Monday, August 30, 2010

More battery testing

I ordered 12 new cells for the upgrade. The plan was to replace the two cells that have had bad sag since day one and 10 new cells. I decided this would be a great time to do another capacity test for comparison against my original cells.

When I got the original cells I was told the factory capacity tests were all above 160, if I recall they were mostly around 165Ah. I charged a group of four new cells the same way I did the old cells. That is, not long after switching from CC stage into CV stage I remove charge and begin testing. The old cells were drained at ~130 amps until 2.5v and the worst cells yielded 145Ah, most around 150Ah. The new cells I only drained down to 2.8v and the reason is that at 2.8v they had produced 183.5Ah!

This raised a few thoughts of course and along with the fact they have improved the cells, I'm lead to believe that Sky Energy (CALB) who sells an equal size and weight 180Ah cell for more money is most likely selling the exact same battery. Unfortunately I don't have the 180Ah cells to test, perhaps they are getting 190-200Ah. I believe the batteries might be coming with more capacity also so that after time, they are still considered to be at their rated capacity or higher.

Trunk Mods Part II

Not much to show here. I've installed 15 additional cells in the area the old fuel tank use to be. This is directly above the rear sub frame. This is too much weight for the original shocks so I'll be modifying the suspension all around. Even though the sag isn't much, the suspension doesn't allow for much correction and the alignment was never back in spec causing inside tire wear. I plan to resolve that this time around.

Friday, August 27, 2010

Too Cool

After completing the trunk modifications I needed to modify the front racks to reduce the number cells and provide space for the air conditioning. Unfortunately during the first stages of the conversion I focused on getting batteries in and soon found I didn't have room for the AC. Wanting to make sure this didn't happen again, I decided to get the AC in and then see how many cells I could fit afterwards.

The first and probably hardest step determining how power the compressor. My first option was to modify the compressor to use a standard V belt. In this case it was easy to create a main pulley to attach to the motor. However I determined, after dismantling the compressor, it was going to be very difficult. My second option was to find/make a pulley that could use the same style of serpentine belt the compressor used. I opted for this method. I used the original pulley which accepted a spline shaft. The ADC 9" motor has a much smaller, round keyed shaft. I bought a 3/4" hub from tractor supply. I was able to get my uncle to turn down the hub and we then pressed it inside the original pulley with a hydraulic press. We ran a weld around one end to make sure it could turn inside. With this done it was just a matter of fabricating a frame that mounted the compressor and tensioner to the motor frame.

Here you can see completed setup. Reusing the tensioner instead of trying to make the compressor adjustable is the best route. The tensioner keeps the belt at the ideal tension as it stretches with age. This setup should be maintenance free for years.

Here is a shot from the other side.

I ordered from Jegs and got a Gates belt K060345. This is actually a bit over 35" and is the six v serpentine style belt used originally, just much shorter. This was stocked and I got a "free" hat. Considering their "free" shipping had a $5 handling fee, I'm not sure which one of the two I actually got free.

Here is a 12v functional test video. It's not nearly as noisy as this little camera picks up.

After everything was functional I needed to charge the AC system. The system had been opened for months, and even if it had only been opened for a day or so you need to do a lengthy evac process. An oil based vacuum pump is required which I bought one from Harbor Freight. You'll also need an AC manifold set which I also got from Harbor Freight.

The process is fairly simple. First connect the high(red) and low(blue) side hoses to the A/C system. The sizes are different so you can't accidentally connect the wrong one. This manifold set has a yellow hose and two spots where the yellow hose can connect, one is open and the other is a pressure fitting. Connect the yellow hose to the open side and then to the vacuum pump. Turn on the vacuum pump and then open the high and low valves. Let this run for several hours, the longer the better. The pump will get the system down fairly quickly, but it won't remove all the moisture this fast. You must leave it running to remove the moisture (3-5 hrs will do it). Once complete, first close the high and low valves, then turn off the vacuum pump.

You'll need to check the service manual to determine how much refrigerant should go into the system. You'll also need to replace any oil that was lost. There are refrigerants that contain oil, but it's not enough for a complete recharge so you'll need to do the math and figure out what you need.

The recharge process is simple. Read and follow the directions on the can first and foremost. Disconnect the vacuum pump and connect your refrigerant. The can should be shaken during the entire process. Open the valve on the can, then open the LOW side ONLY. Never open the high side valve while recharging. You'll hold the can upright and rotate 90 degrees every few seconds again given the can a good shake frequently. You'll want to make sure there is enough refrigerant and oil in the system before turning on the A/C system (again consult your service manual). Most systems should have a low pressure safety switch to prevent this. With the A/C system on max you'll notice the low side gauge drop as it compresses the gas to the high side. As it pulls from the low side more refrigerant from the can will pass into the system. As the can empties it slows down so be patient 5-15 minutes per can. Repeat this process to add oil and more refrigerant as needed. When complete close the low side valve, then close the refrigerant valve. The high and low side connectors can be popped off easily at this point, but when you disassemble the manifold some gases will escape so do this in a well ventilated area so you don't breath it in.

