Mixing Motors?

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Mixing Motors?

Post by EV2Go » Thu, 31 Jul 2008, 18:33

Of the examples I have seen where two motors have been used; all of them have been two of the same kind of motor i.e Warp 9 + TransWarp 9. Is there any reason why two different motors couldn’t be used i.e Warp 9 + TransWarp 11?

Just elaborating on this…
The reason I was asking was I am looking to build an EV with some reasonable grunt but due to space limitations I may need to compromise of the motors used.
Since I will need to spend some reasonable dollars to get reasonable grunt I have been giving thought to the AC90 as an alternative to a DC setup.
Specifications

Peak Torque     Nm     665
Continuous Torque* at Nominal Speed     Nm     330
Nominal Speed     Rpm     1350
Maximum Mechanical Speed     Rpm     5000
Maximum Current     A rms     414
Continuous Shaft Power* at 1000-2500 rpm     kW     50
At a voltage of     VDC     312
Peak Efficiency     %     94
Peak Shaft Power     kW     97
At a voltage of     VDC     312
Weight AC90     Kg     189
Weight DMOC645     Kg     27.5
Diameter AC90     mm     394
Length AC90     mm     520
Length DMOC645     mm     585
Width DMOC645     mm     260
Height DMOC645     mm     310
Minimum Recommended Nominal Battery Voltage     VDC     312
Maximum Nominal Battery Voltage     VDC     336
Minimum Operational Voltage     VDC     100
Maximum Operational Voltage     VDC     400
Maximum Voltage “On Charge”     VDC     450
Minimum/Maximum Operating Temperatures     ˚C     -40 to 60

When I first saw the weight I thought it might be a little on the heavy side until I started researching engine weights.

Obviously this would be totally in appropriate for a lighter car, but since I have always fancied the 300ZX it might make a suitable replacement for the heavy VG30DETT and gearbox.

I figure motor and gearbox has to weigh at least 300kgs…

It would have a mountain of torque but would there be sufficient power?
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Post by markrmarkr » Fri, 01 Aug 2008, 03:03

Are you asking if you can drive 2 AC motors from the same controller? You would probably be ok with two identical induction motors driving the same shaft. But not shore if they drive different shafts - eg one drives the front wheels and the other drives the rear wheels (which motor provides the feedback?)

Thats some kind of mean machine your planning there. You going to challenge Ian?
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Mixing Motors?

Post by EV2Go » Fri, 01 Aug 2008, 03:06

No not planning on 2 AC motors damn that would be leathal!
I was thinking 2 DC motors like the Warp 9 or Warp 11 but cost wise a single AC would be cheaper.

The AC motor sells for about $5.5k which is reasonable I am just a little concerned about the torque that thing makes, I was always complaining that although my last car make plenty of power (around 300 RWKW) it didnt have enough torque to give me jollies, I think that AC motor might just do the trick Image
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Post by priit » Fri, 01 Aug 2008, 03:54

From what I understand about using multiple motors, it makes the system a bit more complicated if you have different motors. With AC motors it will be complicated anyways so if you can manage with one bigger AC motor, then probably worth going that way. With DC motors, if they are identical you can put both of them on the same controller and they should both get similar load. However if you have different motors then puting them on the same controller would make one motor to do most of the work and the other one not running at optimal performance. There could be other issues with that also. I am most definitely not an expert there, but I believe if you want to use 2 different motors then you should use 2 controllers also. You would probably need to balance the loads somehow and make sure that when both controllers are pulling high amps from the battery pack, it wont draw more then the pack wants to give out without damaging batteries.
If Im wrong in some of the points there, please someone correct me.

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Post by zeva » Fri, 01 Aug 2008, 04:02

Yes, as priit suggests, although two different DC motors will work together when powered from the same controller, it's not a very good idea because they will have different operating parameters (e.g winding resistances, commutator timing, cooling ability etc) so will experience different loads, i.e one might overheat before the other, under certain circumstances, etc. Hard to predict with much certainty.

Two AC motors, you'd probably need separate controllers as well because the rotating fields wouldn't synchronise well?

PS: Absolutely no need for more than two Warp 9s in a passenger car, trust me! Your biggest problem would be getting enough power from the batteries and through the controller to make the most of them..
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Post by antiscab » Fri, 01 Aug 2008, 04:20

It depends on how you wire up the warp 9 and warp 11.
If you put them in series you can do it definately. You will however want a high voltage pack and controller.

If you put them in parrallel then the warp 9 will work harder than the warp 11, and bad things will happen.

The AC90 is a heavy motor for its output.
You will get awesome acceleration with it, but only until about 20kmh.

