I have just experienced 3 nights of temperatures below 20 degress. I turned the tank heaters on but I still ended up with a frozen gray water gate valve that wouldn't budge until today. Even then the drain pipe was frozen. It did drain finally when the day time temperature got up above 40. The black tank valve can be opened but nothing comes out so it is frozen. Something tells me these tank heaters do little if anything unless turned on well in advance of decreasing temperatures or mine are not working. The light is on but I can not tell by feeling the pipes if they are one. Any thoughts?
Understanding how the system works is critical to getting the results you anticipate.
1) They are 12 volt heaters. If you are on battery, 3 or 4 heating pads can deplete your single OEM battery overnight. They require 13.5 VDC to operate efficiently (shore power or generator). They draw 78 Watts of power and at 13.5 volts DC draw 5.8 amps each pad. Lower voltages increase amps to maintain wattage.
2) They "heat" anytime the tank heater switch is "on" (red light on) AND the tank surface temperature is colder than 45F or 5C. It will then heat the plastic until the plastic reaches 67F or 20C and then shut off until the tank cools to 45F again. It will cycle on and off on each tank as long as the temp gets below 45F when the system is on.
3) The TANKS (Black, gray and fresh) have square pads. In SOME (not all) models EXPOSED elbows have an elbow heater. If the elbow is inside the belly it does NOT have a separate heater.
If the tank is empty, the heaters are VERY inefficient as the heat is very localized and the valves can freeze if "wet" but not covered in water. The valves get no heat at all except as transmitted through the water in the tank.
Hope this helps.
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Lou & Freya the wonder dog
2008 GMC Sierra 3000HD Allison Duramax
2019 Flagstaff 8529FL
my switches did have lights on them to indicate power was to them. those lights haven't worked in yrs. in my case, i don't know if the problem is a light or no supply. here, i don't need them so they haven't been a priority.
with that, i wondering if u r indicating power to the heaters?
Our black tank is pretty full because we had family over during the holidays.
We had cold temps and I turned on the tank heaters.
Fresh = empty
galley = empty
grey = empty
Black = I don't have a dump drain at the house and I don't have the nerve to pull the valve handle!! LOL!!
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my switches did have lights on them to indicate power was to them. those lights haven't worked in yrs. in my case, i don't know if the problem is a light or no supply. here, i don't need them so they haven't been a priority.
with that, i wondering if u r indicating power to the heaters?
Good point. No light means blown fuse or bad circuit. These fuses may be located BEHIND the power center in a green or black pigtail fuse holder.
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Lou & Freya the wonder dog
2008 GMC Sierra 3000HD Allison Duramax
2019 Flagstaff 8529FL
We've done okay with our tank heaters in temps down to the mid to low 20s. But if the temps stay below freezing long enough, things start freezing up (like a water line to the sink if the sink cabinet drawer isn't left open to the room heat). I don't think the tank heaters alone are more than a delay in the inevitable for temps as low as you have seen.
The user manual says to turn the tank heaters on when temps fall through 45 degrees and are anticipated to get below freezing.
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We've done okay with our tank heaters in temps down to the mid to low 20s. But if the temps stay below freezing long enough, things start freezing up (like a water line to the sink if the sink cabinet drawer isn't left open to the room heat). I don't think the tank heaters alone are more than a delay in the inevitable for temps as low as you have seen.
The user manual says to turn the tank heaters on when temps fall through 45 degrees and are anticipated to get below freezing.
I also open all cabinet doors to allow cabin air to get into the basement (front storage) of the 5th wheel. I also put a fan on the floor to blow heated air into the kitchen cabinet (where 90% of the plumbing is located.)
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Lou & Freya the wonder dog
2008 GMC Sierra 3000HD Allison Duramax
2019 Flagstaff 8529FL
I'm on shore power so batteries are not an issue. Do the pads put out enough power to be able to feel any heat if you touch the exposed pipes near the valves?
I have access to the shower house here in the camp ground. If all else fails I am heading further south Friday morning so things should thaw so I can get the black tank emptied this weekend.
Unless he's got 2 foot of pipe or more between tank and shut-off valve.
Turbs
I can see where that would be a problem, but in this case a pipe heater would have been installed. I suspect his system is not working (or not being used) correctly.
The pads need to be turned on well in advance of the actual cold temperatures. Once stuff freezes there is just not enough heat from the pads to defrost a frozen anything.
In the aircraft we have two types of ice control systems; one "de-ices" and an the other "anti-ices."
A "de-icer" allows ice to form, then it is removed while frozen. Like wing "boots" that let with wing coat with ice and the boot is inflated breaking the ice off or a prop blade deicer that cracks off ice on the blade using prop rotation forces to sling it away.
An "anti-ice" system is turned on BEFORE you go near ice. It warms the part preventing ice from forming (YOU HOPE). Used on a wing, hot engine air is blown into a cavity behind the leading edge keeping the wing well above outside air temperature so ice does not form. When used on props it is used in conjunction with the de-ice on the blades, but only on the hub where rotation forces are insufficient to sling the ice off if it allowed to build. They "modulate on and off" to maintain a temperature range at all times.
