Well, here is a link for serious inspiration for the new battery pack:
Well, here is a link for serious inspiration for the new battery pack:
So, so more thoughts on the new pack. I don’t want to have liquid cooling – I’ve already got enough problems with cooling the motor and controller. This takes out the Tesla batteries as well as the Volt/Bolt batteries. Also, it just doesn’t get as hot in Santa Cruz as it does in San Diego.
However, it does get cold – we’ve had near freezing weather for the last few weeks, and that is not good for driveability (or for the number of amps you can draw).
So I’ll have to heat the pack somehow – this will be built into the pack from the start this time. My thought is to use some kind of ceramic heating pad (gardening shop here I come) under the batteries.
I also want a full-fledged BMS this time as well – the miniBMS did what it promised (tell me when something is wrong but nothing else) – but that isn’t good enough. I need to know which cell is failing, and to be able to do trending on the cells’ capabilities.
I’ve been driving the 914 for 11,000 miles. The current controller does not let me do regen, so I’ve been having to use the brakes.
The 914 is currently in the shop to get all of the brake pads and rotors replaced. They also discovered that the rear calipers were frozen, and one needed to be replaced. *sigh*
Note: this was a draft I had forgotten to post, so this is about a year old – sorry.
The pack is about 8 years old, and was subject to a lot of hot weather (over 100F/38C). Several cells have gone bad, and it is not possible to buy the blue CALB 60AH batteries any more.
I’m investigating different technologies – CALB, Leaf, and Volt. Tesla would be lovely, but I’m not a rich guy. 🙂
I’ve been wondering why the BMS light will partially light up for the last few months. I’ve been busy, so I didn’t follow up on it. However, when driving home last week, the BMS alarm went off just before I was about to get on the freeway. I pulled off to a side-street, and called for a tow truck. While I was waiting, I started checking batteries, and sure enough – one was sitting at 2.94v, when the others were almost all a 3.3v.
Over the weekend I replaced the battery and now I don’t have the partial warning from the BMS. (The partial warning is where the BMS warning light just barely glows – it is a standard incandescent bulb. The full warning is when the light is full on and the audible alarm goes off).
The old DC-DC converter was only producing 12.5v – not adequate for a normal charging system. After asking around, I ended up buying 2 Meanwell PSP-600-13.5 converters. These are great little boxes, in that they are designed to work in parallel. This also means that with two boxes, I now have 1200 watts of power to drive whatever I want – such as a new stereo.
Hmmm, so I got the new 12v battery installed with no trouble. Plugged it in, and it is now fully charged.
Time to charge the main pack. I plug in the pack, turn on the charger, and now it is making an odd hissing noise. I’ve contacted the factory to see what they want me to do. Meanwhile, the car is not a daily driver at all. *sigh*
Well, the old 12v gel battery has finally died. I tried a whole day charging it, but nope, wasn’t taking in current. So I ordered and received a new Odyssey PC925 battery. I’ll get it charging up today, and should be able to install it tomorrow.
Of course, I still have issues with either a few batteries being soft or some BMS boards being bad. Not sure which. I’ll try to determine tomorrow. Turns out there is a new version of the miniBMS that has a 30 minute memory of good/bad/over/under. Would be nice to get, but then I’d have to spend another $1500 to do that. If it turns out that I do have some bad BMS boards, I’ll re-evaluate the whole BMS market.
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.
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. 🙂
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:
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:
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:
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.
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.
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.
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.
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. 🙂
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.
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.
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.