# Subaru Forester for possible conversion



## PStechPaul (May 1, 2012)

I found a 1999 Subaru Forester on Craig's List for $1000/BO. It might be a good vehicle for a conversion, and possibly even as a "hybrid" using an electric motor for the rear and keep the ICE for the front. There was one thread with fairly good information:
http://www.diyelectriccar.com/forums/showthread.php?t=42008&highlight=subaru+forester

The listing is: http://baltimore.craigslist.org/cto/3429897204.html

I don't know if I'm really ready to start a conversion, though. I have some health issue to deal with first (knees, hip, back), and I still haven't really progressed much on my tractor project(s). Maybe I should wait for a cheaper vehicle and perhaps something smaller. 

I was also intrigued by an Eagle Talon:
http://baltimore.craigslist.org/cto/3427475035.html

Here's another Forester:
http://baltimore.craigslist.org/cto/3438658723.html


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## Caps18 (Jun 8, 2008)

The last Forester would be my choice. It looks good, and will be practical.

The Eagle doesn't have a transmission...

And the first one has bad photos...

I would keep it simple and do a basic EV conversion.


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## PStechPaul (May 1, 2012)

The second car is almost 50 miles away, and needs to be towed. The first is about 20 miles, and is driveable. So that would be a major factor if I decide to get it. I might see if I can take a look at the first one while I am out tomorrow in that general vicinity. I can take some better photos and maybe see if he would take a lowball offer, like $600. I'm a bit strapped for funds right now, and also I won't be able to do much on the project until I get something done for my hip/back/knees. I would probably take the car to a local mechanic where he might be able to pull the engine and other ICE stuff. My friend Georgie's son is a mechanic and maybe he'd be willing to help, but he's about 30 miles away while my regular guy is less than 2 miles.

I kinda like Subarus but from the other thread it seems the Forester is rather heavy and has a poor aerodynamic design. However, I will probably only use it for local driving and not much at highway speeds, so it may not be an issue. I definitely want to use a three phase AC motor and industrial controller. I may start with a 15-30 HP motor and about 20 HP controller, and 30 SLA batteries for 360V and 4.3 kWh for about $600. I can upgrade to Lithium after I get everything working.

So a 20 HP motor is about $400:
http://www.ebay.com/itm/U-S-ELECTRI...-256T-FRAME-3-PHASE-MODEL-R352B-/330796583138
http://www.ebay.com/itm/RELIANCE-EL...R-3PHASE-230-460V-1755RPM-57286-/300815452165
http://www.ebay.com/itm/20-HP-BALDOR-MOTOR-256TC-1760-RPM-/140747524695
Or maybe a larger one:
http://www.ebay.com/itm/New-Surplus...tor-73G57245-Cat-No-4-010233-40-/360056080977

An AC VFD 20 HP for about $1000:
http://www.ebay.com/itm/20-HP-3PH-2...IABLE-FREQUENCY-DRIVE-N3-220-N1-/110965620744
Or even larger:
http://www.ebay.com/itm/Toshiba-Tos...rter-VT130G3U4330-VFD-30HP-4330-/110981765670

Maybe I should go for a 600 VDC system so I can use a 480V drive and possibly overclock the motor. That would require 50 batteries or about $1000 for 7.2 kWh. That might give me 10-15 mile range. It would be about 600 pounds of batteries for SLA. So I think I can do the conversion for about $3000. The hardest part I think will be adapting the motor to the clutch and transmission. I can do basic testing with the VFD using a 220 VAC supply and an extension cord. Maybe even get a 10 kW generator and run it like a hybrid for awhile, until I am sure enough to get a full set of Lithium. Just knocking some ideas around to see how they fly...


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## tylerwatts (Feb 9, 2012)

The ideas are flying well sa I read them Paul! I'm also a fan of Subarus. The adaptor will have to be properly engineered, but that doesn't mean the cost will end up high. A well-made welded steel adaptor would work fine. Definately keep the clutch, even with the added headache, the adapter is little different, and it will broaden the usability of your initial build and you can change it later, but I expect you'll always appreciate having it.


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## mk4gti (May 6, 2011)

PStechPaul said:


> I kinda like Subarus but from the other thread it seems the Forester is rather heavy and has a poor aerodynamic design.


I think you hit the "head on the nail" right there. I would find something a little more light.


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## Electroddy (Dec 29, 2009)

Paul; I think that the hardest part will be putting that size motor in a Subaru. Those are larger than they look in the pictures. Will you be doing like Ivan and making a water cooled motor from one of them? Just looking up the weights of two of them, Reliance from their data sheet 315lbs +_ 15%, USMotors around 290lbs.


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## Duncan (Dec 8, 2008)

Hi Paul,
I like Subaru's - my car is built with Subaru parts

Can your intended motor produce enough torque to go direct drive?
Do you require the 4WD?

If you can go RWD - direct drive - you can use the rear diff and throw away the whole engine/gearbox unit
That should give bags of room


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## PStechPaul (May 1, 2012)

I don't know the rear differential ratio, but I can figure that the car will do about 60 MPH in top gear (if that is direct drive) at about 2500 RPM. If the tire is 24" diameter, 60 MPH is 880 RPM, or 2.84:1. If the fully loaded car is 4000 lb and it must be able to climb a 25% grade, it needs 1000 lb-ft of torque at the wheels or 350 lbft torque from the motor. A 30 HP 4 pole motor provides 87 lbft torque, so it would have to be capable of 4x rated torque. Some candidates are:

http://www.ebay.com/itm/181034185940 $389 
http://www.ebay.com/itm/150864025707 $829 94% eff
http://www.ebay.com/itm/200854894737 $450 94% eff 550 lb
http://www.ebay.com/itm/180861524469 $979 NEW 25 HP 92.4% eff Design C (High torque) 350 lb

I could use a 50 HP motor:
http://www.ebay.com/itm/130757549290
which is $750 and 450 lb shipping weight. That would give me 146 lbft and 438 at 3x which should be possible. 

