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Discussion Starter #1
After a long summer break, it is time to get back to my project. I feel like the old build thread had a lot of pre-amble before I even got to any building, so I am going to start a fresh topic. For anyone who has not been following along, I thought I would summarize the progress to date.

Jan 2020: Bought my donor vehicle, a 1996 chevy S-10.


Feb 2020: Bought a Tesla/Mercedes battery pack. Originally rated at 36kwh in 12x 7s modules.

Also got the engine and gas components removed

April 2020: Stripped the rust off the frame and repainted everything I could get to.


May 2020: Pulled out the ICE wiring and started getting the engine bay ready.

I mounted the brake booster, and stripped down the dashboard.
I pulled out the vacuum system that controls the vents, and instead made a mechanical system to switch between the defrost and cabin vent settings.


June 2020: I mounted a pedal assembly from a subaru.


August 2020: I started working on a switch panel for the dash.


I started this project with very little experience, a newborn daughter, and a pandemic to contend with; so I am going to consider my very modest progress to be a win. Today I got the shop cleaned up, put a charger on the 12v battery, and checked the voltage on all the traction battery modules (they were all essentially unchanged). I also started laying out the materials for the battery frame. It was always heartening to hear from you all, and I will undoubtedly have some fresh questions before too long. I will be back soon with some pictures of the latest progress.

Goal #1: Mount the battery on the truck.
 

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Discussion Starter #3
Haha, thanks for the vote of confidence Matt, I am going to finish this project - I cant make any promises as to when.

I spent a lot of time today just moving pieces around and trying to figure out how everything was going to go together, so I did not make as much progress as I had hoped. Also, a bolt shortage made it hard to start fitting pieces up to the truck's frame.

The steel components will support wooden sides, and I am including brackets at the corners to mount short sides or some sort of lumber rack later on.

I am building the bed 5' wide, so the wooden side boards will straddle the tires a little bit. My plan had been to make a curved steel fender and make an arched cut-out in the wood to accommodate it. I am thinking I am going to have to do this step at the end, once the modules are loaded and I have and idea of where it will ride. I am wondering, though, how much space should I leave between the tire and fender? Should I load it up with its estimated max capacity first?
 

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Get the spring rate and use that to calculate the gap. 500# per inch means the spring should move more or less 1" for every 500#, but that includes the empty weight.

Nice build however.
 

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Discussion Starter #5
Thanks for the input, piotrsko. I know next to nothing about leaf springs or really suspensions in general, so its helpful just to know where to start looking! I found a chart of leaf spring rates on an s-10 forum, but I am not really sure which ones my truck has. Seems like 400-600lbs/in is a pretty good ballpark, though. Since I am likely going to have a max load of about 600lbs, I will figure it will ride at most 1" to 1-1/2" lower when fully loaded. Any thoughts on how much clearance should remain between the tire and fender when it is fully loaded? I dont really want to take off too much of the wood, but I also dont want to find out what happens if the wheel bottoms out against the fender.

I did get the frame for the battery finished today:

The battery box will attach with 10x 3/8" bolts, and then the sub-frame bolts to the truck in 6 places. I am only using the fore and aft bolting flanges of the battery box, but it seems like overkill to add another 10 bolts on the sides.

Next up: finish the mounting brackets for the wooden framing.
 

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Discussion Starter #6
Almost done with the mounting brackets, just have to finish up the back.


Then it will be time to slap some paint on before moving on to more fun stuff. I can get the new tail lights mounted, that will be satisfying.
 

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The spring rate of truck leaf springs is usually not a constant - they are designed to get stiffer as they are compressed, which is called a "rising spring rate". This is usually done with leaves that don't engage until the spring pack deflects enough.

For fender clearance I would just assume that at some point the suspension will travel enough to compress the bump stops (the rubber blocks that keep that axle from hitting the frame).
 

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Discussion Starter #8
Thanks Brian, I measured 6 inches from the tip of the bump stops (thanks for giving them a name, I really am out of my element) to the part of the axle that they would hit. I decided to leave 7" of clearance to give them some room to compress.


It leaves enough meat in the wooden frame to carry quite a bit of the eventual load. I am a little concerned that the steel frame is too close to the tire in case one wheel rises really high and it leans inward, but I am hoping it will not be a problem, as this truck is not going off-roading or anything.


I realized when I had finished that the steel uprights in the corners should have been 1 1/2" taller to clear the 2x8 decking that Is going to be on top. In hindsight, it would have looked nicer to have gone with 2x12 sides, and recessed the decking to hide all the endgrain... but oh well. My next flatbed will look really sharp.


