Fuel level sender connections and voltage

[Gridgway]

I am changing fuel tanks in my BDR from the horrible rusty steel one to the standard S3 aluminium one (carbs).  I got a new fuel level sender which is a generic one like this one on the Holden website.  https://www.holden.co.uk/p/sender_for_smiths_classic_fuel_gauges_top_mounting

It has two connectors labelled W and T.  In the Holden video it says that W is the feed and T is to the gauge.  However the Caterham wiring diagram only has the wire from the gauge which is green with black stripe. 

I have two wires that were connected to the old sender (which is the same as the new one).  So I thought that was ok.  But both are +12v in relation to earth which I thought odd.  One wire is green with black stripe (tick) the other is white with green stripe which is a fuel pump 12v according to the standard colours. The old wiring is pictured below.

And finally the Holden info says the instruments should work off 10v (with a regulator somewhere), but I def have battery voltage on both wires of 12 and a bit volts.

I could just connect one of the wires plus earth and see what happens, or go straight for the same connections as before, but I'd prefer to know what I'm doing rather than be guessing!

[OldAndrewE]

The Smiths instrument system used one of these which provides a stabilised 10V

 

Edited November 20, 2023 by OldAndrewE
Thought I would try the picture resizing

[Jonathan Kay]

Two background questions before we get to the gauge:

1. Does the Seven have a modern alternator with built-in regulation, or an older system requiring external regulation, as described by Andrew?
2. Where was the fuel pump before and where will it be eventually? Is it already wired separately from the wires that you are describing and is it working?

Thanks

Jonathan

[Gridgway]

Thanks Andrew, I'll check, bit I suspect I've not got the 10v regulator.

To your questions JK.  The caterham has a normal voltage regulated system from the alternator.  But the Smith's gauges work on 10v (why?) which is why they have the secondary voltage regulator that Andrew has shown.  I'll go searching for one of those next time it in the garage.

Just need to solve the wiring conundrum now.

[OldAndrewE]

This is a wiring diagram that comes with Smiths classic gauges, shows the ones that use 10V

[OldAndrewE]

10V regulator available here if you can't find one

Caerbont | Smiths Classic Voltage Stabiliser | Merlin Motorsport BR1307-00NEG

[Gridgway]

Thanks Andrew, that's very helpful.  The regulators do seem to be in easy supply.

I realised that I didn't answer JKs second question re fuel pump.  Originally with its crossflow it used the mechanical pump.  Then when upgraded to the BDR the owner added a separate feed for the newly added facet pump.  This has its own (additional) switch on the dash which I presume is for safety when hillclimbing (maybe).

In the resto project I might go back to the original wiring and have the satisfaction of removing an extra wire and switch!

[Gridgway]

Solved my core question with a better bit of googling.

The W terminal is from the Windings of the gauge.  The T is to activate the low fuel warning light and connects to the housing earth.

That doesn't seem a terribly good idea to connect the fuel pump feed to earth so I assume it was connected by mistake.  It may well have never been "activated", who knows.  But that's well dodge!!

ETA that means the video in the Holden web site is wrong (unless I misunderstood it)

Edited November 21, 2023 by Gridgway
Added more

[Gridgway]

So to update with progress.  I had duff info about the connections, they are the other way around.  W is the low fuel level warning and T is the Tank level.  After much faffing and careful not shorting of anything, I connected up the two wires.  It seems that the wire used for the low level warning is the white with green one which should be used for a fuel pump. So just the wrong colour wire used in the kit build.

Now I have to fit the new level sender in the new tank.  It's the generic type that you have to get the length of the arm right.  It looks like there is about 19cm lateral distance to the baffle in the tank.  The height above the bottom of the tank is also about 19cm.  So I have to make the arm the right length.  I've got to try and estimate the levels I want the gauge to show empty and the warning light come on.  I'm thinking that the warning light should come on at about 8 litres of fuel left.  Or 10 maybe?  Then I need to estimate the depth of fuel at that volume.