That was it, now I have some really cold air coming out of my EV!

Thursday, August 19, 2010

Trunk Modifications Part I

I've been working on modifications to the car over the past couple weeks. In order to get the AC back into the car some of the cells needed be shifted from the front of the car to back. Additionally, I want to add a more cells. The only solution was to make better use of the trunk. The number of new cells I'll add is still not firm but I'm looking to add as many as possible for multiple reasons.
  1. Greater range. More cells means I have more energy and can travel further before recharging.
  2. Distributed load. The more cells I have, the less they have to work for my daily commute which will increase the life of the cells.
  3. Performance. Currently the 144v system allows the motor to hit about 4k RPM before the controller switches to VMax. Any additional increase in RPM greatly reduces torque requiring you to shift to a higher gear. Increasing the voltage will allow the torque to remain steady for higher RPM meaning the motor will want to rev out higher.

Here is a shot of the original trunk space. You can see there isn't much usable space currently above the fuel tank, about 3" and it opens up to only about 8-10" on the far right.

The old spot I use to have the charger has a curve to it and greatly reduces the usable space.
A couple of minutes with my plasma cutter and the rear most area is opened up and ready for a new battery rack.
This area now allows for storage of all 15 cells that used to take up the remaining trunk space (including charger). The rack is lined with a thin plastic and sealed to keep out water, etc. I used an expanding foam on the outside underneath the car to also fill in any open areas. The sides use a 1/4" thick steel for strength since the rack is also binding the cells together. If you use a thin metal it will bend as the cells begin to swell which is very bad on the cell life. It's amazing how much pressure is needed to contain them properly. The top (black) metal is much more light weight and designed to simply keep the cells from being able to shift upwards on bumpy roads or a rollover.

Next I will be working on the area where the gas tank use to sit. It looks like I can fit another 18 cells here if it all works out. I will need to make some suspension modifications for the extra weight I'm adding with these additional batteries.

Sunday, August 15, 2010

Battery testing

I have removed everything from the car to complete that to do list I created a long time ago and have been putting off (more on this later). While I had the batteries out I wanted to do a test to determine how much capacity is remaining now that the cells are about 1.5 years old and have over 15k miles. I've also calculated it takes me roughly 120Ah to get to work and 80Ah to return home (2k foot elevation climb to get to work). Using 15k miles, and the 70 mile commute that gives me about 214 trips I've made to work so far. Each round trip (120Ah + 80Ah) / 160Ah batteries = 1.25 charge cycles. Therefore, 214 x 1.25 is 267 charge cycles I've used.

Below is my battery testing solution.
  • Costco a 2300 watt power inverter. This allows me to test four batteries at a time to get my 12v source.
  • 1500 watt space heater. This gives me just over 130 amp load on the batteries which is close to 1C and will give a decent enough load to test.
  • E-Xpert pro battery monitor from TBS Electronics with a 500 amp shunt. This will track the Ah used for me and give accurate results compared to trying to calculate this myself based off of ever changing voltage/amperage as the batteries drain.
  • CellLog8 allowed me to easily monitor each cells voltage to determine when a cell was too low during the load test or too high during recharge.
  • For charging I used my original battery charger, a 12v charger I had, and my bench power supply. This allowed me to charge up to 45 amps and helped speed up the testing greatly. I only did quick charges and once the amperage needed was between 5-10 amps I stopped charging and begin the test. This means the cells were NOT fully charged (probably 90 - 95% is my guesstimate) which is important when reviewing the results below.

My original testing plan was going to be to drain the batteries until the first cell reached low voltage, then rotate in another cell and continue testing to get results for each cell. After doing this only once I realized that the capacity of the cells was extremely close and it wasn't worth the extra time. I won't post all the results but basically my lowest cell produced 145Ah. I had other groups producing 148, 150, etc. They were all extremely close. Even the two cells that have terrible voltage sag still produced over 145Ah like the others. Now 145Ah is just over 90% of original capacity, however, remember my charging method was manual and I didn't give it the time to do much constant voltage charging. So to my surprise, I think I'm still near original capacity. The only thing is I didn't do this testing when the cells were new and I'm told they will have at least 160 but usually more, so it's possible I've lost more than I know. Either way this is good news and I'm quite happy with the results.