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Discussion Starter · #1 · (Edited)
Hello all, first post and relatively naive so be gentle ;) I have a very ambitious conversion planned and I would like to have your feedback/expertise. The plan is to use a honda crx hf and create a long range cruiser that can go farther than 200 miles (goal is 300) on a charge at 65 mph. This build will probably closely resemble Wayland's new Insight project to a large degree, but without the sponsored battery pack :)

Ok for project description, here goes nothing.

Budget: <$25k not including donor
Range: >200 miles with 300 being stretch goal
Top speed: >80 mph with 90 being stretch goal
Acceleration: <12s 0-60mph with 10s being stretch
Donor: Honda CRX HF
weight 1713 lbs, gvwr 2240 lbs, CdA 5.7 sq ft, 45 mpg

A CRX had a Wh/mile of 240 on EValbum http://evalbum.com/1058 , but I feel with some aero tweaks and lithium instead of FLA, AC and a high voltage system I might be able to bring that down to 200 at 65 mph. Wayland predicts 185 at 65 mph with the Insight, which is approximately 125 lbs heavier stock with about a 0.04 CdA advantage over the CRX. If I can modify the aero and mess with the rims, tires, and drivetrain to reduce resistance I feel this might be possible.

Preliminary design decisions:
AC motor
lithium batteries (obviously :D)

I have been through the wiki and have run some calculations. Using the 8kWh to 1 gal of gas conversion, I come up with a battery pack of between 35.6 and 53.3 kWh.

Here is what I could use a little help with from the wonderful and friendly people here. I have no idea what model motor to go with, what lithium cells/batteries to go with, what BMS, what charger, what controller, clutch vs no clutch, etc. I could also use a lot of help with the mechanical stuff that I mentioned above (resistance lessening mods, esp drivetrain).

The one thing I have given the most research recently is batteries, so as of now I see some Thunder Skys in my future. Maybe by the time I get around to doing this we will have some carbon-air batteries or something wild like that :) Assuming a 53.3 kWh pack, using 200 ah TS would mean a pack voltage of 266.5, at 3.2 V a piece that is 84 batteries :eek: With a 35.6 pack same batteries it is a 178 V pack made up of 56 batteries. Is this what I am going to need or am I doing something wrong? Are there better batteries for the task? Can I fit this many in a CRX and still drive it?

I am pretty savvy with tools but I have never really worked on cars. I just graduated college with an engineering degree, if that means anything. Thanks in advance for all the help and opinions, please let me know if there is anything else that you would like to know!
 

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Sounds like you have been doing all the right sort of research. To get anywhere near 200 miles of range, you are going to need a lot of battery. Thunder skys or similar are probably your best bet in actual, existing, ready-to-buy batteries without a sponsorship. A CRX is one of the best CdA cars out there so it is a good start as a chassis. I have seen 20 six volt lead acid batteries sunk into the rear floor of a CRX so you can stuff a lot of battery in there. Still, you will probably need to be sacrificing some of your cargo space with a battery as big as what you will need.

Any other EV with that kind of range has at least 50KwH or so of battery (think tesla, and wayland's insight) and you will need it too. This won't be cheap. a hundred, 160AH thunder skys for a 300V, 160AH system would do it. A CRX should be able to carry this if properly set up, but it won't be light (no worse than a 50 mile range lead pack though). If you could achieve 200wh/mile cruising efficiency on this setup you could do 200 miles at about 80% DOD with this pack.

The size and weight of the battery is going to make it a challenge to get to a 12s 0-60 time with an AC system. You could probably do it with the right DC system and a zilla controller though but it would be pushing it.

For motors, there aren't too many options in the AC, 300V range. look at metricmind.com for your options, or try to source a surplus AC55/DMOC setup.

This is probably more like a $40K to $50K build, not a $25K build assuming retail prices for everything.

That said, You can build a pretty nice 100 mile range, DC or AC car out of a CRX on a $25K budget. You can always leave room for more batteries and future upgrades.

