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Old 09-09-2008, 04:15 PM   #1
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Location: Louisville, KY
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Tank/battery monitor is Inacurate


I believe most trailers/motor homes and 5ers
now come with a holding tank monitor?

Our Forest River Ultra Lite has one and I knew from reading
here and elsewhere that they were often inaccurate.
This weekend we found out how inaccurate ;-(

Our monitor panel has 4 LEDs for Full, 2/3, 1/3 & Empty
It monitors fresh tank, gray, black and battery.
We know from experience and visually looking at the fresh tank
that the monitor is not right.
My top "full" sensor in the fresh tank is
so close to the top that as soon as we use any water at all we drop
to 2/3. We still have over half a tank when the monitor says 1/3.
OK so I can live with that. Our gray tank often says 2/3 after just
one sink of dishes. We have a 20+ gallon tank!!
I don't think so!

The real kick in the butt was this past weekend.
We were dry camping at Mammoth Cave National Park.
I foolishly did not plug my trailer in at home the night
before. I thought our battery was full so I just lit the
LP fridge and went to bed. The next day we packed up and
headed out. When we arrived at the CG our monitor panel
said the battery was 2/3. No problem I thought.
By dark with only very minimal use of the lights we noticed
the water pump was sounding tired and the lights were looking
dim. I plugged my truck back in so we would have lights and
could watch the DVD we brought. It was raining outside so
the evening camp fire was out.

The next day I ran my little $130 generator for an hour
with the trailer plugged into it
to charge the RV battery back up, I thought.....

2nd nite same thing-- monitor says battery is 2/3 soon after that
water pump sounds tired and lights are dim.
I plug the truck back in a 2nd time so we can watch the news
and have some lights.

Long story short-- when it came time to leave on Sunday morning
my truck was dead!! I got out my jumpers and prepared to
ask the first guy who drove by for a jump. The campground was 1/3-
1/2 full and people were definitely outside and some were firing up
those big ole motor homes to head on down the road.
After a few minutes of no one coming by my truck I got out
my little generator which just happens to have 12v 8amp output.
I hooked it to my truck battery and fired it up. In 5 minutes my
truck started fine and I shut off the noisy little generator.

When we got home I plugged in the trailer for 24 hours to
charge the battery.
Yesterday at home I did a test of my battery and monitor.
Using a voltage chart downloaded here--
I first measured the voltage at the battery and found it to be
fully charged at 110%

I unplugged the trailer from our house power and
I turned on 3 dual bulb ceiling lights for a total of 6 bulbs
and proceeded to measure battery voltage every 30 minutes.
Using the chart
I watched my battery pretty much discharge at a rate of 25%
per hour. In 3 hours I was down to 12.04 volts using a good
quality digital meter. That is almost exactly 25% charge
remaining. I shut off the lights and ended the test at that
point. I pushed my monitor button and it READ BATTERY 2/3 FULL!!!

No wonder we ran out of juice right after the monitor said
2/3 full. We were actually nearly discharged at that point.
I've since read the manual on my power center and UN-like the
one in my previous Shadow Cruiser, the one I have now does NOT
fast charge the battery so when I ran my generator for an hour,
I thought I was really putting a charge in the battery when
in fact I was just getting started.

Now I am looking for at least a 10 Amp charger and would really
like to have one that will put out 15 or more.
Many have 10 amps with some larger rating for "engine cranking"
but I just want a fast charger.

Moral of the story-- don't believe your cheapie wall monitor.
It gives you a false sense of security when it's probably lying about
tank levels and battery charge too.

You can't beat a digital volt meter. Radio Shack has models
from $20 that will do a good job. I don't know if WalMart
sells digital meters or not.

Sorry to be so long winded but "you've been warned" Hah!!
Happy Camping!

Dan & Rita D
2004 5.3L Silverado 1500 ext. cab 2WD
1999 Suzuki Intruder Motorcycle
Blue Ox WD hitch, AirLift load levelers

Camping days 2010-53, 2011-47, 2012-41,
2013-41, 2014-31, 2015-40, 2016-38
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Old 09-09-2008, 07:55 PM   #2
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powerboatr's Avatar
Join Date: Aug 2006
Location: homebase Quitman Texas at Lake Fork
Posts: 1,388
sorry about your close call
thanks for the great info
but my friend have joined the "inaccurate readings club"

after the first time i boiled my batteries dry, i put myself on a check list to eyeball em every other month.
mine were doing the same thing yours were, 2/3 but, DEAD as a door nail, even my generator battery.
you'd think that the $$$ we pay we could get a better set up
i did install a surge guard for my a/c power that shows current amps used and voltage for both shore power and generator power
i need to add a real 12v watchdog

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Old 09-10-2008, 09:13 AM   #3
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Location: St Louis, Mo
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I have seen some gizmos, volt meter that you plug into an outlet in the camper. I wonder if those would be more accurate.
Seasonal site camping
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Old 09-10-2008, 10:44 AM   #4
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Location: Huron, Ohio
Posts: 67
In regards to the tank levels not being accurate, I've seen the same thing. Has anyone used the sensors that can be installed on the outside. I've seen them advertised, but unsure if they really work.
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Old 09-11-2008, 12:13 AM   #5
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Location: Enumclaw, WA
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This is really not new information to those who are accustomed to RVs. The tank monitors are especially inacurate because of the fact that the sensors are really just two screews drilled through the side of the tank. The fluid in the tank bridges the gap and completes the cirucit. Since they only install these "monitors" at 1/4, 1/2 and 3/4 readings, anytime you drop below one the gauge will read the next one lower. IE if your water drops below 3/4 then the gauge will only read 1/2 full. The same is true of holding tanks just in reverse. It's one of those "quirks" of RVs that you just have to live with. The power "gauges" that use the LEDs are useless too. Much better systems are available. Look for companies that specialize in solar energy for sources of good power level monitoring systems. Or as mentioned above, a good digital multimeter is also a good choice.
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Old 09-11-2008, 01:06 PM   #6
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In WalMart and BassPro Shops you can buy a power meter that plugs into a 12v dc car outlet. You can then buy an outlet from Autozone, connect directly to battery, and check the voltage there. Also, you might to invest in a 5v solar battery charge panel to help battery charged while dry camping.

Is there not a test point on circuit panel to check the battery input?


The Hunts
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Equal-i-zer Hitch
2009 Flagstaff V-Lite 30WRLS
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Old 09-15-2008, 09:03 PM   #7
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Location: Tampa, Fl
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That is a fact NWJeeper. When i first started camping i was wondering why the tank would go so quick from 1/4 to 1/2 and from 1/2 to 3/4 untill i got used to it. I did have a problem with my 08 Forest River Charleston. The black tank was showing on the grey tank indicator at the monitor and the grey tank would show on the black tank. You think i started swapping wires? Wrong!!! I relabeled the monitor pannel.

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