# DC OR AC for electric sport car



## madderscience (Jun 28, 2008)

Howdy-

The first questions shouldn't be AC or DC, it should be

1) How much
2) How fast
3) How far

You can pick 2, and those choices determine the third. Also, knownig your desires or expectations can help us make a more meaningful recommendation to you.

There is lots of information in the wiki regarding technical differences and the tradeoff you have to make when designing an EV. 

Cheers


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## m_k_321 (Nov 29, 2011)

Hello,

Fast enought to beat the gas. Version but same time to be a. Daily use. City car


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## FireCrow (Nov 11, 2011)

I think I'll stick to this subject as well, as I'm planning on doing that sort of conversion in future as well, on my European Focus MK2. City car - which in this case means not very big range. But yeah, quite a bit of power, so we're talking about beating speeds of T5 Volvo engine, which in Focus RS is delivering around 300 horsies to the front wheels. I think I've found enough space for batteries location. Surprisingly, even though it is a front wheel drive, it has a long and wide tunnel underneath, at the moment being used up by exhaust, but there's plenty of space. And, the fuel tank located underneath rear seat will be going as well, so there'll be a lot of space... And some weight reduction will be in order, so I possibly will replace bonnet and wheel arches with either fiberglass, carbon or kevlar, depending on the budget left after buying batteries  I did rather a bit of reading on the forum here, but I'm getting easily lost with all the electro-chat, my electric and electronic knowledge ends at replacing light bulbs with LEDs... There is a lot of factors to consider, but I'd say I'll be probably sticking as many batteries as possible in the tunnel, under rear seat, under bonnet, keeping the gravity centre as low as possible to the ground for proper handling.

So, as m_k_321 didn't really say anything about budget, I'm guessing it's moderate. With my conversion I'd probably go the route that the whole system would be easy to upgrade with more batteries (I'm guessing that should possible with correct controller, right?). Meaning that I'd probably start of with moderate power (just above average Focus 1.8 (my poor thing is just 1.6 and just over 100 horsies right now), then with bigger budget just buying and sticking more batteries in it.


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## Rational (Nov 26, 2011)

m_k_321 said:


> I am lost between AC and DC any suggestions ??


Post a generic rpm/torque curve for each type of motor.


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## dtbaker (Jan 5, 2008)

m_k_321 said:


> what kit do you recommend for best performance and also for normal driving conditions.
> 
> I am lost between AC and DC any suggestions ??



DC will deliver more torque for the money and you have wide range of choice for motor size, motor tandem multiples for big HP and controllers. 

AC may get you a little more range with regen, but the motor/controller cost significantly more than DC. You'd also get added braking, so if you want to race with lots of heavy brake/accel or do lots of stop/go, AC gets to be a better choice.


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## EVfun (Mar 14, 2010)

If he wants a Honda S2000 or BMW Z3 to go faster than stock what are his AC options? He seems to be asking for 5 second 0-60 times.


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## gor (Nov 25, 2009)

madderscience said:


> Howdy-
> 
> The first questions shouldn't be AC or DC, it should be
> 
> ...


exactly

it's not dc or ac, it's motor + controller (power, torque); battery power, price; 
i.e. power (speed, acceleration), range, weight AND cost


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## dtbaker (Jan 5, 2008)

EVfun said:


> If he wants a Honda S2000 or BMW Z3 to go faster than stock what are his AC options? He seems to be asking for 5 second 0-60 times.


thats why I was saying DC might give more options for the very high end accel with tandem Warp 9s, or a Warp11 and monster controller like Soliton, raptor, synkro. 

A big AC55, or perhaps Azure would be fast, but probably not sub-6 0-60.


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## PhantomPholly (Aug 20, 2008)

dtbaker said:


> AC may get you a little more range with regen, but the motor/controller cost significantly more than DC.


Has anyone calculated whether you can buy enough batteries to make up for the lack of regen with the savings on DC vs AC?