Good lucik.
 

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Your project sounds very similar to mine, something I'm planning to do also. I'll be looking for a 0-60 time in the 6s range though haha, but everything else is similar. Low top speed but fast acceleration, and long range (in a super heavy car of course).

the $25k would probably be the cost of the motor and the controller itself already, not saying the battery price which will cost another $20k. I've done a bit of looking up on motors with very high torque, and like what madder said, go look at metricmind. They have a lot of high torque motors that will cater to the heavy weight of the car, so you can get the acceleration from there. it probably wont cost 25k cos that's the one I'm looking for a 6sec 0-60 time, but you can look around there.

Battery wise, I'm still looking for something smaller than TS. Though it's the easier and simplest for DC motor DIYers, I find that it doesn't cater to AC builds since AC needs high voltage but don't need to draw so much current from the batteries. That's why we dont even need 3C discharge since our battery pack is gonna be so big. We probably need 1C max discharge and 3C impulse discharge with a 160 or 200ah battery. Still tryin to find that kind of battery though.

Anyway, I'm subscribing here. Any updates do share :)
 

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You can see here in picture a rough estimate of your need basing on a graph from a diyecar member. Remarked the really good efficiency of the drive systems!

You will need to carry a LOT of cells....... 307 volts (96 cells) 200Ah = 61.4 Kwh, 25000$ and 1500 lbs

Good luck..... But I think it's more like a 100000$ project with best energy density cells availiable on earth!


 

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Discussion Starter · #5 ·
Yeah I feared my budget was just a little too optimistic ;) Looking at the metricmind website there are 6 different motors on there, ranging from $4.3k to $14.7k, so how do I figure out how much power I need if the main concern is efficiency at 65 mph? Also, what controller, DC/DC converter, and charger would you suggest? I forgot to mention in the first post that I would like to charge on 220V and keep the time under 4 hours from 20% SOC to full, faster if possible, with the opportunity for 110V opportunity charging as well.

On a different note, I hear some people mess with the mechanical drivetrain and axles and whatever else to make things turn easier and be more efficient. The main things I am wondering about is how should I couple the ac motor to the rest of the car, and should this be a clutch or clutchless setup? I would like ICElike performance over the entire powerband and not lose power at the top end, one of the reasons I thought it would be better to go ac. Also, do I need any sort of gear reduction or if I go clutch is there any sort of gear ratio that should be swapped instead of the the default gears?

The guy at metricmind did an ac conversion on a crx hf, so I have been trying to learn from that but he seems to be way above my head both mechanically and electrically :eek: He also used a prototype motor so it was really cheap for him. The same motor on his website costs $8k more, granted this is 13 years later but that is a lot! I am wondering with all this cost if it would be a good idea to do like madderscience said and build up the car how I want to, sans expensive lithium, and just use whatever is left in my budget for batteries at the moment. Then I could do the conversion, drive it around a little, and get used to everything and make some tweaks before I really go full out. Then again, for this kind of budget and timeframe might as well just buy a Tesla model S :p

http://www.metricmind.com/ac_honda/main2.htm
 

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Hi Docean
Sounds like a great project,
200 miles at 200wh/mile = 40Kwhrs at 80% = 50Kwhrs
TS are ~ $0.40/Whr and 100Whrs/Kg
So $20,000 and 500Kg
200Ah cells x 250volts
Motor
AC motors are very expensive – or wimpy – or both
I would use a 9 inch Fork lift motor ($200??) or a Warp-9 ($1800) and a Soliton Jr. controller ($2,000?)
This gets down towards your $25,000 target
Don’t worry about the battery voltage and the motor
The controller drops the voltage down to what the motor needs.
You lose the re-gen capability BUT that is mostly useful for city driving – if you are going 200 miles it’s not city driving
Retaining the gearbox and clutch does give more flexibility
80+ 200Ah TS cells will require a degree of ingenuity to stow away, - you are probably looking at stowing them wherever you can cut out a space –
You may need to have some on their sides, this should be OK so long as you avoid stressing them
(I think)
Overall I think your project is doable for about your budget - so long as you ditch the AC
 