Id be surprised if you could get a battery pack that could push a single warp 11 + zilla 2k to their limits (300kw) and still get decent range.

AC (induction) motors by their nature arent particularly torquey to start with. To get decent power density you need a high rpm.
I suggest trying to find a low voltage high current induction motor capable of high frequency and rpm.
Also try and find a 415v 3 phase 500A induction motor controller. this will give you about 200kw. more amps for more power.

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Post by a4x4kiwi » Fri, 01 Aug 2008, 04:51

FYI, the Danfoss manual discusses running multiple motors from a single drive (controller). The key point is you can't use a speed feedback sensor (If the shafts mechanicly conencted you might be able to use a speed sensor.)

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Post by markrmarkr » Fri, 01 Aug 2008, 13:00

Can you imagine trying to use Back EMF with shafts not mechanically connected? HA! Image
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Post by EV2Go » Fri, 01 Aug 2008, 15:30

Would this be a better option than an AC? I am guessing it would be wired to balance the motors more evenly being they are on a common shaft.

JImPulse 9 ™ - Custom made "Siamese ImPulse 9 ™" by Jim Husted - Special Order $5,750.00

Not sure what that would be worth by the time it got to Australia and relevant duties paid.

What does a Zilla2k go for?
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Post by antiscab » Fri, 01 Aug 2008, 16:04

gday ev2go,

my zilla 2k EHV will cost me about $6k AUD, and has a long lead time (6-9 months and probably rising). you have to pay a $2k deposit to get in the wait list.

unless jim husted upgrades the brushes and commutator on the impulse 9s before merging them together, i dont think they will take 2000A.
I think the max is 1000A from what ive heard, but i havent done this personally.
So series/parrallel shifting wont be much use.

max back emf for each impulse 9 is 170v.
so if your pack sags below 170v at full power, you may aswell put the 9s in parrallel permanently.

As for will it be better? that depends on what batteries are being used to drive it, and how much power you want.
Basically, until we can find a high power AC controller (200kw+ or 415v 400A per phase +) you have to go DC to get high power.

DC will be less efficient (batteries to road around %70, versus %90 for AC setups, also you wont have regen).

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Post by EV2Go » Fri, 01 Aug 2008, 17:46

Thanks for that…
I have just printed out the Zilla manual so I can have a bit more of a read and try understand its function a little better.

I haven’t decided on what batteries I would use just yet as I know sweet bugger all about batteries (well just about everything electrical really) but I am figure big power equal big power draw, which means either a lot of weight or I go with a more sophisticated battery to reduce weight.

I am figuring the more expensive / sophisticated option is more than likely the way I would go.

So would you then recommend maybe a Warp 9 + TranWarp 9 Then?

Would I be able to carry enough batteries to do a dual 11”?

Is a single TransWarp 11 a better option than the dual 9’s?

I have sufficient money put aside now to complete the whole project I just need to make sure I am taking a leap of faith in the right direction before I commit to spending $30K+

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Post by antiscab » Fri, 01 Aug 2008, 18:03

a single 11 is good for about 300kw.
ditto on 2xwarp or impulse 9s.

id surprised if you could get more than 300kw out of a battery.

With that sort of budget you have to make a decision between range and power.

what car are you planning to convert?

an example, for the pack for my car (max weight 300kg) i had a choice out of:
1) optima yellow tops 192v
weight: 320kg
Max power: 300kw
usable energy: 6'000wh
cost: $7k

or

2) thundersky LiFePO4 288v 90AH
weight: 270kg
Max Power: 90kw
usable energy: 20'000wh
cost: $15k

or

3) welded together k2 26650 cells 288v 40AH
weight: 150kg
max power: 150kw
usable energy: 8'640wh
Cost $7-8k of the cells + labour + BMS

if you dont need alot of range, but want big power go for the optimas.
If you want good range and some power, go for the thundersks.
If you want both big power and lots of range you need the same capacity as the thunderskys, but in K2 cells, and lots of spare time to weld it together.

As with most things its a compromise.

Matt

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Post by zeva » Fri, 01 Aug 2008, 18:17

Yep I agree with Matt; usually it'll be the battery which is the limiting factor in terms of power. A couple of "rules of thumb" I like to go by:

- The ideal battery would have high capacity, high power and low price, but unfortunately right now you can only have two out of three! i.e Option 1 above with Optimas is high power and low price. 2 (ThunderSkys) is high capacity and low price. 3 (26650s) is high capacity and high power (but high price!)

