over $1B on the development of the Leaf! Curtis Instruments claims to spend 10% of its $110M in annual revenue on R&D... that would make their R&D budget something like 20x bigger than our annual revenue!?!

Also, need I point out that NONE of those fancy-pants AC-powered EVs are *profitable*? Heck, even Tesla lost some $200M, net, in 2011...

And let's not forget Azure Dynamics... Look how betting on AC drive technology worked out for them. Looks like it took them straight to the auction block for liquidation... oops.


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## Stiive (Nov 22, 2008)

Tesseract said:


> Also, need I point out that NONE of those fancy-pants AC-powered EVs are *profitable*? Heck, even Tesla lost some $200M, net, in 2011...


Biggest mistake Tesla ever did was go AC.... rookies


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## Ziggythewiz (May 16, 2010)

AC is far less of a mistake than tying most of their IP to laptop cells.


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## Tesseract (Sep 27, 2008)

Stiive said:


> Biggest mistake Tesla ever did was go AC.... rookies


Obviously I was poking fun there. Don't get your panties in a wad over it, Mr. Sensorless DTC. 

Eventually the DIY market will be worth developing a high powered AC system for, but right now the estimated sales volume is ~200 units per year and that doesn't inspire anything more from me than a long yawn...


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## dragonsgate (May 19, 2012)

One reason for car companies use of AC could be to give the average driver the feel of an ICE car with compression. Possibly lower maintenance and most likely when something does blow out the motor will stop and not plow into the car ahead like a DC setup might do if the controller goes. When AC Motors start taking over at the drag races then will be the time of reckoning.


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## Stiive (Nov 22, 2008)

Tesseract said:


> Obviously I was poking fun there. Don't get your panties in a wad over it, Mr. Sensorless DTC.


lol 



Tesseract said:


> Eventually the DIY market will be worth developing a high powered AC system for, but right now the estimated sales volume is ~200 units per year and that doesn't inspire anything more from me than a long yawn...


Is it public knowledge how many units you guys sell? I'd be very curious.

Yeh, my project is just a personal hobby BTW. Don't worry, I won't be raining on your DC parade  Just want to dispel the myths that AC cant be cheap. I think more DIY'ers should actually make something for themselves, live up to the name DIY, and save some cash along the way.


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## jeremyjs (Sep 22, 2010)

I was under the impression that AC motors were actually cheaper to build for a given quantity than DC. It's the controllers that are the expensive part.


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## Stiive (Nov 22, 2008)

jeremyjs said:


> I was under the impression that AC motors were actually cheaper to build for a given quantity than DC. It's the controllers that are the expensive part.


Permanent magnets motors definitely aren't, but induction motors would be comparable. Not sure if series DC use silicon steel laminations? 

By the same token, there's no reason why the controllers should be so much more expensive, apart from more R&D and development is required. They will still be slightly more expensive though due to more and higher voltage silicon, and they prolly want more capacitance. Well, and also need more feedback which needs to be accurate... but still, shouldn't be double-triple the price of DC equivalent as we see now.

I reckon you could make a 200kw AC controller for under a $1k of components... Tesseract, wanna employ me


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## Ziggythewiz (May 16, 2010)

Stiive said:


> By the same token, there's no reason why the controllers should be so much more expensive,
> ...
> 
> but still, shouldn't be double-triple the price of DC equivalent as we see now.


Try 3 phase = 3x the components.


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## sfk (Nov 18, 2010)

Duncan said:


> SFK said
> _If maximum range is the desired goal, then AC is more efficient use of energy available. And if your commute includes stop/start traffic and hills, AC is better again._
> 
> Nonsense - _If maximum range is the desired goal, - _buy more batteries!


Well actually I said "AC is more efficient use of energy available" which means not increasing the battery pack size (and the weight). AC is a more efficient design meaning, all other things being equal, you will go further with the same battery pack.



Duncan said:


> Re-Gen only scores if you are driving in cities - when range tends not to be important


...or if you have a rather large range of hills to get over and coast down the other side.

My aim is to achieve maximum range on smallest possible battery pack. Isn't AC the better solution?


