DIY Electric Car Forums banner

1 - 15 of 15 Posts

·
Registered
Joined
·
12 Posts
Discussion Starter #1
I'll start with the basic info:

• Top vehicle choices (currently): Honda CRX or Mini Cooper S
• I have 3+ yrs experience as a Mechanical Engineer (CAD, Fabrication). Just a small portion has covered electrical, but nothing on the scale of an EV conversion
• Desired range is at least 60 miles
• I need the car to reach highway speeds, so my goal top speed is 80mph
• Budget at the moment = $15,000 (still need to purchase donor car, < $2000)
• I also would like my build to use LiFePO4 Battery cells, an AC motor (possibly two for AWD if I can cover the costs), and a direct drive single speed reduction gear (rather than coupling to the old transmission)

Since I still need to buy the donor car I want to cover all my bases before I commit.

The biggest question I have so far is regarding current draw of the system. Of the primary drive components (Batteries, Motor, Motor controller) does the unit with the lowest current carrying capacity dictate the maximum power provided by the system? For example, my battery pack has a max continuous discharge of 700A, the motor is rated for 750A, but the motor controller is rated for 500A. Am I incorrect in saying that 500A is the max current the system can handle? Or am I misinterpreting the component specs? I have primarily done calculations with the HPEVS AC Motors and want to make sure my spreadsheet spits out accurate power values.

In addition to the HPEVS AC Motors, I have looked at the HyPer 9 – SRIPM Motor as well as old Tesla Drivetrains (although can’t seem to find full Tesla Motor Specs anywhere).

For batteries, I have primarily looked at Voltronix, CALB, and Bright Star cells.

By no means am I dead set on any of these component choices, so I am very open to suggestions on how to tackle this project!
 

·
Administrator
Joined
·
6,120 Posts
Hi Wut
Your location is important - please put it in your control panel!

CALB and the others are NOT the best bet for cells these days - cells from an actual EV are a much better bet

In fact for what you want I would say that getting a wrecked EV as a "donor" car is your best bet

You will get all of the stuff you need - for a lot less money!

As far as power draw is concerned

Torque is basically proportional to current
Speed is proportional to voltage

So if you get something with a controller that will give 700 amps
You will start off - 700 amps - just a few volts
Then 700 amps - more volts
Then - not enough volts to maintain 700 amps so 600 amps - full battery voltage
Then - not enough volts to maintain 600 amps so 500 amps - full battery voltage

See how that works?

I would have said get a Leaf - one that still goes if you can
Once you have it working then you can look at the guys working on getting more power
Or even stick another Leaf unit in the other end
 

·
Registered
Joined
·
1,364 Posts
CALB and the others are NOT the best bet for cells these days - cells from an actual EV are a much better bet

In fact for what you want I would say that getting a wrecked EV as a "donor" car is your best bet

You will get all of the stuff you need - for a lot less money!
I agree with this completely... iirc the cheapest 2014 Leaf wreck we purchased was ~2000 GBP and that was still drivable :eek:

If you choose Tesla, Leaf, or Volt salvage parts you'll also benefit from the open source developments that are in progress :cool:
 

·
Registered
Joined
·
1,492 Posts
I absolutely would stay away from LiFePO4 prismatic cells unless you can get them used from someone for very little money.

Much better, and much cheaper, to use cells salvaged from an OEM EV.

Re-using an OEM EV drive unit is a much more vehicle-specific task. Personallly it's likely a little beyond my skill level to Frankenstein an electric drive unit which consists of motor, differential and inverter, into another vehicle unless it can be done without a wholesale re-design of the rear suspension. Transplanting anything into a FWD car would be beyond my confidence level by a long shot!

Bolting an AC50 onto the existing tranny like I did with my E-Fire is dead easy in comparison, but more expensive and much less powerful than if you can find a way to re-purpose an OEM EV drive unit.

I'm watching with great interest the conversion of the Panzer BMW with a converted Tesla drive using the open source motor controller lobotomy. If this can be done well and reliably, it's going to be a new world for EV conversions for sure!
 

·
Registered
Joined
·
12 Posts
Discussion Starter #5
Thank you all for the responses!

I'll definitely start doing some deeper searches for OEM components.

@Moltenmetal - I'll also check out that BMW build.

Do any of you know where to find specs on OEM motors/batteries in order to get an idea of how performance of the car is affected? I have found basic info (Ah, voltage, weight) but am struggling to find more specific info (C-rating, max continuous/pulse discharge, rated current, etc.).
 

·
Administrator
Joined
·
6,120 Posts
Hi Wut

I don't think that you will find that sort of spec

What I do is I look at the power that the car uses and that gives me a bottom line

Then I look at how conservative the manufacturer has to be - looking for 200,000 miles and a very very low failure rate

- Then I decide how conservative I need to be! - not very!
 