Our tank heaters are ANTI-FREEZING systems and as such MUST be on before temps drop to where you might need them. Waiting until the tanks are cold enough to freeze then turning them on will not work as the system will be overwhelmed. Just not enough BTU to melt something that has already frozen.
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Lou & Freya the wonder dog
2008 GMC Sierra 3000HD Allison Duramax
2019 Flagstaff 8529FL
... Lower voltages increase amps to maintain wattage.
I believe these pads are purely resistive so amps would decrease at lower voltages. They would have to be fed by a voltage regulator circuit (and operated at a lower voltage than supply) in order to do what you suggest.
I believe these pads are purely resistive so amps would decrease at lower voltages. They would have to be fed by a voltage regulator circuit (and operated at a lower voltage than supply) in order to do what you suggest.
Some definitions are in order.
Resistive Load - An electrical load which is characteristic of not having any significant inrush current. When a resistive load is energised, the current rises instantly to it's steady-state value, without first rising to a higher value. An electrical load in which voltage and current are converted to energy in the form of heat; i.e., an electrical heater, incandescent bulb.
Inductive Load - An electrical load which pulls a large amount of current (an inrush current) when first energized. After a few cycles or seconds the current "settles down" to the full-load running current. The time required for the current to "settle down" depends on the frequency or/and the inductance value of the Inductive load
Being purely resistive, a 1000 watt heater would draw 1000 watts.
My logic using a constant power requirement went like this.
Power = Volts x Amps
Power is measured in watts so a pad that draws 120 watts of power when "on" will draw 10 amp at 12 volts.
That same pad at 13 volts would be 120/13 or 9.2 amps.
For your assertion to be correct, the power requirement would have to vary and not stay fixed. As I understand it, an inductive load varies by applied voltage (like your air conditioner). As the voltage goes down the amount of amps required to turn over the compressor and fan motor goes up A LOT until everything comes up to speed.
I found my error. Those who like seeing me wrong, please bookmark this thread.
When I realized my simultaneous equations were not giving me the results I expected, I threw out all assumptions and went "back to the drawing board".
Here is why you are correct and a valuable lesson is here for everyone who uses a Resistance heater in low power conditions.
My example below assumed the power required stayed constant. It does not.
Power AVAILABLE is voltage dependent. That was my mistaken assumption.
So back to my simultaneous equation.
V=IR or Voltage = amps times circuit resistance in Ohms.
Assuming the resistance of the heating wire in our heating pad (using the ACTUAL numbers from the manual) stays constant for both incoming voltages and that heating coil is RATED at 78 Watts at 13.5 volts.
The instantaneous current required for that 78 Watts to be available is 5.8 amps at 13.5 volts. So, if we decrease the incoming voltage to 12 DCV, then what happens.
We need to solve 2 equations with 2 unknowns R of the heater and I2 of the lower voltage.
First equation:
V1 = I1 x R or 13.5 volts = 5.8 amps x R
Second equation:
V2=I2xR or 12.0 volts = I2 (UNKNOWN amps) x R
Solve the second equation for R
R = 12 volts / I2 (unknown amps)
Substituting the second equation for R in the first equation
13.5 volts = 5.8 amps x (12 volts/I2)
Solve for I2 = (5.8 x 112)/13.5
I2 = 5.15 amps
So the Available power of our "heater" at 12 volts and 5.15 amps is 61.8 Watts. This is only 79% of the "heat" available at 13.5 watts or 21 % LESS efficient.
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Lou & Freya the wonder dog
2008 GMC Sierra 3000HD Allison Duramax
2019 Flagstaff 8529FL
...
My logic using a constant power requirement went like this.
Lou,
there is nothing in a resistive load that indicates that it will have a constant power requirement. A lightbulb, or these pads, will have reduced power usage/output at reduced voltage.
I thought perhaps you had actually measured increased amps at your TT input, and thinking about that made me realize that we are both right.
If you're looking at the operation of these pads as your TT battery voltage drops, then what I said is true. If you're looking at current into your TT from the line, the converter is keeping constant voltage on the battery so the TT input current goes up when the TT input voltage input drops! That makes everything that's 12v in your trailer look inductive (or at least constant-power).
I think I did not learn anything (I am old gimmeee a break!).
My PREVIOUS error on this board was this very same problem! We were talking about running the water heater on electricity or propane as I recall. The result of THAT thread was "if you want hot water in the summer; use propane" for the exact same reason here.
I'm old too, so we all need a break. To simplify matters in DC power we have to understand the known from the un-known. If the heaters are normally 12 v and we know that they are 120 watts then (P=V*A) (120= 12* A) (A=10 amps) Now we need to know the resistance of the heat pad. (E=I*R) (12=10*R) (R= 1.2 ohms) Now the resistance is the only thing that cannot change in this case it's fixed , therefore if the voltage drops so does the power. If the volts are now 10 V and R is 1.2 power is (E=I*R) (10=I*1.2) (I=8.333) Now power or watts will be (P=V*A) (P=10*8.33) P=83.33 watts less heat. The numbers used are for illustrative purposes only!! You're pretty good for a flyboy I too spent 36 years in this mess I mean Aviation. Have a good day!
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