Expensive Speciality Batteries - Watchman Oil Monitor

[awemawson]

On my heating oil tanks I have 'Watchman' monitors, that radio on an infrequent basis to an indoor receiver to tell me how much oil is left.
I have three separate heating systems in three buildings - they all have Watchman monitors of varying vintages, but all have one thing in common. A 6 volt battery encased in a copper tube entirely proprietary and hugely expensive.

I recently took delivery of a 'top up' of oil (2300 litres and that's a top up  ) after which the monitor for my workshop ceased to work. Obvious first thing to look at is the transmitter battery - sure enough it's down to 5 volts off load so change the battery. New genuine battery over £30 !

Now I know from previous investigations that these things consist of a screw connector sealed in the  end of a piece of standard 15 mm copper plumbing pipe, which has a cap at the far end, and a plastic sleeve bringing the bore down to the diameter of an AAA battery. Inside are four AAA batteries and a spring to make contact.

So - mount the pipe in the lathe - carefully part it off down to the plastic liner and clean the ends. Then take a 15 mm compression joiner - bore out the centre stop so that the pipe will slide all the way back together, and re-assemble with new batteries and lashings of Vaseline as that is what it seems to have been previously smeared in.

Actually slightly more complicated - I only had a bulk head fitting with no conical ends for the 'olives' so I had to machine them.

Wack it back on the transmitter and wait to see if now it will talk to the receiver. This can take a long time so the fault may or may not be fixed - but the battery is at least now good 

[appletree]

One phrase springs to mind cheeky Bastards. LOL
Phil

[John Swift]

being curious I had a quick search for the battery and found a youtube video :-
 

and a photo of the connector
I can't see enough detail be it looks like some kind of RF connector

john

[awemawson]

Yes I think that it is an RF connector - certainly co-axial

[howsitwork?]

Did it work??

Don't kill us with suspense!

[Biggles]

Just words of warning; make sure the amperage is the same. Some instruments require lower amperage than the high power Duracell battery. Otherwise you could blow a diode on the circuit board. 

[awemawson]

Biggles, only if ohms law has been revoked - at a given voltage it will draw what it wants to draw 

Howsitwork - in a word no  I've withdrawn the entire gizmo from the tank and got it in the workshop adjacent to the receiver. It works by firing a sound burst down a tube vertically immersed in the oil. It listens for the echo off the surface of the oil and calculates the oil level. Googling it, it has a 'calibration cycle' to go through when it's been powered off for more than two minutes. It fires a few sound bursts for 25 seconds then averages the delay to receiving the echo. After 25 seconds it's supposed to emit three bleeps then it's calibrated. Setting it off you can hear the sound bursts being emitted, but they carry on for several minutes then cease. I assume that the sound receiver has failed and it's not hearing the echos - replacement on  order !

[Biggles]

Yes it will only draw what it needs when working correctly but if there is a circuit fault it could draw more than the circuit will handle. In that case any diodes will burn.

[Will_D]

I know this is slightly OT but my oil tank is monitored by a Conrad electronic oil meter in the utility room.

Its a simple digital display the monitors the Burner on time (via a 220 v connection).

It has a humongous number of settings (on the dip switches) for consumption per minute (data should be on the burner in LPM).
You can read litres/kgs or burn time

Once calibrated its about 1% accurate!

How do I know its accurate?

When it says you've used 860 liters the oil man can just about drop in 850!

[nrml]

I have the same watchman monitor on my LPG bulk storage tank. The service engineer who fitted it told me that the copper cap on the end of the tube comes off with a little persuasion with two pairs of grips. He advised me to just swap the AA cells out rather than buy  replacement tubes which the company he works for happens to sell to their customers .