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Old 08-09-2020, 03:42 PM   #1
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Need Electrical Help

Hey community!

I am hitting a roadblock with my electrical system. Can yall help me think through this? I have a 250amp breaker switch that keeps tripping now that I have connected a small hot water tank. Light on the tank turns on and so I assume that it is working, but somewhere the surge is pulling too much and flipping that breaker.

General system:
600ah batteries
3000w inverter
Hot water heater is 1440w and 12 amp
Hot water heater is wired in through 14 gauge wire into 15amp breaker
Hot water heater instructions say to use a 20 amp breaker switch, but its odd that the 15 amp is not flipping, its the 250 amp that is flipping.
I have nothing else pulling on the system when the 250 is flipping?? I was worried about that breaker being overrated and not flipping ever, so I'm confused about why its flipping. Could the wire be too small? They are 2 gauge.

Any and all help appreciated. Sorry in advance if I am missing any important info or have such a uneducated description about the system.

Thanks
Taylor
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Old 08-09-2020, 04:38 PM   #2
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Looks like 12GA on the AC side?

The 250A resettable fuse is on the DC side, correct? How long is that cable to the battery?
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Old 08-09-2020, 07:13 PM   #3
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Yeah its 12 gauge on the AC side.

The 250 amp is on the DC side and the cables to battery are 3 ft long.
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Old 08-09-2020, 07:23 PM   #4
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Can you describe your battery bank?
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Old 08-09-2020, 08:11 PM   #5
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I have three 200ah sealed batteries in parallel. Going into the bank is 300watt of solar via 30amp charge controller with 40amp inline fuse. There is a 175amp terminal fuse on the cables that go out to the 250 amp fuse before the inverter. Attached photos that kinda show it all.
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Old 08-09-2020, 09:54 PM   #6
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Hey there, if you can reliably get this breaker to trip, can you test a few things:

One, did you test this load on grid power to ensure it actually works? If you can do this with a Kill-A-Watt meter or something similar to see what the actual surge is, that will also help in determining/ ruling out the problem.

Two, use a voltmeter to watch the voltage of the bank. Use the input end of the 250A breaker for positive and the negative on the fuse block.

Before the load: What is the voltage?
During/After the load: What is the lowest voltage recorded?

1440W is about 120A at 12V. Over four batteries this is about 30A each.


Aside from your problem:
  • I think your wiring could be more robust by running equal lengths of wire from each battery to a set of positive a negative bus bars, and from the bus bars through the breaker to the inverter. Its also a good idea to use a different breaker for the fuse block than the one used for the inverter.
  • If your application requires surges near/above 250A, that _is_ the stated rating of your inverter (250A * 12V = 3000). You are likely to blow that thing doing that over and over even if it did work. It also looks like a high frequency inverter, which are ill suited for surge loads. Consider a low frequency inverter for such loads.
  • At 1200W or so (loads or charge) I start recommending people consider a 24V battery bank. For you this would mean quite a bit of effort, starting with changing the bank /configuration from 3P (3 parallel) to 2P2S (two in parallel in series, requiring another battery), a 24V inverter, stepping back down to 12V for that fuse block, and you may be required to change up the charge controller configuration, which is all $$$. Not super attractive.
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Old 08-10-2020, 07:42 AM   #7
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hi

Just a few questions,
what is the wire size between the batteries and the 250 fuse?
between the 250 fuse and the inverter?
Is the water heater a 120v appliance?
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Old 08-10-2020, 12:01 PM   #8
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In addition to all the other advice and questions, I can't help but notice that your inverter says 3000W on it, which is *exactly* 12V times 250A. Is that the 100% duty rating, or the peak surge rating? If it peaks above 3000W, you could easily exceed the 250A rating.

Too small a wire can easily increase the current draw due to resistance of the wiring. That resistance turns into heat, which unchecked could cause a fire. So tripping out your 250A breaker is a good thing.

