Tank contents gauges

[Neeves]

We have 2 identical 200l water tanks and a 200l diesel tank.

The diesel tank has a sight tube, which you can see as you fill the tank and we use a dipstick, 10mm dowel, for the water tanks. The sight tube I marked as I filled the tank with 20l jerry cans and the water tanks are cubic, or rectangular, and as they hold 200l when half full I know they have 100l of water. Crude but pretty failsafe - and the information need not be that precise.

Jonathan

edit - electrical devices just seem unnecessary (when a dip stick or sight tube suffices) and electrical devices have a habit of ..... failing

 

[ylop]

US and EU senders work in different directions, with high resistance at the bottom or top of tank. it's a resistor so swapping wires won't help.

It is rare that I will say this about anything but the US approach is better! A broken wire or corroded connection on an EU sender looks like a full tank.

The tanks are wine glass shape as a result of the tanks being in the upper part of the keel and above. No sender unit would give a true reading.

My tanks are not symmetrical so suffer the same issue, the sender gives you depth in the tank not the volume in the tank. However the gauge is graduated in 1/8ths which are not evenly spaced around the sweep of the needle - ie. by calibrating the divisions on the meter to volume the manufacturer has overcome the non-linearity in the depth:volume relationship. Mine are factory installed but wouldn't be rocket science to do the same yourself.

 

[webcraft]

US and EU senders work in different directions, with high resistance at the bottom or top of tank. it's a resistor so swapping wires won't help. Electronic gauges are able to change between the settings.

European vs American Resistance

I assume this is because EU tanks are more likely to be empty while US tanks more likely to be full based on traditional fuel prices, and in theory lower resistance will use less power.

So in theory I could just fit a different gauge?

- W

 

[Cspirit]

I’ve been through much of this. If anyone wants a brand new American resistance gauge they are welcome to it for the price of postage or collect from East Sussex. Bob

 

[Mistroma]

The gauge on on Avy-J runs backwards - full when empty, empty when full. OK once you get used to it. I reversed the wires from the sender but it made no difference.

- W

So in theory I could just fit a different gauge?

- W

I imagine someone fitted the wrong sender at some time. Reversing the wires will make no difference, it will just measure the same resistance.

Best bet would probably be to change the sender. I'd be tempted to get one that is basically a load of reed switches in a column with a float on the outside. No swing arm or dodgy potentiometer, just a load of switches triggering different resistors into the circuit. Works in exactly the same way as the swing arm type but should be more robust and give reproducible readings. Measure the depth to bottom of the tank and buy a sender that fits and make certain it is the correct type (i.e. high resistance when full or low resistance when full).

It won't magically solve calibration issues with a curved tank and display correct levels. It should provide reproducible readings and allow you to make a calibration chart.

 

[lustyd]

So in theory I could just fit a different gauge?

- W

Either gauge or sender but as you understand what you have neither is worth the money or effort in my opinion

 

[webcraft]

I imagine someone fitted the wrong sender at some time. Reversing the wires will make no difference, it will just measure the same resistance.

Best bet would probably be to change the sender. I'd be tempted to get one that is basically a load of reed switches in a column with a float on the outside. No swing arm or dodgy potentiometer, just a load of switches triggering different resistors into the circuit. Works in exactly the same way as the swing arm type but should be more robust and give reproducible readings. Measure the depth to bottom of the tank and buy a sender that fits and make certain it is the correct type (i.e. high resistance when full or low resistance when full).

It won't magically solve calibration issues with a curved tank and display correct levels. It should provide reproducible readings and allow you to make a calibration chart.

Tank is irregularly shaped and installed at an angle with the filler at one end. Not a hope in hell of getting any normal sender to give any sensible even remotely linear results.

I will stick to knowing that E=F and vise versa.

- W

 

[Jim@sea]

How do they work?
I thought I understood but, when I came to replace the gauge supplied with the float sender, I realised I don't.
The sender resistance varies between 200Ω and 2kΩ.
A simple ammeter will still register some current at 2kΩ. Calibration can be effected with a resistor in series with the meter but how is the min reading adjusted? Shfting the end stop on the meter would work but is hardly elegant.

I one bought a brand new Princess 33, from a boatyard in Northwich, I had arranged that ESSO would deliver 2 forty gallon drums (205 litres each) to the boatyard and asked the boatyard to put it in the boat I had just bought.

So before setting off down the Weaver Navigation Canal and then onto the Manchester Ship Canal in order to go out to sea through Eastham Locks I had a look at the .fuel gauge which has located on top of the fuel tank, and it showed "half empty" So I assumed that they had put the 90 gallons in.

So after arriving at Eastham Locks after a very slow journey down the Navigation Canal (5 knots on 1 engine) and 10 knots on the Ship Canal at Eastham Locks I checked the fuel gauge and it still showed "Half Empty" so I though OK

It was only when I was about to reach Holyhead that the engines started misfiring, I had run out of diesel.

The Fuel Filter still showed "Half Empty" The gauge had stuck on Half Full.

Put 10 gallons of diesel in and carried on.

Moral of the story.
1. Dont assume that your fuel gauge is correct.
2. Dont assume that the boatyard has done what you have asked them to do.
3. Dont assume that when you buy a Brand New Boat that the dealer has not sold you a "Demonstrator and cleaned it up to look like new. (When I arrived at Holyhead the gearbox rear oil seal had blown and was spewing oil out and it later came out that I had seen this particular "demonstrator" boat before and refused it saying I wanted the next new one out of the factory.

 

[Mistroma]

Tank is irregularly shaped and installed at an angle with the filler at one end. Not a hope in hell of getting any normal sender to give any sensible even remotely linear results.

I will stick to knowing that E=F and vise versa.

- W

Hence the calibration chart. I calibrated mine by noting readings as I filled. Easy enough as I usually fill from cans and jotted down readings every 26litre or 20 litre can. Only worked because the tank is quite small, filled once from virtually empty and now know the actual capacity. A couple of fills from different staring points gave pretty good calibration from empty to full. Overkill but I was making a digital gauge and noting Ohms.

Just noting analogue meter readings wouldn't have been difficult and you'd probably just need to note litres to get 1/4. 1/2, 3/4. No need to do anything at all if your current system works and you know that 3/4 full actually means the opposite but still reasonable reserve.