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Old 10-12-2008, 11:12 PM   #1
Join Date: Aug 2008
Location: Idaho
Posts: 4
Question Holding tank heaters

I have a 2007 Sierra Sport sv I bought used 3 months ago and have been menaced with some electrical issue with it every since. The latest problem in the form of a story/question. I flipped the switch to the holding tank heaters and snap- the 15 amp DC fuse blew. Probably a bad fuse, put a new one in it and snap. Well, I recently pulled the "American" converter out due to it's demise and replaced it with a "Xantrex Truecharge" and thought maybe I had done something in this process, as the holding tank heater switch is right next to the distribution panel. Rewired/checked the switch (2 position lighted rocker switch with earth, supply,& load terminals) and all should be well. New 15 amp DC fuse and snap. What in the heck. So 29 degrees and not one to give up easily I crawled under the RV. I spied the romex coming through the floor and into the foam/insulation surrounding the grey water tank area, subsequently leaving in the form of romex and traveling a short distance and into the foam/insulation surrounding the blackwater tank. There are 2 AC style pig tails (look like extension cord ends coming from the foam area the romex disappears into. After a lengthy explanation the questions! Do the tank heaters run off AC or DC? Are the heaters thermostatically controlled(trying to pin down the make and model currently)? There is obviously(maybe not so) a short causing the fuse to blow so quickly, where might this short be likely located? (I have traced all of the wires from the switch, distribution panel, through floor and into the foam). My holding tanks are empty but the fuse blows in less than 2 seconds. I assume that the heater are on the outside of the tank? Any help is much appreciated as I want to hunt and poop safely this weekend!

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Old 10-13-2008, 09:20 AM   #2
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Location: Chelsea, Alabama
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See if there is anything here in the FAQS that will help or maybe a phone number you can call to help trouble shoot the problem.http://

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Old 10-13-2008, 11:04 AM   #3
Join Date: Aug 2008
Location: Idaho
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Thanks for the input. I read the FAQS and did find a little help. I think I have 2 sets of heater but I have to call them. One AC and one DC.
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Old 10-13-2008, 10:39 PM   #4
Join Date: Aug 2008
Location: Idaho
Posts: 4
Thumbs up Problem solved!

I figured it out today. If anybody is curious I will explain my solution.

1 rocker switch + 1 circuit at distribution panel + 1 12 gauge stranded wire + 1 15 or 20 amp DC fuse does not equal the needed amperage for 3 Ultraheat AM-Model 3600 Tank Heaters at 9 amps each (other models have different amp needs). Other info- should run a "minimum 10 gauge stranded wire" for each of these heaters (Ultraheat's engineers)

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Old 10-14-2008, 07:13 AM   #5
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Location: Louisville, KY
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So you're saying you need 27 amps of DC to run your tank heaters?
That's a big load on battery or converter.
I wonder why they aren't AC???
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Old 03-20-2009, 06:49 PM   #6
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Location: Muskegon
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some holding tank heaters are AC/DC. There are aftermarket ones I've seen for about $129 out of the catalog that can operate on either. You can wire them up on their own switches, or leave the 12v completely unhooked to avoid accidental battery drain on a cold day, since the heaters are thermostatically controlled.

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