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

[mechman600]

...but my new battery pack is amazing!

I got all the batteries installed at work today. It required a few new battery cables because the posts are located differently on these new ones. To clear things up, I am using three of my original AGMs with nine new AGMs, a Paccar/TRP rebadged Deka 8A27M.

Let me just say that I cannot believe what a difference it made. I can accelerate...well....like a "normal" car while voltage sags to maybe 69V where it used to go to 62-63 before. As a matter of fact, during my long WOT hill climb on the way home, system voltage never fell below 67V (11.2V/battery, 1.86VPC). I reached 60 km/h on the hill in second where I used to reach 55 km/h. With the old pack I could go into 3rd and "amp" my way up to 60 km/h so I can't imagine what the eBooger will be able to do now if I really want to torture the new pack and do the same.

All 12V pairs stayed dead even with each other. Plus, there was no degradation of performance by the time I got home.

Add $1420 to the total!

I'M INVINCIBLE!!!

Next I fully turn my attention to my PWM field controller.

[Daox]

Woo, glad to hear you're now happ(ier) with the new setup. Are these brand new batteries?

[MetroMPG]

Congrats!

I'm curious:

How did you rationalize/justify the additional $1420? (That's more than the ForkenSwift's final tally!) "Fun money?" Or... does the Booger have to pay for itself to justify its cost, and the math works out in this case?

[mechman600]

Originally Posted by Daox

Woo, glad to hear you're now happ(ier) with the new setup. Are these brand new batteries?

Yes. Brand spanking new. With 2 yr warranty even.

Originally Posted by MetroMPG

Congrats!

I'm curious:

How did you rationalize/justify the additional $1420? (That's more than the ForkenSwift's final tally!) "Fun money?" Or... does the Booger have to pay for itself to justify its cost, and the math works out in this case?

I figure it is a vehicle that I rely on to get to work and anyone would spend that much money on a repair bill for their daily driver without question. I had to step back and stop thinking about it as 63% of my total investment so far and realize that it still is a ridiculously cheap EV in the grand scheme of things. Plus, it is fun money.

Now that I made it work I am going to take a few (and in this case, costly) steps to make it reliable.

[Daox]

I petition for updated pictures of the car.

[sbestca]

Originally Posted by mechman600

<SOME SNIPPED>
I figure it is a vehicle that I rely on to get to work and anyone would spend that much money on a repair bill for their daily driver without question. I had to step back and stop thinking about it as 63% of my total investment so far and realize that it still is a ridiculously cheap EV in the grand scheme of things. Plus, it is fun money.

Now that I made it work I am going to take a few (and in this case, costly) steps to make it reliable.

Excellent reasoning I'd think.
Still a bargain at the price, hats off to the guys who have done it cheaper!
I find developing anything costs much more than you anticipate.
The pathfinders like you show the way.

[mechman600]

It's working! I finally got the field controller installed.

A while back I took delivery of my new Kelly 72100 - 72V/100A controller. I know, I know...it's a Kelly, but I am only using it to half capacity, so it should be good, right?

The LEM amp transducer that I am measuring armature current with has a resting signal of 2.5V. Current going one way causes the signal to go higher and current going the other way causes the signal to go lower. At 450A in the direction I am measuring, the signal is 3.9V. I tested this with a whole bunch of batteries and a carbon pile to load them with.

You can see in the attached Kelly screenshot how I dealt with these odd voltages by moving the throttle effective starting position and throttle effective ending position.

I fine tuned it so that at key on ("idle"), the field is getting 9A. When the armature is at full current, the field is getting 50A.

I was going to employ my idle microswitch to turn the field off altogether, but what I am finding is that when I am coasting down a hill at high motor RPM, if the field is zero and you turn it on, it confuses the Alltrax controller by suddenly generating voltage on the armature and the Alltrax goes brain dead for a few seconds. So I am leaving the field on at idle for now. 81W of power isn't much anyway.

So there you have it. I have only gone for one test drive (with my remote inductive ammeter installed on the field wire) and it worked brilliantly.
The throttle acts completely different now now that the field current is changing with armature current. Where is used to act like a farm tractor (where 50% throttle = 50% rpm), it now acts like a normal car throttle, where 50% throttle = 50% torque).

Tomorrow's commute to work should a better test. No more flicking a toggle switch back and forth on the gearshift lever!

To quote James May: "It's a brilliant solution to a problem that shouldn't have existed in the first place."

[mechman600]

Originally Posted by Daox

I petition for updated pictures of the car.

I know I know...they're coming I promise! I have to paint my hood first because the paint is falling off.

Flat black here we come!

[MetroMPG]

I'm looking forward to seeing the car in the flesh this winter. I'll admit I've never really made the effort to understand SepEx; this will be a good learning opportunity.

[mechman600]

So my PWM field controller system isn't perfect. I ran into an unexpected problem where the motor gets into a very quick (many times per second) surge at part throttle, high motor rpm.

The reason is simple. At a given speed, increasing field current also increases back EMF in the armature which slows armature current down. Since my field controller reads armature current to determine field output, it reacts by reducing field current. Back EMF goes down, allowing more armature current. This oscillation happens 10 times per second and shakes the whole car. Not good.

A simple solution was to increase the "Throttle Up/Down Rate" in the field controller:

I initially had it set to 1, which is very quick reacting. I moved the setting up incrementally, test driving each time. I now have it set to 9, which has eliminated the oscillation. The throttle still feels a bit "surgy" at part throttle but at least it doesn't vibrate my whole car and risk breaking things.

Here is a labelled picture of my entire control system as of right now:


This weekend is "heater weekend". I plan to increase the output of my heater by removing a few rounds of heater coil to reduce resistance. I also plan to switch it with my ex-field interrupt solenoid instead of a 12V 5-pin relay that basically welds internally every time the circuit opens.