[dblaalid]

Hello everyone,

I am leading a team of EEs at my university in reworking an already converted 911S Targa. The car is in perfect shape mechanically and structurally, but the electric power train is outdated and inefficient to say the least. It's a DC system (I wish it were AC) and it's seriously just a series of 10 RV-Marine deep cycle batteries. Our goal is something around 100 mile range, with as much power as the current forklift motor can give. But given our inexperience in this field of work, we aren't quite sure how we are going to get there.

I'd like to get as involved on this site as possible during our rework and build. If you're interested in seeing what we were given (the car was donated) to work with, check out this site http://www.calpolymca.com/project-history.html.

Let me know where you guys think we should start. We're all smart students, but none of us have converted a car before.

I should note that the rework of the car is a huge undertaking, and there is a team of MEs working on drivetrain specifics, a team of people working on the interior restoration, exterior restoration, as well as a team of marketing and sponsorship people. We've got all our bases covered, but we need to have a plan worth pursuing. Which we don't really have right now. We've got the passion to get it done but there's really no point in flying head first in to a tree if you catch my drift.

Thanks again everyone,

 

[Joey]

I checked out your web site. Looks like you are having a lot of fun on this project. I just started converting a 1983 911, and I estimate I will need about 30 to 32 kWh of energy storage to get close to a 100 mile range. Lifepo is the battery chemistry I've chosen. I'm going to try and fit 56 cells, wired in series, of Calb 180 Ah batteries. The batteries will last longer if you only use 80% of the rated battery capacity. The batteries will probably be the biggest expense. It would be great if your PR team can get a sponsership from a battery supplier.

 

[Duncan]

Hi
Had a quick look at your link

Don't understand why you only have 20Hp -
your motor and controller should be capable of producing over 150 Hp -

I suggest you upgrade the batteries and check the setting on the Zilla

AC motors
As university you may be able to get AC Propulsion to let you have one of their AC150's - they won't sell to the DIY guys
Which is related to the Tesla unit and was used in BMW's E-mini

electric power train is outdated and inefficient to say the least

Your DC system does not have re-gen capability but is probably nearly as efficient as an AC system

 

[Yabert]

Your DC system does not have re-gen capability but is probably nearly as efficient as an AC system

Duncan is right!

With proper battery pack, your Zilla and ADC can output more than 200 lbs-ft and close to 150hp.

AC systems can be nice, but pricey.... and you actually have the DC systems, so take a month to build a really good battery pack and drive it.

 

[tomofreno]

Which Zilla 1k is it? My understanding is there are two models, one with max 156V input and the other with max 348V input. The latter offers a big advantage in that using a higher voltage pack permits putting the full 1000A through the motor while pulling less current from the battery pack since power out of the controller equals power in minus the (small) losses. Then you can use for example the CALB 180 Ah cells Joey plans to use and remain below the spec'ed max of 3C (540A) or 4C (I forget) current draw from the cells while running 1000A through the motor if you use a high enough voltage pack.

I'm with Yabert - you already have the DC system, and it will give good performance, so cut your teeth on it. If you can get AC Propulsion or UQM to donate a motor and someone else like Rinehart Motion Systems to donate a controller then great, go for that. Otherwise it will likely break your budget. The max voltage of the ADC motor is about 144V. A similar motor, the WarP9, by Netgain Motors, can go up to 170V because it has different brushes and other modifications. Don't confuse the two and over volt your ADC - set the max motor voltage in the Zilla software. If you want better performance I would upgrade to a WarP11 HV (high voltage) series DC motor if it will fit in the car - unless you can get a high power AC motor donated.

The main supplier for large format, or prismatic LiFePO4 cells to diyers right now is CALB, who has a U.S. office. There is also Hipower and more recently Sinopoly. Try to get them to sponsor you. There are also smaller Ah cylindrical cells like Headway or A123 (hard to get) that can supply a higher multiple of C (capacity) discharge current. These are more popular for high power, shorter range applications such as racing where you want a light, high power pack without that much energy storage. Lots of info here, look around.