- Power from a series DC motor is *reasonably* proportional to its weight (since the technology is fairly well established, and the limiting factor is often magnetic saturation of the iron). The Warp 11 is a little over 100kg, two Warp 9s are about 140kg.. so I'd say two Warps could sustain significantly more power.
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Post by markrmarkr » Fri, 01 Aug 2008, 18:25

he said a 300zx

96 300zx has Weights: gross vehicle weight rating (kg) 1,821, curb weight (kg) 1,513
and
95 300zx has Weights: gross vehicle weight rating (kg) 1,821, curb weight (kg) 1,520

according to http://www.automotive.com/ an American site - but probable still in the ball park.

That doesn't give much room to play. Does the 300ZX have an unusable back seat (I may be thinking of the Sylvia)? If so you can get rid of it and gain some weight margin as well as greatly improving the weight distribution by putting batteries there.
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Post by EV2Go » Fri, 01 Aug 2008, 19:10

The weight of the 300zx varies greatly depending on what options are selected. There are 2 general body shapes a 2 + 2 and a 2 seater obviously the 2 seater is both shorter and lighter. The targa top also adds some weight. I was thinking of a non targa top 2 seater. The seats in the 300zx also weigh a ton, so if I went with the 300zx it would receive a severe diet including removing all the underfelt and noise deadening materials, lighter racing seats, air conditioning gone etc

The biggest weight in the 300zx in the engine and gearbox as the block is cast iron not alloy, and the gearbox isn’t particularly light either so I would guestimate that minus engine and gearbox + diet probably would be starting with a body around 950-1000kgs. Obviously from there I would need to focus on keeping it light, plus since there is minimal space in the back trying to work out the best batteries from a space saving perspective.

The only reason I would go with the 300zx over anything else would be if I needed the extra space in the engine bay for length of motor, if I went with say a TransWarp 11 I might put that in a mini and mid mount it. So battery dimensions, weight and capacity will really factor into any final decision I make.

Matt how far could I typically expect to go on the battery options you suggested?
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Post by markrmarkr » Fri, 01 Aug 2008, 20:19

Looks like the weight is under control. Have you thought about what to do with the power steering and ABS?

Matt, the Coefficient of drag: 0.32.
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Post by antiscab » Fri, 01 Aug 2008, 20:45

youd be looking at around 160-170wh/km.
so 6000wh= 35km
20'000wh=117km
8640wh=50km

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Post by EV2Go » Fri, 01 Aug 2008, 20:50

I don’t think ABS was standard on all models and even if it is it can be removed easily enough.

Power steering won’t really be necessary with massive weight reduction in front / big transmission tunnel and moving weight off the front end and towards the middle of the car / battery weight in back.

But if it is, I was thinking of looking to see if there were any similar models that had a manual rack, Nissan have a tendency to make a lot of parts interchangeable. i.e the brake callipers on the 300zx and the S14 and S15 Silvias are all interchangeable (300zx are alloy to reduce weight).

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Post by EV2Go » Sat, 02 Aug 2008, 00:39

zeva wrote: Yep I agree with Matt; usually it'll be the battery which is the limiting factor in terms of power. A couple of "rules of thumb" I like to go by:

- The ideal battery would have high capacity, high power and low price, but unfortunately right now you can only have two out of three! i.e Option 1 above with Optimas is high power and low price. 2 (ThunderSkys) is high capacity and low price. 3 (26650s) is high capacity and high power (but high price!)


Option 2 is $15k how is that low price?
Option 3 is $7-8k + BMS how is that high price?

Does one of you have it around the wrong way???

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Post by zeva » Sat, 02 Aug 2008, 00:56

Ok I see why that might be confusing.. Option 3 is 1/3rd the battery pack size, so for equivalent range you'd be spending ~$25K. Maybe it's easiest to consider the numbers as follows:

Optimas: $1.16 per watt hour (capacity/range) and $0.02 per watt (power)
ThunderSky: $0.75/wh and $0.16/watt
K2: $0.93/wh and $0.05/watt

So, Optimas give the most power for your dollars, but the least range. ThunderSky give longest range, but lowest power. And K2 are somewhere in between.

Edit: I should also mention the respective weights of each as this is an important factor - often the limiting factor in the case of a lead acid pack:

Optimas: 25wh/kg
ThunderSky: 96wh/kg
K2 26650EV: 125wh/kg

So pack of Optimas with enough energy to give you ~100km range would weight about half a tonne! i.e not practical for most vehicles. The equivalent capacity ThunderSky packs would weigh about 130kg - much more feasible. And you'd only need 100kg of the K2 26650EV cells for the same job (but they're significantly more expensive than TS).
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Post by EV2Go » Sat, 02 Aug 2008, 01:17

Yep so really the best place to start might be with the batteries and let that dictate the motor and let the motor dictate the car...

When you say 300kw and 90kw etc I take it you are saying they are capable of drawing sufficient current to produce that power from the motor?

