Fresh water tank level indicator

[Deomer]

Hello,

The fresh water tank level indicator in my 99 JC is not working.

I have found a diagram of the electronics inside (kindly posted by a member of this forum):

And I have rebuilt it using new resistors and reed switches:


Everything is working as per the schematic. However, I'm facing an issue and I'm not sure why or how to solve it. The indicator panel shows the right number of bars when the floating magnet is near one of the reed switches, which is correct. However, there's plenty of areas where the magnet does not activate any switch (they are far apart) and, in that case, the display shows an empty tank (reads 6.2kΩ) which, although expected by looking at the schematic, is the wrong behaviour.

How is the panel supposed to know the water level in the tank when the floating magnet is not activating any of the magnetic switches??

Thank you!

[Bisiac]

Devi posizionare correttamente i piccoli magneti a ridosso dei reed.
Se può essere di aiuto ecco lo schema e le misure della vetronite dove posizionare i contatti ed i resistori.

[Deomer]

Thank you for that diagram, but my question still remains.

There's plenty of space between reed switches 2 and 3, for example. If the magnet is between those 2 positions, it will not activate neither reed switch 2 nor 3, so the water level indicated on the display will be wrong ("empty" instead of 1 or 2 bars).

[Bisiac]

Come ho scritto, bisogna posizionare i piccoli magneti adiacenti ai contatti reed in modo che il magnete toroide quando passa in un senso o nell'altro faccia mantenere in una posizione definita il contatto reed. Sicuramente é da fare diverse prove affinché la commutazione sia stabile e sicura.

[Deomer]

Wait, are you saying that the reed switches should be latching or bi-stable reed switches?? That actually makes sense and is the only way this works properly.

[SirJames]

Hi,

If it's not possible to fix your tank level indicator you can order a new one here:
https://www.vwbusshop.de/epages/GuenzlC ... /333000367

Regards,
Jonas

[E2nO]

Here are repair / rebuild instructions for the water sensor
https://forum.james-cook-freunde.de/vie ... eed#p39415

The self latching reed contacts listed in that description are no longer available with Conrad, but you can get them through Digi-Key (https://www.digikey.de/product-detail/d ... ND/9687611).

Alternatively you could consider these here: https://www.reichelt.de/reed-sensor-180 ... os_0&nbc=1 but they are more expensive and not "tested" for this kind of application (and thus may not work at all).

[Deomer]

Amazing information E2nO, thanks a lot!

The crucial missing piece of the puzzle are the latching reed switches, it won't work with normal reed switches. I'll buy those and try again, as spending over €130 on a new sensor that I can make for around €15 is a last resort.

Thanks everyone!