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Old 10-10-2016, 12:42 PM   #1
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12 volt circuit amperage question

I am installing a 12 volt tank blanket on the freshwater tank to extend the camping season here in Colorado. I was going to pull power from the circuit for the water pump. The water pump is on a 10 amp circuit. The tank blanket pull 6 amps and the water pump pulls 7.5 amps. It looks like the wiring for the water pump circuit is 14 gauge which will handle 15 amps. Will the existing 10 amp circuit on the WFCO 8735 handle a 15 amp fuse assuming the wiring for that circuit is indeed 14 gauge?
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Old 10-10-2016, 04:51 PM   #2
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Why not use the fridge circuit? it is in the same area and need never be used at the same time to blanket is operating.
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Old 10-10-2016, 05:02 PM   #3
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Check your fuse panel, You may have one or two open positions that just need a fuse. Be aware that on a cold night, you could kill your battery quickly. 6A for 8 hr will deplete a 100 Ahr battery if not connected to shore power..
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Old 10-10-2016, 05:02 PM   #4
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Do you have any unused fuse slots on your converter ? That would be a reasonable way if you have the option.
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Old 10-10-2016, 05:37 PM   #5
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I'd check the panel anyway to see if there is an empty position, but pulling the wire might me difficult as well. Sure 14 GA can handle it anyway, but as the OP said, watch your battery that is a lot of current.
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Old 10-10-2016, 05:48 PM   #6
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For simplicity sake and location, it would be easiest use the water pump circuit as I am also installing a switch for the blanket next to the water pump switch. I measured the wire (not the insulation) with calipers and it was around 1.8 mm which is right around 13 or 14 gauge. So as long as that is correct, is the actual slot on the converter rated for only 10 amps or is it just dependent on the size of wire? Meaning the slot can handle a 30 amp fuse as long as the wire is sized appropriate?

As far as amp/hours, with 200 amp/hours I calculate I can run for close to 18 hours before I hit 50%. I would only be running this at night when temps drop below freezing. I have 200 watts of solar and a generator for backup, so I should be OK.
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Old 10-10-2016, 07:26 PM   #7
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The fuse slots on the converter panel are probably all good for about the same current, they are all "bussed" together ... (see note)
There IS a downside to your approach, the larger fuse will not individually protect the water pump, i.e. if it were to get stalled by frozen impeller, the fuse would not blow and the motor windings would overheat first. While not really so likely, have to mention as a point of full disclosure.
Similarly, same for protecting the heating devices, they will be allowed to draw current up to the fuse value, so if they were to short, get internally wet, whatever, they would be able to draw more current than intended in a failure mode.
Those things said, such failures are somewhat unlikely, and one could always add in-line fuses at the devices to provide individual current limiting protection.
Your approach WILL work to deliver power.
"NOTE" - some older converter panels had a few 12 Volt taps that were isolated, they would see the battery but not the converter output. The one we removed from our previous TC was such. There should be a wiring diagram on or in the converter (or check the manual) for such detail.
Again, not trying to discourage, just trying to be informative / diligent.
"Good Luck"
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Old 10-10-2016, 07:46 PM   #8
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The 14ga wire would be the bus and tapping into that bus to supply power to anything is ok as long as the total current draw for all the items on that bus does not exceed the wire rating. Every item needs to be fused (inline, etc.) to protect the wire and keep from shutting the entire bus down because of one failure.
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Old 10-11-2016, 02:36 PM   #9
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I got a reply from Forest River:

Good morning,

I talked this over with our team here and our suggestion is to have you install the tank blanket on the next circuit with the 7.5 AMP fuse as the only thing on that line is the heat pump and that draws 1 AMP.

Let me know if you have any other questions.

Thank you.


I have my 12 volt TV running on that circuit, so I think I will stick to my original plan but add a separate inline fuse for the water pump and tank blanket as suggested by others. Just wanted to share my experience with FR as they have always been prompt in replying with questions.

I will report back on how the tank blanket preformed and how my batteries fared after this weekend.
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Old 10-11-2016, 02:57 PM   #10
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If the water pump fuse is at the pump just tap off the water pump switch (input terminal) with your fused circuit. If the water pump fuse is before the switch move it to the water pump, splice the wire back together with your fused circuit. Your new circuit fuse can be before your new switch or after. Actually, splicing anywhere on the power side (switch etc.) of the water pump fuse would be ok. You probably have this all figured out.
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