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hello,
if you want 200 miles you going to have to go to the extremes, aero moding and Wight reduction. go with moon wheel covers, belly pan, rear wheel covers, tire boat tail, LRR tires, boat tail, aerodynamic grill, etc. as well as carbon fibber hood, roof, trunk, doors, and lightweight seats, flywheel and lexan windows and windshield, no AC, etc. see: http://aerocivic.com/ and http://ecomodder.com/blog/20-yearold-modified-honda-crx-hf-scores-118-mpg-fuel-economy-run/

also what about a bldc motor the are more efficient the n brushed motors, like this one overvolted: could it work http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=14427?? thanks
 

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Discussion Starter · #8 ·
I was already planning a slew of aero upgrades, but probably not going as far as the boat tail since the crx kind of looks like that anyways :D I had actually already stumbled upon those links you provided, they are a very good source of information. I also found a forum that has a bunch of debating but also a few good aero mods.

http://www.automotiveforums.com/t91...ving_with_an_undertray__anyone_try_this_.html

Duncan, thanks for the details about battery cost, I was wondering how much that would end up being. Maybe if I could get in on one of these group buys that seems to go down every once in a while I could save a little bit more money. If I go the lithium route which I am sure I will, what charger would you recommend and would you have a BMS or no?

AC v DC. This question never seems to be answered! :) It seems that if you have the big budget, connections or economies of scale then AC is worth it but for the rest of us DC is the only economical way to go. It makes me sad but money talks. I would still like to hear suggestions on the AC side of things as far as motor and controller suggestions go, but I will look into the warP 9. I do have a question about shifting an EV, is it just like shifting in an ICE car? I drive a stick shift now so if it is the same if I retain the clutch then no worries, otherwise maybe a little description or a video would be cool :cool: If you happen to know of the top of your head, what kind of highway speeds, highway passing performance, and acceleration will a Warp9 give with around a 2800 lb crx?
 

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Budget: <$25k not including donor
Range: >200 miles with 300 being stretch goal
Top speed: >80 mph with 90 being stretch goal
Acceleration: <12s 0-60mph with 10s being stretch
Donor: Honda CRX HF
weight 1713 lbs, gvwr 2240 lbs, CdA 5.7 sq ft, 45 mpg
Im sorry, but I don't think you can achieve all of these targets. They are all achievable...but not together IMHO. If you have done that much research on batteries, you would have probably figured out that this much LiFePo prismatic cells like TS, probably won't fit in your car (Unless u use every bit of space except where ur sitting...lol,m and maybe some strapped to the roof ). Also, the weight is gonna tax ur other targets. Now ur talking a different chemistry like li-poly (per J. Wayland)... weight goes down, price goes up, ... a lot. Double your budget and then some.. . or change your goals a bit. But hey, Welcome aboard and good luck! :)
 

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just a quick question, might be a little off topic. I've read lipo batteries (e.g. LiCo or LiMn) does have a much longer charging time, as well as a bigger safety hazard, than LiFePO4 right? Does this mean even if weight goes down, price and charge time goes up AND safety goes down, it's not going to be worth it already?
 

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Discussion Starter · #12 ·
Yeah I might alter the aerodynamics before I even start converting the car. If the conversion of 8 kWh per gallon is true, getting the crx from 45 mpg to 90 mpg per the aerocivic would cut my stretch battery pack from 53.3 kWh to 26.65 kWh and a shorter range from 35.6 kWh to 17.8 kWh. That seems like a much more reasonable battery pack and might bring it much closer to in budget if I can do all the aero mods for under $500 like the civic guy did. Still looking for suggestions on chargers, any ideas?
 