Also earlier it was mentioned that a Warp 11 could make 300kw, from the graphs I have been looking at they are struggling to make 40HP. Can the Warp motors take 288V to make that much more power or is the 300KW figure brought about by something else?

If a TransWarp9 could make 90kw (the TS max) that would be sufficient power for a mini weighing around 1000kgs (660 std).

What would happen if you used 45 x LFP160AHA 3.2V 160AH 480A giving 144V and slightly less weight.
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Post by antiscab » Sat, 02 Aug 2008, 03:39

the power ratings i gave is the amount of power that can be drawn from the battery safely.
optimas can give a good 2000A at around 10v.
thunderskys can give 5C at 2.3v (or 450A@2.3v for lp90AH cells).
K2 26650 cells can give 45A@2.3v.

a Warp 11 has a max voltage of 170v and max current of 2000A, both are limitations on the commutator.
this gives max input power at max power point of 340kw, which gives about 340hp mechanical, if the batteries can give the power.

both the transwarp 9 and the warp 9 (since theyre the same motor) have commutator limitations of 170v and 1000A.

The max power 45xlfp160AH pack will give is 800A@103.5v=82.8kw.
Less weight means less energy and less power.

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Post by EV2Go » Sat, 02 Aug 2008, 04:48

LiFePO4 288v 90AH (90 batteries)
weight: 270kg
Max Power: 90kw
usable energy: 20'000wh

< 3 CA (Constant Current) @2.5v?
< 10 CA (Impulse Current) @ 2.5v?
LFP160AHA 160v 160AH (50 batteries)
Weight 5.6kgs x 50 = 280kgs (added 10kgs)
Ok if a Warp 11 is limited to 170V, 50 batteries still give 10v headroom for overcharge.
Does the extra 5 batteries bring us back to 90kw?
Wouldn’t the 160AH give further distance as well?
5C x 160AH = 800A @144v = 115.2Kw
5C x 160AH = 800A@103.5v=82.8kw
5C x 160AH = 800A @160v = 128Kw
5C x 160AH = 800A @115v = 92Kw? (not sure what the voltage drop? reduction percentage is)
If as the brochure says it can do 10C does that mean it could potentially do 184Kw for a short period? (If the broachure says that I am just guessing)
Just thinking if you put the 90 x 90AH in parallel wouldn’t that give 180AH@144V?
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Post by antiscab » Sat, 02 Aug 2008, 08:48

the controller controls how much voltage and current the motor sees, mostly irrelevant of the battery voltage.
Thats how i can run a 170v max motor from a 288v battery pack.

Ideally you want your battery voltage to be above the max voltage of the motor so your controller can run the motor across its entire electrical operating range.

If you only have a 144v pack, and it sags to 100v at full power, the most the controller can deliver to the motor is about 97v (as theres voltage drop going through the controller).
As rpm (and speed) rises, 97V will not be able to maintain the full current output from the batteries through the motor resulting in a rapid fall off of mechanical power developed.

Its your controller than determines the max pack voltage you can have.
The max pack voltage of Lithiums that a zilla EHV will support is 320v.

The voltage drop i have witnessed on the thundersky batteries is 0.2v per C discharge rate, using 3.2v as 0C.
so at 5C, the voltage will be 2.2v.
90AH cells give 450A*2.2v=990w per cell.
160Ah cells give 800A*2.2v=1760w per cell.

The datasheet says the cells will survive a 10C loading for a few seconds. however the max power point is actually at 8C (1.6v).
Im not sure what the effect on cycle life is pushing the cells this hard. i know most people limit the discharge rate to 5C. ive only seen one conversion go to 8C.

At 8C, a 160AH cell can give 1280A@1.6v=2.048kw*50cells=102.4kw

The range you get out of your EV is a function of the energy used per km, and the usable energy available from the pack.
To work out the usable energy available:
               Voltage                             AH
energy avail=(3.2-(continuous A draw / AH)*0.2)*(1C AH rating * 0.8)) * number of cells.

energy per km * average speed = continuous A draw * pack voltage.

You have to iterate the last bit as the pack voltage sags with greater current.

yes if you were to series/parrallel 90 90AH cells you could get 144v@180AH. you would however be better of using either 160AH or 200AH cells if you watn 144v, or just using the full 288v.

Matt

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Post by woody » Sat, 02 Aug 2008, 16:41

300kW from a 10 kWh pack of LiPos should be possible with 90 of these RC Helicopter Batteries ($24,300). Downsides: cost, cycle life (200 cycles -> 10-20,000km -> $1-2/km), heat, charging complexity. Upsides: weight (81kg), size. Would make a good pack for racing, but expensive for street.
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