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Old 09-02-2012, 12:46 AM   #21
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Lou used 1000 watts, which he indicated was what his water heater is equipped with, to demonstrate the math. I followed his example.
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Old 09-02-2012, 05:58 AM   #22
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Originally Posted by jk31668 View Post
i have a 6 gal suburban elect/gas water heater. i am being told the elect mode has limited use particulary in the summer when the ac is being used as it pulls too much juice when the ac, refer, and other applicances are on. so, i guess my question is...what good is it? only use when weather is cooler?
Since this is the heater I have and my manual states it has a 1000 watt element and the amperage can vary up to 12 amps. I made the leap.
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Old 09-02-2012, 06:29 AM   #23
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By the way - love your posts - keep up the good work! This is only the second one I disagreed with ... gives you about a 99.9999% hit rate!
Well thank you.

I think I see what you are saying. That as the voltage drops, and since the resistance of the element is fixed, it forces the amperage to decrease as well effectively reducing the efficiency of the heater. IE you won't get the full 1000 Watts of heat transfer to the water. (Like a dim bulb trying to light a room).

I was not using Ohm's Law V (or E) = IR to do the calculations; but the one to calculate P (or Power). Power as you may remember is the application of electricity (in Joules) over time (in seconds).

1 Joule of electricity delivered in 1 second is a Watt.

The formula to calculate Watts is Amps times Volts or P=IV
The effective delivery of that electricity is over time is P or power.

So in order to calculate the actual effect of a voltage reduction we would need to use the equations in this article http://en.wikipedia.org/wiki/Power_(physics)) to determine the new current being drawn at the reduced voltage based on the "mostly fixed" - temperature dependent - resistance (R) in the heating element core at the lower voltage.

Then you can multiply the actual incoming voltage (say 100 Volts) times the calculated (or observed) amperage to find the actual watts being delivered to the water.

So if the heater at "standard conditions" delivers 1000 Watts to the water by consuming 120 volts at 8.33 amps we can use that amperage to calculate the resistance (R) of the element using Ohms's Law E=IR or 120=8.33xR

This gives the 6 Gallon Suburban heating element an R of 120/8.33 or 14.4 Ohms. So if the incoming voltage is dropped to 100 volts and the resistance stays "almost" fixed at 14.4 Ohms, then the current consumed will be V=IR or I=V/R or 6.9 amps instead of 8.333

Since there is only 6.9 Amps of current at 100 Volts being delivered to the heating element the Wattage of the element falls to 694 Watts (an almost 30% reduction in an already inefficient way of heating the hot water heater).

If I got that right, it makes even MORE sense to use propane to heat the water in the summer when delivered volts are reduced by the power company and the physics of the campground's power grid.

I assume that since a motor or "Inductive" load will not function at all at reduced power, the capacitors keep the watts being delivered pretty much constant and as such increase the amperage demand as the voltage drops until the breaker pops.

I got it now. Thank you.

HE CAN BE TAUGHT!
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Old 05-15-2019, 01:46 AM   #24
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Originally Posted by kozzy View Post
I did read with my hot water heater, that you should use both the gas and electric part. I have a quick recovery model. When I am just using it in electric mode, it takes awhile to heat the water after a tank has been used, for instance, after a shower. If I use just gas, the heat up and recovery time is quick, but you are using your propane.
Using both, the electric heating element pretty much is all that is used to maintain temperature, and my propane only kicks on when that quick recovery mode sets in. So the way I understand it, and some others that have confirmend it for me is use both when you can, the electric will maintain the water, and the propane will give it a bost when needed. I am assuming that your water heater is of course a quick revcovery model. I have tested this theory, and it does really work great/ With just electric, i had to wat a few hours if I used all the hot water while giving the kids a bath for instance and I wanted to shower after. With both on, and the quick recovery mode, I have yet to run out of hot water doing anything. Good Luck
I have a surburban 6 gallon and it pulls around 15 amps at start up. Running the 15000 btu ac unit trips the breaker every time on a 30 amp circuit. I am not sure what the watt raiting is on my heating element.
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Old 05-15-2019, 01:52 AM   #25
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I have a surburban 6 gallon and it pulls around 15 amps at start up. Running the 15000 btu ac unit trips the breaker every time on a 30 amp circuit. I am not sure what the watt raiting is on my heating element.
Actualy what i meant to say is on a 30 amp circuit if you are running a 15000 btu ac unit anf your fridge on electric and your water heater on electric it will trip the breaker every time.
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Old 05-15-2019, 07:17 AM   #26
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so now we know the reason for those electrical load shedding devices.
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Old 06-13-2019, 04:42 PM   #27
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Upgrading from a SW6PE to an SW6DEL

