February 28th, 2013
Living in San Diego I didn’t expect to have to deal with cold batteries. Turns out the CALBs do not like getting under 45F – they really can’t produce the current I need to drive the car – setting off the miniBMS alarm.
I’m working with a machinist to come up with some insulation for the rear pack, and adding some heating to the packs. Simplest solution is to use plant seedling mats – they heat up whenever the temp drops below 74F. However, I couldn’t use mats due to the criss-cross of support beams. Solution: use soil heating cable. The cable I bought has a built-in thermostat and can cover up to 10 square feet. So now, all I’ll have to do is plug in the car each night – something I already do.
So when you design your pack, make sure you add in the heating lines for cold weather, as well as the necessary insulation.
November 27th, 2012
I was able to replace the failed battery without trouble, however, due to that misbehaving battery, the rest of the batteries were no longer in sync – meaning some had a lot more charge than others. I tried bringing the new battery down to the rest of the pack level using a 0.4 ohm resistor (50 feet of 16 gauge wire) – doing this for 5 minutes at a time. It came close, but when charging, the rear half of the pack reached top charge before the top half.
So, after some consultation with battery experts at work, I realized that if I did a REALLY slow charge (2.3A at 110v), then the resistors on the BMS would be able to discharge as fast as I was charging, thus allowing ALL cells to reach that same point. Please note that I have 108 cells, so I had to do some math. 2.3A * 110v = 253W. 108*3.4 = 367v. 253W / 367v = 0.69A. So I’m pushing 0.69A through the pack…ok, resistors can handle that… V = I*R, or I = V / R. Resistor on the BMS is 4.7 ohm. 3.4 / 4.7 = 0.723A. Easy.
November 3rd, 2012
The BMS was complaining about a battery for some time now, but when it got to the point where the complaint was EVERY morning, it was time to find out which one was bad. This is difficult when there are 108 of them. However, there is a method to finding the bad one:
- Drive a few miles to drop all the batteries to normal operational voltage (3.33 for LiFePO4)
- Expose all the batteries so you can see the BMS chips
- Measure the voltage at all batteries (mark the ones that are low)
- Start charging.
- Mark the batteries that go into shunt mode first
- When charging is done unplug the charger and measure all the batteries.
- Wait 1 hour for batteries to settle and again measure voltage.
Quite likely you will have identified the bad battery in step 3, but steps 5 and 6 will clearly confirm this.
What makes a battery go bad? If the battery is new, then it will fail within a month or less. If the battery has been in the pack for a while, then it has received some form of trauma (such as a connector flopping on and off or been hit or something like that).
In my case, the battery had a loose connector, which caused one of the bars to bounce on and off the battery. This is a Bad Thing ™. To see why, check out this photo:
July 10th, 2012
Well, the old potbox was severely misbehaving, so I replaced it with a Curtis FP-6. Very solid, very nice. Well, it’s kinda big. But solid.
So, I pulled out the old gas pedal, and tried placing it on the floor. It sorta worked, but quite awkward to use. So I took out the old floorboard behind the gas pedal, made a new one I could mount the pedal to, and it is now quite usable. Especially when the carpet covers the wire and box.
Here’s what it looks like:
New potbox on new footboard.
July 1st, 2012
It took a while, but I now have an embedded computer listening to the current going in and out of the battery. It is able to calculate the state of charge (SOC) of the pack, and display that value on a LCD screen. Simple enough, right? Just took time and shaking rust off some very old skills (wire-wrapping and soldering). In order to save the life of the auxillary battery, I have two power sources going into the computer. The battery directly powers the computer, and the keyed +12v drives the display. I’ll get some photos up later.
June 24th, 2012
The controller is still working – the problem was in the potbox. Apparently, the cheaper potboxes can have the rheostat inside slip. Who knew?
I’ve replaced the old potbox with an all-in-one pedal and potbox from Curtis. Nice solid construction, but I’ll need to work on the position of the box – the cable from the box is currently under my foot – not good.
June 21st, 2012
Well, I had to get the car towed home yesterday. Symptoms: gradual decrease in power until the motor was no longer spinning. Fortunately, I was in the right-hand lane of the freeway and was able to pull off on an offramp.
1) Check the batteries of your test equipment on a regular basis. My portable voltmeter’s battery was dead.
2) Keep your towing service – you never know when your car is gonna stop working. AAA was excellent and only took 15 minutes to arrive.
I REALLY hope the controller isn’t dead, as I didn’t want to buy a different controller just yet. At least I’ve got a lead on a (hopefully) more reliable one. Nothing solid yet.
May 16th, 2012
Neat. I calculated the power / mile, and got 290 Wh/mile. That’s less than with the smaller motor (about 300Wh/mile). Plus, there is no regen, so *IF* I can ever get that to work with this new motor, the power usage will be even better.
Lesson learned: larger motors can be more efficient than smaller ones.
May 9th, 2012
I realized when I posted the pictures of the new radiators and such that I neglected to include a picture of the new controller and wiring layout in the rear trunk. Hopefully this will satisfy those who are curious.
April 24th, 2012
Well, I tried two different CANBus sniffers, and there was too much noise on the line for either to work. I’m going to see if I can isolate the noise (one guess: the controller), but still not holding out much hope.
