Ex-7 - Electric RX-7 conversion

**no_hazmats** · 01-13-2010, 06:24 AM

I don't know if I agree that running it off the wheels will give meaningful information about range. Power = Volts x Amps. It will take many more amps to move a 3500 lb car 50 miles than it will take just spinning the wheels the same number of turns.

Right now I don't have the batteries enclosed or insulated, don't have them heated (Which I doubt I'll do), and it's 18 degrees outside! I won't get nearly the range that I will in the summer. Furthermore, Lead Acid batteries need to be exercised before they meet their max capacity. From what I've read, it takes about 30 to 50 charge / discharge cycles for them to get to max. After that they gradually degrade over time.

I don't want to ever kill the batteries to the extent the car won't go. There is a trade-off between how deeply discharged they go and how long they last. Probably never want to go below about 50%. The controller has a lower limit of battery voltage, under which it disables the drive anyway. Too deep of a drain really kills battery life.

My plan is to start out with short hops around the neighborhood and never go more than 3-4 miles away. I'll start out putting no more than 20-30 miles on it and monitor the battery voltage. As it starts to drop to anywhere near the limit I'll head home for a recharge. As soon as I'm confident, I'll start driving it to work - I can also recharge it there. It's about 17 miles each way. When the weather starts to warm, I'll get more range and the batteries will begin to be broken in. Based on conversations with people that have the same system on similar cars, I expect 60 to 100 miles.

Another factor is where / how the car is driven. I live in a rural area near a couple of rivers. So there's a good bit of up & down terrain. That will be different than straight & level. I expect range will be different at 65 mph on a highway than at 35 mph on country roads too.

I will try to set up the GPS to record trips so I get an accurate distance measurement and speeds.

**cgalpin** · 01-13-2010, 07:08 AM

Congrats

If you haven't looked at the OBDII logger, please do. You can plot your battery data against the speed and gps data with it

http://www.mp3car.com/vbulletin/obdii-gps-logger/

I assume once you put a decent number of miles on it (say 20) you could extrapolate reasonably accurately to get you max range (keeping the batteries above 50%). I hope you prove us wrong, but I'm still skeptical about your expected range.

**no_hazmats** · 01-13-2010, 08:48 AM

Originally Posted by cgalpin

...If you haven't looked at the OBDII logger, please do. You can plot your battery data against the speed and gps data with it.

Wow! This is great. It looks like I can run it under windows using a linux simulator?? Does anyone know if this could be embedded within RR? Even if it runs as a separate app, that would be fine.

I've mentioned in the past that all things SW are somewhat elusive to me. Do you think anyone would be able to assist in moving the data from the SW I'm using into the GPS Logger to record Watts, Amps, etc agains the GPS Data? I know there are ways to access the data from other programs, and I have all the documentation, but I get lost somewhere between global variables and def_lib_whatevertheheckyoudonext. That is to say ... HELP!

Anyway, I'll download it into the car computer when I get some time this weekend and begin playing with it and setting it up with my GPS receiver. Thanks for the suggestion. If I had time to read this entire forum, that would mean I have nothing else in the world to do. Sigh.... Someday.

**cgalpin** · 01-13-2010, 09:01 AM

I'd post up for help in that forum and I am sure someone can help you out. I never got my obdii reader working under linux and haven't had time to get back to carputer stuff in months. But it looks like someone built it under cygwin and ran it on windows.

**sxott** · 01-13-2010, 09:32 AM

Originally Posted by no_hazmats

But the batteries I chose have about the highest energy / Lb and the highest energy / Cu. Ft of any commercially available battery.

You do realize that no LA has anywhere near the energy or power density of Lithium Ion so I assume you mean these are nice compared to LA batteries.

A good choice for a cheap quick conversion is the blue top style optima cells.

If you want to swap to lithium ions later you could try the thunder LiFePO4 based cells. They are relatively cheap. Getting the chargers, balancers, and so on really is not that big a deal compared to the work you already did. http://cgi.ebay.com/Prius-Plugin-Con...item2c5065c924 Lots of people are selling kits like that now (I think the batteries are made by a chinese company called thunder sky battery or something). I haven't tested those specific batteries, but I have tested many others. It is really obvious that if you want decent range and actual usability (cycle life) you will have to move past LA batteries. Another cheap option is to scavenge prius batteries and use a bunch of them instead.

BTW that isn't your rav4 is it? I think I recognize it

You do know that most regular LA batteries die extremely quickly under high DoD scenarios right? You will lose significant capacity in less than 100 cycles if you do that.
As far is range is concerned you could calculate some rough ideas easily.

Find the force to over come rolling resistance, and the Cd then make some calculations to see what you could do at a constant speed. That will give you an upper bound and you will know you can never do any better than that.

**no_hazmats** · 01-13-2010, 10:06 AM