I had to replace the SW6PE (6 Gal Propane Only WH) in my '96 Wildwood due the the previous owner's neglect. First time we took it out and pressurized the lines I noticed a small leak, spent some time investigating and turned that small leak into a steady drip. The tank was rusted and cracked.

I just found a brand new SW6DEL (6 Gal Propane/Electric/Electric Ignition WH) on Ebay for cheap and ordered it.
Obviously, my trailer isn't wired for the electronics for this new WH so I will have to set that up myself. Does anyone have any info on how to run the 120VAC from the controller to the switch and the WH from the Controller or how to run the 12v wiring?

I assume that I can tap into the 12v system from almost anywhere in the trailer but I expect that running the 120 VAC is going to be a bit tricky. I may need to add in a fuse as well.

I have the Installation Manual from Suburban but it doesn't really get into making a switch like this.

Any advice?
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Old 06-13-2019, 05:06 PM   #28
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Originally Posted by MFGeoff View Post
I had to replace the SW6PE (6 Gal Propane Only WH) in my '96 Wildwood due the the previous owner's neglect. First time we took it out and pressurized the lines I noticed a small leak, spent some time investigating and turned that small leak into a steady drip. The tank was rusted and cracked.

I just found a brand new SW6DEL (6 Gal Propane/Electric/Electric Ignition WH) on Ebay for cheap and ordered it.
Obviously, my trailer isn't wired for the electronics for this new WH so I will have to set that up myself. Does anyone have any info on how to run the 120VAC from the controller to the switch and the WH from the Controller or how to run the 12v wiring?

I assume that I can tap into the 12v system from almost anywhere in the trailer but I expect that running the 120 VAC is going to be a bit tricky. I may need to add in a fuse as well.

I have the Installation Manual from Suburban but it doesn't really get into making a switch like this.

Any advice?
See the attached wiring diagrams.

For the 110VAC (right side schematic), the WH will simply have a standard 3-prong plug. So you'll need to run 110VAC from a breaker in your power center to a standard duplex outlet (in an appropriate electrical box) next to the WH. Then simply plug it in.

For the DSI and electric switch portion (left side schematic), you'll have to decide where you're going to mount the switches and light. Usually this would be done near your control center, which probably has 12VDC already available there. Then you just run the wiring from the switches to the WH. If you put them somewhere without 12VDC, then you'll have to run 12VDC to that location.

Unless you find someone with your exact model Wildwood (unlikely), none of can really help you much on actual routing of the wiring.
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Old 06-13-2019, 06:11 PM   #29
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Originally Posted by rockfordroo View Post
See the attached wiring diagrams.

For the 110VAC (right side schematic), the WH will simply have a standard 3-prong plug. So you'll need to run 110VAC from a breaker in your power center to a standard duplex outlet (in an appropriate electrical box) next to the WH. Then simply plug it in.

For the DSI and electric switch portion (left side schematic), you'll have to decide where you're going to mount the switches and light. Usually this would be done near your control center, which probably has 12VDC already available there. Then you just run the wiring from the switches to the WH. If you put them somewhere without 12VDC, then you'll have to run 12VDC to that location.

Unless you find someone with your exact model Wildwood (unlikely), none of can really help you much on actual routing of the wiring.
Yes! That is exactly the info I needed. Routing the wiring and installing the switches I can handle no problem. It was really the 110VAC connection that I wasn't sure about. I can easily connect to the AC outlet for the Fridge since there is an extra connection there. Thanks for this!
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