Need to have a think.  It's not an easy thing to test.  It's not much fun putting fuel in and pumping it out again to test it, but I guess not impossible.

[rkeywood]

After several attempts to make the original VDO sender in my car read accurately by trial and error I went for the Blue Peter solution - make a section of tank out of corrugated card (actually correx) and set it up off the car. To get the warning level I've just put a gallon in and dipped with the sender out to find the level (I've probably got this written down somewhere). I've done this subsequently with a generic vertical rod and float arm type and a top pivot type and it all makes sense when you can see it! You'll probably need to twist the float and, depending on the type, you may need to bend the arm or rotate the sender on it's mounting - the Caerbont (Smiths Classic) universal, for example, works best rotated one screw hole. 

[Gridgway]

Thanks, that's helpful.  It'll definitely need some trial and error as the bottom of the tank isn't horizontal.

I think I'll fill it to 5l then 10l and measure the height to set the arm length somewhere in-between.  Then I can install the sender and empty fuel out with the fuel pump until the warning light comes on.

[Jonathan Kay]

Is the tank in the car?

How about using water rather than petrol while you're at the stage of filling and emptying in order to calibrate?

Jonathan

[Gridgway]

I did think of this but I fuelled it to run up the motor then pumped it out again with the fuel pump.  The tank is just laid in at the moment so I could take it out and tip the rest of the fuel out 

If I put water in then I don't really want to run water through the fuel pump to empty it and I'm not sure how I'd get all the water out again.

But it's much nicer to use than petrol for these purposes!

[rkeywood]

I'm not sure about 'calibration', the tricky bit is setting the orientation of the float arm and angle of the float so it sits in the slope at bottom part of the tank. Once you've done that you can adjust the float arm length (and pivot height, if that type of sender), so there's correct travel from bottom to top. If you do it in situ with liquid then you end up chasing your tail - you get the bottom set, then the top is out, or you hit the baffle etc. Doing this in a mock up where you can see things is a 5 minute job. A lot of the older installs just had the travel set at the mid point height of the tank with the float arm parallel to the long side of the tank and left it at that. As a quick improvement, and starting point for trial and error, you can bend the float arm to angle it forward so the float almost touches the front of the tank, tweek the angle of the float on the arm so it's the same as the slope on the tank and increase the travel for the height at that point. The Caerbont and some of the universals need soldering once set and cut making adjust after more of a pain

[Gridgway]

Yes, you are right about calibration as that needs Revilla's gauge magic or similar really.

It's about setting the arm as best as possible and (along with shaping) there is only one variable really - the length of the arm.  For me I'd prefer the bottom part to be more accurate - so that I know that when the warning light comes on there's (say) 5 litres of usable fuel left.  I need to do a test to find the point where the warning light comes on and see what that says on the gauge.

My wife has some foamboard for some crafty purpose, I might steel some of that and make a mockup of the tank - just the bit between the baffles to see how the arm might fit.  If I do then put a known amount of fuel in I can get a level - although with the float you don't know how much of it submerges for the weight of the arm.  I assume not much.

Trial and error indeed!

[John Vine]

I'm wondering whether the Spiyda Gauge Wizard might work here.  If so, I have a Spiyda unit I can lend you to try out.  

(I had planned to use one on my R400D but eventually had to abandon the experiment due to spurious voltages in the sender circuit which adversely affected the gauge needle position.)

JV

[Gridgway]

Oooh, sorry John didn't reply, most rude!  It would be very interesting to try out, so yes please.

I see they also do a 10v voltage regulator which is cheaper than the "Smiths" one - although I've just bought one.

And @rkeywood I have taken up your idea of making a mock-up - I have stolen some foamboard my wife has got to do that with.

[John Vine]

23 hours ago, Gridgway said:

It would be very interesting to try out, so yes please.

Hi Graham,

PM me your address and I'll pop it in the post.  But I'm away at the moment, so won't be able to deal with it until the end of next week.

JV

Edited December 7, 2023 by John Vine