Project: The Electric Booger (budget EV conversion - '92 Mazda MX-3)

[Daox]

Woohoo, congrats on going for your first good run!

[Ryland]

As far as the motor getting hot, the outside is not as much of an issue as the brushes and commutator getting hot, 350F/175C is about where it will start to cause damage.

[mechman600]

Originally Posted by Daox

Woohoo, congrats on going for your first good run!

Thanks! Man, what a feeling. You watch all these YouTube videos of guys excited to be on their first EV run but it is a feeling that I could never have imagined. Never before has such low speeds been so thrilling!

Originally Posted by Ryland

As far as the motor getting hot, the outside is not as much of an issue as the brushes and commutator getting hot, 350F/175C is about where it will start to cause damage.

Thanks for that info. 350F seems really hot to me. I will carry my infrared temp gun with me and stop to get an armature temp reading, especially after going up the hill on the way from work.

I also installed my hair dryer heater and wired it in last night. I wired it in so there is no way it will get power unless the heater fan is on. I turned the heat on for about 10 minutes and it blows...well...warm air. So it isn't as hot as with the ICE providing heat, but it is warmer than no heater. As long as it keeps the windshield clear, I'm happy.

As an experiment I am switching the 72VDC heater power with a regular old 12V 5-pin relay. After ten minutes it was slightly warm to the touch, but that's it. I also switch the 72 VDC key signal to the controller with one of these relays as well. I am concluding that at least to 72 volts, these relays work fine, keeping in mind that I am still using 12V on the control side (pins 85/86).

[mechman600]

Today was my first commute in the eBooger. It was a smashing success.

12V is not enough for the field in my sepex motor. Too little start off torque and it has to rev much too high to make decent power - the shift from first to second at 6000+ RPM. Plus, I can hear arcing brushes at higher revs. As soon as I switch to 24V field, the brush crackling sound goes away.

I measured field current today. It turns out that the field windings are 1 ohm. 12V = 12.5A, 24V = 25.0A.

I still have a major problem with a massive voltage surge from the field whenever the relay goes open. I tried to eliminate it with a large(ish) diode across the field terminals, which helped, but it's still there. When the field relay opens on 24V, the arcing lasts a few seconds and the relay gets smoking hot after a few on/offs.

I decided to run pin 87a of this relay to ground so the field surge goes straight to ground. At 24V it seems to have cured the arcing. However, when I tried 36V on the field, as soon as the relay opened sparks flew, and stink filled the air. Not good

What do I need to eliminate this voltage spike completely? What resistors, capacitors, diodes, etc. do I need and how do I do it?

How many amps can I safely give the field?

[mechman600]

Here's a thought: couldn't I buy a tiny 72V/100A controller to control the field current?
Controller Kelly 24-48V 50A Super High Efficiency #KDS48050E

[jakobnev]

ATF

I suspect the electric motor will heat your tranny less than an ICE would, so ATF shouldn't be a problem even if your climate is warmer.

[Daox]

Originally Posted by mechman600

What do I need to eliminate this voltage spike completely? What resistors, capacitors, diodes, etc. do I need and how do I do it?

I don't think you can eliminate it completely. Some additional super fast (transil) diodes are what I have always heard suggested.

How many amps can I safely give the field?

It might be best to take the motor apart and see what gauge wire the field wires are. From there you can at least get some idea how many amps they can take.

[95curd]

nice bulid! looks like it's coming together real nice. Are you planning on any luxuries like radio and AC?

[mechman600]

Originally Posted by 95curd

nice bulid! looks like it's coming together real nice. Are you planning on any luxuries like radio and AC?

The car never had AC. But it does have a fully functional 6-CD changer in the trunk (a la 1992).

-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.

A question that I have been asked three times in the last two days is:
"Have you thought about putting an alternator on the drive axle so you can charge the batteries while you drive?"

Oi. As a response, I usually refer to this video:
http://www.lghs.net/ourpages/users/d...boardMotor.mov

Field Power Problems

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.

Battery Diagnostics

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.

Alltrax Controller

A buddy of mine 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:

I absolutely love the old school red LED numbers. Dr. Emmett Brown would indeed be proud!

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.

Heater

I did use it today. It was pouring rain outside and about 10C. It was merely a ploy to keep the windshield from fogging up and it completely worked. When I got home I put the inductive ammeter on the supply wire: 7 amps. 72V X 7A = 504 watts. Not substantial, but it's better than nothing!

Here is a picture of the organized mess formerly known as the engine compartment:

I hope to have some videos soon. Until then, you will have to be patient!

[mechman600]

The last few days I have been trying to get my battery pack in as good of condition as possible. This is relatively speaking, of course, because these are all used "dual purpose" group 31 batteries taken out of heavy trucks.

Last week I replaced one battery because after it took forever to charge, it failed my half CCA (350 amp) 15 second load test, sagging to 7.0V. 9.6V is minimum for a good battery.

The next day I went out for some errands on an 11 km long run and I barely made it home because the pack was sagging so hard by the end (down to 49V on acceleration at one point!). So the next day after driving to work and before charging, I gave each battery a 200 amp load test and found all batteries sagging to 10.3V-10.8V except one that was sagging to 8.5V, so I replaced it.

Now I have one battery that performs well, but once charged drops in voltage to 0.2V below all others. It slowly discharges and takes it's "buddy" down with it unless I keep the car plugged in, and then the charger cycles on and off to keep these two fully charged. Today at work I will swap it out for my very last free spare battery and hope for the best.

I am not sure what I will do if (or when?) the next battery lays an egg because my free battery supply is dwindling. I hope that the batteries I murdered so far were faulty all along (which is likely because they were removed from trucks for a reason) and that they are not being prematurely murdered by my car. I guess I will know soon enough.

If these Paccar Dual-Purpose batteries cannot handle duty in my electric car I may start replacing them two at a time with new deep cycle batteries from Interstate Battery. Through my work I get a smoking deal at Interstate and I would have 30 month warranty that way. But I wonder if I should replace dead ones with new as they fail or just pull the pin and drop $1000 on a new pack so I can just forget about it and be happy....