You definitely need to provide information about the water heater, whether it is new or used, the ratings, etc.

jim
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Old 08-10-2020, 11:20 PM   #9
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Kazetsukai- I am having a hard time getting a solid reading out of the voltometer. I tried the suggested contact points and it is reading 8 volts?? Im not very versed in that instrument, I will try to get someone who has used one to help me out. The problem with testing with shore power is that it is hardwired through the NGL port on the inverter. I suppose I could wire it into adapter head to plug into wall and test, but the water heater is brand new so it should be working. I was not able to tell if the inverter is high frequency or not, but manual does indicate that it is suitable for surge power of 6000W.Here is the manual if you are able to tell from that. https://www.renogy.com/content/RNG-I...-P2-Manual.pdf

Bubb- all the wires in the batter/inverter/fuse set up are 2 gauge. Water heater is 120v ac.

bp1797- The water heater is new and here is the link to the user manual. https://www.bosch-climate.us/files/F..._2015_US_1.pdf

The inverter is 3000w with a peak surge of 6000w. I think you may be onto something there with it tripping out because of that. But I am confused because the water heater is the only thing operating and it is rated at 1440w. I suppose having the water heater go through the inverter is actually draining more energy than just the 1440 that the water heater needs to function? If this is the case, would it be more logical to have a 500amp fuse to accomodate the full 6000w surge potential of the inverter?

Thank you all for assisting!
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Old 08-10-2020, 11:23 PM   #10
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Kazetsukai- I am having a hard time getting a solid reading out of the voltometer. I tried the suggested contact points and it is reading 8 volts?? Im not very versed in that instrument, I will try to get someone who has used one to help me out. The problem with testing with shore power is that it is hardwired through the NGL port on the inverter. I suppose I could wire it into adapter head to plug into wall and test, but the water heater is brand new so it should be working. I was not able to tell if the inverter is high frequency or not, but manual does indicate that it is suitable for surge power of 6000W.Here is the manual if you are able to tell from that. https://www.renogy.com/content/RNG-I...-P2-Manual.pdf

Bubb- all the wires in the batter/inverter/fuse set up are 2 gauge. Water heater is 120v ac.

bp1797- The water heater is new and here is the link to the user manual. https://www.bosch-climate.us/files/F..._2015_US_1.pdf

The inverter is 3000w with a peak surge of 6000w. I think you may be onto something there with it tripping out because of that. But I am confused because the water heater is the only thing operating and it is rated at 1440w. I suppose having the water heater go through the inverter is actually draining more energy than just the 1440 that the water heater needs to function? If this is the case, would it be more logical to have a 500amp fuse to accomodate the full 6000w surge potential of the inverter?

Thank you all for assisting!
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Old 08-10-2020, 11:42 PM   #11
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Kazetsukai- I am having a hard time getting a solid reading out of the voltometer. I tried the suggested contact points and it is reading 8 volts?? Im not very versed in that instrument, I will try to get someone who has used one to help me out. The problem with testing with shore power is that it is hardwired through the NGL port on the inverter. I suppose I could wire it into adapter head to plug into wall and test, but the water heater is brand new so it should be working. I was not able to tell if the inverter is high frequency or not, but manual does indicate that it is suitable for surge power of 6000W.Here is the manual if you are able to tell from that. https://www.renogy.com/content/RNG-I...-P2-Manual.pdf

Bubb- all the wires in the batter/inverter/fuse set up are 2 gauge. Water heater is 120v ac.

bp1797- The water heater is new and here is the link to the user manual. https://www.bosch-climate.us/files/F..._2015_US_1.pdf

The inverter is 3000w with a peak surge of 6000w. I think you may be onto something there with it tripping out because of that. But I am confused because the water heater is the only thing operating and it is rated at 1440w. I suppose having the water heater go through the inverter is actually draining more energy than just the 1440 that the water heater needs to function? If this is the case, would it be more logical to have a 500amp fuse to accomodate the full 6000w surge potential of the inverter?

Thank you all for assisting!
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Old 08-11-2020, 03:20 PM   #12
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LRA and 120v vs 12v

I hate to break it to you but you are pulling more than 250 amps from your battery.


To pull 12 amps at 120v from your inverter, your inverter is pulling at least 120 amps from your battery in DC,
A inverter takes 10 amps from a 12v source to make a 1amp device run, probably a little more with all the inherent inefficiencies.


Even beyond that is the LRA issue, most electric motors take 2 to 3 times the power to start as what they need to run so you are certainly trying to pull over 250 amps from your batteries.
Generally speaking you dont want to pull more than 10% of a batteries capacity or it will drop the volts and start heating up, this means a 100ah battery can only supply up to 10amps at a time or it causes problems such as the batteries voltage will drop below 11v and the inverter will shut itself down.
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Old 08-11-2020, 05:25 PM   #13
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Two problems... The water heater has a small inrush current caused by the lower temperature at startup. This effect can be largwr depending on the heater style..inconel wire or PTC style.

The 250 amp DC breaker is likely magnetic and will trip immediately .

So if the breaker trips during startup then you need a little heavier breaker.


