melting temperature of waste tanks

I think your idea is a good one and you will not overly soften the tank . I assume you won't turn it on until the temps drop to 32F or less and that the 166F that you measured was directly on the inside face of the heater(that would interface with the tank). In that cold temp there would be a lot of heat loss getting to the inside of the tank so you won't see 166 F inside the tank. I would lay a 1/4 in piece of any plastic on top of the heater like a plastic bowl with water inside it at the temperature you would use the heater and them measure the temp inside the bowl to assure yourself you won't soften the plastic tank too much. Good luck with your project.

Another snide remark brought to you by the forums latest Troll: Happycamper

He wasn't responding to me genius. Give it a rest because it's getting old

garyemunson wrote:
Hehehehe! I was going to ask what on earth did you eat......

Per your response to SCVJeff,

He had just his fruit loops for breakfast. Still digging through the carton for those giveaway toys.
Just a spike in his glucose and hopefully things will make more sense next time.

As for PT's query about ABS melting coefficient, I suggest looking up under ABS properties on ASTM (American Society for Testing Material.) There is also a section in there for military specs.
Right off my head, ABS is rated 140 degrees F. Your initial test at 166F is a bit pushing it. It will suffer deformity but probably won't melt owing to heat transfer to tank.
Also as I understand, most water bed heaters are rated 300 watts.

Hi,

I do plan on using a thermostat. But feed back to the control may not be what I get when using a 600 watt fan based heater.

One time in another century, we were moving so I drained the waterbed. I forgot to turn off the heater. About an hour later we smelled something. The heater had melted the waterbed and charred the plywood deck black.

I don't know if I would use one on a tank that might be dry.

As others have noted, the mass and the amount of surface are going to keep the temperature of the interface lower. If it was my heater of choice, I'd like to control the heating pad so that it operates at the right temperature for the application.

FWIW, I'm going to try an unorthodox tank heating apparatus on my trailer. I plan to use a gutter heating cable deployed under the black tank and, if it's possible, alongside the drain piping. I've actually succumbed to the design idea of totally enclosing the tank with a framed, insulated enclosure and extending the enclosure to envelop the waste plumbing and dump valves. This would be an effort to make the tank and dump lines serviceable at very low temperatures. An added benefit of heating the waste tank is that it is located beneath the bathroom floor and extends under the bunk area.

My effort will be to build a steel cage under the tank, face it off with sheet goods, probably vinyl coated aluminum as I have some and it is inexpensive. I will also face off the inside of the enclosure walls with a sheet foam insulation board. This will make that insulated enclosure very easy to heat and if my gutter tape is deployed correctly, heat the tank and dump piping.

One wrinkle into this is I now have a single tank. Do I install a second gray tank into this enclosure and how will that fit? It is just a wrinkle. Anything can be done.

Sorry to go so far off topic with my own needs but I hope it illustrates that there is more than one way to keep a waste tank heated. The waterbed heater make work excellently. One test you could perform is deploy the heater under some filled water jugs to see how the heat transfer works and what temperatures are at hand. Good luck!

Hehehehe! I was going to ask what on earth did you eat......

Yeah they do get hot, but don't forget that those heaters have 400g of water on top of them, so in THAT service hardly get warm. You want to turn frozen into cold with nowhere near that volume and a considerably denser insulator, so IMO you might have a problem attempting to back it down. Might want to see if it can stand an AC dimmer on it, or bond it to a thin aluminum plate to protect both.

pianotuna wrote:
The reason for the question is someone has given me a water bed heater. It is a large flexible pad. In testing it gets up to 166 f (76 c).

Are the holding tanks ABS or are they polyethylene?

ABS.....waste tanks

IF you plan on using that water bed heater then you need to use a thermocube to control on/off temp

TC-3 would work (on at 35*F/off at 45*F)------rv waste tank heater pads turn on at 40*F off at 60*F
but the TC-3 thermocube would keep liquids in tanks from freezing

Thenocube

The reason for the question is someone has given me a water bed heater. It is a large flexible pad. In testing it gets up to 166 f (76 c).

Are the holding tanks ABS or are they polyethylene?