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Old 11-06-2013, 07:34 PM   #1
Join Date: Aug 2013
Posts: 60
2005 Jayco 24SS: Tank heaters are wired in series - normal or mistake?

Each tank (black, gray, fresh) has a single Ultraheat TH-726 heater pad, nominally 13.5 volts @ 8.6 amps. The total heater current draw is about 12.5 amps on a circuit fused at 15 amps. It appears the black and gray tank heaters are wired in series, as each draws only 4.3 amps, instead of 8.6 amps. I haven't measured the fresh water tank heater, but since the remaining heater current is 8.2 amps (12.5 - 4.3), it's probably getting the full 13.5 volts.

If they are in series, the black and gray tank heaters are producing only 28 watts each, instead of the 116 watts each if they were in parallel with the fresh water tank heater, and also getting the full 13.5 volts. That's a lot less wattage, so I'm thinking these tanks are not going to be protected very well.


1) Are the two tank heaters supposed to be wired in series?

2) If not, is there an easy way to correct the situation? I could run two extra wires between the tank heaters to put them in parallel, then change the 15 amp fuse to 20A, but maybe someone has a better idea.

3) Is there good way to add insulation to the tanks? The bottoms of the black and gray tanks are fully exposed, so I'm thinking of strapping some 1/2" pink building insulation foam to the bottom of each, and wrapping the drains with heat tape and pipe insulation. The fresh water tank is harder to reach, but pink foan could glued to the metal plate supporting it.

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Old 11-09-2013, 10:55 PM   #2
Join Date: Aug 2013
Posts: 60
Update: the heaters are NOT wired in series.

I determined the heaters are NOT wired in series, but in parallel. Each one (black, gray, fresh) draws about 4.3 amps with 13.5 volts on the pad, contrary to the label, which states the pad uses 8.3 amps at 13.5 volts. Now I'm wondering if the pads are mislabeled or incorrectly manufactured.

Question: Do other owners with the TH-726 heater pads also have the same current draw?

Perhaps more troubling is the gray tank heater pad cycles on/off (15-20 seconds each), even though it's 42 deg f (air temperature and there is 7 or 8 gallons of water in the tank that is 45 deg F. The other pads stay on for a long time, until they get near 60 deg F. The pad seems to be well adhered to the tank at the thermostat lump, but I don't have any experience with heater pads. It's not the voltage to the pad, as that stays at 13 volts.

Question: does anyone know why the pad is cycling so quickly, and what can be done to fix it?

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Old 11-14-2013, 11:09 AM   #3
Join Date: Aug 2013
Posts: 60
I called Ultraheat about the pads drawing less than labeled current: basically, the label value applies at the rated voltage when manufactured, but as the panels age, they will draw less current. Also, you must be sure you use the rated voltage when making the measurement, or adjust the measurement accordingly. I didn't ask specifically about the effect of temperature, but got the impression the current draw will change as the temperature of the pad changes.

So, my pads are probably working as designed.
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