# Planning Honda CRX Conversion



## madderscience (Jun 28, 2008)

Hello and welcome to the forum. If you haven't already, the wiki can provide a lot of insight for somebody just getting going. 

To answer some of your questions:

A CRX is a good conversion candidate from the standpoint of its light weight and good aerodynamics. The 2nd generation CRX's (89-91) are about the most aerodynamic cars you can get from that era, though they are more expensive than the 1st generation one you are considering.

An 11" motor is overkill for that car. an 8" motor if the car will have a final weight of 3000lbs or less, or a 9" motor if the car is heavier than that will be fine. Also consider that forklift motors may only be rated for 3000 RPM, you will probably want more than that. the motors sold specifically for EVs usually are good for 5000RPM for the 9" motor sizes, and a bit more for the smaller motors. It is very possible to prep a forklift motor for EV usage. There is a very good thread on that very subject on this forum. Read up on it.

a 72V car is going to have a low top speed, especially with a large diameter motor. To get to freeway speeds you should be going for 120 volts at least, better to do 144V.

You haven't specified the important details of the batteries you want to use, which is the voltage and AH capacity. But I would recommend against using anything except real traction batteries (better known as golf cart batteries). There are other lead acid batteries that deliver more power with less weight (but NOT more energy), but no other lead acid that beats golf cart batteries for overall durability and life cycle costs in an EV application. The range you can expect using golf cart batteries and an 8" or 9" motor in a properly dialed-in CRX will be 3 to 5 miles of driving range per 100lbs of battery. The wide range factors in different driving conditions. If it is flat and warm and you are doing a constant 55mph, you will get the higher end of the range. If it is cold, rainy and windy and you are climbing hills, you will see the low end of that range.

My car is a 1985 toyota MR2, which is only a little bigger and has similar aerodynamics to the CRX. It has a 9" motor, 21 golf cart batteries weighing 1250lbs and has 3400lbs total curb weight. I have had it up to 70mph, which is about redline for the motor, but I usually cruise at 55 in the freeway. The maximum drive distance I have achieved was 66 miles on one charge (mostly flat freeway at 55) but for most of my driving I don't go more than 30 miles or so before recharging.

Continue your research, and Good Luck.


----------



## dtbaker (Jan 5, 2008)

looks like madder just about covered it.... I would second the opinion to go with a 8" dc traction motor (not a forklift motor). if you want highway speed capability, you will need 120v. If you go with 12v batteries, you will likely have shorter range and batteries will not last long... If you go with 14 x 8v golf cart floodies (assuming you can fit them in...) you'll have no prob with speed, but probably still only get 50-ish mile range. You could go further with Li, but at much higher expense.

Unless you are a really good scrounger, and willing to go with some old used or questionable parts, you should budget closer to $8k for all the stuff plus new FLA batteries.


----------



## neljoshua (Oct 21, 2008)

I just started my own conversion. As a college student myself, I can relate to your desire to keep costs low.
My original budget was $6300. It looks as though I will be able to come close, but it is quite tight. Items such as dc/dc converters (so you can run your headlights, etc), battery chargers, and so on really add to the cost. Keep these in mind.
These guys are more experienced than I--I would listen to their advice.
I actually decided to use a BLDC motor and controller, so my speed is not as dependent on voltage as it is on frequency. Even so, I am using 120V.
I think you would need to know the specs on the motor to know if it would be able to handle 120V.


----------



## JimDanielson (Oct 19, 2008)

Thanks for the replies.

The batteries from walmart are $62 a piece, 12v, deep cycle, 115Ah. I think the brand may have been Maxx but I didnt write that down.

Second hand forklift motors seem to be the only thing in my budget. New motors seem to range from 1k-2k and even higher. There is a used forklift parts dealer near me who could probably get me any sized motor for $100~$300. I have read that rotating the brushes 8-10degrees on a forklift motor will allow it to run at higher rpms.

It is important that I reach speeds up to at least 60mph. So, was wondering if a kelly controller at 120v would get me the extra rpm I need, acceleration is not a priority. http://www.kellycontroller.com/shop/?mod=product&cat_id=19&product_id=494

Basically, would a forkllift motor work at 120volts? Has anyone else achieved this or higher?


----------



## dtbaker (Jan 5, 2008)

jimbo12d said:


> Thanks for the replies.
> 
> The batteries from walmart are $62 a piece, 12v, deep cycle, 115Ah. I think the brand may have been Maxx but I didnt write that down.


hhmmm, 115ah at what rate? the 20hr rating is meaningless for an EV, you need the 1-hr rate for when you are sucking amps. if you decide on 12v, you ought to pony up for quality battieries. check out usbattery.com



jimbo12d said:


> It is important that I reach speeds up to at least 60mph. So, was wondering if a kelly controller at 120v would get me the extra rpm I need,


120v to an 8" ADC would do it, but I dunno about a forklift motor.


----------



## JimDanielson (Oct 19, 2008)

I don't know the Ah at that rate, but did see a few people on here who used the walmart batteries and weren't disappointed.

How much lower Ah rating should I expect at a 1-4hr rate?

How much does the motor you suggest cost? Where do I get it, could I find it used?


