Hello From Castlemaine

Technical discussion on converting internal combustion to electric
Madmax
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Post by Madmax » Wed, 18 May 2016, 15:42

Hi Everyone,

My name is Matt and this is my first post on AEVA. I am a mechanical engineer and have a reasonable skillset with mechanical systems and tools.

I am interested in performing an EV conversion and would like some input into what car to convert.
Ideally the EV would have the same or better acceleration up to ~120km/h, top speed around that or higher and a range of 130kms+

The options I have at the moment are:
1976 VW Mk1 Golf 2 Door             Cda 0.8, 810kg, 80kW, 140NM,
1968 Alfa Romeo 1750 Berlina      Cda ??, 1050kg, 115kW, 200NM
1990 Alfa Romeo 75          Cda 0.65, 1120kg, 110kW, 186NM
1992 Suzuki Sierra/Maruti Ute      Cda 1.0? 900kg, 60kW, 73NM

All have pros and cons. For instance, the golf is light, would be an easy conversion with the gearbox retained, seats 4 but has a terrible Cda.

The Berlina is a bit of a rocket so it may cost a bit to replicate performance, and the chassis may not be up to carrying battery mass. It does have a 4.5:1 final drive so maybe a direct drive candidate….

The 75 would ideally use a direct drive motor in place of the transaxle. This would potentially yield a car with decent range at the same weight as original however a direct drive motor and sourcing an IRS differential will add significant cost.

The suzuki would be super easy (low powered to start with, transfer case has 2 speeds, lots of room for a battery under the tray, no power brakes or steering) but is a 2 seater....Also, the zuke would easily accept 800+ watts of PV over the tray and cabin, meaning that its battery is getting a tickle. The zuke would only be used locally so 50 Kms range would be fine.

Newer cars typically have better Cd but they generally suck in many other ways... So I would prefer to extend the useful life of a more classic car than something with no charm.
I am interested in using a re-wound 3phase induction motor and will almost certainly be using lithium over lead.

Constructive opinions on these cars and configurations welcome.

I look forward to participating in the EV community!

Matt

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Post by Madmax » Wed, 18 May 2016, 16:23


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woody
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Post by woody » Wed, 18 May 2016, 17:00

Welcome Matt!

I am not super familiar with the Alfas.
(For anyone wanting to catch up on how a 75 is put together: http://www.curbsideclassic.com/curbside ... -swansong/)

For me a measure of success is how much the car is driven as an EV, which makes how much fun it is to drive a big factor.

An option for the 75 is to keep the gearbox locked in 4th (1:1) to keep the diff and everything. An IRS diff from a Nissan Silvia/ etc. I think is not too hard to come by, but hooking up inboard disk brakes may be more work than you want/need to do.

cheers,
Woody
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Post by Johny » Wed, 18 May 2016, 17:47

The advantage of the Golf and Berlina is that they pre-date ADRs. That makes engineering approval just that little bit easier.

Are all of these cars yours? If so what is their state of repair?
If a classic ICE is working perfectly then I'd tend not to touch it.

Your 130km range will be difficult at high speeds. You may need to do a heap of work to get the 30kw/h+ pack into the car - engineering wise.

If a lot of your travel is NOT at high speed then the Cd doesn't matter that much (I sense that you know this already).

Just to conflict with what I've just written - convert a car that you will love to drive. You may be in it a long time.

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Post by Madmax » Wed, 18 May 2016, 18:34

Thanks guys for the warm welcome!

Fortunately (or not), I love driving all of them. The Golf is a bare shell at present and the Berlina is a rolling chassis. I have two 75s, one is a daily driver and the other a parts car (but intact enough for a conversion).

The suzuki is running but not registered, a farm ute. Its also probably worth the most as is and would be used the least if converted.

I think a 75 monster or sensible Golf are the best candidates.

As the golf would retain the gearbox motor selection is a bit easier... For a direct drive 75 with similar starting torque to the original car in 2nd gear the emotor would need to produce 300NM (with a 4.1 final drive) and spin to at least 5000 rpm to be any fun.

Does such a motor and controller exist? Can this be achieved with a re-wound ac induction motor?