Second .. If your inverter is more sophisticated like most are by now it wants to make 120 vac independent from the battery voltage applied to it.
So even with out losses the 1440 watts at 12volt is 120 Amps but when the dc voltage at the inverter terminal drops to 10 volts the current goes up to 144 Amps.

This is only an example..most inverters switch of at 10.5 volts. It shows you that you need a quality connection at the high current DC side.

Good luck
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Old 08-11-2020, 05:45 PM   #14
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The math I use to estimate the max current on the DC side of the inverter is:


[inverter continuous watt rating] ÷ [inverter inefficiency] ÷ [low voltage disconnect voltage] = [DC Current]


For example (assuming LiFePO4 batteries and an average efficiency high frequency inverter):


3000W / 0.85 / 12V = 295A


Then take that number and multiply by 1.25, the fuse should be at least this size. The wire should be greater.



If it is a low frequency inverter (big, heavy, pricey, usually inverter/charger, with substantial surge rating measured in seconds or minutes) I use the same math but use the surge rating, not the continuous rating.


An easier option is to follow the recommendations given in your inverter manual.
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Old 08-11-2020, 07:46 PM   #15
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Quote:
Originally Posted by TayterTots View Post
Kazetsukai- I am having a hard time getting a solid reading out of the voltometer. I tried the suggested contact points and it is reading 8 volts??

Can you show in an image how you are measuring? Might require a second set of hands.


Also try measuring positive and negative on the inverter, if you're actually getting 8 volts and not incorrectly measuring I think we're on to something.
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Old 08-15-2020, 09:06 PM   #16
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Do not trust the manufacturers ratings. This will end all of your confusion. The Water heater is drawing more than the rated breaker. That's all, it's not a mystery even though it seems like one. Eliminate the breaker. You don't need it there.
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Old 08-16-2020, 01:12 AM   #17
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I bought a 400 amp breaker that kept tripping on me. It ended up being a faulty cheap breaker. I went to a 400 amp fuse (recommended by my inverter) and it hadn’t been a problem
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Old 08-16-2020, 03:02 AM   #18
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Wink

Isolation ... disconnect the fuse block from the breaker and try the heater to see if it still pops the breaker. This will tell you which leg off the breaker is causing the problem. I think you will find it is the inverter side. At least you will know there are no parasitic drains from the other DC loads via the fuse block.


I do think it is the initial surge from when the heater turns on.


I'm with Bon Voyage ... install a fuse inline ... meaning battery --> fuse --> inverter ...
and take the fuse block from the battery, through the breaker if you want.


Code:
+12 ---+-----> 500A Fuse ------> Inverter
       |
       |
       +-----> 100A Fuse ------> Fuse Block
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Old 08-16-2020, 03:47 AM   #19
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You will want to replace the 175A in-line fuse with a 400A or better, 500A (assuming your inverter has a 6000W surge capability) and wires to support the surge.


Of course, once you solve the breaker-popping issue, you may care to think over your power needs.



I did not see the type of heater in your posts, but you mentioned a water heater tank. If it is a demand heater (tankless actually), then the following analysis does not hold. If it is a traditional water heater, then follow along and use the actual useage (wattage) indicated in the manufacturer's literature to get your anticipated useage.



Assuming the full load of 12A AC, you'll be drawing 140A DC (taking into account an 85% inverter efficiency ....... many are much higher).

If you need to run your water heater for even 2 hours a day, you will run out of capacity in your battery bank to supply it. The calculations/assumptions follow.



You mention a sealed battery ... I assume gel. Thus, you can get 50% of the capacity out of the battery bank safely. This means you get 300Ah of battery life.


300Ah / 140A = 2.14 hours of battery life at that load.


Let's say your heater is turned on and the water is hot. Every once in a while, it will turn on and heat the water again. Let's say it is on for 5 minutes an hour. Then you will use up the battery charge in just under 26 hours just to keep the water hot. Then there is time you use hot water which will cause the heater to turn on. Of course, your solar will supply some power (300W over a few hours in a day ... maybe 200 Ah), but not enough to fully replenish the battery bank.


Of course, this assumed no additional loads on the battery bank ... such as lights and phone chargers, computer, etc.
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Old 08-16-2020, 09:51 PM   #20
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Resolution

Thanks for all the input and knowledge people! This is truly and amazing resource

For the time being I have decided to wire the water heater to shore power only as it seems to be too much draw to sustainably run off just my 300w solar power. But I appreciate all of the lessons and this has taught me a good deal about the electrical system overall.

Peace
Tay
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