Monday, September 29, 2008

The Battery Dilemma

All the trunk interior panels and spare wheel were removed to completely expose the trunk floor for the eventual floor cutting to fit the main battery pack box which is to be recessed partly below the floor. I was under the impression that the spare wheel compartment was centered in the trunk but it turns out that it is not. This will make things more complicated. I was envisioning cutting a square or rectangular shaped opening in the floor but now it may have to change to a beaker shaped opening with additional angles.

Here are two views of the trunk floor:

After measuring the available trunk space for cutting and taking into account the average dimensions of 12 volt lead acid batteries, I estimate that I will be able to fit eight batteries in the trunk box. I also estimate that I would just barely fit forty lithium batteries like the Thundersky TS-LFP160. I did this extra calculation with future expansion in mind. The average weight for twelve 12V PbA batteries is 900 lbs versus 600 lbs for forty 3.6V lithium-ion batteries. For obvious reasons, I am leaning towards 12 x 12vdc @ 100 AH sealed lead acid batteries (Group 31, GEL or AGM type). This would give me 144 vdc and 14.4 KWh of power. Hope I get the range I want. We'll have to wait and see. Just to compare, the 40 x 3.6vdc @ 160AH lithium batteries would also give me 144vdc but 23 KWh of power.

Here are some of the PbA batteries I am considering:

PowerBattery (MRG-31)
TrojanBattery (31-GEL / 31-AGM)
Deka (8G31DTM / 9A31)
OdysseyBattery (PC2150)
DiscoverEnergy (EV31A-A)

Batteries have always been the Achilles heel of electric vehicles causing much frustration for EV converters. The battery dilemma will not go away until advanced battery technology is proven and more affordable. Speaking of affordability, Thundersky quoted me $240US per battery not including shipping and accessories which amounts to $9600US. Everspring quoted me $281.60US for the same batteries. Another important thing to keep in mind is that Lithium batteries require a sophisticated BMS (Battery Monitoring System) to keep every cell in balance and preventing over charging/over discharging.

Thunder-sky (TS-LFP160)

More to come regarding the battery system.

by Jim

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