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## dtbaker (Jan 5, 2008)

PhantomPholly said:


> Has anyone calculated whether you can buy enough batteries to make up for the lack of regen with the savings on DC vs AC?



well.... its not quite apples to apples.... but lets start with:

Warp9 + Soliton Jr ($1800+2000) being pretty close in performance to an AC50+Controller ($4400)?

so.... maybe $500-$1000 difference all else being equal, especially if you went with a lower cost DC controller like a Curtis 1231 which run down around $1500

for that difference you get about 10%-15% range extension from AC if you need range, or 10%-15% reduction on electric bill in pure consumption. but electricity is the cheap part of all this... only pennies per mile of the operational cost. so say just a fraction of a penny per mile 'saved' with AC regen.

which is why I went DC.

now, if I was a mailman with all stop/go driving, or had huge hills like san francisco, I might go otherwise.


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## mizlplix (May 1, 2011)

OK, I might as well stick my oar in the water too,,,LOL.

"My opinion", {others might differ, but this is what I feel}

Use a 9" DC motor/1000AMP controller if you value zippy acceleration.
Your RPM range is 1/2 of an AC motor so you will use more gear changes.


Use an AC motor if you want a friendly car to drive. Moderate acceleration, but fewer shifts due to the higher RPM ability. Regen braking is just an added plus and should not be a major deciding factor. Longer motor life than DC. 

BOTH will need a PRIMO battery pack. Do not rely on a few 12 VDC car batteries, you are just kidding yourself. 

4-5 thousand dollars for motor/controller.

6-8 thousand for that good battery pack/charger system.

I am not trying to dissuade you. You need to know these things going into it, not find out half way through.

BTW" look at my signature below to see what I am running.

Welcome to the community. Miz


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## dtbaker (Jan 5, 2008)

mizlplix said:


> BOTH will need a PRIMO battery pack. Do not rely on a few 12 VDC car batteries, you are just kidding yourself.
> 
> 4-5 thousand dollars for motor/controller.
> 
> 6-8 thousand for that good battery pack/charger system.



definitely do not even consider lead.....
$5K li gets you 50-ish miles max, linearly up from there. 

as I said.... ac50 combo is around $4400, DC is going to be between $500-1000 less for comparable performance.


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## Duncan (Dec 8, 2008)

Hi Guys

_Warp9 + Soliton Jr ($1800+2000) being pretty close in performance to an AC50+Controller ($4400)?_

The AC50 is 50Hp peak 
The Warp9 + Soliton Jr is 175Kw - 234Hp peak

That does not sound "pretty close" to me!

As far as I can see if you want it to go then you need DC - 

Unless you can get one of the few powerful AC motors - $20,000+ 

http://www.acpropulsion.com/products-drivesystem.html


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## mizlplix (May 1, 2011)

Drive both then compare. Figures alone do not always accurately indicate what "real world" conditions are like.

If you can feed that 1000 amp controller, then yes, it is a LOT faster....but you are limited to a short squirt before it sags and you are faced with your sustainable amp output. That can be in the 250-350 amp range.

It is very dependent on your battery choice and how much room is in the vehicle for them.

Miz


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## Yabert (Feb 7, 2010)

dtbaker said:


> as I said.... ac50 combo is around $4400, DC is going to be between $500-1000 less for comparable performance.


So, you can see that from a different manner. For the same price, you can put your hand on a Warp 9 and a Soliton 1 to have access at a potential 150-200 hp

Well, almost double torque and double power for a similar price!
We all waiting for a high power AC motor controller for less than 4-5K$...


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## FireCrow (Nov 11, 2011)

so, basically, DC all the way then!!! Do you guys think that placing batteries in the tunnel and under bonnet is good enough for something quick? I mean do you think it would give enough space and be practical enough for it? Additional space would be where petrol tank is right now. I don't need much range, but speed and acceleration are things I am addicted to.


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## dtbaker (Jan 5, 2008)

FireCrow said:


> so, basically, DC all the way then!!! Do you guys think that placing batteries in the tunnel and under bonnet is good enough for something quick? I mean do you think it would give enough space and be practical enough for it? Additional space would be where petrol tank is right now. I don't need much range, but speed and acceleration are things I am addicted to.


If you want to minimize space AND maximize output, you would need to consider stepping up from prismatic cells to cylindrical (like headways), or 'pouch' style like Kokams if you have unlimited funds. They are higher cost, and much more time consuming to build into a pack; but can output at a much higher level without damage if you design in a little forced air to cool them.

for example. if a 50 mile max range is all you need, you'd be fine with 156v and 100ah pack. But if you go with prismatics you *should* only burst for short periods to 5C (500 amps) and continuous no more than 3C (300amps). With 100ah of headways at same voltage you could burst to 20C and drive around at 5C comfortably (limited by motor and controller cooling).