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Post by Madmax » Wed, 18 May 2016, 18:43

heres a dyno run of a lightly modified alfa 75 motor

http://www.alfabb.com/bb/forums/attachm ... a_dyno.pdf

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Post by Johny » Wed, 18 May 2016, 20:12

Madmax wrote:....
in 2nd gear the emotor would need to produce 300NM (with a 4.1 final drive) and spin to at least 5000 rpm to be any fun.
Just clarifying - do you mean 300NM after the gearbox in 2nd?

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Post by Madmax » Wed, 18 May 2016, 20:40

Hi Johny,

Yep, With the original motor producing 180NM with 1.72:1 2nd gear torque to the final drive is ~300NM

I really like the idea of ditching the gearbox and coupling the emotor directly to the final drive (until i have to perform maintenance on the motor).

It looks like the AC75 would achieve this along with a top speed around 130km/hr which would be an acceptable compromise over the current top speed of ~200km/hr (ive not driven it that fast in public)

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Post by Madmax » Wed, 18 May 2016, 20:56

I've just calculated starting torque based on incline for 1100kg vehicle and the torque requirement is somewhat less... around 100NM at motor shaft with a 4:1 final drive to hold a car on a 15 degree (27% grade) slope...

To match stock 0-100 average accleration of ~3m/s/s acceleration torque is about 157NM at motor shaft.

So 300NM at the motor shaft would be great!
Last edited by Madmax on Wed, 18 May 2016, 11:00, edited 1 time in total.

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Post by Johny » Wed, 18 May 2016, 21:36

180NM is easily achievable with any off the shelf 132 Frame 4 Pole AC Motor. Mine is a 220V Delta direct drive running 630 VDC battery pack so I get full torque to 3000 RPM = about 73km/h.
Controller is the big thing.

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Post by Madmax » Thu, 19 May 2016, 19:45

Another option is to wait for a Tesla 3...

A fair bit of the Alfa ICE torque is not available to accelerate the car as the drive train has a bit more inertia than a standard front engine rear wheel drive arrangement, due to the clutch at the back. This is very noticeable in first gear...

So a direct drive emotor wont have this issue!

This is a very complex first conversion...

Last edited by Madmax on Thu, 19 May 2016, 12:01, edited 1 time in total.

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Post by Madmax » Fri, 20 May 2016, 00:44

Would a 160 frame 15kw 4 pole motor be suitable for a rewind for this application?
Last edited by Madmax on Thu, 19 May 2016, 15:34, edited 1 time in total.

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Post by Johny » Fri, 20 May 2016, 15:33

Madmax wrote: Would a 160 frame 15kw 4 pole motor be suitable for a rewind for this application?
If you can fit it and it's not too heavy - yes. My 132 Frame weighs 72kg if that's any guide.
Make sure that the controller you are planning on using can actually get enough current into the motor to make the larger, heavier motor worthwhile.

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Post by woody » Fri, 20 May 2016, 15:44

A 160 can be big. a4x4kiwi had a 15kW in his Hilux which was huge. I have an 18.5kW 132 (long) 4 pole which is 92 kg, and a 160 11kW 2 pole which is smaller except for the mounting ring.

If it's small like my 2 pole then it will fit in a transmission tunnel.

If it's big like a4x4kiwis then it will not fit in the tunnel, but would fit in the engine bay.
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Post by Madmax » Mon, 23 May 2016, 16:51

I dont think it would be a good outcome to do a direct drive in this case.... I've come to my senses...!

Instead a motor coupled directly to the transaxle and mounted toward the rear of the transmission tunnel could work. This would allow for battery mass to be distributed toward the front of the car. I would need to factor into the cost of the conversion a hoist in the shed in order to easily access the motor.

I have measured the tunnel at this location and its pretty big. This is due to the centerline of the transaxle input shaft being higher than the diff pinion, and with the whole shebang bolted to the chassis, the tailshaft is actually quite high up relative to the floorpan. The exhaust actually runs directly beneath the tailshaft in the tunnel.

A dual AC35 is almost a perfect match in terms of performance and available space... too bad they're $15000 with import duty and exchange rates.... I can see why DC motors are so popular!