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## Ziggythewiz (May 16, 2010)

Max range on smallest (capacity or cost) battery pack?

You can coast down an hill with DC as well. AC is only really helping you if you're needing to slow down lots or stop on that hill.


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## Stiive (Nov 22, 2008)

Ziggythewiz said:


> Try 3 phase = 3x the components.


Yes but the cost increase of silicon is only sqrt3 (1.707x)..... I did say they need more silicon. 
Though for total power match, you need RMS, therefore 2.4x. But then again, an AC controller is +-kW because of regen, so therefore double the amount of usable power 
The silicon isn't the only expensive part, albeit a high % of total cost.

Because a DC controller is $3k, doesn't mean an AC controller needs to be $9k


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## sfk (Nov 18, 2010)

Ziggythewiz said:


> Max range on smallest (capacity or cost) battery pack?
> 
> You can coast down an hill with DC as well. AC is only really helping you if you're needing to slow down lots or stop on that hill.


a balance of both of course! I have a limited space to fit the batteries and a limited budget to pay for them.

present intention to convert a 3rd gen RX-7 and install the battery pack behind the front seats where the silly occasional seats are. Replacing the rotary with an electric motor is probably going to be only a small difference in weight up front. Putting the batteries behind the front seats will keep the additional weight between the axles and have less impact on balance and handling than putting them in the boot or spare type well.

The regen down hill probably won't be significant, as you say. But a little bit = better than zero.

I do understand hill climbing is more suited to AC?


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## few2many (Jun 23, 2009)

Tesseract said:


> Eventually the DIY market will be worth developing a high powered AC system for, but right now the estimated sales volume is ~200 units per year and that doesn't inspire anything more from me than a long yawn...


As you mentioned with Soliton 1, Its not making you rich. However, thats what we need. Not someone expecting to create a whole car company, not someone expecting to leave their day job to get rich. We need someone Like you, Tesseract, who makes it in their spare time and makes it viable and available to DIY.


hint hint, do it for the fun!


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## Ziggythewiz (May 16, 2010)

Hill *climbing* is better with DC, at least compared to PM AC...slowing while coasting down the other side would be better with AC due to regen.

The main issue with cost vs space is that with a cheaper DC system if you can afford the extra space, you can afford more batteries that give you more range than you would get with the regen.


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## Stiive (Nov 22, 2008)

Ziggythewiz said:


> Hill *climbing* is better with DC


What makes you say this? IMO A hill climb (especially continuous) would be better with AC because of its ability to be water cooled.

Working flat out, DC would get hot quickly even with forced air cooling - especially because they tend to be low voltage high amps.


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## Ziggythewiz (May 16, 2010)

The P in PM is not so P under heat. Best Pikes Peak racer lost his PM this year while a DIY DC went all the way.


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## Stiive (Nov 22, 2008)

Ziggythewiz said:


> The P in PM is not so P under heat. Best Pikes Peak racer lost his PM this year while a DIY DC went all the way.


Sure if you don't treat it well, he must've been pushing it too hard - any component can fail when pushed too hard. This is a problem in PM motors though, seems to happen all too often in race applications. 

I still think the continuous rating of a water cooled AC motor of the same peak power would be higher or at least rated for longer. It all comes down to cooling in the end.

It'd be hard to prove this with manufacturer data though, because there doesn't seem to be a standard on how to rate peak and continuous power levels. 
The guy at pikes peak prob looked at the peak power figure, and then tried to run it continuously when its prob rated < a few seconds. 


I guess what your getting at is if you damage a DC motor by overloading it, itll still somewhat work - whereas a PM motor will die off quickly. Sure. Again it comes down to how the motor was spec'd to how quickly irreversible damage in either motor will occur.
But then, probably the motor with the most overload capacity would be water cooled induction motor, which is AC. 

So either way the answer to the original question is still AC FTW


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## Qer (May 7, 2008)

Stiive said:


> What makes you say this? IMO A hill climb (especially continuous) would be better with AC because of its ability to be water cooled.


That is only partly true. The squirrel cage is still air cooled in an AC motor, even though it's not using external air to cool down, so there's a limit how badly you can overload an AC motor.