·
Registered
Joined
·
12 Posts
Discussion Starter #7
For batteries, kind of confused by Leaf Modules (with the 2 cells in series, 2 in parallel thing they got going on). The specs seem somewhat underwhelming compared to other battery cells. Would I be able to get decent performance/power out of a used Leaf Battery? Only need about 50-60 mile range, but want a fun-to-drive car (good acceleration) with highway-capable top speed.

For motors, I am struggling to find a good deal on a Tesla Drive Unit. Gonna keep searching.

On the other side, I have been looking at other AC motors and am intrigued by the HyPer 9 (from NetGain) and the Siemens Azure 1PV5135 4WS14.

Both motors are comfortably within my budget and was wondering if anyone has any experience with them (Performance, ease of installation, etc.)?

Also, I am considering a dual motor setup (not connected to each other, rather one motor for each side of the rear axle). My understanding is that this would give me more torque with less current. Is this correct? Is the extra cost worth the performance gains?

- Wut
 

·
Registered
Joined
·
4,791 Posts
Also, I am considering a dual motor setup (not connected to each other, rather one motor for each side of the rear axle). My understanding is that this would give me more torque with less current. Is this correct? Is the extra cost worth the performance gains?
Comparing one of a motor with two of the same motor with the same overall drive ratio - regardless of how the connection to the wheels is mechanically arranged - is doubling the amount of motor. That certainly changes the performance (including doubling the total torque available), but I don't know why that would be assumed to reduce total current demand.
 

·
Registered
Joined
·
4,791 Posts
Two motors is a bad idea because you will then need two reduction gears
And you will also need two controllers, programmed to work together.

But you don't need a differential, and you can control side-to-side torque distribution in controller software instead of mechanically complex (and not highly controllable) differential mechanisms or with friction brakes.

For equivalent performance, each motor, controller, and gearbox of the split design can be half the power of the equivalent components of a single-motor design.

While separate motors has production precedents and is the direction of the future, it seems like a bit much for a novice project. The details of controller programming and the challenge of finding suitable gearboxes without differentials in single quantity could easily be overwhelming. Perhaps this approach should be left to a second project... a few years from now when Tesla Roadster 2 rear drive units become available as salvage.
 

·
Registered
Joined
·
4,791 Posts
On the other side, I have been looking at other AC motors and am intrigued by the HyPer 9 (from NetGain) and the Siemens Azure 1PV5135 4WS14.

Both motors are comfortably within my budget and was wondering if anyone has any experience with them (Performance, ease of installation, etc.)?
The availability of the Hyper9 was announced in this forum less than four months ago. I haven't noticed anyone posting that they had built anything with one.

In contrast, that Siemens motor has been around since the days of the long-gone Azure Dynamics.
 

·
Registered
Joined
·
4,791 Posts
For batteries, kind of confused by Leaf Modules (with the 2 cells in series, 2 in parallel thing they got going on). The specs seem somewhat underwhelming compared to other battery cells.
Compared to other cells used in production EVs which need to actually work, or compared to the claims associated with cells offered for sale to DIY builders in competition with other claims on websites?

See Duncan's comments about expectations for reliability...
 

·
Registered
Joined
·
4,791 Posts
I'll also check out that BMW build.
This one: Tesla Powered BMW E31 8 Series
Sure, it's an interesting project, but note that neither of your target vehicles have a suspension and structure - at either end - which is anything like the ideal semi-trailing-arm RWD setup of the previous-century BMW. The front suspensions are not arranged to fit around a drive unit which is wide in the portion behind the axle, and the rear suspensions are not set up to be driven at all.
 

·
Registered
Joined
·
4,791 Posts
A good bet for a FWD car, especially a CRX is to transplant a rear-wrecked leaf drivetrain.
https://www.youtube.com/watch?v=d_r_HKV_ZgQ
I agree that the Leaf powertrain is a logical fit to a typical transverse-engine front-drive car. Of course mounts will likely all be in the wrong places. ;)

It's hard to find useful information in random videos, but using the name from that YouTube page some searching found...

NEDRA (SC) Street Conversion Record Holders
"Far From Good" 1988 Honda CRX
462 volts
Owner / Driver: Arlin Sansome
Sponsor: Underground Electrics

Time (sec) 12.683
Speed (mph) 116.9
NOPAC, Mission Raceway, Mission, BC
September 8, 2017
Facebook post by Underground Electrics
The CRX is consistant at 300+hp at the wheels, with the peak torque at 295 ft-lbs (motor) which is 2349ft-lbs at the wheels! I know I can get more and we tried to play a bit but as always time run out with everything being a cluster...
I took many people for rides and they were all blown away! The Dyno operator said it was the coolest car he has dyno'd :) All and all a good day. Oh and they had a Z28 come in after me... He was bragging nothing was stock and this and that he figured as much as 700whp lmfao.... I posted his run on my youtube channel lol
https://www.youtube.com/watch?v=S6OInkLWAhk
 
1 - 15 of 15 Posts
Top