On the good news: I’m in touch with Paul of http://www.paulandsabrinasevstuff.com fame. They have a beta AC controller designed, and I think I will give it a shot. Certainly better than nothing.
April 16th, 2012
Ok, car seems to be running ok now. I have a loose battery connection somewhere that I need to tighten, so that will be my task for the next few nights.
Got the embeded computer installed, and of course, the data coming from the motor is nonsense. Speed is reported from 0 (although it says 768 at rest) up to 55k RPM. Temp ranges from 16 to 32K. So it is obvious that the serial comm is not up to the task.
Since there was a request for a picture of the radiators, here is a picture:
Also a picture of the lousy connectors that I had to replace:
The connector that is circled was smashed during shipment, and the others had wires that would just pop out.
April 9th, 2012
Ok, so I got the cooling working – had to reseat the pump, as the o-ring has come loose somehow.
So I still have problems with the controller. However, no way to know what is up without the RS232 hookup. Well, I spent about 5 hours on Sunday getting the comm to work. Sort of. First off, the wires out of the controller are backwards. Secondly, the controller itself keeps getting confused.
Example: turn on the controller, listen to the RS232, status is ok. Spin the motor a bit, and the motor thinks it is in overtemp. Spin it again, and the overtemp goes away.
Example: motor speed is a 16-bit value. This value NEVER goes below 762.
Example: voltage is a 16-bit value. This value ranges from 700 to 20,000. Never stable.
Next stop is CANBus to see if that is any better.
So far, this controller is rating a C (or maybe C-). Or for those of the digital persuasion: 4/10.
Oh – and still haven’t gotten regen to work – no clue why not.
April 1st, 2012
So I was right – it was the cracked/cheap/broken connectors to the motor controller. I replaced all of the connectors on the controller, and the motor now works VERY well. I really can’t use first gear anymore.
However, I discovered that I mounted the water pump in a bad position. According to some sites, I’m not supposed to put the inlet of the pump in a vertical position. Will keep you appraised of that.
Meanwhile, the new motor is just awesome. Once I get more comfortable with it, I just might burn rubber. O_O
March 23rd, 2012
I took the car for a brief drive up and down the block. Really sad performance – I need to find out what is wrong, as this is not how it should perform.
Will keep you posted.
March 17th, 2012
Ok, so the cooling system is all in place now – no leaks. I’ve got the pump hooked up to run whenever the key is on. Makes a small gurgle noise, so there is still some air in the system.
Hints: when installing new hoses, stretch the new hose where it will go over the barbs – makes life a LOT easier for the installer. Also, make sure the fittings are snug – otherwise, while the hose might be water-tight, the fitting could leak.
I was hoping to bring the car off the jackstands this weekend, but with the rain coming through, it is not very likely. Really don’t want to mix rain and electrical parts – especially since I haven’t re-installed the rear trunk lid.
I’ll post a picture of the radiators later.
March 9th, 2012
Ok, the adaptor is complete, and ready to install. We’ve made a few attempts to put it in, but had a problem with the spacing around the clutch. This has been resolved by allowing the pressure plate to move back 0.2″. During the wait, I’ve rewired the relays, added in a pump and resevoir, and a third brake light. Hope to have the motor and transmission installed on Sunday.
The brake light is a strip of weatherproof side-facing LEDs from www.superbrightleds.com. The wires are hidden behind the chrome.
Since both the motor and the controller use liquid cooling, I had to add in a pump and reservoir. I’ll be running coolant lines from the pump to the controller to the motor to the radiators and back.
The new motor is heavy – 98kg! (216lb). So we have to use this hoist to get the motor and transmission into the car.
Motor hanging on a chain
The new motor is significantly larger than the old one. The gap between the new motor and the battery rack is about 6mm (1/4″).
January 25th, 2012
I was told 3 weeks for a new adaptor, and its only been 2 weeks. I must be getting impatient. Meantime, I’ve updated my wiring diagram, and will start the rewiring this weekend (subject to the usual interruptions).
I’m also trying to find some software so I can talk to the motor controller, but that’s a very difficult proposition.
December 11th, 2011
As a public service, I hereby proclaim:
DO NOT USE PERMANENT LOCTITE!
At some point in the future, you will need to dismantle your machine, and using permanent loctite will make this a very painful experience.
Use blue loctite instead.
(This was discovered as we were trying to dismantle the old motor adaptor).
November 24th, 2011
Well, I’m going to use a different machinist to create the motor adaptor. It’s going to be a big project, as the current motor is only 9″ in diameter and the new motor is about 13.5″ in diameter. So we have to move the rear battery pack up 1.5″, and create a new motor mount for the motor – so it will be a squeeze fitting it in.
Plus, we have to mill a brand new motor adaptor – this will mate the motor to the transmission. This adaptor has to be precisely a certain length in order for the clutch to work properly.
Work starts on monday. Will keep you posted on the progress.
October 31st, 2011
Well, my mechanic informed me that the shops that would do computer-controlled CNC are backed up for 2 to 4 months. So he’s going to do it the old fashioned way – milling machines and measuring. This is, of course, for the new motor adaptor for the new motor. Hey – with luck I’ll be driving the new motor by New Years.