There's nothing magic with AC motors really. They just convert electrical energy to mechanical energy as DC motors, they just do it in a very fancy way...


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## Ziggythewiz (May 16, 2010)

Stiive said:


> I guess what your getting at is if you damage a DC motor by overloading it, itll still somewhat work - whereas a PM motor will die off quickly. Sure. Again it comes down to how the motor was spec'd to how quickly irreversible damage in either motor will occur.
> But then, probably the motor with the most overload capacity would be water cooled induction motor, which is AC.
> 
> So either way the answer to the original question is still AC FTW


Most motors will work until they don't, though a scorched DC motor is probably much easier to repair than PMs that have essentially lost their magic smoke. Also, for a DC motor that point is higher than a PM can take, and can go much higher by upgrading the insulation if needed, but that's unlikely anyway.

How exactly do you liquid cool the rotor anyway?

I'm not interested in liquid cooling anyway, I'd rather keep it simple. The Volt and Karma had serious issues due to liquid cooling. Why mess with it? Radiator, water pump, antifreeze are all things we brag about not needing...until you go and stick em back in the car.


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## Stiive (Nov 22, 2008)

Qer said:


> There's nothing magic with AC motors really. They just convert electrical energy to mechanical energy as DC motors, they just do it in a very fancy way...


Lies, all electricity is magic!


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## Stiive (Nov 22, 2008)

Ziggythewiz said:


> How exactly do you liquid cool the rotor anyway?


Hose of course... Hose that sucker down.
OR a hollow rotor shaft with some sort of bearing seal fitting each end. Haha. Wonder if that's been done, no need though really.

Of course you could leave the motor unsealed, as is a series DC, and have the rotor air cooled a bit better. If you get a decent copper rotor, the rotor resistance and therefore heat build up will be quite minimal though anyway. 
Most of the heat generated when overloading an induction motor would be due to saturation of the iron I think.

Anyway, had my share. Thanks for the debate.. Love a bit of ACDC


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## steven4601 (Nov 11, 2010)

Being experimental from nature, I wondered if the rotor would become hot from 'sporty' driving. Around the city where I live there's quite a lot of stop & go trafic signs in the 50MPH speed limit roads. That allowed me to test thermal limits of the (AC) system. However, it appears the windings heat up more than the rotor. Parking the vehicle / stop liquid cooling system and observe stator winding temperature does not increase. In other words, the heat from the rotor does not reach the windings or the rotor is no hotter than the windings.

I did these tests with the M3AC60/4L from EVE with a WS200 and a 430V battery pack. (about ~ 95kW @ 18Celcius)


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## aeroscott (Jan 5, 2008)

In the SF bay area brake dust is the #2 polluter . Brake jobs run into big money , new rotors , pads, seals, master cylinder , brake lines and brake fluid . Try that on a 3/4 ton Dodge pickup (as I have ) with me doing the work and you just blew over $1000 . Or on a high end car and you could be into $5000 . Then tell me regin is over rated . I have done far to many brake jobs on my cars over 40 years , and I am easy on my brakes . I know an engineer that is so late on the brakes and brakes so hard he has to replace the rotors on every brake job , which is common on high performance braking systems using high metallic pads. With regin you have the metallic pads and never replace pads and rotors, retaining the best braking performance for emergency stops .


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## Duncan (Dec 8, 2008)

aeroscott said:


> In the SF bay area brake dust is the #2 polluter . Brake jobs run into big money , new rotors , pads, seals, master cylinder , brake lines and brake fluid . Try that on a 3/4 ton Dodge pickup (as I have ) with me doing the work and you just blew over $1000 . Or on a high end car and you could be into $5000 . Then tell me regin is over rated . I have done far to many brake jobs on my cars over 40 years , and I am easy on my brakes . I know an engineer that is so late on the brakes and brakes so hard he has to replace the rotors on every brake job , which is common on high performance braking systems using high metallic pads. With regin you have the metallic pads and never replace pads and rotors, retaining the best braking performance for emergency stops .


