RXV chassis based road car

[ThreeCW]

Bob,
Glad to see that you are back working on your car (not sure if you refer to it as a car or a cart)!
You have gone with a stout battery pack with 51.2v nominal x 200 AH. What kind of range do you expect with this setup? What is your estimated vehicle weight? Good luck with the rest of your build ... we will be cheering you on from the sidelines.
Regards, 3CW

[BobBoyce]

Originally Posted by ThreeCW

Bob,
Glad to see that you are back working on your car (not sure if you refer to it as a car or a cart)!
You have gone with a stout battery pack with 51.2v nominal x 200 AH. What kind of range do you expect with this setup? What is your estimated vehicle weight? Good luck with the rest of your build ... we will be cheering you on from the sidelines.
Regards, 3CW

The last time I performed a measured load of my 2012 lead/acid RXV, it was around 375 WattHours per mile when averaged out over 10 miles of roadway driving at near 30 MPH. The weight of that cart was near 1000 pounds, not counting my weight.

The Bandolero car is planned to weigh in at around 700 pounds. I originally anticipated about 200 pounds in battery weight, but it will be a bit heavier due to 2 X 100 AH in parallel vs 1 X 200 AH per cell location. That will add near 30 pounds to the battery pack weight.

Since the final gear ratio and weight will be different, old power consumption numbers will be out the window. We will have to wait for new numbers to figure out the range with the LiFeMnPO4 pack.

The day after I bought the cells and BMS for this car, I bought another 16 of the new 100 AH cells for another project.

Bob

[BobBoyce]

I spent half a day yesterday and all day today working on the Bandolero. I cut the old rear roll cage apart and salvaged the mounting plates and rear tubes from them for use on the new rear roll cage assembly. I started out by fabricating a near rectangular frame that fit down into the roll cage channels of the rear body. It was measured, cut, welded and fitted with the rear body upside down. One finished, the rear body was set into place and clamped to the doors and adjusted for fit. Then measurements were made for the 4 vertical tubes. The mounting plates and mounting tubes were welded to the verticals. They were them put in place. Here are the photos of that fabrication work. Drivers side mounting plate, Passenger side mounting plate, rear mounts, rear view of roll cage, and of Thomas welding on the bumper horns

Bob

[BobBoyce]

I took a photo of the rear roll cage as it looks from the front looking through the windshield opening. Then a photo after the rear bumper cover and rear bumper were installed. I took a rear passenger side photo before putting the rear body on. Then a photo with the rear body set in place over the roll cage... A view from the rear. The elongated hole in center of the rear body is for a middle brake light.

[BobBoyce]

The two last photos of this update. A driver side rear angle view, and a passenger side rear angle view. The door rears were clamped to the rear body. The bottoms of the doors are up against the tires because the wheel well openings have not been cut larger yet for larger diameter tires in the new wheelbase locations that using this chassis requires. This body originally used 6" wheels with small diameter but wide racing tires.

There may be a wait for the next update. I spent $6,045 on the recent lithium cells and BMS purchase, so funds may be short for a while.

Bob

[ThreeCW]

Originally Posted by BobBoyce

I spent $6,045 on the recent lithium cells and BMS purchase
Bob

A pricey lithium systm!
Is that just for the Bandolero or does that include the other "16 of the new 100 AH cells for another project"?

[BobBoyce]

Originally Posted by ThreeCW

A pricey lithium systm!
Is that just for the Bandolero or does that include the other "16 of the new 100 AH cells for another project"?

I'm finally back from Florida and am in central NC with the Bandolero...

That was total price for 48 of the 100 AH cells and a 24 cell true BMS system. 32 cells and the BMS24T will go into the Bandolero, and the 16 extra cells may end up going into a 2008 Curtis upgraded RXV, along with a BMS16-Pro. I already bought a 6 X 8V battery tray for the RXV. The price is higher than the LiPo packs most are using, but those are typically used and I bought all new. Mine are also a safer cell chemistry and they have literally 10 times the rated 80% DOD (Depth of Discharge) charge/discharge cycles of most new LiPo cells. Of course, few actual LiPo users run their packs down to 80% DOD so they can extend the life of their packs. More important to me is knowing that I can charge my Bandolero in my garage with literally no chance of a cell bursting into flames or exploding. I turned down a potentially lucrative offer from Tesla Motors because I wanted no part of their battery technology. When their packs go up in flames, anyone involved in the battery or charger technology may get sued. I am not willing to put my charging technology into a vehicle with that potential issue.

Found an issue with my rear bumper mount, will have to fix it before getting the measurements for a battery box. One of the mounts was not flush against the roll cage when tacked and welded so it'll have to be cut loose, straightened, and rewelded. It caused the rear bumper to be 1/2" out of square with the rear body.

Bob

[BobBoyce]

The angle grinder brushes went out yesterday, so I had to buy a replacement today. Finished the cuts and cleaned the surfaces to prep for a reweld. I used triangulation to get 3D positions on the good welded side and to plot the ideal mounting location on the other side. Clamped and rechecked multiple times, then tacked it in place. Removed the clamp and checked triangulation again... Spot on! Welded full beads and put the rear end back together. Much better fit of everything, and squared. The bumper cover to rear body fit is much better than before. The larger gap on that side is gone, so less fitting will be required when drilling the holes for the Dzus fasteners that will mount the rear body to the bumper cover.

I removed the rear body and went back to measuring for the battery box. I took 8 of the LiFeMnPO4 cells and mocked up a 12.8V 200 AH battery string, measured it in all 3 dimensions, and planned the best layout for the box. I settled on 4 rows of series/parallel 8 cell strings next to one another. This resulted in an internal battery box dimension of 19.75" X 22.00" and an external height of 12". I will use 3/16" 6061 T6 aluminum for the battery box and lid. I intend to use 3 sections of 18-8 stainless steel all-thread (centered over the joints of the series strings) to help prevent spreading of the aluminum box near to the top. The bottom seams will have exterior welds to maintain cell clamping pressure at the bottom of the box. I will post photos when I have them. I intend to farm out the fabrication of the battery box. I must travel home soon for a doctor appt, so that will allow at least some work to continue in my absense.

Bob

[BobBoyce]

The measured ampacity of each LiFeMnPO4 cell is on a label, so I chose to match up ampacities in pairs that equal 208 AH. For example, 16 of the cells are marked as 104 AH, so those became 8 cell pairs at 208 AH. I paired up 3 of the 106 AH cells with 3 of the 102 AH cells to make 3 more cell pairs at 208 AH. Then I paired up a 108 AH cell with a 100 AH cell to make a final 208 AH cell pair. That gives me my 16 pairs needed for my 32 cell pack.

I bonded each cell pair with the electrical bonding straps, using the half of the screws on each that are closest to the center of the pair. I set the cell pairs next to each other and strapped them together in parallel with more electrical bonding straps, using the outer half of the holes.

I am using a bottom balance technique, so this paralleling is used to balance all cell voltages to the exact same voltage. I will leave these connected in this way for a few days. I have another week to go before the battery box will be ready to be picked up.

I will need to assemble the cells into the battery box before I can do the final rebonding and wiring the BMS

Bob

[ThreeCW]

Bob,

What are the advantages of using the 2P16S configuration of 100 AH batteries to get a 200 AH pack vs using a 16S configuration of 200 AH batteries ? More effective BMS? Redundancy in case of a failed cell?

Would the same logic apply if a person was to build a 100 AH pack using 2P of 50 AH batteries or a 120 AH pack using 2P of 60 AH batteries?

There is lots to learn about these "new fangled" lithium battery systems. I look forward to following your build.

Regards, 3CW