I am in the process of replacing the twenty (20) six volt lead acid golf cart batteries that power my electric pickup truck with 48 Nissan Leaf battery modules. Because the battery bays in the truck are specificity designed to hold 20 golf cart batteries (and the Leaf modules have a different form factor), it’s not a straight-forward drop in replacement.
My initial design (not showing the compression plates that hold the six modules together in compression):
In the image above, the black bar is negative, the red bar is positive, the purple bar is connecting the two sets of 3 in series (positive to negative), and the blue bars are joining together the sense connectors on the 3 parallel modules. Just to confuse things more, the modules are actually made up of internal cells in a 2P2S configuration…so we care about the “middle” voltage of the series.) The green boards show one possible position for the miniBMS boards.
Other complicating issues involve the need to hold the leaf modules in compression, and the requirement of installing a battery management system (BMS) that connects to each module. Also, the leaf modules are only 60 AH, and I have decided to provision 180AH of capacity for my pack (due to the overall system voltage being limited to under 145 volts by the current motor controller and DC-DC converter) so I am having to put sets of three modules in parallel.
3 modules in parallel gives me 60Ah * 3 or 180 Ah. Since I have 48 modules (a complete 2013 Nissan Leaf battery pack) I can make 16 sets of 3. I’m grouping two sets of three into an 6 module “battery” so that they are reasonably sized and I have fewer “things” to build, move around, and connect with heavy 00 welding cable.
Due to the 8 lb weight of each module, I decided to build a “battery” using six modules (two sets of 3 parallel modules, wired in series). This will give each battery a nominal 16 volts and 180 Ah capacity, while keeping each individual battery to a manageable 50 lbs.
The only problem with this plan is that I’m 95% certain that I won’t be able to mount the batteries vertically. The Leaf modules (at 13″) are taller than a regular Golf Cart battery (10-11″), and my battery boxes don’t have much extra vertical room. I *may* be able to put them in vertically if I can keep the buss-bars and associated connections very short, and have absolutely no insulation or air circulation space on the bottom of the battery box. But I’m almost certain that I’m going to have to lay the battery units sideways to make them fit. This adds extra complexity in wiring.
Here is a CAD model of my existing battery boxes with 8 batteries (8 x 6 modules per battery = 48 modules) on their sides. Luckily for me, the Lithium Ion modules take up less volume (and weight) than the lead acid golf cart batteries they are replacing.
This will fit the 8 batteries I need into three of the four existing battery bays. I’m planning on placing my updated charger in the current front battery bay (not shown in the diagram) under the hood.
I would much prefer placing 3 battery units (18 modules) in each of my side battery bays (leaving only 2 in the rear bay) as this would move more of the battery weight forward of the rear axle. My S-10 pickup will never handle like a sports car…but with the Lithium-Ion upgrade I’m dropping a lot of battery weight so I expect the truck to get a bit more sprightly and would like to improve the handling if possible. As I’m removing 4 lead acid golf cart batteries from under the hood, I’d like to move the CG of the remaining batteries forward.
That’s the plan so far, which I’m sure will get modified as I actually start building a test battery. See my next post for the actual physical mockup battery I’m building.