Thursday, January 24, 2013

Wiring Schematic

I finally got around to making a proper wiring schematic for the Electric Booger. I thought it would be a good idea in case I end up selling the car in the future. Chances are by then I will have forgotten how I wired the whole thing!

Sunday, January 20, 2013

Motor Basics

I think it is time to clear the air surrounding the DC motor in my car. All this talk of armature controllers and field controllers must be confusing to many, so I will do my best to explain these things further.

First off: electric motor basics. Take a nail and wrap some wire around it to make a coil. Hook the wire up to a power source, and you have turned the nail into an electromagnet. Now, take another electromagnet, put it end to end with the first one and power it up. The two nails will pull themselves together. Reverse the polarity (direction of current flow) in one of the electromagnets and they will push themselves away from each other. If you hold one electromagnet stationary (stator) and fasten the other to something that will rotate (armature), you have an electric motor.

Here is a drawing of an electric motor:

The commutator is a ring on the armature that spins with the armature. The brushes press against the commutator so current can flow through them to and from the armature windings. The commutator also acts as a switch that constantly changes the polarity of each pole of armature windings so that as they spin, the magnetized armature poles are always pulling towards one field magnet and pushing away from the other.

Simple, right? To complicated it a little, there are several types of DC motors. The most common type of motor in EV conversions is a series-wound motor. This means that current goes into armature POS, out armature NEG, straight into field POS and out field NEG. The field windings are made of heavy gauge wire designed to handle the same amount of current as the armature. Therefore, only one current control device is necessary.

The motor in the Electric Booger is a sepex (separately excited) DC motor. This means that the field windings have much smaller wires, making many more revolutions around the stator poles so that relatively little current is required for the electromagnets to have the same effect. Since the armature is identical to (and requires the same amount of current as) a series-wound motor, two current control devices are required - one that controls a large amount of current (armature) and one that controls a smaller amount of current (field).

A proper sepex controller is actually two controllers in one. These controllers generally have the ability to output field current in a non-linear manner, relative to armature current, giving a much broader power curve than a series-wound motor. Unfortunately, a proper sepex controller is double the price of a series wound controller, and since I had already purchased a used series controller on eBay, I had to improvise.

The separate field controller that I ended up purchasing is a small controller meant for vehicles like electric scooters. It is rated for 100A and 72V. Its throttle input is provided by an amp transducer that measures armature current. I have it set so that whenever the key is on, this controller outputs a 7A "idle current" to the field so there is absolutely no chance of powering the armature with no field current present, as this would cause all sorts of nastiness with the brushes.

Here is a graph showing the relationship between my field current and armature current:
Unlike a series-wound motor, the relationship between field current and armature current can be adjusted in a sepex motor. The relationship between the two is rather interesting:
-A higher amount of field current provides more torque but a lower max RPM
-A lower amount of field current provides less torque but a higher max RPM

Like I mentioned above, a properly set up sepex controller has the ability to achieve the best of both scenarios by implementing a non-linear relationship between armature and field like this:
Right now I am going with 50A of field current which is a nice balance of torque and max RPM. This allows me to start off in second gear most of the time and top out at 60 km/h (4600 RPM) in second, although I usually shift into third at 50-55 km/h.

When I first drove the Electric Booger, I was powering the field with a 12V battery, which equated to 12A of current. With such a small amount of current it barely had any torque and first gear starts were mandatory, but it would pull all the way up to 30 km/h in first which is 6000 RPM. I even shifted into second at 40 km/h a few times which is 8000 RPM! I guess it was a good test of resilience for my motor to transmission adapter.

Anyway, this is all to show how unique a sepex motor is. Hopefully I have simplified things for a few people so when I throw a bunch of terms out there you know what I am talking about!

Friday, January 18, 2013

Charger Efficiency

Here is an illustration of the dramatic effect that charging efficiency has affected the Electric Booger over time:
Any modern charger will be a PWM charger, so it usually isn't an issue in a "normal" EV conversion. But when a guy like me decides he needs to cheap out and buy "hardware store type" chargers, the difference is amazing.