I also found a 25 HP 6 pole motor for $825:
http://www.ebay.com/itm/230672775328
It would give 109 lbft rated torque so it might do almost 350 lbft. But I'd have to use more than 2x overclocking to get 2500 RPM for 60 MPH. It's also 800 lb shipping weight.


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## tylerwatts (Feb 9, 2012)

Steady Paul, 4th gear is usually 1:1 in the trans, leaving only the diff ratio. I'm sure your ratio is higher. Also, Subarus share parts, and everyone knows how many aftermarket parts are available for Imprezas, you could get higher ratio Impreza gear sets to increase that diff ratio, giving many more motor options!

Remember you calculations must include vehicle speed, 1000lb.ft might be enough at 20mph, but at 50 it will be perhaps twice as much, increasing nearly exponentially as speed increases.


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## PStechPaul (May 1, 2012)

I tried using my http://enginuitysystems.com/EVCalculator.htm for a 4000 lb (1818 KG) vehicle, and for 0 acceleration I get *504* Newtons (113 lb force) of thrust at 100 kM/h (62 MPH), and *356* Newtons (80 lb force - rolling resistance) at 0 MPH (after fixing my formula):

```
fForce = (fMass*fGrav*fRoll) + ((fAir*fDrag*fArea*(fSpeed/3.6)^2)/2) + (fMass*fAccel);
fPower = fForce*fSpeed/3.6;
```
The power required seems to be about right, with *5.46 kW* at 31 MPH and *18.8 kW* at 62 MPH, so it is somewhat a square law function related to speed.

But the most force will be from the acceleration (or incline), which is *4901 Newtons* (1100 lb force) for a 25% grade or 2.5 m/sec/sec acceleration.

I think I see the error in my formula - a misplaced parenthesis - since the sum of all the speed terms should be squared. 

Bottom line, however, seems to be in favor of keeping the transmission and 4WD and using a smaller motor. 

[edit] I found some references for estimations of power and force for vehicles:
http://craig.backfire.ca/pages/autos/drag
http://www.engr.colostate.edu/~allan/fluids/page8/page8.html

The second document shows the following formula:

F = Cr*m*g + 0.5*p*Cd*A*V^2

Where g = gravity constant (9.8), Cr = Coefficient of rolling resistance (0.015 typ), p = Density of air (1.2), and Cd = Coefficient of drag (0.3 typ)

My formula appears to be correct, but perhaps there is a problem with operator precedence in JavaScript.

[edit2]

The problem was that JavaScript does not use ^2 for square. I corrected the calculator and the correct (AFAIK) values are as above.


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## Duncan (Dec 8, 2008)

Hi Paul
My Subaru Legacy diff is 4.1:1 - a Forester would be similar


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## PStechPaul (May 1, 2012)

Hmm. So with a 4.11 ratio 60 MPH would be just about 3600 RPM. A 4 pole 30 HP motor gives 87.5 lbft torque so the wheels see 360 lbft. For 1000 lb peak thrust (assuming 24" dia tires) it would be just under 3x rated torque, so it's doable. Probably a 40 HP would be a better choice. And there might be situations where a short grade of over 25% might need to be negotiated. 

I might call the guy and have a look, but I think I'm not quite ready yet to "bite", unless I get a super good deal. I may stop at some local junk yards and have them keep an eye out for a nice little car with a blown engine. I really don't _need_ an EV at this time, but it would be fun to work on one. I already have a 5 HP 4 pole motor and a 10 HP 460V controller, so I'm thinking I could get started by using those and a 600V battery pack and overclock the motor to get 10 HP at 3600 RPM. I'd just need to get the 50 12V/12Ah batteries (7.2 kWh) which would be about $1000. 

Or maybe I could get 15 40 Ah lithium cells for 48 VDC (about 2 kWh) and use four 1000/2000W 120 VAC inverters in series to get the 600 VDC. The LiFePO4 cells would be about $810, and the four inverters would be about $136 each:
http://www.ebay.com/itm/1000W-DC-12...r-Sine-Wave-For-Household-Solar-/360500018801

But I think I can make my own DC-DC converter for 48V to 600V at 4kW.


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## TEV (Nov 25, 2011)

Someone did one , and he did it by the book :

http://www.evalbum.com/3766


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## PStechPaul (May 1, 2012)

That's a nice looking build, but $40k+ is more than I can afford. It would be nice to know the energy consumption, but I can figure it out. 320V system with 60 Ah cells is 19.2 kWh. 45 mile range: 427 Wh/m. Ouch! But probably reasonable for a 3300 lb car that carries 5 adults and a big dog. 

I'm anxious to get started on a project but now is probably not the right time for me. I have other projects that are lagging and I will probably need back surgery soon. So for now I'm testing the waters and maybe looking for a super good deal so I might be able to do something by next summer.


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## Coulomb (Apr 22, 2009)

PStechPaul said:


> 320V system with 60 Ah cells is 19.2 kWh. 45 mile range: 427 Wh/m. Ouch!


That's if the range of 45 miles is to 100% DOD. If it's to 80% DOD, then it's a more reasonable 427 * 0.8 = 341 Wh/mi.


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