Next up: I am going to extend those uprights, and then the frame will be ready to prep for paint.
 

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Discussion Starter #9
I got the frame finished up and slapped some paint on it yesterday. Today I got it mounted to the frame, and bolted on the box. I weighed the steel frame, and it came in at about 70 lbs. I need to get weights on the wooden parts, but I think I am doing pretty well so far. I figure 400 lbs came off the back, and only 170 are back on so far. The modules add 500, so that will eat into the cargo capacity, but I think I might have 600 or 700 pounds left on the rear axle rating.

I am basically ready to start loading the modules into the box.

The guy who I got the pack from had numbered all the modules, and provided me with initial voltages and internal resistances. Does anyone have thoughts about how they should go back in? Should I use the original order? Should I try and sort them? Since I am going to be doing 2 strings, should I strive to have both strings have a similar resistance?

In the bottom left you can see the flat (aluminum?) bar that was the positive terminal. I will probably keep that in place, and then make grooves for the 4/0 cable that will split the pack into 2 strings. Its going to be tight to fit 2 fuses, 2 contactos, and 4 BMS boxes in the little channel at the bottom of the image, but I think It will be doable. I have decided to spend the extra money and just have a BMS monitoring each cell-group in each string instead of trying to join them together somehow.

I am going to review my plans for the high voltage wiring, and I will probably have some questions to post later on...

Goal #2: Wire up the main contactors to my main power switch.
 

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Discussion Starter #11
I worked a little bit on getting the tail lights mounted today.

Once I pulled apart the wiring it dawned on me that the truck used a single bulb for brake and turn lights - so there is no way to wire up the amber turn signals. I am going to look over the wiring diagrams and see if I cant maybe splice in a new wire to make them work right. I am daunted by trying to trace the wires behind the dash, but I am going to have to dig into it a little bit anyway to redirect the ignition switch through my dash panel.
 

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Once I pulled apart the wiring it dawned on me that the truck used a single bulb for brake and turn lights - so there is no way to wire up the amber turn signals. I am going to look over the wiring diagrams and see if I cant maybe splice in a new wire to make them work right. I am daunted by trying to trace the wires behind the dash, but I am going to have to dig into it a little bit anyway to redirect the ignition switch through my dash panel.
It shouldn't be necessary to dig around the dash. Even in vehicles with combined stop and turn functions at the rear, the front turn signals are separate, so you can tap into those for the rear. With regular bulbs that can be a load problem, but the LEDs should use so little current that it isn't an issue for whatever the S-10 has for lighting circuit capacity.

Unfortunately the wires for the left and right stop/turn lamps will still have the combined signal behaviour, but there's a solution for that, too: connect the centre high-mounted stop lamp (CHMSL, or "third brake light") wire to the bright (stop) input of both tail lamps. The original combined stop/turn circuits won't be needed for anything, so you could even re-use those wires for the turn signals from the front, depending on where those wires come from (presumably somewhere under the hood).
 

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Discussion Starter #13
Thanks Brian, I had not thought about the front turn signals! I know exactly where the wiring to the rear lights goes, because I pulled apart that whole loom to remove the fuel system wiring. It would be a piece of cake to tie those wires to the front blinkers. I have no idea where the wiring for the CHMSL goes - and since the whole cab is gutted, I am surprised I have not seen them.

I did find the diagram in the chilton's, and I was thinking it would be easy to just cut the white wire coming off the back of the brake switch (which I can get to pretty easily) and routing it back to the rear brake lights. The hazard and flasher circuits would keep powering the turn signal bulbs through the existing wiring, if I am reading the diagram correctly.

Now that I look at it, though, I am realizing that I do not know where that junction that feeds the CHMSL is. If I cut ahead of that junction, it will knock out the center light. I guess I could tie it back in if I can find where it goes when it leaves the dash... I think I need to find some more wires...
 

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Discussion Starter #14
Spent some time tracing wires today, and I thought I had a pretty good idea of what was going on... I have pulled off the brake switch, and jumping the orange to the white does indeed light up the brake lights, but it is also closing a relay somewhere in the engine compartment. I tried unplugging all the relays I could find one by one, but it still clicks. I might make a longer jumper so I can activate it from closer to where the noise is coming from. Could there be something in the ECM, maybe related to the ABS system?

I also located the wiring harness to the CHMSL, so I think I will be able to split all the brake lights onto their own circuit, which will eliminate the need to splice into the front signals.

