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Replacing batteries in Oil Level Sender (unsuccessfully)

Discussion in 'Plumbing and Central Heating' started by Kes, 22 Feb 2010.

  1. Kes

    Kes

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    I have an oil tank with a Sensor Systems Watchman level monitor. It transmits the oil level to a display in the kitchen. All was well for the last two years. A couple of day's ago the display went from 2 to r, with a flashing light. This is, according to the instructions, the display going into listening mode (i.e no signal from the transmitter). There was no indication of a low transmitter battery, but the remedy is to replace the battery at the transmitter.

    Now the battery, or Powertube, is an engineer's delight. It is a length of 15mm copper tube with a s/s screwed insert at one end with the electrical connections. At the other end is a permanently pressed-on copper cap. Inside is a plastic sleeve holding four Duracell Procell AAA batteries costing around £1.20 in total. The Powertube is £25+ and you have to throw the old one away.

    So I took off the Powertube and checked it with my amateur's multimeter. Voltage 5.75, and current (meter set to 10A) 0.16. I then knocked off the end cap and took out the batteries, covered in silicon grease. I tested the batteries out of the tube all in line and the voltage was 5.25 and the current was 3.6 (I assume this is amps). I bought a set of Duracell Ultra batteries and fitted them in the sleeve. On the end of the tube I fitted a 15mm comp cap (and the little spring that preloads the batteries). Voltage is now 6.33, but current 0.18A (sorry, can't remember what the current was out of the tube, but it was far, far more than this).

    So why does the current fall when the batteries are in the tube? Does this matter? (It must use milliamps in use).

    I refitted the Powertube and the display worked, for an hour or so, then it reverted to the irritating r. I took off the tube, checked it, all OK, refitted it, display worked. For another hour or so.

    Any clues why the thing isn't working? What more can it need than volts and some current? What else could be causing this problem? The sender is inside the tank bund, clean and dry and undamaged.
     
  2. Burnerman

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    I've no idea at all on this one - but would really like to hear the outcome, if there is one....
    How full is the oil tank?
    You presumably tested the batteries with them lying on the bench - or off load. You need the batts to be powering something to measure the correct voltage. However, you popped new ones in? :confused:
    How did you check the current draw? This again can only be checked with the meter in series with a powered component, and the draw willl be in microamps.
    It could be worth a call to the manufacturer...my own gear is an Apollo, but there's a few of your type around me. Cheers!
    John :)
     
  3. TicklyT

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    The current measurements you made are meaningless and could easily have done for the batteries!

    An ammeter (or current range on a multimeter) presents near enough a short circuit between the meter leads.

    With a dead short across their terminals, the batteries will deliver all the current they can. The only limit is the internal resistance of the batteries. If they had been, say, lead-acid cells instead of alkaline cells, you would also now need a new meter. 3.6 Amps is probably ten times the maximum current the batteries are designed to deliver without any internal damage to them.

    If you need to measure the current, the correct way to measure it is to connect the meter in series with the load the batteries supply.

    A more significant reading is the voltage across the battery terminals whilst supplying the load. At the end of their life, the voltage of one or more cells in a battery may collapse completely when the load is connected, only recovering when they are disconnected. That's something a high impedance volt meter will not detect when applied to a battery with no load connected.
     
  4. Kes

    Kes

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    Thanks, I shall stop trying to fry my meter.

    Strangely enough the display worked for an hour or so then stopped, and did this both times after I disconnected and reconnected the Powertube. However after leaving it for several hours I noticed that the display was now showing a level instead of an error message, so I'll see if this happy state continues. The level is 1 (the display failed at the end of the level 2 phase). We have ordered a supply and I'll see what the display shows when the tank is filled.

    One wouldn't think that there's a lot that can go wrong when refitting batteries (apart from meddling with meters) so the behaviour of the display is puzzling. Let's hope it has settled down now.
     
