Concept

Problem

The car originally had 6 pcs of 8V deep cycle lead acid batteries: Trojan T875. They are 170Ah nominal capacity wet batteries.

Apparently the size is a standard for golf carts: BCI Group Size: GC2 - Dimensions: Length: 10.27” (261mm); Width: 7.10” (180mm); Height: 11.14” (283mm).

They use a 17A charger with them. The motor is 3.3 HP = 2500W.

The batteries are held down by some brackets. We will need to remove those, and find a new way to ensure the packs don't go flying.

Ideally, the new pack:

• Has a low centre of gravity
• Distributes the weight equally left-to-right
• Has as few screwed connections as possible

Design goals

• Can be fully assembled in workshop and installed into golf cart in the field
  • Easy to lift in and out as one unit, even though it is heavy
    • Circa 35 kg in total
    • Will be a two-person job
• Durable and high quality
• Protects the battery against buildup of dust and water
  • Therefore open at the bottom
  • Maybe a bit tilted top so that things drop off fast?
• Safe
  • Fuse and/or safety switch on top (200A)
  • Does not fall out if the golf cart flips over
    • Using the same solution as the original?
• Provides a professional outlook
  • Hides the wiring and allows for professional routing
  • Has branding on top
• As cheap as possible
• Ideal for the vehicle
  • Low point of gravity
  • Equal weight distribution right-left
• Is somewhat flexible to work with different types of modules

The mothership plate design

A single plate laser or CNC cut out of a strong (10mm?) plastic plate, onto which everything is bolted from the bottom. On the top there is branding and carry straps.

Assembly process

1. Double check that all modules have the right and identical voltage
2. Bolt in the three battery modules to the mother plate
   1. Follow the orientations!
   2. M8 bolts w/ Loctite
3. Produce the 3 inter-module power cables of appropriate length, crimp on ends, and bolt them in
   1. 8 AWG, colour does not matter
   2. M6 bolts w/ Loctite
4. Flip it over (2 people!)
5. Secure the power wires to the top plate so they have little play
6. Bolt in the BMS using the 3D printed holder
   1. Also the bluetooth module!
   2. Secure the wire of the bluetooth module
7. Install sense harness
   1. Cut to appropriate length
   2. Install ends
   3. Plug in to modules
   4. Verify order with multimeter
   5. Do not plug into BMS yet!
   6. Secure the wires to the top plate so they have little play
8. Flip it back (2 people!)
9. Install fuse box on top
10. Connect BMS power wires
    1. P- to fuse box
    2. B- to B-
    3. Now plug in the sense harness too
    4. Verify that it is on!
11. Install + receiver and the final power cable
12. Put in covers over holes and receviers
13. Install carry handles
14. Prep anchor hook

Installation in golf cart

1. Remove seat by tilting it forward and unhinging it
2. Clean everything out of the battery compartment and wipe in clean until it looks at least as good as on the photo
3. Cut the middle piece out with a multitool
4. Carefully pull wires out of the way, maybe using a cable tie to keep them out of the way until you lift the battery in
5. Lift in the battery - two person job!
6. Install the two anchors
7. Switch the BMS off
8. Install the positive and negative wires, also the charger!
9. Switch BMS on
10. Put the seat back on

BOM

• Plate
• Fastening the modules (M8)
  • 12x bolts
  • 12x self-locking nuts
  • 12x washers
• Fastening the BMS
  • M6 bolts and nuts?
• Anchoring (M12)
  • 2x hooks, RS 9086779
  • 2x connecting nuts, RS 0276550
  • Some M12 rods
  • 2x M12 mudguard washers
  • 2x M12 self-locking nuts
• BMS: 12S 80A Daly
• 4x power wires
• 8x crimp ends
• 3x connectors for sense