fuel cell with stock gauge?

[323IJOE]

is this possible to do, from what i have gathered in the past couple hours it doesn't look good for me. most cells i find have senders 0-90ohms and from what i found our gauges are 0-75ohms. is there anyway to make them work with each other? I would honestly rather just buy a fuel cell than refurbing my old tank.

[Kpeters]

is this possible to do, from what i have gathered in the past couple hours it doesn't look good for me. most cells i find have senders 0-90ohms and from what i found our gauges are 0-75ohms. is there anyway to make them work with each other? I would honestly rather just buy a fuel cell than refurbing my old tank.

I guess using a resistor on the line? I'm no electrics expert but sounds like that should work shouldn't it?

[tinkwithanr]

The stock sender is actually 3-75 ohm, but the 3 ohm can be replicated with an in-line resistor pretty easily.

As for the top end, if you just hooked it up as is the gauge would read empty when the tank was still 1/6th full. If that doesn't bother you to much you could just hook up the 3 ohm resistor and call it a day.

If you want it to be more accurate, then a bit more work is needed. I'm going to be running a 20 gallon fuel cell, so I'm planning to make a 'black box' to be hooked up to the system in line between the sender and the gauge that will successfully convert the 0-90 ohm signal to 3-75 ohm. I just haven't sat down and worked out the specific values yet. My thought process for doing so is as follows, if anyone has any input please feel free speak up.

The circuit for the fuel gauge consists of:

1) Voltage Source (I'm assuming +12V, haven't double checked yet)

2) Fuel Level Sending Unit - varying internal resistance of 3-75 ohm

3) Fuel Level Gauge

Basically the system functions by letting the internal resistance of the sending unit control (limit) the amount of current (amps) that gets fed into the gauge. The lower the resistance of the sending unit, the more amps can flow through the circuit, and the fuller the gauge reads.

In order to match the new 0-90 ohm sending unit to the stock fuel gauge, it needs to limit the current the same amount as the stock 3-75 ohm unit. As mentioned above the low end can be limited by a simple 3 ohm resister wired in series. However it gets trickier when converting the 'empty' range of the unit. The new sending unit will limit the current to much at the low end of the range (90 ohms lets less current through than 75 ohms), so more current needs to be put back into the system in a controlled manner. This means the 'black box' will also need a +12v input separate from the original gauge circuit. The new 12V input will be limited in a manner that raises the total amperage output of the circuit by ~16.6%, matching the original output from the gauge.

Another possible option would be to by a fuel cell that is close to the depth of the stock gas tank and adapt the stock sender unit to bolt into the new tank. More fab, less electrical. I don't know the length of the stock sending unit off the top of my head, but it seems like it would work just fine.

[MKINNA]

where are you located, I have a refurbished tank leftover from my car.

if your interested, and local.

[TobyB]

adapt the stock sender unit to bolt into the new tank

That was my thought too. Most cells have a large top plate- fab one up with

a hole for the stock sender.

t

[323IJOE]

thank, i really wouldnt mind the extra gas in the tank when it says im on empty, itd act as a emergency reserve kinda, when you get around to figuring out the box to adapt the current it would be awesome if you could do a writeup on it.

as far as fabricating a plate it seems easy enough to do but the problem with that is that most of the fuel cells i have seen with the hole for the sending unit come with out and are more expensive, all the others arent equiped for a sending unit as far as i can tell and i would rather not have to spend the extra $$ for a SU im not going to use,

another fairly simple question is would i HAVE to go electric pump or can i stick with the mechanical? i plan on getting a fuel cell with a 2" sump on it, and from what i have seen so far is that first of all the sump has to face the back and that there might be problems with the mechanical pump not being able to pull enough fuel from the cell on start up/take offs.

just for referance i am using this as a summer daily driver with maybe some autoX here and there, but mostly i just want a reliable fuel system and a little bit bigger tank than the stock 12 gallon for longer trips.

[TobyB]

The stock pump should be OK.

From the above posts, if you want to use the 0- 90 sender,

just find a 3 ohm resistor, wire it in line with the sender,

and you're good to go. It's probably not strictly necessary,

but I'd do it. And having "R" mean "5 gallons" rather than 1

would be fine by me, too.

t

[M3M3]

if you have a bladder than can outlast a stock 02 fuel tank on a road trip, you must be a younger man than I! ;-)

[FunkyLaneO]

The generic sending units that are usually used on fuel cells are a different style where the float is at the end of the wire, you can bend and/or shorten this wire so that the angle of the sender is 75 ohms when it hits the bottom of the tank and 0 when it is at the top, all you need to do is figure out the depth of the tank, where the pivot point is and what angle 75 ohms is at and you can figure from there, on some the pivot point is adjustable which makes it even easier. We used to do this alot on boats when we had odd sized custom tanks made.

[tinkwithanr]

Ha, that's a great idea.

[323IJOE]

if you have a bladder than can outlast a stock 02 fuel tank on a road trip, you must be a younger man than I! ;-)

haha ya i dont think I'll be able to outlast the tank but its just nice to have that little bit extra time before you have to stop just for gas, even in daily driving it around town i can put of having to wait in those crappy lines at the gas station.

and as far as bending the wire to make it 75 ohms that sounds a little sketchy to me lol ill have to do a search on it and see exactly how you would do that, it sounds like it might be a delicate process and knowing me id screw a perfectly good sender lol

these are the two im considering:

http://www.summitracing.com/parts/sum-293215-s/overview/

http://www.summitracing.com/parts/rci-2150as/overview/

pretty much identical, but for the price im inclined to think that for a little extra i should go with the RCI, but then again whos to say the summit isnt just as good.

Any input?

[tinkwithanr]

Bending the sender to read 75 ohm as opposed to 90 would be very simple assuming you have a digital multimeter. Just bend the arm on the sender down so that it hits the bottom of the tank sooner, and double check the new resistance in the empty position.

As far as the two posted fuel cells, they are basically identical. Both should work fine, though the internal foam will deteriorate over time and clog the fuel filter etc. Thats why I went with a fuel cell with internal metal baffles and no foam.

[323IJOE]

interesting ill have to find one with metal baffles, where did you end up getting yours? the only site i can really find that has a variety of them is summit.

[tinkwithanr]

I got mine from Summit, their retail store is local to me.

[FunkyLaneO]

Here is they type of sender I was talking about

http://www.summitracing.com/parts/sww-439361-f/media/images

you just bend the wire the float is attached to, not too sketchy at all.