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Discussion Starter · #13 ·
Ok back with some more questions. Assuming I have a CRX HF with all the properties stated earlier, here are my numbers to get 203 miles per charge.

Speed = 65 mph
Drive System Efficiency = 85%
Rolling Resistance = 0.01
Conversion & Passenger lbs = 400
Battery Capacity (kWh) = 40
DOD = 80%
Cd = 0.20

Are my numbers realistic? I was hoping I might be able to push the drive system efficiency to 90% and the rolling resistance to .008, while also getting the Cd down to 0.17 like the aerocivic. If I do all of these things, I would get 258 miles at 65 mph. At 55 this is 318 miles per charge.

The biggest question is probably the weight associated with this. How much for a dc conversion, ac conversion taking into account removing all the old ICE stuff but probably adding AC since 1/2-3/4 of the year temps can get above 80 F easy, 100+ in the summer. Battery weight using 200 AH TS would be 1000 pounds and 63 batteries, with a system voltage of about 200V. Assuming a dollar per AH this would be 12,500 in batteries, leaving half my budget for everything else. Possible? Better ways?
 

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I believe Sky Energy has a LiFePO4 battery that approaches 115 wh/kg these days, so that would help compared to the 100wh/kg Duncan posted (or my ~85wh/kg batteries for that matter).

To give you an idea, my car recently covered 100 miles @ 243 wh/mile and speeds of roughly 50 MPH (there was also some stop and go traffic along the way in 30 MPH speed zones where consumption per mile went up). Its a 4 door saturn with larger frontal cross section, higher CD, cheap tires, no aero mods, and only a 32kwh battery pack. I'm not sure if you can shoe horn a 40kwh battery in a CRX, but I think 200 miles at 55 MPH could be within reach if you optimize the heck out of the car and a battery that size.
 

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Discussion Starter · #15 · (Edited)
Rather than pick AC or DC now, I have decided to build configurations for both and see what happens :D As always, opinions are welcome because I am trying to get as much performance (read: range at 65 mph and <10s 0-60 with lots of lithium) as possible. Right now I am assuming the same lithium pack for both configurations. This will be somewhere between 32 and 40 kWh and probably about 180W to 270W. Battery pack cost is estimated at around $15,000 as of right now.

AC
Drive System Efficiency: 90%
Motor: MES 200-330 40kW, $6425
Controller: MES-DEA TIM-600 AC Inverter, $3653
DC converter: MES 400-2000, $1674
Total: $11,752

DC
Drive System Efficiency: 85%
Motor: WarP9, $1875
Controller: Soliton 1, $2895
DC converter: Sp 500, $300
Total: $5,070

So AC is probably about 2x as costly, possibly 5-10% more efficient. Just adding battery cost to the AC conversion puts me over my $25k goal, something to keep in mind.

Are these comparable setups as far as size, power, etc is concerned? Can I get the highway performance I want out of the DC setup? Are there cheaper places to buy the AC parts? Are my estimations on efficiency and battery voltage, size, reasonable? Any other alternative suggestions to get what I want (esp AC side)? Am I overlooking anything that would push me to one side or the other?
 

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In response to "are my numbers realistic?":

I wouldn't presume less than 0.02 for rolling resistance to be conservative. I got my car down to 0.01 measured resistance but only after a set of LRR tires, an alignment job, internal transmission modifications, and some slight (safe) brake modifications.

As for total system efficiency, 85% might be a bit optimistic if you are thinking battery-to-wheels efficiency unless you are going to have a very simple drivetrain (direct drive) connected to a very efficient motor that will be running at its peak efficiency under your expected cruise conditions. 75% to 80% is probably a better estimate for most conversions. After doing some math, I used 78% battery-to-wheels efficiency for the range calculations I did with my car. This was with using 89% motor efficiency for the peak efficiency of an ADC 9" motor. The rest of the losses were in wiring, battery internal resistance, controller, transmission, and CV joints; All of this will be very similar in your CRX to what my MR2 looks like, unless you go with direct drive which will buy back a few percent for not having the tranny.
 

