Thursday, April 16, 2009

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 , 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.


Andy said...

I'm going to pronounce the "Lead" in "Lead Junkie" as if it rhymed with "speed."

Why do you use higher-gage wire for the || connections than series?

Ray Good said...

I thought the pronunciation might be confusing when I wrote about the Lead Junkie. It's lead, as in "my dog wanted to be fed, but went to bed instead. If he ate any lead, he'd probably be dead." Got it?

As for the wire gauge, it has nothing to do with how the battery pack is wired. A higher gauge wire simply allows for more current and less loss (voltage drop) in the cable. Bigger is always better! TWSS.