Yes folks: three days in a row to work, and back, with the Electric Booger. It was actually quite uneventful, other than the fact that I was driving on BC Hydro fuel.
I started writing this post with a whole bunch of technical stuff to say but soon realized that most readers don't care about that kind of stuff. They just want to know stuff like top speed and range. So here is what I have figured out so far.
-Top Speed on flat ground (so far): 80 km/h and still accelerating. I just haven't had the opportunity nor the space to do a true top speed run yet.
-Range: I have no idea. But it gets me to work and gets me back from work without putting a dent in the system voltmeter's reading.
-Charging time: after 6.5 km (with a big downhill) commute to work, three hours; after the commute home (with a big uphill), four hours.
So I guess I haven't divulged much information, but I guess it was worth a try.
Here is a question that I have been asked three times in the last two days:
"Have you thought about putting an alternator on the drive axle so you can charge the batteries while you drive?"
No. That will not work. Even if the hypothetical alternator is 100% efficient, it will take energy to turn the alternator, and this energy will have to come from the battery pack, cancelling out any energy produced by the alternator in the first place.
While not the best analogy, here is a highly educational video that might help explain what I am saying: WILE E COYOTE
Now to the technical stuff.
Field Power Problems
I quickly learned that 12V is not enough for the motor field. There is not enough torque for starting off and the motor revs much too high. This makes starting off in first gear mandatory (because of the lack of torque) and a shift to second gear at 35 km/h (when it starts to lose power), which is 7000 rpm. I even shifted at 40 km/h a few times, which is 8000 rpm. This is a good testament to my friend Matt's machining job on the motor to transmission coupler because it is still smooth as silk at those speeds.
Another problem with 12V to the field is that I can hear lots of brush arcing when the revs are high. I suspect that a weak field is much like running a series wound motor with too many volts at high speeds without advancing the brush timing, but I could be wrong.
Unfortunately there was a huge problem when I first put 24V to the field - a gigantic arc inside the field interrupt relay every time the relay opened the circuit. I could hear a sizzling noise every time this relay turned the field off. This is because the field windings are like a giant coil - thousands of revolutions of windings around the outside of the motor. Electricity has momentum and the coil acts like a 100 foot long electricity train that suddenly has no place to go when the relay is opened. The result is a giant voltage spike produced on the negative side of the relay contacts. It turns out that a normal 5-pin 40A relay is not made to handle this sort of spike. I think it is because the contacts do not move away from each other enough, allowing the arc to continue long after the contacts are open.
I was able to suppress this spike by using the 87a (normally closed) pin of the same relay to dump this spike to field ground. This worked with 24V to the field but when I tried 36V field power, it was again too much of a voltage spike and the relay quickly had sparks and funny burning smells flying out of it.
Yesterday I installed a larger relay to turn the field on and off - a relay that closely resembles a starter relay on some Ford vehicles. Now that the field power is being interupted with the larger relay, there is no arcing or funny relay noises even with 48 volts going to it. I seem to have solved this arcing issue for the time being. I am not sure the field voltage choice relay will last very long with the amount current I am forcing through it (it is merely a plastic, square 40A 5-pin relay) but I guess I will have to find out the hard way. I do have a spare relay in the glove box after all!
The other day I measured field current, which for power curve sakes is probably a more important figure than field voltage. But it turns out that the field winding resistance is exactly one ohm, so 12.5V applied = 12.5 amps, 25V = 25 amps, etc. Now I am at 48V for start off, and it makes quite a difference in torque. Most times I can take off from a stop in second gear.
I was originally going to install six small digital volt meters in an array to monitor each battery pair. I even bought a bunch of meters off eBay. However, in my great haste to get this car on the road I left them out. But it turns out that detecting bad batteries will not require individual volt meters.
Yesterday I charged the batteries after my commute home from work. I noticed that it took one pair an extra hour to charge, and one of these two batteries was making bubbling sounds. The next day when I got to work I immediately unhooked these two batteries from each other and measured their resting voltage. The one that had been bubbling while charging was a full volt lower than the other, so I charged it, removed it and load tested it. Yup, toast. 350 amps instantly brought it down to 7 volts. A battery should be about to handle half its cold cranking amps (these are 700CCA batteries) for 15 seconds and still be at 9.6V or greater. I quickly found a replacement in the core shed at work, tested it (9.8V on a load test) and replaced the dud. One the next full charge all of the chargers turned off within 15 minutes of each other. Problem solved. I guess this is another advantage of using individual 12 volt battery chargers.
My friend Trevor lent me his remote inductive ammeter so I could monitor motor current. I am proud to say that Alltrax does not lie in their specs of 450A for two minutes and 350A for five minutes. On the way home from work yesterday I floored it all the way up the long hill. When I reached peak voltage (which is also peak power) and the current started to fall (57 km/h in second gear) I shifted into third and it held 450A all the way up the hill while still gaining speed. I am highly impressed with this controller.
Other than a little bit more tweaking and tinkering, I believe I can truly say that this project is quickly coming to a close. Today I finished my control panel that looks much better than the gaping hole under the radio:
The extra meter in the centre will be the voltmeter for the 12V accessory battery. The switch on the right is the heater switch and the switch under the system voltmeter will be used to turn the voltmeter on and off. This switch is my solution to the fact that the [super cheap eBay] system voltmeter is causing a shared ground between the chassis and the traction system. I plan to power this voltmeter with a 9 volt battery through this switch to eliminate this problem.
Here is a picture of the organized mess formerly known as the engine compartment: