Decreasing amp draw of an electric element

[AZJoe]

Just ordered a 1200 watt inverter with automatic transfer switch (my manual transfer switch will bypass this for the water heater). Good thing about this is that it will make the outlets hot that are now only functioning when the inverter are on. I'll sell the 2000 watt inverter on Ebay.

[AZJoe]

Sunking, if you actually read the posts in this thread, you would see that the novel you just posted is completely irrelevant to the OP at this point. This system has changed.

I purchased anot Atwood combination gas/electric unit and I'm swapping out the 1440 Watt element with a 1000 watt element and have decided against using any format of dimmer or voltage reducer. I'll use the electric element when plugged in or to use up surplus electricity while the sun is out and that should help with voltage sag. I did look at possibly swapping out the 2000 watt pure sine wave inverter for a 1000 or 1200 watt version since I'm not planning on using, nor can I use a 2000 watt inverter with my current setup and I can not justify getting rid of the camper and most all of the stuff that I have done to get a larger camper that I could fit a bigger battery setup just to use a electric watet heater (the first one I started out with) instead of a gas electric version intended for my application. By going with the Atwood I'm able to save space by getting rid of my Zodi shower.
I appreciate the pointers on making this a more ideal set up able to power more then I'm realistically going to need. I got the extra panels and the 6 volt batteries (I had 6 of the 12 volt batteries before) to try and make things work that I knew going into things were problematic.

[sensij]

Sunking, if you actually read the posts in this thread, you would see that the novel you just posted is completely irrelevant to the OP at this point. This system has changed.

[Sunking]

I have a 690 amp hour battery bank (6 of the 6volt 230 ah golf cart batteries run in series parallel with bus bar and equal length 0/2 gauge pure copper cable), 1,200 watts of solar panels (12 of the Renogy 100 watt panels), a Midnite Solar Classic 150, and I plan on using almost all dc powered stuff with the power inverter now being limited to under 1,000 watts of usage (or less).

I rest my case, you just admitted I am correct, your system is undersized, and using to low of a voltage on your battery. That is why you are having the troubles you are having,So why do you ask what is wrong if you do not want to hear what is wrong. The minimum voltage you should be running is 24 volts, and if you had thought about future growth and minimum expense should be running 48 volts and NO PARALLEL BATtERIES. It is like you tried to do everything you could possible do wrong. You made it as expensive as you posible could, as inefficient as you could possible make it, as dangerous as it can be, and planned for it to fail like you are experiencing.

Example you used 6-volt 230 AH batteries which is fine if you needed a 230 AH battery at 36 volts, Instead being trapped inside a 12 volt box, you used 12 volts. To do that you had to make sacrifices, and workaround the problems and extra expense that creates like using a Buss Bar and 3-pairs of of 2/0 AWG cable. Lot of bad things are going to happen with that choice like cutting your battery cycle life in half. You are going to be replacing those batteries in a year or two.

Those 6-volt 230 AH batteries I am guessing are Duracell Golf Cart batteries or similar and can deliver up to 35 to 40 amps before voltage drop exceeds 2% only leaving you 2% allowance for cable loses between batteries and Inverter. 2% of 12 volts = .25 volts and another .25 volts for cable losses. At most your batteries and set up can only supply a 1000 watt load and at that high of a discharge rate turns your 230 AH battery into 180 AH batteries or only 70% as much as you thought you had. You did not take any of that into account and is creating the headaches you are having.

No you want to compound your errors, and only want to hear that wil work. It is not going to work, and anyone telling you it will work is wrong or lying to you. So your water heater is designed to heat water with 1400 watts. Using a conservative estimation will run 1 maybe 2 hours per day. So let's sugar coat it and pretend 1 hour per day at 1400 watts or 1400 Watt hours. Initially you might think if you reduced power by 75% down to 350 watts all your troubles are over and all it means instead of 1 hour run time is now 4 hours run time. Nothing could be further from the truth no one has the guts to tell you. That heater is designed to run at 1400 watts. If you force it down to 350 watts is going to take a lot longer than 4 hours because you are ignoring thermal losses. At 350 watts is not likely enough power to heat the water to a high enough temperature to allow the thermostat to turn the power off, or have to run a lot longer than you expect. You are throwing more energy away compounding efficiency issues running 12 volts.

If you had added up all your daily energy needs, and sized thing correctly to begin with, you would have known instantly your battery capacity is undersized. If that water heater uses 1400 watt hours per day, which is unrealistic and uses more than that, you would have known the water heater uses more than 25% of your battery capacity in a day when Peukert Factor is accounted for. You've already exceeded you daily limit in just the water heater alone.

I know you do not want to hear this, too bad I am not politically correct (a forked tongue liar). I will tell you the truth and not gloss over anything. What I can tell you is you can correct the problem to some degree. Buy two more batteries like you have, configure them for 48 volts (all in series), and get a 2000 watt 48 volt Inverter for you to grow into. Keep in mind even at 48 volts, you are still pushing your system to its maximum limits. and even though the batteries label indicates you have a 48 volt 230 AH battery is really a 48 volt 160 AH battery with a 1400 watt load (aka C/6 discharge) .

Your minimum size battery has to meet two objectives, and use the worse case scenario.

1. Max discharge rate not to exceed C/8. With a 2000 watt Inverter requires a minimum:
340 AH @ 48 volts
680 AH @ 24 volts
1360 AH @ 12 volts.

2. Minimum 5 Day Reserve Capacity. So if that water heater only ran 1-hour per day is 1400 watt hours, so a 7000 watt hours. So you would need:
150 AH @ 48 volts
300 AH @ 24 volts
600 AH @ 12 volts.
\
Worse case is numero uno, 340 AH @ 48 volts.

With that battery comes minimum charge requirement of C/12 or 1400 watts of panels and at 48 volts is a 30 amp charge controller. Not a 96 amp controller you have now.

[AZJoe]

I am absolutely certain his battery is undersized and his panel wattage. No question about it. If you had read what he says you would know it to. Either that or you do not know what you are doing. What is so hard to understand?

12-volt 2000 watt rectifier requires a minimum 12 volt @ 1600 AH, 1100 pound battery with short 4/0 Copper cable between the battery and Inverter. Otherwise when he tries to draw 150 to 200 amps of current the voltage is going to sag and cause the inverter to trip off-line. That is if his undersized wire does not burn up first. That simple. To keep that battery charged up will require 1500 watts or more in panel wattage, and two very expensive 60-amp charge controllers. He is no where close to that.

That is why I asked what he is complaining about. It is doing exactly what he planned for it to do. Fail. FWIW a 12 volt 2000 watt Inverter is a ticking time bomb and you know it. I am a PE and like a doctor if you are going to smoke, all I can say is quit or you will die,. Get out of my office, I cannot help you unless you quit what you are doing.

I have a 690 amp hour battery bank (6 of the 6volt 230 ah golf cart batteries run in series parallel with bus bar and equal length 0/2 gauge pure copper cable), 1,200 watts of solar panels (12 of the Renogy 100 watt panels), a Midnite Solar Classic 150, and I plan on using almost all dc powered stuff with the power inverter now being limited to under 1,000 watts of usage (or less).

[Sunking]

And you don't know the system is undersized.

I am absolutely certain his battery is undersized and his panel wattage. No question about it. If you had read what he says you would know it to. Either that or you do not know what you are doing. What is so hard to understand?

12-volt 2000 watt rectifier requires a minimum 12 volt @ 1600 AH, 1100 pound battery with short 4/0 Copper cable between the battery and Inverter. Otherwise when he tries to draw 150 to 200 amps of current the voltage is going to sag and cause the inverter to trip off-line. That is if his undersized wire does not burn up first. That simple. To keep that battery charged up will require 1500 watts or more in panel wattage, and two very expensive 60-amp charge controllers. He is no where close to that.

That is why I asked what he is complaining about. It is doing exactly what he planned for it to do. Fail. FWIW a 12 volt 2000 watt Inverter is a ticking time bomb and you know it. I am a PE and like a doctor if you are going to smoke, all I can say is quit or you will die,. Get out of my office, I cannot help you unless you quit what you are doing.

[AZJoe]

I have a good feel about it. The OP knew what the problem was, overdrawing the battery bank, and decided to solve that by buying a propane/electric combo water heater, and to dump his excess daytime solar watts into a heating element half the size of his previous troublesome one. What's so terrible? The worst that can happen is he still trips out with a 1000W element and decides to put his spare daytime watts into something different while taking a nice proprane enabled hot shower.

Thank you for actually reading my post. I'm happy with my solar project even if it'still not perfect, it works for the space constraints I had and will do just about everything I need. The new 6 gallon water heater replaces my Zodi setup and sloves my probless. Since you can use both gas and electric together, it should take stress off of an electric only system.

[AzRoute66]

I have a good feel about it. The OP knew what the problem was, overdrawing the battery bank, and decided to solve that by buying a propane/electric combo water heater, and to dump his excess daytime solar watts into a heating element half the size of his previous troublesome one. What's so terrible? The worst that can happen is he still trips out with a 1000W element and decides to put his spare daytime watts into something different while taking a nice proprane enabled hot shower.

[jflorey2]

Senji the issue is there is no fix for the problem. You cannot fix an undersized system.

And you don't know the system is undersized. He may have a very limited need for hot water when operating away from shore power, in which case energy requirements go way down. And if he can solve the power problem, he's solved his problem.

If you are so concerned tell the OP the TRUTH for a change.

I have a feeling the OP is just going to do it and get something that works for him no matter what sort of names you call him. Which is a good outcome.

[Sunking]

Senji the issue is there is no fix for the problem. You cannot fix an undersized system. If Sag and Peukert is causing problems, that is a design issue and the only way to fix it is start over. Sure you could use a transformer to cut the power by 75%. All that means is it takes 4 times longer to heat the water. In the end you use just as much energy and when done either way the battery is drained. Slowing down the process is most likely going to make it inefficient meaning more energy required and bigger problems. .

I am not even going to touch the compatibility issues with lower voltage and electrical control circuits/switches. If you are so concerned tell the OP the TRUTH for a change.

[sensij]

I have never heard such poor advice anywhere.

If I try to turn this comment into a productive contribution, it is probably to point out that while reducing the voltage can address the *power* problem, water heating also has an *energy* problem to solve too. Reducing the current draw by reducing the supply voltage will reduce the voltage sag and peukert loss, but has the OP attempted to calculate the how much energy is needed to heat the required volume of water, or quantify the heat loss of the system? A system that is so mis-matched in power requirements is probably going to be mis-matched in energy requirements, too.

[Sunking]

I have never heard such poor advice anywhere.

[bcroe]

OR.........
Just use a standard 2,000W 120Vac water heater and feed it from the 36V PV string. These are 7.6 ohm element. When panels are operated at power point, I get all the hot water I want from just excess PV and a 10 gal tank. Your results may vary.

Keep in mind, the thermostat switches in AC water heaters are not intended for breaking
DC current. Generally their voltage rating would need to be drastically reduced. Bruce Roe

[PNPmacnab]

OR.........
Just use a standard 2,000W 120Vac water heater and feed it from the 36V PV string. These are 7.6 ohm element. When panels are operated at power point, I get all the hot water I want from just excess PV and a 10 gal tank. Your results may vary.

[NukeEngineer]

Just use a standard 240Vac water heater and feed it 120v. These typically have 4500 watt elements. 4500/240 = 18.75A, 240/18.75 = 12.8 ohms per element, and they only run one at a time.

With 120v feed, you'd have 120/12.8 = 9.375 amps, times 120v = 1125 watts. Problem solved