Sunday, November 21, 2010

Back on the road

It's been awhile but I have been working on the car as often as possible and I'm finally back on the road.

The original BMS didn't have any wire protection, if for some reason a wire got shorted out and burned up, you'd have to rerun that wire. I added small inline fuses to each cell at the battery. It's a little more cost and time, but something that's worth it in my opinion.

Here is a picture of the completed front end. Six batteries were removed from the original design to all for the AC compressor and pulley assembly. The good news is I finally have AC, but the news is it's winter time and I have to wait awhile to use it. However, part of this was to add the heater and on the cold mornings it really heats up the small cab space of this car quickly.

The motor controller was modified in multiple ways. First the Curtis "whine" was removed and the car is now completely silent, as an electric car should be. The maximum voltage was increased to allow for my fully charged voltage on 54 cells (I charge up to about 184v). Finally the amps was increased from 500 to 750. This made a huge difference in acceleration and overall power. My 0-30 went from (I think it was 7 seconds) down to less than 4 seconds. Overall the total power of the controller went from 72kW to just over 130kW.

I removed that large, and unreliable BMS screen from the dash and replaced it with the E-xpert Pro. This has turned out to be a great little display. On top of showing pack voltage, amps, Ah, and remaining runtime, it has some other extras and is highly configurable. You can customize this meter to your battery, driving needs and how hard you want to push your battery by setting what is considered full, empty, when to raise alarms, etc. So for example I setup mine to alert me when the pack is 30% SOC and to consider 20% SOC empty. This affects how the "fuel" gauge displays its bars. I also turned on a feature that will automatically add the back light as long as >1 amp is going through the shunt. As I drive the back light is on, and 10 seconds or so after stopping it turns off. I also configured the meter to consider the battery full when 184v is reached and the charger is at about 2 amps for at least 1 minute. This then resets the Ah counters and gauge and avoids any calibration errors that might allow the meter to slowly drift over time.



Here is the trunk now. I wouldn't call it finished because things are still a little messy and I'd like to get carpet back in there. Trunk space is still reduce, but I can at least fit something in there now if needed. The little black things on top of the charger are the new Cell Log 8 modules that I'm using to monitor high and low voltage conditions. These are about $13 a piece and will monitor 8 cells each. I build a little circuit board for each to simplify the wiring. They have an internal relay that allows you to provide signalling to the charger, a buzzer, light, etc. They are not isolated, however, so expect to use an additional relay on each module to isolate it. These modules will turn on when the charger is connected to AC power or the key is on.


Another thing I modified this round was the suspension. I added another 9 cells (over 100 lbs) and with so much additional weight in the rear I knew I couldn't avoid it this time. Online I found the spring rates saw that the rear springs were much stiffer than the front. The front springs were 245 lbs/in while the rear springs were 311 lbs/in. I moved the rear springs to the front of the car and replaced the rear with 10" (original springs are 11" unbound) 400 lbs/in springs. The put the rear exactly back to stock ride height and my front is still 1/4" lower but I think within range for alignment. I still need to take the car back down for an alignment to see if this will do.

It's great finally being back on the road. The gas to drive my truck 70 miles to work each day was really adding up. That and I just missed my car, too much fun to drive. I'll keep you posted on miles. I think around 16-17k miles total at this point.

12 comments:

Berg said...

Fantastic job. I admire the quality of your work. Maybe a video on youtube showing the improved acceleration of the car? Greetings from Poland!

Anonymous said...

Looks like a good improvement. What BMS are you using now?

Brian said...

They are mentioned in the post and seen on top of the charger. They are called CellLog 8 and designed for hobby use but have proven to be a very low cost and reliable solution for HV LV monitoring. The displays themselves are a little buggy but the protection seems to be solid.

aphex4000 said...

Wow, that is a huge performance improvement with the increased power! Nice work

Anonymous said...

Very impressive upgrades and improvements in performance. But what happened to the modular BMS you designed for cell balancing? Aren't the cells going to drift too much without it?

Brian said...

I was wondering if anyone would notice that. I wanted to test this first hand and see how long it takes for the cells to drift.

The CellLog8s are all connected with relays for each cell. I wanted to make sure that nothing is connected individually to the cells (except during driving/charging) so that nothing could be draining them at different rates.

I'm going to wait until a cell is drained by the time I get to work and then after recharging calculate how far out of balance it was.

Some people say they don't drift, others say they do. I'd be interested in knowing exactly how quickly they drift as well. Is it a month or 10 years? Once we have that number, more people can determine how vital the balancing is for their application.

b2600ev said...

How was the Curtis whine removed?

Brian said...

I honestly don't know the details. I know a guy that works for Curtis who modified the controller for me to remove the whine and increase the power.

Mark said...

Hi Brian, is it possible that the Curtis guy you know would be willing to take on another modification? I have pretty much the same setup as you do. Great job btw.

Mark

Lee Morehead said...

Is it possible to get the guys info that did the mod for you?

Brian said...

I talked with my friend who did the controller modifications for me. He is willing to do the mods for others but wants to channel it all through me. I'm not sure what the cost would be. Your warranty through Curtis, if you have one still, would be void as well. Both of our modded controllers have been working great for awhile now though. Contact me directly if you're interested. brianblocher@ymail.com

Anonymous said...

So it's been almost a year since you posted... What's the status of this awesome auto?