That's what I said - Regen is only useful if you drive like a hooligan 
With sensible (non Regen) driving pads last 10 years and rotors last 20+ years

I have not had to replace rotors on any of the family cars since I had an overpowered mini over 25 years ago
(that did eat one set of discs (rotors))


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## Jan (Oct 5, 2009)

Ziggythewiz said:


> The P in PM is not so P under heat. Best Pikes Peak racer lost his PM this year while a DIY DC went all the way.


I don't think he lost due to failing P... If you take Pikes Peak as a reference, you also see that AC does better than DC. Not so much better, that it's worth the price difference in my personal opinion. But if you want to win at all costs, I don’t think, there's a real choice.

The reasons real car producers ignore DC is because, I think, two main safety reasons:
1.	The risk of a runaway failure. You can't sell a production car with big red emergency button. That’s just not right. I know AC has that risk too, but far far less. I think a runaway failure risk with AC is just as high as with an ICE. 
2.	Downhill engine braking. I would not dare to drive a heavy car downhill in European mountains with only brake pads slowing the lot down. I don’t think it’s even legal. In a DIY case, where you’re sure you never or seldom find yourself in such a situation it is irrelevant. But if you sell cars, you might sell it to someone who does this on a daily basis. That’s really dangerous, and very expensive on brake pads. And if you sell cars, you can’t pick your customers. Let alone control their usage of their car.

And then there are some marketing reasons:
1.	Regen again. In advertising it’s one of the biggest issues. It makes electric standout from ICE. People may say it’s just 10%. It doesn’t matter, it’s the idea. Besides that 10% is a number worth nothing. It all depends of the usage. If you drive your car most of the time on highways, it’s probably not even 1%. But in big cities, and very hilly area’s, it can reach much much higher numbers. 
2.	Very little maintenance. Again, it works in advertising. “Just one moving part”. We know it’s not true. Or the complete truth. But again, it’s what makes it stand out against ICE. The unique selling points. You better not ruin that with extra brake wear or something primitive like brushes.

The other advantages of AC versus DC, like weight/power ratio, better cooling, etc, are, I reckon, less important.

But in a DIY case, all these reasons can be totally irrelevant, or less important when it comes to costs. Money, is the only reason DC is still around. But I admit completely, a very very important reason.


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## Tesseract (Sep 27, 2008)

Stiive said:


> Is it public knowledge how many units you guys sell? I'd be very curious.


Nah, 200 units per year was just my most optimistic sales estimate for an inverter that would be about as powerful as a Jr but cost nearly 3x more. Maybe I'm just being too rational, but that doesn't strike me as a particularly compelling value proposition. I mean, compared to a Jr an inverter would need 3x as many IGBT modules, and they would need to be half-bridges instead of choppers, and they would need 6x the number of gate drive component along with a control board that is several times more complex to run everything. And what would I have? An inverter that is no more powerful than a $2000 Jr but costs somewhere between $5500 and $6500... Who the hell is going to buy that? 



Stiive said:


> Just want to dispel the myths that AC cant be cheap. I think more DIY'ers should actually make something for themselves, live up to the name DIY, and save some cash along the way.


So should DIYers make their own motors? How about their own wire? Or their own LFP cells? Where do you draw the line for DIY? Obviously, I don't think DIYers should be making their own controllers and at least part of that is rational self-interest (I make no apologies for being a capitalist) but some of it is because I see people doing some seriously dumb (and dangerous) things.


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## Tesseract (Sep 27, 2008)

Jan said:


> I don't think he lost due to failing P...


We don't actually know for sure what failed on Tajima's car, but anecdotal reports are that torque rapidly declined about 1.6km into the race and then the motor caught on fire. This could be a catastrophic demagnetization event, or an insulation failure in the stator windings... Note that you can also demagnetize the PMs in this type of motor by applying too much current to the stator, especially at the wrong time. It's not just overtemperature that kills them.



Jan said:


> The reasons real car producers ignore DC is because, I think, two main safety reasons:
> 1. The risk of a runaway failure. You can't sell a production car with big red emergency button. That’s just not right. I know AC has that risk too, but far far less. I think a runaway failure risk with AC is just as high as with an ICE.
> 2. Downhill engine braking. I would not dare to drive a heavy car downhill in European mountains with only brake pads slowing the lot down. I don’t think it’s even legal.