 

[dblaalid]

Wow, thanks for the input so far. I guess I misspoke in claiming the system was outdated and inefficient. It just has always felt that way when driving it. It sounds like the majority of the bottleneck right now is in the batteries and some settings in the Zilla. I'll check on those and get back to you. But the batteries are something we should start investing in now regardless. I'll go ahead and look around the forums for figuring out the amount of battery power we'll need to get our range. Joey, you mentioned that you estimated the amount of power that you needed. How did you go about doing that? Is there a guide to those kind of calculations on the forum that I haven't ran in to yet? Thanks again everyone!

 

[Joey]

Someone sent me this link: http://physics.ucsd.edu/do-the-math/2011/07/100-mpg-on-gasoline/

The calculations for range are discussed on the first page of my build thread: http://www.diyelectriccar.com/forums/showthread.php/electric-porsche-66464.html

On page 6, Maxvtol provides a spreadsheet with acceleration calculations.

 

[drgrieve]

Then you can use for example the CALB 180 Ah cells Joey plans to use and remain below the spec'ed max of 3C (540A) or 4C

A Calb 180ah can easily put out 1000 amps. At 1000 amps (5.5 C) the sag will a bit higher than 20% at 25 degrees C and with good pack connections.

See this thread for more details http://www.diyelectriccar.com/forums/showthread.php/cell-comparisons-please-contribute-62326.html

 

[DavidDymaxion]

Great choice of car! I also am converting a 1977 Porsche 911S: http://ExplodingDinosaurs.com

I'm very much looking forward to reading your web page in detail.

Your motor well could be more stout than you realize -- check out the NEDRA guys to see how much power they dump through a motor. Definitely 2 thumbs up for moving up to better batteries!

If you want speed, Headway "P" batteries are great batteries for power (good cost per kW). Thundersky/Calbs/etc. are great for Ahr (range) for the dollar.

 

[tomofreno]

A Calb 180ah can easily put out 1000 amps. At 1000 amps (5.5 C) the sag will a bit higher than 20% at 25 degrees C and with good pack connections.

See this thread for more details http://www.diyelectriccar.com/forums/showthread.php/cell-comparisons-please-contribute-62326.html

What cycle life did you get dr?

 

[drgrieve]

What cycle life did you get dr?

Good question but I don't think anyone knows definitely either way.

I haven't seen any reports that low amounts of sag (up to 25%) damages LiFePO4 cells in any way. I believe the only demonstrable damage to cells is via reverse current, by over temperature, or by raising static cell voltage over 4.3V.

We may need to wait a few years for the answer unless someone decides to do some actual testing.

Perhaps some folks out there with small packs that run high C rates can chime in with some anecdotal reports?

 

[dblaalid]

Hello again guys. We are moving on buying some batteries, and a few of you said that we could squeeze about 100+ hp and almost 200 ft-lbs from our Zilla 1K and ADC motor. How would you recommend we go about doing that? We are currently looking at getting A123, Thunderskys, or CALBs. Please help me understand the best course of action. Thanks!

 

[dblaalid]

Also, this is our motor:
http://www.evparts.com/products/str...-to-192-volt-street-vehicle-motors/mt2120.htm

 

[EVfun]

Roughly 52, CALB 180 amp hour cells for the battery pack. If you set the battery amps to max at 720 (4C) and the motor current limit to 1000 (the max for a Z1k) you will have about 110 peak horsepower with a peak torque in the range of 200-210 ft-lb. You could likely bump the max motor current up to 900 amps (5C) for a bit more peak horsepower. The motor current sets the motor torque. Voltage roughly dictates rpm, with the understanding that energy is conserved (in other words, dependent on amps and efficiency.)

