2.7 t. Disco

Technical discussion on converting internal combustion to electric
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Sparky Brother
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2.7 t. Disco

Post by Sparky Brother » Tue, 15 Apr 2008, 03:58

Just recently started searching the net about serious EV conversion. My Idea about that is quite ancient though .

I my self am pretty far from the physical conversion becuse of lots of unclear to me things. However already set some milestones. Here is the picture. Donor car Land Rover Discovery!!! 2.7 t. in weight. I want to keep it as a4WD so obviously the plan is to get 2 x AC Motors (have no intention to even speak about DCs) and put them where the gear box was. Question; While the V8 Petrol engine is designed for 134kW, 304Nm at some 2600rpm (got some idea combustion engines are kW rated differently) What should be the combined (Peak) power of the two AC motors. Speaking of ACs we`ve got several types of Inductive AC Motors and while the big hassle is the regenerative braking what exactly is the motor I should go for. I can only guess we are talking a Squirrel Cage Inductive Motor. Right?

Also how about using some sort of capacitors set in regard of making it less harsh to the bateries when accellerating/breaking. The talk about the invertor is yet to come because I`m still struggling to understand what`s the difference between "controller, drive and invertor". As for a beginning if someone lights the bulb will be really something.

Any idea - much appreciated

p.s.
I really believe we don`t need those pre-packed ultra expensive EV conversion kits. Wht is the point of them?!

antiscab
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Post by antiscab » Tue, 15 Apr 2008, 05:40

The really expensive AC EV conversion kits are lighter weight and smaller than the standard industrial VFD's budget conversions use.

There are a few names for the motor controller, VFD and inverter. All do the same thing, convert a DC bus voltage (usually around 600vdc for greatest effectiveness) to a 3 phase voltage to run and control a motor.

For 2 motors you will need two VFDs.

Re comparing a combustion engines peak power to an electric motors peak power point, this can be a bit complicated to explain so bear with me.

For setups where the battery is the limiting component power wise, there is a flat spot in the power-speed curve, meaning there is no max power point rather a max power plateau. so a peak kw unit for an electric is worth more than for a combustion engine

For setups where the motor or controller is the limiting factor, the measure is the same.

For your setup it will most probably be the later.

you will need to find a pair of VFD's rated to about 145kw peak combined, which will probably mean about 170KVA since the motor side is unlikely to be in phase. It doesnt matter as much if they arent the same size. make sure they are 415v or higher voltage units.

If you can find a good source for second hand units please let us know, they usually run to $8k when new for a 50kva continuous 90kva peak.

As for the motors, look for 4 poles, and about 20kw continuous each, 208v rated and able to accept high frequency input. The peak rating will be much higher. running them at a higher voltage will allow you to maintain full torque at higher rpm.

antiscab
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Post by antiscab » Tue, 15 Apr 2008, 05:46

out of curiosity, why dont you want to go DC?

Sparky Brother
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Post by Sparky Brother » Wed, 16 Apr 2008, 04:14

Hi antiscab

Thank you for the time spared for me!

It is obvious though I`ve got a lot of home work to do before I get it started. I am glad to hear that the weight of the car doesn`t bother you efficiency-wise of course.

The choice of the motor? Well I know there are bunch of newly developed and really sofisticated DC motors I heard about however the main point of my conversion will be a budget AC conversion with on the shelf parts combined from non EV parts retailers (nothing wrong about them) for the everyday hobbyist with a bench mark of not less than a 100km range. From what I read in the AEVA forum that might sound like a fiction but as I sed before I am not starting the Project before I put together all the pieces of info I am trying to get from a vast range of specialists, suppliers etc. Bottom line - ACs are well developed and with superior qualities to the ordinary DC motors not to mention, cheaper than the new fansy DCs which I wouldn`t dream about.

Just one last question (for now) Image does it make any difference if I go for an armature wound or squirrel cage rotor in terms of regenerating the breaking power because I`ve got the feeling I`ll manage to get cheaper ACs in the Squirrel cage version? And yes if I manage to gig out an affordable sourse (got something in mind) of motors you`ll get to know. By the way have you heard something about some "Kostov Motor" as far as I know this is a cheap 32 V rated forklift DC motor which some entousiasts in USA claim could be pushed up to 800V?!

Once again thank you for all the guide lines. It was very important for me to stop findin excuses not to get it started.

Cheers!

antiscab
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Post by antiscab » Sat, 19 Apr 2008, 05:22

No worries,
sorry for the late reply, i lost the thread for a couple of days.
The kostovs are actually relatively well made, but ive never heard of anyone pushing the voltage to 800V. John wayland used to run an 11" kostov at 200v under load at 2000A, until the carbon buildup resulted in a short, destroying the motor in a spectacular manner.

As far as the weight of the vehicle, does it really weigh 2.7t? or is that just its gvm?
The weight will just affect your acceleration and hill climbing ability. If the electric drivetrain you put in is the same power or better as the original, this shouldnt be a problem.
For a vehicle of this weight regen would be important, since theres a real amount of energy to be recovered.

As far as how much energy it will use per km, to guesstimate, take the L/100km of diesel it uses now (i assumed its diesel based on what the engine power was, if its petrol use 1.875) and multiply by 2.625. this will give you the kwh/100km need from the batteries. For kwh/100km need from the grid, this depends on how efficient your chargers and batteries are.

basically if its a fuel hog as a diesel car, it'll be a energy hog as an EV.

As far as will it work, make sure the continuous rating of the motors are above the amount of energy used per 100km. ie if you need 30kwh/100km, make sure the continuous rating is at least 30kw. preferably more.

From personal preference, i would get a cage motor. As i understand it the cage motors can be pushed harder electrically, and are stronger mechanically. As far as regenerative power goes, the max regen power is the same as max acceleration power, assuming of course your conrtoller/VFD can take it.

What is the GVM on the land rover? If its really high, fitting the batteries in wont be a problem. I understand thy are rather quite roomy, with lots of large places to hide things. If your doing AC this is important, as the "cheap" controllers arent overly small.

To get large amounts of range you almost definately need to use lihtium.   

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Post by jpcw » Mon, 21 Apr 2008, 16:56

antiscab wrote:
you will need to find a pair of VFD's rated to about 145kw peak combined,

I was under the impression that most electric motors were rated at their continuous power rating not the peek. The figure I was given was that you can get a peek power of almost 4 times the continuous rating meaning you need something significantly less. Also take in to account the fact that electric motors have more grunt at low revs than a ICE has.
Please feel free to correct me if I’m wrong but I would have thought that something between 50 – 100kw would be more than ample.
“The best way to predict the future is to invent it,” Alan Kay 1971

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