I think the first reason is definitely true, but the second reason might not be too important because I think a lot of automatic transmissions don't let you engine brake at all - my 2007 Nissan Frontier certainly didn't. A 3rd reason that you didn't mention, but which I think is a major plus for OEMs, is that you don't have to worry about leakage current from brush dust with AC. That's certainly a valid point in its favor. 

Like I've said before, I don't disagree that AC is "better" technology, I just don't see developing an inverter for the DIY market as a very sensible business decision, is all. I mean, look how many people here are running Tritium Wavesculptor or Rinehart Motion inverters... Maybe a couple each.


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## Jan (Oct 5, 2009)

Tesseract said:


> I think a lot of automatic transmissions don't let you engine brake at all - my 2007 Nissan Frontier certainly didn't.


I've never seen such an ommision. In Europe automatics are already rare, but the very old once I've seen always had at least a 1 and sometimes a 2 position for engin braking. Maybe it's a difference between Europe and the US. Maybe I'm wrong. But I kown from experience driving in the Alpes without engin braking is no fun. I've learned that from our first holiday with my own car in the Alpes, as an ignorant flat lander.



> Like I've said before, I don't disagree that AC is "better" technology, I just don't see developing an inverter for the DIY market as a very sensible business decision, is all. I mean, look how many people here are running Tritium Wavesculptor or Rinehart Motion inverters... Maybe a couple each.


Tess, I understand. I really understand. DC might only have one advantage, but it's a really big one. 

But I don’t think this will be a fact forever. At some point in the future the price difference will get irrelevant. And eventually that over complicated AC inverter even gets cheaper due to mass production than that rare partly handcrafted DC controller.


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## mizlplix (May 1, 2011)

You guys sound like Edison and Tesla down at the local pub......

1. Regen is not a primary selection criteria. It is just a side benefit.

2. Both work nicely in a commuter role when geared correctly.

3. If I had a truck or an auto that had a load or pulled a trailer, I would choose AC due to the commutator heating issue, I killed one once.......

4. The wider RPM range of the AC motor is nice, It felt like I was "short shifting" all the time in my DC cars.

5. I do miss that occasional chirp of the tires my DC cars had.

At this point, I can not recommend an AC system due to the huge gap in the product offerings. An AC50 is really too small for most normal full sized vehicles and the high end stuff is just too costly for most of us to even get excited about.

I suggest that anyone thinking about a DIY project, go out and drive each before you decide which to invest in.

Yes, I will be replacing my AC50 with something else. AC, certainly. Probably a custom wound motor. Something with twice to three times the power.

Miz


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## aeroscott (Jan 5, 2008)

That doesn't sound like city driving of 4 or 5 stops /mile .


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## Qer (May 7, 2008)

mizlplix said:


> You guys sound like Edison and Tesla down at the local pub......


Which is perhaps why the moderators should close all further AC versus DC "debates" and point every newbie asking that loaded question to use the search function instead since this horse isn't just dead but also rather tenderized by now. I wish people would stop repeating the same myths and exaggerations over and over again.

Your list of personal observations felt very balanced and accurate. Sounds like a rather good starting point for a more constructive collection of recommendations.

Out of curiosity about your point 4, what pack voltage did you use in the DC system?


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## mizlplix (May 1, 2011)

Q: 

My first car was a factory original Jet Electrica with the 20 HP Prestolite motor and the wimpy 400 amp controller and 16 GC batteries for a 96 volt system. It would accelerate like a 1965 VW sedan......................

My second was another Jet, same motor but a 500 amp Curtis controller, and 4 more batteries for a 120 volt system. It was actually fairly normal to drive and at least keep up in traffic. 

They both had a 4 speed manual transaxle. thank goodness they both had a clutch, those synchros were very small and were difficult to clutch less shift.

I used every gear because it caused high current draw when skipping.

They were good learner cars.

Miz


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## Qer (May 7, 2008)

Thank you. Always nice to get verified what I started to suspect even back in the days when most controllers couldn't handle more than max 144 Volt; that ~100 Volt is way too low for building a DC-system with good performance, especially if it's also a system that's on the low side when it comes to current.

