Friday, June 22, 2007

Installed lightweight 4.5 pound battery in BMW M3, replacing stock 50 pounder!

So, we've made a lightweight 4 pound starter battery for gas cars. Took us several prototypes before we got to our final working configuration. Issues like power, charging, casing, configuration, balancing, hookup terminals, etc, had to be figured out. But in the end, it was worth it! We've saved almost 45 pounds from the BMW M3. Notice the lack of a spare tire in the M3, there's run-flat tires and an air compressor instead, to save weight. The stock 3 series has a spare.

This is the battery we are replacing! Notice how much smaller it's going to be.

A size comparison versus the stock M3 battery. The battery in front is from the Scion xA, and was hooked up so that we wouldn't lose our settings from the car.

Installed battery. We needed to use a one foot extension cable because the stock positive clamp on the M3 wasn't flexible enough to reach the positive terminal of the battery.

Saturday, June 9, 2007

Adapter plate and motor hub adapter is being made!

So, last week, dropped off my manual transaxle and AC55 motor to Left Coast Electric to get the custom motor mount adapter and hub made! Met and talked to Reverend Gadget, and got to look around his workshop. Very interesting, and he seems busy with a lot of projects. Anyways he recommended going without the clutch, and leaving the car in second gear. I did some calculations for top speed, since my gut tells me top speed in second should be around 85mph at 10k RPM (the AC55 is rated for 8k RPM, but it can go higher):

10k RPM, 83mph
8k RPM, 67mph

Not as fast as I'd like, but decent enough. Now in third gear, assuming the car can spin at 10k RPM:

10k RPM, 121mph
8k RPM, 97mph

Much better! Anyways I used the below data for the stock tire size and gear ratios:
8.189 gear ratio for 2nd gear
876.1 revs per mile

Wednesday, May 16, 2007

Short video of my conversion project

Some people made a short video of my conversion project for some film thing! I was pretty nervous and don't like the way I sound on it, but anyways, it was a pretty fun experience.

Tuesday, March 27, 2007

Makeshift battery holder using magnets

It was very hard to find holders for 18650 sized cells, so instead, I bought some neodynium magnets, and covered them with copper tape. Works perfect as a battery holder! Lets me make various "pack" configurations. Here's a 7S3P pack. The magnets are attracted to the alligator clips and the cell bodies. I think using magnets with tape must have more resistance than a spring battery holder, but I don't think it's gonna affect the test results that much, since I'm not doing high discharge tests. I can do single cell, max 8 amp discharge tests, don't have the necessary equipment to do more.

Testing AC55 fitment, it's gonna be tight!

So, made a foamboard/cardboard mock-up of the AC55 engine (without all the fins, and without the box sticking out the side, or the bottom "feet"). I think I made the diameter a few mm too short, but it appears that cutting the fins is enough to clear the drive axles! At worst, I'd maybe have to shave a few millimeters into the front casing of the AC55 engine, which seems like it will be ok, since it's pretty thick. As for the side to side clearance, the box in the back of the AC55 is just about touching the passenger side frame. Tight fit, hopefully this won't be an issue! I wonder if you can move that box somewhere else. I need a thin motor mount adapter, maybe 1.5 or so inches.

I wish the AC55 was just slightly smaller, it seems like a great motor, except for the size/weight issue. Size-wise, it's not THAT much bigger than the MES-DEA 200-250, about 1.5" of the diameter is the fins. It's about 100 pounds heavier though, at 235 pounds vs. 134 pounds.

Friday, March 16, 2007

Changing system to AC55 Azure Dynamics

So, due to cost reasons, I'm changing my drive system from the MES DEA system (about $9k cost) to a AC55 system from Azure Dynamics (about $6k cost). Found a buyer for the MES DEA system at not too far from what I paid for it. The one thing that worries me is if the AC55 will fit properly with the drive axles. The motor itself will fit, I just don't know if the drive axles will clear! The motor's diameter including cooling fins is a massive 13.7 inches! Another thing about this motor is that it's torque is quite good, up to about 3000 RPM. Here's the torque-speed curve of the AC55/DMOC445 system (look at the "D" lines only, pink and blue):

Tuesday, March 6, 2007

12V lead acid SLI battery replacement

Did some testing with a potential replacement for lead-acid 12V starter batteries, using lithium iron phosphate (Li-Fe-Po4) cells from batteryspace. Charged and discharged a string of 4 18650 LiFe cells as a lead-acid cell, and got this from CBA (btw, I made a data entry error in CBA chart says 1.4Ah@1.30A rate, but the capacity of the cells is actually rated at 1.3Ah):

This is the same test done on an Odyssey PC680 lead acid battery:

