I am installing a fuel cell near the stock location of the gas tank.
I modified the floor to fit the cell. Will access it thru the floor via a billet, gasketed screw on door.

The cell will be held by a cage I will fabricate. Then the cage will mount under the car.
My question is, with the cage being mild steel and the cell being aluminum, do I need to apply some sort of rubber bumper to keep the two different metals from touching?
Like rubber tape or feet mounted to the cage, so the cell is only touching rubber via the feet that are mounted to the cage.

I have looked around at off the shelf solutions and I don't see this sort of isolation, but it makes sense to me. Maybe even make it quieter and safer.

Thoughts?

 

Anything like that which is dissimilar metal should have some sort of isolator between them. No matter how tight straps are used to hold a cell in place, it will still vibrate and rub through the soft aluminum plus the dissimilar metals will corrode. Rubber tape will be your best bet.

 

Thanks for the advice. I was searching the internet for any sort of advice or direction on what seemed like an obvious need to isolate the frame from the cell and couldn't find anything.
Maybe it is the mechanical engineer in me, but I hate adhesives. Prefer mechanical means of attachment.
Going to try some rubber pads that install into holes, like how OEMs do bumpers. Found a universal kit on Amazon I am going to try out.


Was planning on using square stock to make the strapping/frame. Drill a small hole on one side and push one of these in. Most likely go with the lowest profile ones.

 

What is best practice for preventing static discharge?

 

I have thought about that. I belive grounding makes sense. This will be my first EFI build up of a car and from what I heave learned thus far, ground everything. Twice if you can.

Only issue I see with using rubber bunpers on the bottom of the cell cage is that they become pressure points. Instead of installing a bunch, maybe a strong adhesive makes sense so the load of a full cell gets distributed.

I CADed up a frame for the cell yesterday at work. I will snap a pic and share it here for critique. Thinking of 1" square tubing for construction with 1" straps over the top to hold it down. Then legs that will sit in cradles that I build on the car. I want the cell to stay put even if the bolts holding it in vibrate out.

 

First idea and it seems a bit over built, but for a gas tank, I like that idea.

 

I used Camper tape on my setup.. Most NAPA stores carry it.

 

Thanks for the suggestion. Sorry if this is a stupid question, but what is "Camper Tape"?

When I google it I get a lot of seemingly soft foam tapes that doesn't look very strong.
Can you share any more details you may have?

 

It's a 2" wide foam tape that's put around the top edge of a truck bed before you cl. amp down a truck cap or camper. Waterproof and very strong. I've used it on gas tank straps as well.

 

So a metal fuel cell mounted on isolators will need a grounding strap. Doesn't need to be anything high tech. A mesh battery ground cable would be overkill. A simple 14 gauge wire with some eye rings to attach the tank to the frame is more than enough. If there's a metal ring around the inlet port, it can be attached there.

I wouldn't recommend foam tape mainly because it will compress over time. You can always cut up an inner tube to make rubber mounting strips. Glue them on with some spray adhesive so they won't move around.

The lowest tech you can so is good quality duct tape. Something that you need scissors or a knife to cut. Some semi trailers still have steel crossmembers that are riveted to the aluminum rub rails. A simple strip of duct tape between the steel and aluminum is enough to prevent dissimilar metals from reacting with each other.

 

Will ground the cell for sure. No brainer.

I am guessing camper tape is tough stuff. Will check it out.

 

In the aerospace industry we use black silicon based seal for dissimilar materials. Apply a bead onto a Fay surface, spread evenly, bolt it down, and fair the squeeze out. It seals, isolates, and is somewhat structural. Another tip: Use rivnuts for your ground locations. They transfer more energy across a larger surface area. I hope this helps.

 

Link to a place I can buy this black sealant? Sounds perfect.

I use rivnuts a lot. Not sure I follow the recommendation, I must me missing some understanding. I am a mechanical engineer and have a good grasp on how stuff works but don't get why a rivnut would work better than a bolt and nut (assuming clean connection). I plan to weld in nuts on the frame I make and either weld in nuts of rivnuts on the body.

 

The sealant we use on aircraft is not typical available to the public, but black silicone sealant from the auto parts store will suffice in this situation and perform the same functions. As for the Rivnuts (or Huck ground stud), the shell is swagged into a larger hole in the structure, therefore more contact area to the bare metal around it's curcumference. Primarily used for ring post or stack ups, a fay bond is always better for large surface areas, ie plates or lugs. I've always seen an improvement in Ohm readings when going from a GM standard "screw in the frame" to a Rivnut. Usually measured in mOhms.

 

You can also use vibration matting like Hush Matt or Dynamat. You can cut small squares and it will stick to anything without moving around.

 

Great idea about the hush mat. I will swing by AutoZone to see if there is anything there. If not, hush mat type stuff it is.
I used to have my entire interior covered in a knock off Dynamat Extreme called FatMat.
Crazy sticky and took dozens of hours to get off so I could do floor board repair. Young me did a lot of dumb stuff to this car...

 

You can drill a hole for a self-tapper and shakeproof washer into an nearby channel for a good body ground.

You can also drill a hole in the bottom of the tank to connect the grounding wire so that you can check it more easily in the future, but I wouldn't do that, personally.

Seriously, grounding from the tank top to the body AND to the sending unit might be a good idea since the locking rings for the in-tank units often corrode, and the O-ring seal of the tank insert may turn into the insulator. A separate ground may be helpful for both the level sender and as a redundant ground for the pump motor to prevent long ground loops/paths in case the pump wiring harness ground ever gets sketchy.

If you hunt around, you might also find an original ground strap from the tank neck to the body near the filler cap to dissipate static from the refueling process.

 

Thanks for the suggestions about additional grounds. I will be sure to be extra careful and add extra grounds when the time comes to wire this thing up.

Not sure what you meant by "original ground strap from the tank neck", at least on my car that is. There is zero, and I mean zero on this thing that is stock right now.
If there ever was a grounding strap that was stock it has been gone for 15+ years now.

I will be running all new grounds when it comes time to wire up the entire car. Zero from stock harness there too. That has also been gone for almost 2 decades. haha.

Got the tank in the mail yesterday. Welds look amazing and the unit looks much higher quality than my old no-name brand cells.

Went with an Aeromotive 15 gallon cell with in tank 340 pump.

Will post pics on my build thread as I go about fabricating the cage and mounting for it. Now to find that RV tape...

 

Is this what people mean when they say RV tape? This is what I thought of as weather stripping for your house.
Seems much to weak for what I want, but maybe I am mistaken. Thoughts?

 

Opening up an old thread, but curious if Dennis ever finished his car, or if he has a build thread on tgo or elsewhere.

 

Still working on it. The final thread is in my sig. You can see the latest on the fuel cell cage and install there.

Lot more updates coming soon!