'07 H38 - WEMA 2 Tank Gauge - Correct Voltage Output to Senders?

[flightlead404]

I have the two tank WEMA gauge for fresh water and holding tank. The gauge body itself is marked UPWH and uses a DPDT selector switch to switch between tanks.

Recently both tanks stopped indicating. I suspected the gauge since I think it unlikely that two sensors failed at the same time. However the gauge checks out. I have good ground, good power to it, and doing the troubleshooting open circuit/shorting shows empty/full.

The only thing I question, while there is +12v going to the indicator, the indicator output to the senders is 5.4v. Is this correct, or should it be 12v?

 

[JamesG161]

WEMA = KUS-USA
This is their troubleshooting guide...

 

[Peggie Hall HeadMistress]

All tank level monitors that use internal sensors in a waste holding tank have the same problem: the animal fats in waste build up on the sensor causing it to cease reading the level in the tank. The only cure: remove the sensor and clean it by hand with scrub brush in a strong solution of detergent (Dawn will do) and water...usually necessary every couple of years. Although this isn't a problem in water and fuel tanks, it may be possible that the buildup on the holding tank sensor could cause the panel to stop reading either tank.

Just a top of the head thought...

--Peggie

 

[flightlead404]

WEMA = KUS-USA
This is their troubleshooting guide...

Have that, does not answer the question

 

[flightlead404]

All tank level monitors that use internal sensors in a waste holding tank have the same problem: the animal fats in waste build up on the sensor causing it to cease reading the level in the tank. The only cure: remove the sensor and clean it by hand with scrub brush in a strong solution of detergent (Dawn will do) and water...usually necessary every couple of years. Although this isn't a problem in water and fuel tanks, it may be possible that the buildup on the holding tank sensor could cause the panel to stop reading either tank.

Just a top of the head thought...

--Peggie

Can't imagine how one stuck sensor would cause the other to fail. Circuits are completely isolated. A DPDT switch disconnects one and connects the other to read. Either none or one are connected at a time.

Also, tanks read empty, not some intermediate value.

 

[JoeWhite]

Can you remove both he gauge and sensor from one tank and wire them on a bench and see if it works. If so then there must be a wiring problem. You can also measure all the voltages when they are working as expected.

 

[flightlead404]

Can you remove both he gauge and sensor from one tank and wire them on a bench and see if it works. If so then there must be a wiring problem. You can also measure all the voltages when they are working as expected.

Yeah, the the intent here is to avoid doing exactly that. If I know the voltage output from the gauge is correct then its almost certainly a common ground issue (still looking for that) or unlikely but possible both senders failed.

If the voltage is incorrect then I know the answer right away.

 

[justsomeguy]

Although this isn't a problem in water and fuel tanks

I do find this problem in my aluminum water tank. After a boisterous sail, the chlorine hydrate precipitates in the bottom of the tank get stirred up and limits the float's ability to remain true.
Not a big deal to pull the gauge and rinse, but if lumpy conditions persist...

 

[sailcapt340]

After my Wema Sensor fresh water float completely deteriorated, still trying to figure that one out. I spoke with Henry at Wema in the UK. He can outline the proper testing voltage and procedure for you. He is really very helpful. hello@wema.co.uk
He can better tell you the major difference in Wema USA and Wema UK. You want Wema UK.
I have an earlier posting from about 2 months ago “Wema Fresh Water Gauge Sending Unit” you can read here for some help.

 

[Ward H]

Is this correct, or should it be 12v?

No, it shouldn't be 12v, according to the guide:

5.) Check to see if you have power from the gauge, to the sending unit (black wire). The sending unit receives DC power from the gauge. The reading at the sending unit (black wire) will be less than the input voltage at the gauge (red wire).

I have good ground, good power to it, and doing the troubleshooting open circuit/shorting shows empty/full.

d. The gauge needle, will:

• On the American version gauge (240 . 30 ohms), stay at Empty. Ground the black wire (at
  the gauge end), and the needle will go to Full.
  IF THE ABOVE-MENTIONED TEST IS SUCCESSFUL, THERE IS NOTHING WRONG WITH THE GAUGE. IF NOT SUCCESSFUL, REPLACE THE GAUGE.

Sounds like it is time to check the ohms of each sender. Maybe fill the water tank half way. Ohms should be between 30 and 240.

Did you check the continuity of the DPDT switch?

 

[flightlead404]

No, it shouldn't be 12v, according to the guide:

5.) Check to see if you have power from the gauge, to the sending unit (black wire). The sending unit receives DC power from the gauge. The reading at the sending unit (black wire) will be less than the input voltage at the gauge (red wire).



d. The gauge needle, will:

• On the American version gauge (240 . 30 ohms), stay at Empty. Ground the black wire (at
  the gauge end), and the needle will go to Full.
  IF THE ABOVE-MENTIONED TEST IS SUCCESSFUL, THERE IS NOTHING WRONG WITH THE GAUGE. IF NOT SUCCESSFUL, REPLACE THE GAUGE.

Sounds like it is time to check the ohms of each sender. Maybe fill the water tank half way. Ohms should be between 30 and 240.

Did you check the continuity of the DPDT switch?

yeah I wish the doc actually stated a voltage rather than that very handwavey statement. I'm convinced people that write "technical" documents never actually have to use them. Certainly in my space they don't. Which is partly why I have a job I guess lol

yep, tested the switch. its fine.

 

[Dan_Y]

The water tank sensor went bad on our '08 h36. But because both the water tank and holding tanks read empty with some contents, i made the bad assumption it was the display. I installed new tank sensors and display only to find the holding tank side still not working, but water tank now worked. Then i realized that the holding tank, which has the curved hull shape on one side, is 16" deep on the square side opposite the curved side. The 8-INCH deep sensor sits on the 16-INCH deep side of the tank. So it takes at least 4 or 5 inches of waste water in the tank before it registers anything above Empty...so i did not need to replace the waste tank sensor....doh.
Dan

 

[flightlead404]

The water tank sensor went bad on our '08 h36. But because both the water tank and holding tanks read empty with some contents, i made the bad assumption it was the display. I installed new tank sensors and display only to find the holding tank side still not working, but water tank now worked. Then i realized that the holding tank, which has the curved hull shape on one side, is 16" deep on the square side opposite the curved side. The 8-INCH deep sensor sits on the 16-INCH deep side of the tank. So it takes at least 4 or 5 inches of waste water in the tank before it registers anything above Empty...so i did not need to replace the waste tank sensor....doh.
Dan

Right now the holding tank has to be pretty close to full, as we pumped out a week ago and have been living on board. The water on the other hand is dead empty as we actually unexpectedly ran out of water and had to raid a local marina in the dink with a couple of home depot buckets (can't get in anywhere here for water, pump out, or fuel, its a mess rn).