  5. jonvic42

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    There are a few red herrings here !
    As TicklyT says the current reading is irrelevant.
    The batteries will only last about five years and the important information is that you can knock the end cap off the copper tube.
    I held the tube as gently as possible in a vice and used a small chisel around the perimeter of the cap.
    A little damage doesn't matter, since pushing the cap back on after the new batteries are in place will reform the profile.
    It is also worth mentioning that the battery voltage can be checked with a meter at the bnc type connector before removing the cap. It should be at least six volts.
     
  6. muggles

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    Welcome to the forums Jonvic. The last post on this topic was in February, I should imagine the issue is sorted by now. Newer stuff is on the first page ;)
     
  7. dave88

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    The transmitter is placed right on top of the tank in a Hazardous area. (Risk of fire and explosion.) Threrefore the technical spec and maintenance of the device is stringent although the average user may not realise it. Watchman do not quote a spec such as ATEX but do state the suitable use of the device.

    There will be a resistor in series with the batteries to limit short circuit current and thereby reduce the risk of having a spark right where the inflamable gasses are. That is why the batteries will show a much higher short circuit current when tested out of the battery container and very much restricted when in the container.

    The device suppliers have a commitment to safety and must meet the Hazardous area specifications in design manufacture and testing. There is a cost to doing this. £50 plus per battery tube perhaps!
    If you break the rules and refit the batteries in the tube yourself, then best to take it well away from the tank when doing this as would be natural anyway. Make sure it is well sealed before putting it back.

    Replacing the 4 AAA cells should be all that is needed for another 2 to 5 years operation. If not then you have a fault in your system. Bad battery connections being the most likely. I have tried myself with limited success. I had an intermittent fault which I put down to dirt or grease in the battery connections and eventually gave up.

    The Watchman Sonic is the latest model and comes with a procedure for changing the battery (I am told by my installer every 2 to 5 years). I have just upgraded to the Sonic and hopefully I will be OK for some years to come.

    Best of luck.
     
  8. Grantgardens

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    I Had a similar problem with a powertube! Unscrewed it from the transmitter and holding it in my hand used the side of a chisel to gradually knock the end cap off. removed the spring and placed it in the cap, knocked out the 4 aaa batteries, replaced with a little grease to help, tapped the end cap back on, all working fine. Total time 5 mins, tools used old chisel (not the sharp end!). Very, very, easy job.
     
  9. nealcrowborough

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    I have had the same problem with the batteries going flat. As has been pointed out, the 4 AAA batteries are stacked up inside a length of 15mm copper tube. Rather than risking distorting the tube, I found that a 15mm compression nut could be slid along from the bottom end (I found it easier to remove the plastic info label) and by drifting it with a piece of wood, the copper cap came off very cleanly. Replacing the batteries is dead simple (all +ves downwards), and the cap fitted back perfectly.

    Thanks for the posting - saved me £30!
     
  10. RobDen

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    Up in the Lake District ... rain ... removed the whole thing and took it inside ... found this wonderful blog, followed the instructions, took the copper top off, inserted 4 AAA batteries and hey presto it worked. Thanks again gang ... would have bought a new one or replaced the whole system. Thank God for the internet! I suggest we change the title of the Post
     
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  11. crocky48

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    Thanks everyone. I can't describe the feeling of elation that swept over me when, after slipping four reasonably-priced AAA batteries into the tube and plugging the device in, it all worked. Not that I'm expecting a reply but I've written to the manufacturer suggesting they supply screw tops to render the whole business much simpler. In an age of combating waste, how can they justify the disposal of all those perfectly good copper sleeves simply to boost their ill-gotten gains. In the unlikely event I get a reply, I'll let you know what they said. Meanwhile, thanks again.[/b][/quote]
     
  12. steveM4

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    Ditto crocky48 - appreciate the advice here on how to replace the batteries.

    Just to help anyone who has the same display that I did:
    The watchman was flashing 3 and c alternately.
    If you look at the watchman instructions it states that c is a "connection fault" and "This indicates that damage may have ocurred to your Watchman transmitter and it has an internal fault. A replacement product will be required, please contact Sensor Systems"

    However, for me it was just a case of new batteries - job done

    Cheers
     

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