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Test Drive!

I use that term loosely, but I did sit on the bike while it moved under its own power. This photo really captures my excitement. Honestly, the first run was somewhat of a disappointment, with the bike's performance being more sluggish than I expected. That can easily be fixed by changed the current limit in the controller. The controller is capable of delivering 300 Amps, but I have it dialed back to 120 Amps right now. There were also a number of other small issues: the chain tension was too slack, causing a lot of noise; the speedometer was not working (broken cable), and the controller kept cutting out. I believe this last problem can be fixed by changing the controller's low voltage set point.

It's been almost two weeks since the test drive, and I've made no progress on the bike since then. I hope to accomplish more this weekend and get motivated again.

Back in Business

This picture shows my new battery tray fitted on the bike. Just behind the side tray is the motor controller, which did fit nicely below the motor. I had to make a few new cables, due to their lengths changing with this layout. Overall, I think it was a good decision to go ahead with this redesign. The ground clearance is now similar to the stock bike and will not be something additional I have to worry about when riding.

Back to the Drawing Board

Last weekend, I mounted the rear tire back on its wheel, and so for the first time I was able to drop the bike off its centerstand to test the ground clearance (or lack thereof) of the battery tray. It doesn't look good. On the centerstand, the bike has about 5 inches of ground clearance. After dropping the centerstand, the bike's weight compresses the rear suspension, then I sat on the seat with my 180 lbs. The result is about 1-1.5" of clearance. That's a no-go in my book.
So... a little rearranging is in order.


The battery below the motor has got to move. I'm going to swap it with the motor controller. The battery will stick out further than the comtroller, but i don't think it will inhibit the function of the bike. Then the stack of 4 batteries in the front can all be moved up about 2.25 inches.

Minty Fresh Power Supply

I put together a small 5 Volt power supply for the ammeter in my instrument gauges. It also supplies 12 Volts to the temperature sensor. The voltage regulator requires a heatsink, and I used a scrap of Al. plate. Everything is housed in an Altoids tin for some environmental protection.

With this power supply and the other electrics wired on the bike, the gauges are ready to go into the bike...


And I'll be damned, they work!!! The red display is the battery pack voltage, and the green display shows the amount of current flowing through the pack. The cool thing is that these work in real time, so when you twist the throttle, the current goes up and the voltage drops. Very cool.

Wiring

It's been a while since my last post, but it's not for a lack of working. After painting the battery tray, I reassembled the bike and started in on the wiring. With so many batteries, this is a huge undertaking. The picture above shows all of the ancillary bits that connect between the battery pack and the motor. At the top is a high current, keyed switch. I added this switch in after deciding the contactor by itself was insufficient. The contactor is to the right of the switch, with the metal band around it. It is an electrical switch, or solenoid, that is actuated by the motorcycle's ignition switch. As recommended, there is a 1000 ohm resistor across the main contacts. I found that this resistor got hot when the contactor is open (whenever the bike is turned off). To the right of the contactor is the main fuse. Below all that is the controller, an Alltrax AXE-7234. This controller is pretty sophisti-ma-cated, allowing you to program a number of parameters on your computer.

Lead Junkie

A typical electric motorcycle has 4 to 8 batteries. My bike has 18 batteries! The battery pack that I am building is probably less efficient in size, weight, and capacity than a similar pack with fewer cells, but what I lose in efficiency, I gain in its ability to fit into small spaces.
When postimg on evalbum.com , I need a name for my bike so I've decided to call this bike Lead Junkie. You know, because the batteries are made of lead, and it can't seem to get enough of them. Pretty clever, right?

Without giving it much thought, my plan was to connect the batteries in a series-parallel layout, which is shown in the image below.

After doing some reading on the Internet, I've decided that a Parallel-Series connection is more desirable. The resulting battery pack is the same (72V, 68Ahr), but the effect on individual batteries is different. I'll try to explain.


One issue with connecting batteries in series is that the voltage of a single battery can drop, dropping the entire pack voltage and putting a higher load on the other 5 batteries. If the batteries are paralleled first, then the other two paralleled batteries can maintain the pack voltage, while only increasing the load on 2 batteries.
Perpabst I'm not explaining this very well, so suffice it to say that I think the latter configuration is better, and this is how I will test my pack. From a physical wiring perspective, this config requires more wire and more connections. I have increased the gauge of my wire to 8 AWG for the parallel connections and 4 AWG for the series.

Another Day, Another Tray

This tray holds 4 of the smaller B&B batteries. It will be mounted underneath the seat where the engine's airbox and battery box were originally located. When installed, there's just enough room on top of this tray to hold the DC to DC converter (see below). This converter takes the 72 Volts from the battery pack and converts it to the 12 Volts that is required to run the motorcycle's accessories.

Paint Shop

Today, I added a second battery tray to the to the upper front of my main tray. I also put in diagonal supports in the bottom front corners. Previously, I wrote about adding lateral stiffeners, but I did not put these in. If I find that I need them, I'll add them in later.

Major Milestone

I felt like I finally made some progress last night, when I completed enough of the battery tray to mount it with batteries on the bike. This image shows how the 6 Optima batteries are arranged around the motor. As an unexpected bonus, there is enough space above the front stack to position 2 of the B&B batteries. Very cool.
The battery tray feels stiff when in place, except in the lateral direction. I am going to weld some cross members diagonally across the front face of the tray to stiffen it up in this direction. Also. I'm concerned about fatigue under the vibration environment of the motorcycle. I think regular inspection of the weld joints is my only solution to know if fatigue becomes an issue. The quality of some I my weld joints is suspect, so I'll be going over them again.