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Level (liquid tanks} sensors, always full or always empty

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donc13

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Level (liquid tanks} sensors, always full or always empty
« on: September 16, 2018, 10:45:23 am »
So, here's the deal, my fresh water tank reads always full, my grey water tank always reads 2/3rds and my black water tank, always reads empty.   The LP and Battery readings are fine. This is a recent occurrence after driving over a few hundred miles of crappy roads.

I pulled the sensor panel and found 9 wires attach to it.  It would appear 2 wires are ground and +12v wires.  Another 1 for the LP sensor.  I presume the battery level is read via the +12v line.  That leaves 6 wires for sensing the 12 wires for the 3 liquid tank sensors.
That doesn't compute....thus, I presume there is a separate "switch" or relay where all 3 liquid tanks attach and based on which button you push, the relay feeds the appropriate tank leads to the sensor panel.

Can anyone verify that?   And does anyone know where this relay or switch may be installed?

Thanks in advance for any information!

Don
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bftownes

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Re: Level (liquid tanks} sensors, always full or always empty
« Reply #1 on: September 16, 2018, 10:24:27 pm »
So, here's the deal, my fresh water tank reads always full, my grey water tank always reads 2/3rds and my black water tank, always reads empty.   The LP and Battery readings are fine. This is a recent occurrence after driving over a few hundred miles of crappy roads.

I pulled the sensor panel and found 9 wires attach to it.  It would appear 2 wires are ground and +12v wires.  Another 1 for the LP sensor.  I presume the battery level is read via the +12v line.  That leaves 6 wires for sensing the 12 wires for the 3 liquid tank sensors.
That doesn't compute....thus, I presume there is a separate "switch" or relay where all 3 liquid tanks attach and based on which button you push, the relay feeds the appropriate tank leads to the sensor panel.

Can anyone verify that?   And does anyone know where this relay or switch may be installed?

Thanks in advance for any information!

Don

My PC will be my 4th motorhome and I have had 1 travel trailer.  The tank monitors (black and grey)  on everyone of them has never been accurate.  Sorry this doesn't answer your question, but it seems to be a fact of life.

Cheers...
Barry T

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donc13

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Re: Level (liquid tanks} sensors, always full or always empty
« Reply #2 on: September 17, 2018, 07:29:17 am »
Barry,

That I agree with, the usual tank sensors are lousy.  Mine at least used to give me a clue.. Not anymore!
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Ron Dittmer

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Re: Level (liquid tanks} sensors, always full or always empty
« Reply #3 on: September 17, 2018, 01:20:45 pm »
On our old style 2007 monitor panel, the fresh water and both waste water sensors have not been terribly accurate, but have been consistent and useful.  I am not quite as confident with the propane monitor.  The battery monitor is a real deceiver.  When the battery monitor goes from green to yellow, it's already too late.

About our fresh water and waste tank sensors.  We do bleach the fresh water system at the beginning of the season, and the waste systems at the end of the season.  That might be keeping them operating consistently.  Oh.....and we never do toilet #2 in our PC which also might be influential.  We cannot tolerate sewer gas given our at-home bed is only a few feet above the waste vent all year long.

« Last Edit: September 17, 2018, 01:26:16 pm by Ron Dittmer »
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Cropduster

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Re: Level (liquid tanks} sensors, always full or always empty
« Reply #4 on: September 18, 2018, 06:16:10 pm »
I hear you.  We have had some luck in cleaning the tanks well enough to improve the readings.  But still no readings which I would trust.  Same experience as Herr Dittmer, the battery reading is not worth considering. I installed a separate voltmeter which -- knock wood -- appears to be accurate.  The panel LP reading is fairly accurate, although I check the gauge on the tank when I want confirmation.

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Re: Level (liquid tanks} sensors, always full or always empty
« Reply #5 on: September 19, 2018, 02:34:45 pm »
Agree with Crop-duster on the battery & LPG - I try to REALLY purge both black & grey tanks with fresh water when I dump.  Also, some have put ice cubes in the black tank, driven around and said it seems to work.  I had Phoenix install sensors I had bought for a previous unit, and so far they seem pretty good.  Also, others have installed the sensors that mount externally on the sides of the tanks.

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Re: Level (liquid tanks} sensors, always full or always empty
« Reply #6 on: September 21, 2018, 07:15:54 pm »
As I understand how these work there is a sensor at each level with a resistor between them.  The level is determined by the resistance of the circuit.

I think I would be looking at the wires on the tanks to see if they are still all intact.

These sensors are not particularly accurate but what Donc13 reports seems more as if something has changed not just inaccurate.  He also reports rough road so maybe some of the wires on the tanks came loose?

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donc13

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Re: Level (liquid tanks} sensors, always full or always empty
« Reply #7 on: September 23, 2018, 05:27:51 pm »

As I understand how these work there is a sensor at each level with a resistor between them.  The level is determined by the resistance of the circuit.

I think I would be looking at the wires on the tanks to see if they are still all intact.

These sensors are not particularly accurate but what Donc13 reports seems more as if something has changed not just inaccurate.  He also reports rough road so maybe some of the wires on the tanks came loose?

Exactly!   Fresh water tank always full... That's a short.  Black tank, now seems ok.  Grey tank.. Will check wiring.

It's the fact there is only a nine wire connector into the panel.  Let's say a common +12v for all.  Has to be a ground also..  That takes care of 2 wires.  1 for the LPG gauge, no wires needed for battery (other than the already accounted for +12v and GND).  So +12V, GND & LPG is 3 leads.  Leaves me 6 wires yet to account for.

Each tank has 3 level wires and 1 hot (+12v).   

Now I suppose you could tie all the individual 1/3rd, 2/3rds and Full sensor leads to each other... That'd be 3 more wires to the sensor panel (instead of 9 wires) and then just switch the +12v wire to the proper tank.

Ahhh... Screwed up my math.. 3 +12v leads.. One to each tank... Then 1 full lead for all tanks, 1 2/3rds lead for all tanks... And 1 1/3rd full for all tanks.

That's 6.  And that fits! 

 I'll dig more when I get back home.
« Last Edit: September 23, 2018, 05:47:47 pm by donc13 »
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