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Discussion Starter · #17 ·
Thanks for the update, I tweaked a few numbers to take into account what you said. I went with 75% but I will be using lithium batteries and I figure these have a little less internal resistance than PbA, but maybe the sheer amount of batteries will increase resistance in the wiring to cancel out any effect there might be in the battery resistance department. Madderscience, did you do any aero mods besides the air dam and the rear visor? I have been really looking into these and I bet most EV's could add a (partial/full) grill block, belly pan, and maybe even some smooth wheel covers and wheel skirts if you don't mind the look. I saw that you wanted 80 mile range at 55 mph, and you probably get around 62 miles of theoretical max range? By lowering your Cd by .02 or so you can add 3 miles of theoretical range. Not sure if you are interested but that undertray alone should net you that, plus if you could lower your ride a little you might be able to shave a few more points off. Alas, these things cost money and if you are happy with it the way it is then no problem. I am trying to eek out every last mile so any low cost, low weight way to lower that drag is going to be tried :D
 

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Hi Docean,

(Warning my car is not yet complete I could be blowing smoke)

My take is that AC systems are normally limited by the inverter system, so if it is 40Kw that is what you get!

DC systems are also limited by the controller BUT a Soliton can handle 1000 amps and 250v = 250Kw
The motor can take that - for a short time!

So your comparison is a 40Kw AC system
and a DC system that is ~ 40Kw continuous and 250Kw for about one minute

You can also go a lot cheaper on DC

My system
11 inch Fork lift motor - $100
OpenRevolt controller - $600 - 150v, 500A = 75Kw = 100Hp
BadBoy Charger ~-$150 (would be no good to you - only useful for small battery packs)

Leaving more money for batteries!
 

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AC vs DC often comes down to a choice between power and economy and more often than not, you get more peak power out of a DC system than an AC system of the same continuous rating. Its also generally much easier to get high peak power out of a DC than a 3 phase motor.

AC is most of the time more efficient and offers regen however (And sometimes water cooling too), so its a matter of what you want more of. Although it turns out that even without regen, I am able to get an acceptable range with my car on the highway (but I still wish I had regen!).

One last thing to consider is AC (or BLDC) motors will typically have a wider torque range than a brushed DC motor so the raw Hp comparison isn't quite so straight forward.

And having said all that, these guys were able to get 200Hp out of their MES motor:

http://www.illuminatimotorworks.org/about.php
 

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Yes, my original hope was to try and reach 80 mile range at "ideal" 55mph. After everything came into place and I accounted for all the variables, my math said a bit over 60 miles of usable range to 80% DOD, and my longest ever real drive was 66 miles, of which 55 were at 55mph near-ideal driving.

As for aero mods, I have intentionally kept the car fairly normal looking as I wanted a relatively incognito car. I did block my front air intake in addition to the front air dam. I have also removed the passenger side mirror and most of the trim kit (most notably the rear spoiler and side skirts) Not sure If either of these changes made it into my website, which I haven't done much with for a while (clearly) The bottom of my car is already pretty flat so not sure a belly pan would buy me much, and I'm not doing much more to my MR2 as I'm going to be starting over with a new conversion, hopefully beginning the process within a year or so. (gotta build a workspace first)

FWIW when I first started out I was like you- I wanted maximum possible range at freeway speeds on a given budget (was about 10K for me) and so I optimized for aerodynamic efficiency within reason and put in a big battery and the most efficient motor I could afford. Having driven the car for a while now I can say that under most of the driving I do (a mix of freeway and local, but most drives between 20 and 30 miles) I could have optimized more for weight and done just as well with a smaller battery pack and some other differences. The other big mistake I made, which may not be as big of an issue with lithium, is I didn't insulate my batteries. I drive in the winter and it makes a big difference.

Cheers
 
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