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Old 13-01-2016, 15:56   #1
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Can't figure out the electrics on my holding tank.

I have a Sealand holding tank with three tubes suspended in the tank with floats at the end to measure the level of fluid. Each tube has two wires coming out the top of the tank. The wires have been cut and the display is missing. I therefore want to make my own simple light panel display but I cannot figure out how the circuit works.
I assumed that a hanging float would just interrupt a live (or negative) feed and that the rising float would complete a circuit similar to a float switch but this is not the case. I've put a continuity tester on the wires but they do not form a circuit either with the float up or down. Google is not interested in helping and just wants to sell me a whole new system. Can anyone assist?
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Old 13-01-2016, 16:46   #2
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Re: Can't figure out the electrics on my holding tank.

Not sure but I would try an ohm meter. It probably works like a fuel tank float sensor. I would hazard that the swipers are NFG. You can YouTube checking a fuel tank guage and it will give you an idea .

Hope this helps
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Old 13-01-2016, 18:41   #3
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Re: Can't figure out the electrics on my holding tank.

Thanks for the idea, I just tried it but it didn't work. The literature for the (missing) display says that there are four display options; empty, 1/3, 2/3 and full. Also, the floats on the tubes don't have much movement, they move a maximum of 1/2" up the tube. Seeing as there are three tubes this would perhaps suggest that the sensors are more of an on/off than a gradual resistance...but I really don't know!
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Old 13-01-2016, 19:03   #4
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Re: Can't figure out the electrics on my holding tank.

I agree. Perhaps it is one of the systems that work on air pressure. I can't remeber the name right now but will have a look tomorrow. Do you have any info on the make or pics?
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Old 13-01-2016, 19:11   #5
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Re: Can't figure out the electrics on my holding tank.

If set at different depths the three transducers would correspond to the levels of the gauge and would be simple on/off mechanical switches (indicated by two wires and not three). It's entirely possible they no longer work, hence why they've been disconnected.
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Old 13-01-2016, 19:47   #6
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Re: Can't figure out the electrics on my holding tank.

It's a Sealand 8846. Here is a photo...

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Old 13-01-2016, 19:59   #7
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Re: Can't figure out the electrics on my holding tank.

You've got a commoned wire and 3 outputs - one for each sensor. I'd still reckon they're an on/off mechanical switch, especially if the float thingies move up and down. Remote possibility they could be a resistive or capacitive sensor like a MAF sensor. If the former I'd bet they relied on the contact to close when the float moved upwards and they are now gunked up. If the latter, the gauge would have needed the electronics and calibration circuitry to correctly interpret the sensor output and testing with a meter becomes that little bit harder. Looks like they could be disassembled easily enough?
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Old 13-01-2016, 20:08   #8
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Re: Can't figure out the electrics on my holding tank.

This may be the wiring diagram. It has three sensors like you say and came up when I searched for it.

http://dometic3frontend.qbank.se/epi...10ff08f14c.pdf
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Old 13-01-2016, 20:31   #9
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Re: Can't figure out the electrics on my holding tank.

I've managed to find the instruction manual which shows the electrical diagram... http://www.leesan.com/uploaded_files...s%20manual.pdf

It seems that they are simple on/off switches. My continuity test shows none of them making a circuit so I guess they are all dead. Thanks everyone for your help.
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Old 13-01-2016, 20:53   #10
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Re: Can't figure out the electrics on my holding tank.

I had a similar unit, they are magnetic reed switches, with a magnet in each float. If any liquid got into the tubes, the switches and/or wiring has corroded. The magnets can also deteriorate. If your ohmmeter shows a contact closure when you slide the float, you can wire a small LED with series resistor on each for your 1/3, 2/3, full indications.

I replaced the reed switches once (messy) but they eventually failed again. Went for a Wemo resistive sensor when I changed the tank.


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Old 13-01-2016, 21:12   #11
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Re: Can't figure out the electrics on my holding tank.

The air pressure type ( not vacuum ) is a tank tender. You manually pump to create a very small pressure. The gauge reading is differential pressure.

You need to calibrate them so you can correlate the differential pressure with volume empty or full. Any shape tank.

We have a 10 port tank tender. They were invented for medical use. Very reliable, very high quality. No moving parts on the tanks. Just a pressure feed line.

If you use them on a holding tank you need to include a check valve to avoid clogging the pressure line.

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Old 13-01-2016, 22:17   #12
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Re: Can't figure out the electrics on my holding tank.

Quote:
Originally Posted by Privilege View Post
I have a Sealand holding tank with three tubes suspended in the tank with floats at the end to measure the level of fluid. Each tube has two wires coming out the top of the tank. The wires have been cut and the display is missing. I therefore want to make my own simple light panel display but I cannot figure out how the circuit works.
I assumed that a hanging float would just interrupt a live (or negative) feed and that the rising float would complete a circuit similar to a float switch but this is not the case. I've put a continuity tester on the wires but they do not form a circuit either with the float up or down. Google is not interested in helping and just wants to sell me a whole new system. Can anyone assist?
The wiring for the SCAD Profile gauges Scad Tank Monitors is the same as the wiring for your SeaLand Tankwatch III (or whatever Dometic has re-named it)...the external sender is the only real difference. Scroll down to the instructions for the "Solo" unit for all the instructions you need to do what you want to do.

However, IMO you'd be better off buying a whole new system with a sender that attaches to the outside of the tank. 'Cuz by the time you assemble all the components to make your own panel you'll prob'ly have spent more than 50% of the price of the Solo panel...and, internal senders are ok for fuel and water, but the animal fats in waste build up on 'em and clog 'em...making it necessary to remove the sending unit about every two years to clean 'em. Fun job.
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Old 13-01-2016, 23:03   #13
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Re: Can't figure out the electrics on my holding tank.

I'd say your sensor switches are crapped up. You can make an Arduino based display for about $40 in materials if you want to spend the time.
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