I also worked on the brake booster a bit more. I added a new relay, and removed a big casting defect on the vacuum switch that I think was letting air back into the system. It now mostly works. Once the booster drum is vacated there is an annoying hysteresis that sets in, where it clicks the relay on for a pump stroke or two, then shuts off, and repeats. If I force the pump to run for an extra second, it develops enough vacuum to stay off. Anyone have a thought on how to make the relay stay on for a bit after the switch initially closes?
 

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Discussion Starter #15
Well, I found the mystery relay in the engine compartment- and it seems to be doing absolutely nothing. Two wires (hot when the pedal is pressed) go in, one ground and a wire that feeds the lamps comes out... Anyway, I have now removed that needless failure point, and one of the hot wires is now routed back to the rear signals. I tested all the lights, and everything checks out perfectly! I have ordered a license plate light, and some surface mount amber and red indicators to put on the outside corners of the flat bed, which I think will be all that I need to get it back to being street-legal.

I also found an unused fuse that is always hot that I will route to my main switch to turn on main contactors and some of the other systems that I want to always be on. I am excited about the prospect of getting the HV system installed.

I think I am going to try plumbing a reservoir into my vacuum line, and see if that helps hold the switch open and cuts down on that chatter.

I have been thinking a little bit about how to connect the two strings in my battery box

I only have 2 contactors for the box, and I like that arrangement 2 gives a level of redundancy - both contacts would have to weld shut simultaneously to cause a failure. I feel like I have read a lot of opinions though that each string in a parallel arrangement should have its own contactor - presumably as a fail-safe so that eddy currents from one pack cannot drive current into the other pack when things are shut down. Since there are cell level fuses in these Tesla packs, I am trying to imagine a scenario where something bad would happen if they were left connected while the vehicle is powered down. All I am coming up with would involve puncturing the 1/2" thick box with a steel pry-bar or something, and even a catastrophic short would blow the main fuse. Am I overlooking something?
 

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Discussion Starter #16
Cut the last lumber for the flatbed today, and have started staining it. The 2x8 decking adds a lot of weight, I think I figured it came in at about 125 lbs. It might lose some as it dries, but if I had it to do over again I would think about using cedar, or perhaps thinner decking with more joists. Also, I kept the width to 5 feet to reduce lumber waste, but it maybe would have looked better if it was a few inches wider. Maybe on the next one I will really "nail it."



Once the stain dries I can get the sides bolted in place, and then start routing the conduit for my power cables. It might be overkill, but I am going to try and keep all the HV wiring inside liquid-tite electrical conduit (painted orange). I have done a lot of DC wiring, but never over about 60 volts, so I am still a little nervous about running 144.
 

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The width looks fine to me, especially with the metal fenders that I understand are coming. If the deck is wider than the cab you have either awkward protruding square corners or more work to make nice rounded corners.

So is there just empty space under the deck at the rear, behind the battery pack?
 

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Discussion Starter #18
Yep, The battery box takes up just about half of the space under the flatbed. I will probably make the front half lift up on hinges to get access to the battery box. There are a LOT of screws that hold the steel lid onto the aluminum battery box, so I am hoping that once I seal it up, I wont be back in there much at all.

There would be room and weight capacity for another complete pack of this style, but that would max out the stock rear springs. This flatbed design does seem like a pretty easy way to load up on these big bulky Tesla modules and still have some functionality as a truck. As it stands, I will only have about 550lbs of capacity in the back, but if I upgraded the rear springs, I could get closer to 900lbs. That would get me up to the max gross weight, though, and upgrading the brakes might be needed at that point.

I am definitely going to try and put together a lumber rack at some point, as the 6' flatbed is going to be pretty limiting for moving lumber.
 

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Discussion Starter #19
Well, I ran into a snag on splitting the pack up, as I did not have as much clearance as I thought I did to run new cables. The red arrows show where the main positive and negative bars cross the aluminum support at the front of the pack. To add my thicker cables, I had to bump up the sheet metal lid to make a slot for them in the middle. I should probably do more practice with welding thin sheet...

Anyway, now there should be room to get my two cables through. Its going to be very tight to get everything in there, but I think it will work. The fuses are mounted to little plastic feet, which will need an attachment point. I think I am going to end up fabricating a weird little shelf to hold everything. The BMSes should fit on the other side, but I have not figured out how I am going to secure them.

There is still a lot of fiddly work to do, but it feels good to at least have a plan.
 
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