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Post by Richo » Mon, 23 May 2016, 20:51

So a 160 frame would give ~300+Nm (320mm Dia).
A 132 frame would give ~200Nm (164mm Dia).
Fit the biggest that goes in ;)

You need to look at the motor + controller as a complete cost.

Given the level of integration of the gearbox+diff on the Alfa it would be a hard conversion.
The Diff to tail shaft conversions are much easier.
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Post by coulomb » Tue, 24 May 2016, 14:13

Richo wrote: A 132 frame would give ~200Nm (164mm Dia).

The 132 frame motor in Mexy (MX-5) manages 350 Nm (with the low voltage controller; since replaced with one that does twice the voltage and a little more than half the current and hence torque). But it's absolutely packed with copper and iron, and cost about as much as a DC motor at the time. It was also custom made, and took months to be delivered (from Norway I think), despite the fact that it is listed in an ABB catalogue.

Image     Image

The second image doesn't really give the sense of packing you get from seeing it up close.

See also from motor arrives .
Fit the biggest that goes in ;)
But also give it the most current you can afford, with the highest voltage you can achieve. In the lightest frame, with the most amount of room and comfort. And to fit your budget. It's always a difficult juggle.
Last edited by coulomb on Tue, 24 May 2016, 04:15, edited 1 time in total.
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Post by Richo » Tue, 24 May 2016, 20:39

Yep I'd say you got the best there is in that size.
Just like I probably got the best there is in the 112-frame.
All better than the DC eqv.

Still it makes me wonder - these motors are only so efficient - the heat has to go somewhere...


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Post by Richo » Tue, 24 May 2016, 20:42

Madmax wrote:A dual AC35... too bad they're $15000

Image
Dual AC35 100kW motor for $15k?!?

Tell'em they're dreaming Image

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Post by Johny » Tue, 24 May 2016, 21:00

If mine ever snuffed it (and I thought maybe I could do better at a modest price) I was kind of wondering if these guys could supply a lower voltage motor (than their standard). Since I have a penchant for 132 frame, 4 pole (transmission tunnel max. size) I liked the look of the *11 kW here (at 58kg).
Slightly lower breakdown Torque than my current motor but I have a feeling that it doesn't matter so much with VFD control.

CEG Aluminium frame MEPS motors

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Post by Madmax » Tue, 24 May 2016, 21:07

Yeah, at ~$15K plus a decent battery and install I might as well just save up for a Model 3.... But that comes with a whole lot of stuff I dont want...!

Am I right that it seems an industrial motor of acceptable size/mass can have acceptable/great torque but is limited in speed range?

In terms of performance, the conversion should be same as ICE or better with the exception of top speed which i can accept to be a fair bit less.

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Post by Johny » Tue, 24 May 2016, 22:10

Madmax wrote:Am I right that it seems an industrial motor of acceptable size/mass can have acceptable/great torque but is limited in speed range?
Not at all. Mine is balanced acceptably to 5000 RPM (aftermarket balancing - long story).

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Post by coulomb » Tue, 24 May 2016, 22:15

Madmax wrote: Am I right that it seems an industrial motor of acceptable size/mass can have acceptable/great torque but is limited in speed range?
Pretty much. You need to go out to around 13,000 RPM to get decent top speed without a gearbox. Of course, there is one solution: keep the gearbox, but make sure it and the differential can take the torque.

[ Edit: decent speed -> decent top speed ]
Last edited by coulomb on Tue, 24 May 2016, 12:16, edited 1 time in total.
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Post by Johny » Tue, 24 May 2016, 22:18

coulomb wrote:
Madmax wrote: Am I right that it seems an industrial motor of acceptable size/mass can have acceptable/great torque but is limited in speed range?
Pretty much. You need to go out to around 13,000 RPM to get decent top speed without a gearbox.
Wow where do you get 10:1 diffs?

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Post by Madmax » Wed, 25 May 2016, 13:30

The direct drive idea has been replaced with a mid mount motor close coupled to the gearbox idea. I am not sure exactly how this would work mechanically, whether a short drive shaft with a pair of flexible couplings is required to minimise radial loads on the motor/clutch shaft or if a single flexible coupling would suffice (with very well aligned mounts for the motor and gearbox).

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