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## Qer (May 7, 2008)

dtbaker said:


> But if you go with prismatics you *should* only burst for short periods to 5C (500 amps) and continuous no more than 3C (300amps).


Just to clarify (or confuse) things:

This is *battery* amps. It still means that you can get a full 1kA *motor* amps from, for example, a Soliton 1 as long as motor voltage is half of pack voltage or less. So even if prismatics will limit peak power it won't limit your zero RPM torque and will still give you a helluva takeoff at red lights...


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## JRP3 (Mar 7, 2008)

Plus you can push prismatics higher occasionally for short bursts.


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## tomofreno (Mar 3, 2009)

> Warp9 + Soliton Jr ($1800+2000) being pretty close in performance to an AC50+Controller ($4400)?


 The AC50 with 650A controller has peak torque of about 108 ft-lb and peak about 80 HP shaft power with a nominal 115V pack. The WarP9 has about 110 ft-lb torque at 500A and can be run up to about 170V max without arcing things, so maybe 85 -90 HP shaft power. So they are somewhat comparable. *Edit: No they aren't. I wasn't thinking at all here. Shouldn't post when I am so tired. The 500A on the SolitonJr is current into the controller, output current can be much larger. Power out equals power in minus losses and the Jr has max input V =340V, so over 200 HP input power. I've even posted that before, sheesh.* * Doesn't change the conclusion below though:*

Neither will come close to the performance the OP wants though. He will require much higher torque and HP, which makes AC ridiculously expensive. So unless price is no object, his only choice is DC.


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## gor (Nov 25, 2009)

tomofreno said:


> The AC50 with 650A controller has peak torque of about 108 ft-lb and peak about 80 HP shaft power with a nominal 115V pack. The WarP9 has about 110 ft-lb torque at 500A and can be run up to about 170V max without arcing things, so maybe 85 -90 HP shaft power. So they are somewhat comparable.
> 
> Neither will come close to the performance the OP wants though. He will require much higher torque and HP, which makes AC ridiculously expensive. So unless price is no object, his only choice is DC.


trure, ac50 data 115v700a, 110 ft-lbs 70hp - been proven on evtv's Spyder dynoruns

on their other dynoruns warp9: 
500a ~140 ft-lbs; 110hp
1000a -277 ft-lbs 157hp

warp9 can take 2000a for10 sec; survived 3000a

what the peak hp, torque of ac50?
what it amps and volts limits?
what highest A & V ac50 been actually run, what controller, price?


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## dtbaker (Jan 5, 2008)

tomofreno said:


> The AC50 with 650A controller has peak torque of about 108 ft-lb and peak about 80 HP shaft power with a nominal 115V pack. The WarP9 has about 110 ft-lb torque at 500A and can be run up to about 170V max without arcing things, so maybe 85 -90 HP shaft power. So they are somewhat comparable.
> 
> Neither will come close to the performance the OP wants though. He will require much higher torque and HP, which makes AC ridiculously expensive. So unless price is no object, his only choice is DC.



right.... the only reason I used the warp9 in this example is that it is probably the closest comparable to the largest reasonably available AC motor. With a Soliton you CAN burst 1000amps thru the motor and double the output, but not for long. 

With DC you can also move up to Warp11 or Warp13s...... Where comparable AC is hard to find and very expensive.

so.... yes, DC seems like the way to go for 'street muscle' unless you really want regen braking coming into corners racing, and the money doesn't matter.


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## drgrieve (Apr 14, 2011)

The best "bang for buck" combo for dc is a kostov 220v 9" 45 kg with a Soliton Jr.

Thats 220v at 600 amps. 132 kW input to motor. Enough for a sedan (think 2.5L V6) or a small sports car.

Warp 9 is more upgradable if you swap to a higher amp controller to get V8 power.


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## m_k_321 (Nov 29, 2011)

Cant regen work on DC motor in any way ?


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## JRP3 (Mar 7, 2008)

Yes, but no.  Advanced motor timing will cause brush arcing, leading to destruction. Neutral timed motors can do it, if you can find a controller that supports it. Basically it's not worth the hassle.


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## m_k_321 (Nov 29, 2011)

May i ask what is arcing ?