746 watts = 1 horsepower (but slightly less because no motor is 100% efficient)
rpm * ft-lb / 5252 = 1 horsepower

 

[Duncan]

Hi,

You are looking for 100 miles range - at 300watthours/mile = 30 Kwhrs
You should not exceed 80% draw-down so 30/0.8 = 37.5Kwhrs battery pack

So you need a 37.5Kwhrs pack

Type of battery -
Prismatic - CALB, Thundersky
Cylindrical - Headway
Pouch - A123

Prismatic can do 3C - 3 x One hour rate - for 37.5Kwhrs = 112Kw
Cylindrical can do 10C - 10 x One hour rate - for 37.5Kwhrs = 375Kw
Pouch can do 20C? - 20 x One hour rate - for 37.5Kwhrs = 750Kw

These are continuous - burst will be more - 150%

Prismatic will be cheaper, easier to use, and provide more power than you can use

The others are more for the banzai performance for less miles

 

[dblaalid]

Wow thank you guys for such a quick response. I think what I'm still concerned with is whether or not the motor will support those currents for extended periods of time. I have a feeling this might come off as a stupid question, but all I need is a little explanation. Is that something well within the capabilities of the motor? It just seems so far fetched to me, seeing as most specs I've found of the motor top it out around 30 rated HP. Thanks again for putting up with my seemingly uneducated questions. I'm still new to this game.

 

[Duncan]

Hi

How much power do you need - and for how long
30Hp will maintain 100mph
at 100mph you have 1 hour of battery

300hp will overheat in seconds - 30 seconds??
but 300Hp will propel you to 100mph in less than 10 seconds

Limitations
Heat
Your motor will get hot - the heat input is proportional to the current,

at about 3000rpm and 30Hp it will stabilize at a temperature which is OK for a long time

If you feed it more current it will get hotter
If you allow it to rev faster it's internal fan will enable it to stabilize at a lower temperature

If you add additional cooling you can run at a higher power output for longer


Limitations
Brushes
At some point you will zorch your brushes - over 1000amps

Overspeed
At some rpm your motor will blow up - 7000rpm????

I'm still concerned with is whether or not the motor will support those currents for extended periods of time.

It won't - but you can't load it for "extended periods of time" - at 1C you have an hour at 3C you have 20 minutes

Stick a bit of power under its tail - and you will soon run out of road and have to back off

 

[Yabert]

With 30 hp you can maintain speed over 60 mph.

Motor will stay cold with 1000A for few sec. and you don't need to push 1000A in motor for more thant few sec. because 1000A x 144v (for example) give around 140-150 hp at motor shaft and the car will reach high speed in few second with this power.

 

[kerrymann]

Wow thank you guys for such a quick response. I think what I'm still concerned with is whether or not the motor will support those currents for extended periods of time. I have a feeling this might come off as a stupid question, but all I need is a little explanation. Is that something well within the capabilities of the motor? It just seems so far fetched to me, seeing as most specs I've found of the motor top it out around 30 rated HP. Thanks again for putting up with my seemingly uneducated questions. I'm still new to this game.

No worries, I had the exact same concern about my conversion and I am running the exact same motor that you have.

http://www.diyelectriccar.com/forums/showthread.php/electric-miata-my-2nd-ev-conversion-69675.html

So I put together a excel sheet yesterday over lunch calculating drag and rolling resistance. My ideal is being able to cruise at 80mph. I don't have the drag coefficients or area for a 911 but once you have them you (or one of the ME's on your team) can easily calculate the power you need to sustain a cruise speed. For me with a Cd of .34 and a Area of 1.6m^2 I get the power to overcome air resistance of 15.6kW or 20.9hp. Then you need to add in rolling resistance for and a weight of 2200lbs (watch your units you need another 10.2kW or 13.7hp. Add them up and you will see that our are already fleeting with overheating. Add in friction losses in the transmission/diff axles and the fact that you probably dumped in a lot of heat accelerating to that speed it means that I will likely need a some additional cooling (your numbers may say different. In fact for the 9" motors people even sell cooling kits for this reason:

http://www.evsource.com/tls_motor_cooling.php

But being a group of engineers I think you could make something cheaper/better.

BTW, I hope you guys have fun! I remember doing my design projects (Formula SAE and SAE walking machine) years ago (ME as CSU) and they were one of the most important parts of my education because you really applied theory in to practice.