Ultrasonic Water Tank Gauge

[Bigted]

We have a Rapido 7086F and the fresh water tank gauge is worse than useless. After reading about the Merlin Ultrasonic gauge in MMM we are seriously thinking of having one fitted. Before I spend £100 could anyone advise if they have had one fitted and whether they work accurately.

[Derek Uzzell]

I don't recall seeing the Merlin product mentioned in MMM (Can you say which issue it was in?), but I did find the website that relates to it.

 

http://www.merlinequipment.com/news/article.asp?id=100

 

Although motorhome fresh-water tank gauges have no reputation for extreme accuracy, I would expect most to provide readings that are 'near enough' to be useful. If your Rapido's gauge is genuinely hopeless, then it sounds like there's either something technically wrong with your present system, or your motorhome's water tank is such a strange shape that its contents reduce in volume unpredictably. In the unlikely event that the latter is true, then the Merlin system won't be able to provide the accuracy you are seeking.

 

I'm doubtful that Rapido would choose to install a system that can't even provide rough-and-ready read-outs (which will be sufficient for most motorcaravanners). So, if I were in your shoes, before expensively modifying your present system, I'd first try to check with owners of similar Rapido models whether or not they are in the same boat.

 

As the 7086F is a relatively recent Rapido model, I'm assuming you've owned it from new and that the water-tank gauge's inaccuracy has always been present. If that's the case, what has the Rapido dealer from whom you bought the vehicle had to say about the problem?

[Guest Tracker]

This is another of those well aired topics!

 

As far as I know you can't rely on any of these water gauges and the best way is to mentally note your water consumption per day and deduct it from the total available before refilling.

 

I know we use about 3.5 gallons a day without showering - more when we do - and with a 16 gallon tank I know to fill up every three or four days - at the same time that the loo needs emptying usually - if one needed a reminder!

[Derek Uzzell]

Derek Uzzell - 2009-12-18 9:26 AM

 

I don't recall seeing the Merlin product mentioned in MMM (Can you say which issue it was in?)....

 

I've answered my own question - the gauge was mentioned on page 217 of MMM November 2009.

 

As far as I can make out, this product was never intended for the types of tank used in motorhomes. I think it highly unlikely that the Merlin 'sender' will directly replace the probe-type sender used on many motorhome tanks. (Clearly it won't directly replace 'stud-type' senders.) I'm also very dubious about the suggestion that the Merlin sender should work satisfactorily with existing motorhome display-units - it certainly wouldn't work with the CBE display fitted to my Hobby.

 

If I were considering replacing a motorhome water-tank gauge, I'd choose to employ CBE products of the type marketed by CAK.

[BarnacleBob]

Hello Bigted,

As a Rapido7086F (2005) owner until May this year, I am sorry to hear that your freshwater guage is "worse than useless". Perhaps I was lucky because my gauge was very accurate. I don't know how old your 7086F is but if it is the same make of sender unit as fitted to my vehicle, I would definitely get the supplying dealer to look at it and adjust/replace it before buying a new one. The shape of the tank, being straight sided and rectangular makes it an easy one for accurate gauge readings (provided you are on the level) so I think your unit must be faulty or in need of adjustment if that is possible.

Good luck,

Barnacle Bob

 

 

[Brambles]

An idea I have just thought of......

With the level system using bare probes sticking into the water tank at various heights to detect the conductivity of the water, is to replace with a series of cheap float switches. These are wired to progressively connect each existing connection wire to the botton probe wire via individual 100K resitors. Probably not needed but just makes sure damage will not be done to any of the probe inputs at the electronic end - just worked out resistance inputs will see for each probe is about 500K in a tank of tap water.

You will now have a system which does not depend on the conductivety of the water, or any acidity or alkalinity of the water generating voltages on the probe pins balancing out the voltage supplied to measure the conductvity so no detection is possible.

As far as I can see this should work well.

Parts.. under £10.

example float switch http://www.suntekstore.co.uk/Liquid-Water-Level-Sensor-Horizontal-Float-Switch-Down.html

 

You can also figure out best positions to place for when you want to detect full - why? no need to, water flows out when full, so full position could be 3/4. and empty could be whatever reserve you want by where you position the 1st float switch. You could bore out existing probe holes or drill new ones.

 

p.s. My guage also werks well, but deos not work with water from Fort William area - no indication at all. Also had same when filling up on one campsite in the south but cannot remember where now. So maybe you have same problem, your house tap water is of a nature the probes will not detect. On both occassions a teaspoon of Milton made teh gauge work and is quite safe in a full tank. I think they recommend a teaspoon per 5 (??) litres to make drinking water sterile and safe to drink.

 

Might be a test worth doing, add some Milton to a full tank and see as you drain tank if gauge is more reliable. ( Am I starting to havor on now? - probably, so shall shut up)

[SBS]

There's this one on ebay, item number: 200418987106

 

Mike

[peter lambert]

Also as 7086F owners, we have found no problems with our water level guage in the 4+ years we have had the Van. It does sound, as others suggest. that you have a duff one and should get it checked by your supplier. As a general guide, we can get by on a full tank of water for a complete weekend away, each showering morning and night, with all the washing up etc. We hardly ever use site facilities as the ones in the Van are so good.

[Walker]

We have a Rapido 927F and are experiencing problems with the fresh water tank probe. i.e we only get 100% or 80% even when empty. The van is 2006. We have had our electrician check all the connections and OK, we have taken off the inspection cover to the water tank and cleaned the tank out, the probe is looking clean and shiny. If we detach the connection from the fresh water tank probe to the main fuse box and then connect the van to the mains we get a reading of 10%. We have telephoned the dealers but they cannot help unless we take the van to them but as we live in Cornwall it is a long way and we really want to find out how to correct this problem. We wondered if it could be a calibration problem, but cannot find anyone who knows how to check this. As we have said the problem is not with the electrics or with the probe, but very annoying - can anyone offer any suggestions. (!)

[lennyhb]

Most of the problems with the probe type gauges is a faulty probe unit, 5min job to replace. Not sure what they cost in the UK but in Belgium 27€ (full retail).

 

 

[Walker]

Thank you for your advice, however, the probe is only accessible from below the van, the cap in the van is half under the water heater (great design fault) and only partially visible no way to get a grip on it, so we cannot get to it. I presume that it can be removed from below i.e under the van- have not had a look yet as it is a pig of a job to get the cover, insulation etc off besides getting a good soaking in the process.

 

Will keep you informed of progress albeit a bit slow.

 

8-)

[lennyhb]

If it is the one I think it is you will need to get your hand inside the tank to undo the retaining nut (had to use a large adjustable on mine) & you will need at least 10" clear above the sender to get it out.