Of course, that also depends on other things like sag etc, it won't help much if you have a 200 Volt pack if it drops to 100 Volt under load. It seems that the battery rather than motor or controller/inverter is often the weakest link when people start to aim for performance...

Now we just need AC-batteries instead of these pesky DC-batteries...


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## Ziggythewiz (May 16, 2010)

Qer said:


> Now we just need AC-batteries instead of these pesky DC-batteries...


Just scale up the microinverters going on solar panels now  It would even serve as an isolated BMS and you would size your pack cell count based on the range needed, instead of the voltage.


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## Panhard (Nov 9, 2012)

Tesseract said:


> I am the hardware design engineer for Evnetics . . .


Regen, as in Tesla Roadster 2010, is major. It is powerful, such that you typically only use the brakes when you wish to come to a full stop. It is convenient, in that it is seamless and smooth to employ using one's right foot. Going down a long grade you can control your speed by either backing off (charging the batt) or by coasting (gauge at 12 o'clock, nothing going into or out of the batt). Having this whole range of control is effortless and intuitive. And it really adds to your range. 

To try to replicate this performance in a DIY DC 5 speed car I guess you would shift into neutral at the pass and then use the brakes when necessary to keep speed at a safe rate. All the heat from the brakes is wasted to the atmosphere. You might even stop the ICE if it is a long grade in order to save fuel. If you go fast enough you can mount each rise that you encounter. If there is traffic behind you, you may have to start the ICE to maintain speed. But you can get pretty much a free ride down the mountain. But do you want to go to all this trouble?

Yesterday in the Roadster I climbed 3000 ft (steep) and then dropped 4000 ft (not so steep) employing the regen that derives from just careful driving speeds (it was getting dark). Like any bike rider knows, you try not to over brake such that you need to add power to correct the over braking. From that point of view it was an efficient descent, even though done at a slower speed than one might use during daylight. Reaching the bottom my SOC was the same as if I had taken the alternate route that is slightly longer but only has a 1500 ft climb. Oh yes, I took this route in the opposite direction a few hours earlier- the first time I chanced it. Started with '220 miles' in the batt, went 166 actual miles, and ended up with '57 miles' in the batt. So '163 batt miles' = 166 actual miles, which is pretty close and means that 'the mountain was not really there' due to the effectiveness of regen. 

'Batt miles' are called Ideal Miles in the Roadster and are based on level driving at 55 miles per hour driving. I used cruise at 60 and 65 on flat stretches with no wind or tailwind, or 52 with headwind to try to replicate the Ideal expectations and to conserve power. So if you travel in mountainous areas the Roadster's balls-to-the-wall regen really is significant, not the 5% (10%) you allow. You really have to see this to believe it. 
--


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## Ziggythewiz (May 16, 2010)

Panhard said:


> So '163 batt miles' = 166 actual miles, which is pretty close and means that 'the mountain was not really there' due to the effectiveness of regen.


So either Tesla has conquered inefficiency and has a 100% regen rate, or measuring in battery miles is not as accurate as using kWh which us DIYers rely on for our DIY mathematics.


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## Panhard (Nov 9, 2012)

Ziggythewiz said:


> So either Tesla has conquered inefficiency and has a 100% regen rate, or measuring in battery miles is not as accurate as using kWh which us DIYers rely on for our DIY mathematics.


Just ballparking it of course. Tesla uses an algorithm to convert SOC to Ideal Miles and I'm trying to compare two different mountain routes. Better if I could compare it to a totally flat test route, so I'm looking for a good one to try. To regen, the motor has to go back thru the 20kw charger resulting in more losses of course, so my figures are pretty much anecdotal. I can pull up a kwh graph on the screen so I'll add this reading to my clipboard charting of waypoint data. KWHs & KWHs/mile = more accurate than anything out of an algorithm.
--


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## Tesseract (Sep 27, 2008)

Panhard said:


> Regen, as in Tesla Roadster 2010, is major. It is powerful, such that you typically only use the brakes when you wish t
> ...So if you travel in mountainous areas the Roadster's balls-to-the-wall regen really is significant, not the 5% (10%) you allow. You really have to see this to believe it.
> --


Yep. If you live in the mountains then regen is worth more and I don't disbelieve it. That doesn't apply to anyone in flat states like Florida, Texas, Nebraska, etc...