It seems like the lithium phosphates can be used as lead-acid cells! The LiFePo4 cells don't fully charge, and don't fully discharge when treated as a lead-acid, but at a loss of under 150mAh (on a 1300mAh cell). It leaves about 90mAh capacity left, and less than 50mAh or so undercharged, based on how much capacity I was able to get from these cells (about 1200mAh or so) using the LiFe charging/discharging profile. I think the amount of undercharge will vary by which lead-acid charger you are using. (I'm using a Schulze isl 6-330D charger, which charges LiFe cells BTW) This will actually increase cell life by undercharging them, so I think it's ok. To maximize life of a lead-acid cell, you're only supposed to use 50% of it's capacity anyways. The PC680 is rated for 17Ah at the 20 hour rate, and I was able to only get slightly more than 9Ah at a 6.8A discharge rate.

Wednesday, February 28, 2007

Engine is out! WOOOOOHOOOOOO

WOOOOOO a milestone has been reached! We got the engine out! :) Took like almost a month working weekends. ;) Experience is really worth a lot, I can see how it should have only taken a day, if I knew what I was doing. Now I just don't know where to put the engine, currently it's sitting on two tires, but still hoisted, since I don't want to mess anything up by laying it on it's side.

Wednesday, February 21, 2007

SLI (starting-lighting-ignition) battery for EV

Most EV conversions I know of use a DC-to-DC converter to convert the traction pack's high voltage into 13.8V for the 12V car system. The converter is pretty expensive ($400+), especially for a high voltage (300V+) pack. Also it needs to be isolated since you don't want to share the ground of the high voltage pack with the car's 12V system!!!!!

So, I figure why get a converter, when you can just make a seperate 12V battery? It doesn't need to deliver as much current as a lead-acid in a ICE car, since there's no need for ignition and starting.

So, I wired up some 18650's, an amp meter (using a Watt's up meter), and an Orion DC-DC. There's no need for the converter to be isolated, since we are dealing with only 24V or so (the lithium pack contains 8S7P cells as of now). I tried hooking this up to my Lexus RX400h hybrid, and found out, there's no alternator! So I had to find another car to test this in. Ended up trying it on a Chevy S-10, and found that idling, with headlights on, it was drawing around 10 amps from the battery pack, but it works!

Hopefully the electric scion will draw less than 10 amps. My plan now is to wire it up so that when the car's ignition is off, power will be drawn directly from the lithium pack (going to be 12V instead of 24V). Then you turn on the ignition, it puts the Orion DC-DC into the circuit. Wondering if that idea will work.

Taking out engine requires so many tools

Still working on taking out the engine! It requires a lot of tools that I don't have, which requires me to purchase them, including some tools I had to get from Toyota. Waiting for it to come in the mail, specifically engine hooks that bolt onto the engine, and which you attach the chain to. Hopefully those parts will come tomorrow. As of now, the car looks like this. Below is the gas tank. I'm planning on using that area where the gas tank/muffler/cat used to be to store the batteries. There seems to be a lot of space down there! Just not contiguous space (not suitable for lead-acid's), so I'm going with a massively parallel 18650 lithium iron phosphate pack. This should avoid all the safety issues associated with lithium colbalt chemistries.

Monday, February 5, 2007

Started taking the car apart!

Started taking the car apart this weekend, worked on it basically 5 hours each day! Lots of work but then again it's a learning process. Here's the car's current state:

Here's the engine bay:

Here's the pile of parts taken out. It really looks like a lot, and the engine isn't even out:

Tuesday, January 16, 2007

Testing 18650 lithiums with Schulze charger

Bought a Schulze charger, it's pretty nice, to test how parallel 18650's behave. It seems you can charge and discharge single cells in parallel. I tried purposely mismatching them, and over time it kind of self balances over a few charge/discharge cycles. Been using magnets since I don't have battery holders, it works very well. The magnets are neodymium types, and they conduct.

MES DEA controller and motor

Look what I got! Neat. The motor is very compact, and the vacuum pump and water pumps seem very well made. Can't wait to start the physical installation.

Wednesday, January 3, 2007

Funniest thing, artificial engine noise, Jeri Unser at Pikes Peak


"Since the ER3 is nearly silent, the crew put a sound system on the car to
produce an engine-like noise to make sure that spectators lining the course would be aware that the ER3 was coming down the track. This sound system was programmed to make a buzz or whine that was proportional to the speed of the car. It seemed to fool everyone as most people at the track were very surprised when I revealed that the sound was artificial. This was a big improvement over the annoying siren used on the ER2.

That's the funniest thing, speakers to fake the engine noise. I've had a similar thought about EVs, since they are silent, people can't hear them coming. I once saw a Prius going slowly by, and I couldn't hear it at all. Could potentially be dangerous since you can't hear it coming like a normal ICE car.