For those wondering about this fancy graph, has a great feature to help keep track of your fuel mileage. All you have to do is register on the forum and then add a vehicle to your "garage" to start keeping track.

I finally got a chance to register at the forum. I introduced myself with a whole bunch of pictures of the eBooger conversion just to see what the reaction was. It was kind of funny - mostly "wows" and "that's kind of neat" type stuff. One guy said the original 1.6L is such a gas sipper that I am probably paying more for electricity now. Right. I attempted to teach him about to virtues of EV efficiency.

Other than that, it's mostly just drive -> charge -> repeat these days. I am already starting to wonder what my next one will be. I really want to convert a motorcycle.....

Wednesday, January 16, 2013

Adding Up Costs

Time to tally up how much this all really cost me.

Original Performance Goals

Top speed: 80 km/h
Range: 25 km
Budget: $2000

Well, lets just say I blew the budget on this one. But I think I ended up with a car that is proportionally better. The main budget offender was the batteries that I ended up buying. I originally thought I could get away with using free truck battery cores, but the Electric Booger just kept murdering them.

Total Costs

Car: $448
Controller: $358
Contactor: $48
USB Serial Adapter: $6
Vacuum Pump: $70
Volt Meters: $44
Motor: $463
Adapter Plate: $100
Adapter Plate Machining: $50
TPS, Fuses, Resistors, Vacuum Switch: $160
Battery Rack Steel: $70
Extension cords, battery hold downs, zip ties: $82
Relays, Connectors, terminals, wire, loom, etc.: $116
Field Controller system: $220
Chargers: $270
Batteries: $1491

TOTAL: $3996

Actual performance

Top Speed: 90 km/h - this is as fast as I have been, but I know it will go faster. Once the weather warms up and my batteries are more willing to comply with my demands, I will have to do an official top speed run.
Range: 30 km - just a guess, going by how it feels after 15 km (in winter with the heater running). I haven't tested this either. Do I really want to?

So I blew the budget....but I have been told by other EV conversionists that for an EV conversion under $4K, this one is quite good. I will just have to go along with that and agree!

Monday, January 14, 2013

Photo of a proud EV owner

Here is a picture that Darin took after I gave him the grand tour of the eBooger. Check out the sweet black hood that I painted (the original paint was falling off):

Sunday, January 13, 2013

Charging Problem Solved

The new chargers arrived from China the other day. What blew me away is that they shipped on Tuesday and arrived on Thursday. Two days from China - go figure.

This shows how small each charger is:
Some testing revealed that they work exactly like I want them to. They bulk charge to 14.7-14.8V, then absorption charge for about half an hour at this voltage, and then float at 13.6-13.7V. I measured them to be 75% efficient no matter what output current/voltage is at.

I fastened pairs together as "charger stacks". One stack is behind each seat and the other stack is on my control board under the hood.
Someone warned me not to stack them or they might overheat, but each of these chargers has a cooling fan. After a couple of hours of charging they are still cool to touch.

And here is a picture of something that I have yet to do with any of my chargers so far:
Float charge. Probably something that most other EV owners take for granted. I left them on float for about five hours to make sure the batteries were fully saturated and extra happy (for once).

Now my electric car charges up in less than half the time of my Mastercraft chargers because the current does not slow down as the battery voltage and resistance rises. Finally! A charging solution that works!

Monday, January 7, 2013

Sweet New Decal

Today Darin ("MetroMPG" on came over to check out the Electric Booger. We took it for a rip to Wired Monk for coffee, and I think he was fairly impressed. Darin is the one of the low-budget EV conversion pioneers who built the Forkenswift. His website is HERE.

He gave me a sweet decal. I wasted no time putting it on the back of the eBooger.
Nobody ever notices that this car is different than other cars. I guess that's a good thing. But I would have expected more reactions in parking lots when silently driving past people. Maybe with enough decals people will notice?

Now that this project is basically finished, it's actually kind of dull. Drive. Plug it in. Repeat. That's kind of it. It's kind of weird to think that this car hasn't been on a service station premises since Spring. Maybe I should go to fill up a tire or something.....