110v PLUS 24v on the SAME water heater

[TomC]

If you have an inverter already, don't bother with the low voltage dedicated heating coil.  What I have is two 10gal water heaters-one plumbed to the next with the final water heater wired through the inverter so I can have hot water during the day going down the road.  Simple, works well, and if on only 30amp power pole, what I do is heat the inverter water heater first (the second in the series) then heat the first water heater and leave that on.  Then when using the hot water, the cold water is coming into the first water heater being heated before going into the second water heater that no longer needs to have power to it.  Has worked flawlessly now for 15 years, and am repeating it on my truck.  Good Luck, TomC

[miles2go]

Good advice. I flushed it well before testing it and it was clean, but I will check the anode, element, and the rest. What does TPV stand for....thermo protection valve?  The pressure relief valve?

A heat exchanger is a great idea (and I would like one) but later (time and money). Powering the hot water heater through the inverter will heat the water while under way, that is enough for starters. Or is running the roof airs, two 13.5k BTU units, and trying to power the HWH too much? 20 amps each for the airs on start up, but I am not sure what the roof airs pull once they are just running. Then for 2000 watts of water heating element, about 16 amps? 20+20+16=56 amps. That is almost right at the 60 amps pass through of the 4024 when on shore power or generator. But it is inverting while underway.

I think the D50 on the 8v71 is only 270 amps or 6480 watts... thats not enough is it. 2x2400 watts for the A/C units and 2000 for the HWH is 6800 watts... thats why I need a heat exchanger. 6480 watts going in to the batteries and then the inverter from the D50 and 6800 coming out, plus what's already in the batteries, minus inefficiencies, probably will not work.

Ok, I looked at the roof airs. the locked rotor amps is a whopping 63.5. That is to start the compressor? The full load amps is 12.4 while running. The fan draws 3.0 amps running and 8.5 amps to start. The minimum circuit ampacity and circuit protection is 20 amps. How does the momentary start up of 63.5 not trip a breaker? Never mind, it doesn't, it works.

Does one try to calculate wattage using 120v or 115v? This is way too complicated.
Trace 4024=33.3 amps (I guess, 4000 watts at 120v.). Each roof air draws 15.5 amps while running, that's tight if it will work.

Don't let me have formulas anymore, I overcomplicate things. A little (miniscule) knowledge can be a dangerous thing. I suppose this is why I do need a heat exchanger after all. Woe is me, and I haven't even connected the Generator yet. :-/

Andrew.

[Sean]

... What does TPV stand for...?

"Temperature and Pressure relief Valve."  It will be located near the top of the tank, will have an outlet directed downwards, and a little lever on it that pulls a plunger out.  The discharge needs to be plumbed out the bottom of the coach.  You operate the lever with the tank under city water pressure and make sure water comes out.  That doesn't guarantee the valve is good, but you will at least know that it is not obstructed and the plunger is not corroded in place.

... Or is running the roof airs, two 13.5k BTU units, and trying to power the HWH too much?

Looks like you've already answered your own question, but, yes, that's too much.  You will be able to run two out of the three.  The roof airs will draw from 13 to 15 each amps when running "steady state" (as opposed to starting up), and at the 120 volts that your SW4024 will put out, your 2000-watt water heater will draw over 16.  The 4024 can produce a steady 30-33 amps under ideal conditions; as the temperature starts creeping up near the unit, that will actually go down.  So even two out of the three might be a stretch.  Which, as you surmised, is why I recommended a marine water heater with a built-in heat exchanger.

I think the D50 on the 8v71 is only 270 amps or 6480 watts

It's actually over 7,000 watts because the 270 amps is being pumped out at over 28 volts.  The 50DN is not the limiting factor here; the SW4024 is.  At max continuous load of 4kW, even accounting for the ~10% efficiency loss, you'll only be using a little over 60% of the capacity of the alternator, leaving plenty left over for battery charging.  BTW, we do this all the time, running two air conditioners totaling 3,600 watts or so.

.... 6480 watts going in to the batteries and then the inverter from the D50 and 6800 coming out, plus what's already in the batteries, minus inefficiencies, probably will not work.

Just to be clear, 6,800 will not be coming out.  Again, your SW4024 is rated for 4,000 watts continuous.  It can supply nearly twice that as a "surge" rating, but this is for a matter of a few seconds, not minutes or hours.

Ok, I looked at the roof airs. the locked rotor amps is a whopping 63.5. That is to start the compressor? The full load amps is 12.4 while running. The fan draws 3.0 amps running and 8.5 amps to start. The minimum circuit ampacity and circuit protection is 20 amps. How does the momentary start up of 63.5 not trip a breaker?

It will trip a conventional circuit breaker.  Air conditioners need a type of breaker known as "HACR" and if you look at the breaker I am sure you will find this marked on it.  In practice, most circuit breakers sold today for residential panels are HACR type.  That stands for "Heating, Air Conditioning, Refrigeration" and the breaker has a "surge" capacity that lets it carry large currents for short durations in order to start compressors.

Does one try to calculate wattage using 120v or 115v?

You use the actual voltage you are working with.  Your SW4024 is set to produce output at exactly 120 VAC.  120 is also the current North American standard for residential and light industrial voltage, although in practice voltages between 110 and 125 can be encountered.  "110" is an older standard, even though old-timers tend to use that number (and it's companion "220") when talking about 120 (240) volt circuits.

-Sean
http://OurOdyssey.BlogSpot.com

[miles2go]

Now I know what I need to do. Thanks.