So, please go right ahead and enjoy your regen. I'm certainly not going to argue you shouldn't...


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## Ziggythewiz (May 16, 2010)

Panhard said:


> I'm trying to compare two different mountain routes. Better if I could compare it to a totally flat test route, so I'm looking for a good one to try.
> --


Even better would be if you can compare a non-regen drive to one with full regen. Is there a way to disable the regen, or would you have to just carefully do that with your foot? Is the regen controlled just by letting off the gas, or is it additionally applied with the brake pedal as well?



Panhard said:


> I can pull up a kwh graph on the screen so I'll add this reading to my clipboard charting of waypoint data. KWHs & KWHs/mile = more accurate than anything out of an algorithm.
> --


More data is always great! I'm still plotting to see if I can fit 8 gauges where my glovebox used to be.


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## otedawg (Apr 23, 2012)

Ziggy,
I've got my AC drive up and running (37kW max), and in my car (geo metro 4d) 12 mi with a net 0, -1000ft +1000ft elevation gain, I use 2.4kWh with regen on, and 2.9kWh with regen off. That's averaging 40mph, with the drive limited to 16kWh (in/out). I still haven't tested the drive with the full wattage, but I'd expect it to go down a bit.

I'm pretty happy with AC, although I wish I had the torque/power of DC. 

Sidenote: my DMOC445 runs regen the same way as a Tesla! Cool!

Otedawg


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## WarpedOne (Jun 26, 2009)

> Even better would be if you can compare a non-regen drive to one with full regen. Is there a way to disable the regen, or would you have to just carefully do that with your foot? Is the regen controlled just by letting off the gas, or is it additionally applied with the brake pedal as well?


Regen in Tesla Roadster is controlled by computer monitoring the "Go-Pedal" movements, battery SOC and temperature and traction conditions. Brake pedal doesn't effect regen directly.

There is no switch to disable regen. It is automaticaly 'disabled' when roadster is fully charged in range mode or TC computer senses poor rear traction. So, the only way to 'disable' regen is not to lift the right foot from the go pedal.

No offense ziggy, but I am very disappointed that people who make their own EVs know so little about the only real production EV out there. Especialy so becouse all the info is out there on the nets, if not elsewhere then on the Tesla Motors Club forum.

Regen has an interesting effect on drivers. Those who don't have it (DC systems, ...) swear they don't need it nor wan't it, those who have it swear thay cannot live without it anymore.

At the end of the day it all comes down to price. AC systems costs twice as much as DC systems. But they are not "twice as good". On poorly defined scale that is.



> Yep. If you live in the mountains then regen is worth more and I don't disbelieve it.


Not only mountains, it depends on amount of total energy used to heat brakes. 
In DC systems all "braking" results in heat, in AC systems about half of "braking energy" is recycled.


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## Qer (May 7, 2008)

WarpedOne said:


> No offense ziggy, but I am very disappointed that people who make their own EVs know so little about the only real production EV out there.


Well, no offence WarpedOne, but I really don't understand people that read up on every little detail on something they can't afford anyway.

Considering the price of the Roadster it's so totally out of my league that I don't see a point in learning every little detail about it. It's not just the Roadster I happily ignore though, I don't know very much about Koenigsegg, Veyron, or even Imelda Marcos' shoe collection as well.

So it's the only real production EV in the world? Big deal since I can't afford it anyway...


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## WarpedOne (Jun 26, 2009)

Every little detail? 

I have read even bigger blunders here on DIY... that roadster is 'just an electric Elise', etc.
The make of cooler fan motor in PEM is a detail. How tesla roadster drives and how regen is triggered is not a detail, it is part of basic education in the field of EVs. It kinda shows your primary interest. Is it technology, is it cars per se, is it money, ...


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## rochesterricer (Jan 5, 2011)

I think one of the big reasons people like AC is that the wider rpm range makes it easier to get away a single gear transmission. Perhaps advances in brush technology will allow higher voltage DC motors to do the same in the future.