----------



## JimDanielson (Oct 19, 2008)

I was looking at Ni-Mh options to try and save weight. I called up Tenergy and asked the price of 1500 of their F size 14Ah batteries. This would give me about the same Ah rating as the lead acid batteries I plan on getting. I like Ni-Mh because they aren't as sensitive to temperature, they are pretty light, they don't need super fancy chargers, and I thought they would be priced inbetween lead acid and lithium.

The price I got would be $8.50 per cell. This price beats the price I could find for this same cell anywhere else, but totals at 12,750 not including shipping. 

When I added up the costs to the thundersky batteries for the total Wh I want, it came to be only ~8,000 not inlcuding shipping. I was hoping I could find Ni-Mh for 3,000-4,000 but I guess I will be using Lead acid batteries unless someone knows a good place to buy from.


----------



## TheSGC (Nov 15, 2007)

I am a little concerned with the 11" motor and a CRX. I know an 11" DC motor will not fit in a Civic due to it's diameter and the motor will literally be in the way of the driver's axle, but I am unsure about the CRX. Most people put 8" motors in Honda's and a few put in 9" (I am installing a 9" in my Civic now), but the only Civic that has an 11" had to have it's transmission replaced with an Acura's in order for it to fit.

As for batteries, LiFePO4 is cheaper than Ni-MH and that won't change for a while because Ni-MH are controlled battery chemistries and have limits on large format productions, thanks to oil companies.


----------



## JimDanielson (Oct 19, 2008)

11" was what I originally saw the guy local to me selling so I just posted that. He sells a large array of forklift motors, so I will see how much a 9" is.

Also, haven't decided for sure on the CRX. It really all depends what is on craigslist the week I start building it. But most likely a fiero, crx, geo metro, or civic hatchback.

I have been looking at the logisystems 750amp 144v controller. My main concern is what guage wire will handle 750amps? Obviously that won't be continuous, but should I get the 0000 stuff or what?

Thanks


----------



## JimDanielson (Oct 19, 2008)

Besides the wire guage,

Do I need a contactor? Where would I get one? Could I just use a heavy duty circuit breaker and flip it off when needed?

Also, where should I get a tach that can be used on an electric motor?

Thanks


----------



## TheSGC (Nov 15, 2007)

Contactors and fuses/circuit breaker are a must. You can get them from EV suppliers or eBay. A Curtis SW200 is a decent contactor and you can look for Airpax circuit breakers. 

In my EV I have a contactor and circuit breaker in series. The purpose of this is to install a precharge resistor over the contactor to slowly charge the controller caps, then use the breaker as an emergency disconnect switch. The more safety the better and contactors can weld shut is deactived under load, so a fuse/breaker is also good for those emergencies. 

Tachs seem to be a hard thing to come by, but any hall effect tach sensor and the apporiate meter should be fine. You can try eBay and a search through this forum should bring up a few since it is becoming a hot topic these days.


----------



## dtbaker (Jan 5, 2008)

jimbo12d said:


> Do I need a contactor? Where would I get one?


yes, absolutely you should have a 'keyed' contactor from your switched 12v power so you can switch on/off from the driver's seat, AND a circuit breaker with MANUAL pull from the driver's seat in addition to internal overload protection, as well as a big fat fuse in the middle of your traction battery pack cable. I would also advise an 'inertia switch' wired to open the contactor in case of impact.... all these things available at various EV suppliers like www.KTA-ev.com and others...


Could I just use a heavy duty circuit breaker and flip it off when needed?
----
you probably should use ke switched power for some level of security. 




jimbo12d said:


> Also, where should I get a tach that can be used on an electric motor?


You don't really need a tach. you can back-calculate 'redlines' from known gear ratios and tire size... and just mark right on your speedo.... see
http://envirokarma.org/ev/13.Instruments.shtml for example.


----------



## Arlo (Dec 27, 2009)

Did this ever get finnished?
My GF and i just bought a 1988si for 450 and it needs a bit of work but we are just going to get it on the road so she can save gas money as I save up to make it electric! I am planing 4wd with either 2 or 4 motors. So I will electrify the rear wheels first then once I get that working well pull the motor and do the front so it can be driven as a hybrid for a while and save on batteries as they come down in price!


----------



## dtbaker (Jan 5, 2008)

Arlo said:


> Did this ever get finnished?
> My GF and i just bought a 1988si for 450 and it needs a bit of work but we are just going to get it on the road so she can save gas money as I save up to make it electric! I am planing 4wd with either 2 or 4 motors. So I will electrify the rear wheels first then once I get that working well pull the motor and do the front so it can be driven as a hybrid for a while and save on batteries as they come down in price!


I think you will find that the complexity of a DIY hybrid control system is unrealistic for the average person, and that given limited space its pretty tough to retrofit and leave the ICE in place. Hub motors are really not ready for prime-time at an affordable price.... you will be much better off saving up, gathering parts, and going 100% electric when you are ready.


----------



## Arlo (Dec 27, 2009)

dtbaker said:


> I think you will find that the complexity of a DIY hybrid control system is unrealistic for the average person, and that given limited space its pretty tough to retrofit and leave the ICE in place. Hub motors are really not ready for prime-time at an affordable price.... you will be much better off saving up, gathering parts, and going 100% electric when you are ready.


 I already have 2 almost perfact BLDC motors one for each rear wheel. If its going to be 4wd which It will. I midas well do the rear first.


----------

