Aluminium Fuel tank Fabrication

14/5/2005

I need a new fuel tank, so thought this would be a good welding project.
First step was to make cardboard template.
carboard fuel tank mockup carboard fuel tank mockup
Calculated volume is 71 Litres (15 Gallons)

I had all the metal cut to the exact size (14 gauge ns4), justed needed to make the baffles.
Interal baffles

Then things went wrong, the heat from even the light tack welds warped the metal beyond repair.
carboard fuel tank mockup carboard fuel tank mockup

My design includes a sump, so I thought I would see how much the metal warps trying to attach a test piece.

So how do you weld 14 gauge ally without it warping like mad?

6/8/06

Have been quoted 155 to have this made by Bryn at Allyfab, so I thought stuff it - it's not worth the time and effort trying to make another one. New one will be folded up as once piece, with just the end-tanks welded on.

27/10/2006

After a considerable wait, my tank is ready. Total cost including a new fuel sender and fuel gauge was 215 delivered. You will notice even this tank has slight warpage near the sump, which makes me feel better!

5/11/06 Fuel Tank installation

Spent most of the day figuring out and making a cradle to sit the tank on in the back of the car. With the rising cost of electricity, you will interested to know that I used about 5Kw of electricity in about 5 minutes to weld that cradle which is more than the amount of power I consume overnight running my computers, washing machine and dishwasher.


Spent another 150 on plumbing. I elected to use -10 fittings for the low pressure side, which means I had to replace my existing FSE pre-pump filter with a -10 sized one too. Although -10 means the hose is approximately 15mm ID - the actual ID of the plumbing fittings actually only around 12mm. The inlet into the Bosch 044 motorsport pump is M18x1.5, hence why I went for -10 fittings. I think -8 for the low pressure side to the 044 pump is sufficient, My tank has dual -10 bosses fitted so capable of flowing enough fuel for over 1000BHP :-o

Here's the lineup:
-10 Male on the tank
-10 Female for push-on hose
-10 Push on hose
-10 Female for push-on hose
-10 to -10 BSR Aerotek mesh fuel filter
-10 female/female
-10 to M18x1.5 adapter
Bosch "044" motorsport pump
M12x1.5 to -6 adapter
-6 to -6 female/female adapter
(Above replaced with homemade M12-M12 M/M adapter)
M12x1.5 to -6 adapter
(you could just replace those three with a M12x1.5 to M12x1.5 female/female)
Hengst H80WK05 fuel filter
M12x1.5 to -6 adapter
-6 to braided steel hose adapter

20/11/2006 Completed

Here's the setup before and after making the little adapter to shorten the overall layout


Another few weekends of work and its all completed - I'm pleased with how its all turned out. I made a little cradle for the pump which is suspended by rubber mounts underneath the rear floor.


The filler is 2", the breather is -8 sized and the fuel return is -6. For anyone who own's a Dakar, you can see that the tank fills the void at the rear of the car.


There is a flaw in this design, given that its in a 4x4 - if you get stuck at an angle all the fuel will run to the one side, if your'e low on fuel it wont pick-up. this could be solved by having two smaller sumps at either end and Teeing them together.

2/1/07 Self Calibrated Digital LED fuel gauge

You may of noticed that my fuel tank is triangular shaped - this meant that the fuel gauge would show half empty after about 2 gallons had gone because it expects the tank to be linear. Therefore I needed a way of having a gauge that I could calibrate accurately - and here's my solution.

It uses an LM339 comparator which simply compares two voltages - one input it connected to a multi-turn trim pot, which creates a voltage divider - the other input goes to the fuel level gauge, which varies in resistance as the arm moves up and down - this placed with a resistor forms another voltage divider.

My tank hold nearly 80 Litres of fuel so I simply went to the petrol station with an assistant, added 10L of fuel, twiddled the pot until the first LED comes on, then keep adding fuel in 10L increments - adjusting each pot in turn.
I made a prototype that used a 5V regulator, but the change in voltage wasn't wide enough for the LM339 to detect - i got better results running the full 12v into it. I did try to make an 8v regulator, but it turns out that you don't need a regulated (constant) voltage as the whole thing simply divides the available voltage. Electronics buffs would probably add some noise caps and protection diodes - but it worked as a prototype for a few days so I'm going to see how this one lasts as-is.

I was worried about the lights all flashing on and off as the fuel sloshed around, requiring some form of electronic damping - but it doesn't really need it.


Here's the circuit diagram:

I haven't shown the 12v (pin 3) and ground (pin 12)to going to each of the comparitors, The exact pin layout can be found here

Parts List from Maplin:

D220R 2W Res 220R 0.18
2 x UH31J LM339N 0.69 (would also suggest you get some chip sockets, so you can replace and test things without the chip)
UK15R LED Clip Concave 5mm 3.60
WL27E 5mm Red LED 0.34
WL28F 5mm Green LED 1.02
WL29G 5mm Orange LED 0.17
WR49D 18-Turn Cermet 10k 6.77

The value of the 220ohm resistor may need to be changed slightly, it needs to roughly match the lowest value of your level sender and you dont want too much current going through the sender, I measued mine at a few hundred milliamps.

I then needed to get the LEDS into a gauge, original plan was to make a little aluminium insert to go into a standard smiths gauge - but got a little carried away and made a whole new gauge from a solid billet. It gave me a good excuse to try out my rotary dividing table for the first time - I'm very pleased with the results.


Circuit needs to go in its own little box hidden behind the dash.

Here is someone else whos made one for his MEV Rocket

Some discussion about the circuit here

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