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## Caps18 (Jun 8, 2008)

While DC isn't perfect, I think it is a little better and progressed for the DIY'er living in flat states at least. 

I would love to see Mythbuster-like testing from EVTV or the manufactuer's of DC motors or AC as to how much regen helps, driving style, environment, and cost. Plus the maintenance issues with carbon dust in DC motors.

5-10 years from now, DC might not be the correct choice. And if I was a big company with lots of engineers, AC would probably be better. But, I will be able to take a photo of my Dad's AC motor and my future DC motor and put this image by it:
http://images2.fanpop.com/images/photos/8200000/AC-DC-ac-dc-8277118-1600-1200.jpg


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## Tesseract (Sep 27, 2008)

WarpedOne said:


> ...Not only mountains, it depends on amount of total energy used to heat brakes.
> In DC systems all "braking" results in heat, in AC systems about half of "braking energy" is recycled.


The only energy that can be recovered by regen is that expended to increase velocity (ie - acceleration) or elevation. Period. I recently wrote an article for Charged EVs magazine about this: 

http://www.chargedevs.com/content/features-inside/closer-look-regenerative-braking

That said, I don't disagree that in most metrics (save absolute torque and peak power output) AC is superior to DC. I'd gladly develop an inverter for the DIY market if I could just be convinced that I wouldn't go bankrupt in the process. The problem is that there just aren't that many people that convert their cars to electric each year. Either that or we are getting *smoked* by every other motor controller manufacturer out there...


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## Ziggythewiz (May 16, 2010)

WarpedOne said:


> There is no switch to disable regen. It is automaticaly 'disabled' when roadster is fully charged in range mode or TC computer senses poor rear traction. So, the only way to 'disable' regen is not to lift the right foot from the go pedal.
> 
> No offense ziggy, but I am very disappointed that people who make their own EVs know so little about the only real production EV out there. Especialy so becouse all the info is out there on the nets, if not elsewhere then on the Tesla Motors Club forum.


That's what I thought, I just wanted to confirm. And no, I'm not an expert on every EV out there, especially the ones I'll never own even 2nd hand.

If I were designing a car I'd go a different route. To me it makes sense to brake using the brake pedal. You shouldn't have to balance the pedal between go and slow in order to coast...which I love to do. Based on what's been said here, I would expect to recover ~20 wH per stop, or 4%. AC needs to get lots cheaper to be useful in Flatville, TX.


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## WarpedOne (Jun 26, 2009)

> If I were designing a car I'd go a different route. To me it makes sense to brake using the brake pedal. You shouldn't have to balance the pedal between go and slow in order to coast...which I love to do. Based on what's been said here, I would expect to recover ~20 wH per stop, or 4%. AC needs to get lots cheaper to be useful in Flatville, TX.


Yes, this is the intuitive way of doing regen - nothing realy changes in the way you drive.
Prius does it this way yet people report that when brakes engage it is never smooth nor really predictable.
On the other hand 'braking' with go pedal is kinda unintuitive plus it also doesn't always behave the same way (disabled under certain circumstances etc; same can happen with brake-activated regen). When people get used to single foot driving they generaly like it. Balancing the go-pedal between "positive and negative" power is not necessary that hard as one would think. When done right, it can be almost effortless.

The real problem is max regen power and effect it has on car stability. It works through differential and thus tries to slip the wheel with less traction. A can of worms that is hard to appretiate until you are the one that has to iron out as much problematic situations as possible. Or until regen couses you to pirouete..


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## rochesterricer (Jan 5, 2011)

People who have tried strong regen seem to love "single pedal driving" once they get used to it and hate going back after.


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## Panhard (Nov 9, 2012)

> The only energy that can be recovered by regen is that expended to increase velocity (ie - acceleration) or elevation. Period. I recently wrote an article for Charged EVs magazine about this: [tesseract]
http://www.chargedevs.com/content/fe...rative-braking

You state the obvious i.e.: 

regen ~ momentum (as a limit)

then write an article to prove it. LOL.

And someone said these rehashed threads are too boring.
--


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