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## dtbaker (Jan 5, 2008)

m_k_321 said:


> May i ask what is arcing ?


arcing is the 'zap' that crosses air gaps in a open circuit. The higher the voltage, the further the arc possible to close the circuit. It is destructive at high voltages because it can melt whatever the arc is touching.


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## EVfun (Mar 14, 2010)

m_k_321 said:


> May i ask what is arcing ?


A voltage is imposed on each commutator bar by the interaction of the armature and field. Ideally the brushes are located where the voltage applied to the brush equals the voltage that is trying to be imposed on that bar by the interaction. To make this pretty close to happening the brushes are advanced from the neutral position (they don't quite like up with the field poles.) When you make the current flow the other way (regen) you need the brushes moved the opposite direction relative to the field to find this approximately neutral location. Since the timing is quite wrong you get arcing is off the back edge of the brushes to the commutator bar that is coming out from under the brush. This, if carried to far, will destroy the brushes and commutator. The arcing sometimes creates enough electrical noise that the controller fails first.


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## gor (Nov 25, 2009)

you familiar with arching - arc welding...

powerful high end $20,000-40,000+ AC systems run on 320-450-600-700 volts

you can pull more current from battery on demand (10-15c+) when needed, but you can't pull more volts that easy - your battery should be built to support high voltage constantly 

on 10 kwh battery - 100v x 100ah, what would be left for ah(range) on 300-750v? 
how costly, heavy, efficient and effective boosters, converters, inverters etc for high voltage applications?


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## MN Driver (Sep 29, 2009)

Gor, I'll start by saying that an AC motor that can put out 800nm of torque is one hell of a powerful motor! That's 590 ft-lbs. In fact its powerful enough to where you couldn't cruise in its 96% efficient zone unless you have a road load over about 12.7kw (17 hp or more) AND are able to keep speed at 1250RPM. ...otherwise the torque level drops even more and the motor will fail to even reach the 75% mark. This would be the perfect motor for a large SUV though but efficiency is trashed at that point anyway. Nice specs though, I wonder who is using it.

...but you said this.

"powerful high end $20,000-40,000+ AC systems run on 320-450-600-700 volts"

A 320 volt AC system would be great and I know someone who is using one. With 700 volts you could use 20Ah batteries for a 14kwh pack that could punch out more power than the car could likely handle unless it was purpose built as a dragster or had an incredible transmission and very grippy tires. 40Ah cells and you've got a 28kwh pack which is pretty big.

" you can pull more current from battery on demand (10-15c+) when needed, but you can't pull more volts that easy - your battery should be built to support high voltage constantly "

Not quite correct. If you want more volts, use more cells to get the voltage you want. With a high voltage system you won't be pulling 10-15c unless you are using a very small capacity pack or a very powerful system. Lets say you've got a 320v 100Ah pack, that's 32kwh. 10C would be 320,000 watts or 429hp electrical input. What's the application for that much power? It's a little beside the point. If you have enough cells you WILL have "high voltage constantly"

on 10 kwh battery - 100v x 100ah, what would be left for ah(range) on 300-750v? 
how costly, heavy, efficient and effective boosters, converters, inverters etc for high voltage applications?"

32kwh pack is tons of range. Ah is NOT range. Kilowatthours is range. Volts times amps is power(watts). Power and time together as a function is energy (kilowatthours).

Your statement doesn't make sense 300v is not a 100v pack, those are two different voltages. A 10kwh pack at 300v would be 33.33Ah. A 300v 100Ah pack would be a 30kwh pack. A 10kwh pack is a 10kwh pack, the applications, motor, and controller will control the range but in the end the capacities are the same and therefore range, if efficiencies and performance of all components were to match would be the same.


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## gor (Nov 25, 2009)

MN, 10kwh, 300v vs 100v pack means 10kwh batt bank (syst) build 100v100ah vs 300v33ah - make sense?

that's why lets discuss in more detail and shift from AC vs DC to Higher voltage systems vs Lower voltage - 10kwh: 100v100ah vs 300-500v/33-20ah - not just one long cell string vs 3-5 short, but power, efficiency, weight, range, and cost of the whole system, be it AC, DC, or BLDC
p.s. cost of cheapest 150kw 300-600v system above (motor+contr.only) - $20 000+


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