2000w inverter with long wire, will it work (safely)?

[sunrise]

I plan to tackle the under powered inverter (1000w) problem, but due to the constraint of available space (I have a 16-foot trailer, space is very limited), the inverter has to be mounted far from the batteries. about 10 feet of cable run.

I have read many posts on similar topics. In most posts, "bigger is better" suggestion was often offered, which I understand - can't hurt if the size of the wire isn't going to get in the way. But I want to really understand the problem that a setup could run into will smaller gauge wires (say 2awg). So here is the setup I am considering -

- Renogy 2000w pure sine wave inverter (11v - 16v working voltage range)
- 210ah LiFePo4 batteries (2 105ah in parallel with 2 120a JBD smart BMS)
- 9-10 feet 2awg from batteries to inverter, roundtrip 20 feet
- Load - most of time < 200w AC, 2-3 minutes 800w microwave, 2-3 minutes 1200w coffee machine, 1500w hair dryer for 2-3 minutes(very rarely), 15A AC breaker ensures the load would never go above 1800W.

BTW, my original factory installed 1000W inverter also has a very long 4awg cable run between battery and inverter (9 feet or so). I tested it with a space heater @ 800w for about 5 minutes and it seems to be fine, without any cable overheating.

AWG 2 pure copper wire is rated for 200A, so I don't think I need to worry about safety here, especially when I will never go above 150A, anything above 100A would only be used for ~ 3 minutes. But for safety's sake let's say I will run 150A for 2 hours, I expect the wire will get warm, but shouldn't be a fire hazard anywhere.

The next one is voltage drop. according to Blue Sea Wire Wizard, 12v, 150A, 20 feet (roundtrip) would have up to 4%(0.48v) voltage drop, my LiFePo4 batteries should stay above 12v most of it's discharge cycle, so 12v - 0.48 = 11.52v, still well within inverter's operational range. not too mention this is the extreme case @ 150A.

So are there any other problem this setup would likely run into? Again I am full aware a 4/0 wire would be better than 2awg, but I just want to understand the issue with smaller gauged wire.

Anyway, I think the folks that came up with amp ratings for different wire sizes already built safety margin into them. So I am wondering if layers of oversizing are really necessary.

Thanks in advance!

 

[DThames]

Understanding the power loss and the voltage drop are what is needed to decide for yourself.

 

[Hedges]

A 2000W inverter isn't terribly large. How about proudly displaying it on the wall?
Current draw at 12V is over 10x the current at 120VAC ("over" due to inefficiency), so routing the distance with AC wires is preferred.

A 15A AC breaker will carry 30A for a while. The inverter will probably give up after delivering a brief surge.

2000W/11V/90% efficiency*1.12 ripple factor = 226Arms current in battery (DC + ripple)
Fuse should be 25% higher than that to avoid nuisance trips. Fuse must be no greater than ampacity of wire.

For such current I would like 2/0 cable. If 20' round trip, 0.1 milliohm per foot gives 0.45V drop, so battery (actually BMS output) at 11.45V will put inverter at 11V minimum. 2/0 also has ampacity 300A (if 90 degree C insulation and free air available to cool individual conductors).

Sounds like full load will be near 100% rating of BMS.

A 24V system would have reduced the DC routing issue by a factor of 4 (power loss) and 2 (ampacity).

 

[chrisski]

I have a 12 volt volt 2000 watt inverter with 4/0 wire. and is located 2' from the battery bank, but took about 10' of wire total to make the connections. Those darned turns and tight areas never let me run a straigt line.

I only go up to 2000 watts for a couple minutes four to six times a day, and mostly when the sun is shining to run the microwave.

I plan on using these high wattage appliances in the 2000 watt range a lot more often, so what I am doing now is building a battery 24 volt battery bank.

Instead of the blue sea, try using this voltage loss calculator.

To me I think 2 AWG is a terrible idea for a 12 volt inverter at 2000 watts, and its even worst if the inverter is being used more than a couple minutes at a time.

 

[NwCali]

To me I think 2 AWG is a terrible idea for a 12 volt inverter at 2000 watts, and its even worst if the inverter is being used more than a couple minutes at a time.

Can you explain why and what would be better?

 

[chrisski]

Best thing to do would be to run the math and see the voltage drops for some cables. When the cables start to show voltage drops, that is when inverters draw more amps because they have less volts in a cycle that gets it close to a low voltage cutoff of the inverter. An undersized battery has more to do with this, but thinner wires contribute to that also.

Also, when the ampacity of a wire approaches the amps you have running through it, it also can start to heat up. I mention I run my microwave for two minutes at a time. For the sized wires I have, I do not notice any heat on the wire, but that is because it takes time to heat up and two minutes is not enough. When a wire is rated at 30 amps at 90 degrees celcius and you are running 30 amps through it constantly, it could get hot enough to burn you, the more so the poorer the cooling in the area the wire is at. I don't want my wires to burn me.

If you look at a lot of reviews in Amazon on inverters that are high wattage that have low amps, you'll see that these people sent them up with wires that are too thin, but left a bad rating and returned the inverter.

As for a recommendation, run the math on the calculator for each wire you're putting in like inverter to bus bar and bus bar to battery, shoot for a 1 to 3% loss total. Once you, have decided on that wire AWG, check for ampacity at 60 Celsius and make sure that max amps are less than that. For volts that I recommend the calculation, use inverter cutoff, and for amps, use inverter wattage / inverter cutoff voltage * 1.15. That is really conservative. If you do it this way, you'll turn on the system and when you stress the inverter, the actual voltage may not dip close to the low voltage cutoff, but this gives you some area to work.

300k+ electric fires a year in the US. I'm going to err to the conservative side.

 

[MisterSandals]

Lets try some math:
(2000 ac watts / .85 inverter efficiency) / 12.8 volts low cutoff = ~184 dc amps

Running the voltage drop calculator,
2awg is 5.8% drop (too high)
4/0awg is 1.8% drop (good)

Voltage Drop Calculator

This free voltage drop calculator estimates the voltage drop of an electrical circuit based on the wire size, distance, and anticipated load current.

www.calculator.net

 

[Zwy]

I plan to tackle the under powered inverter (1000w) problem, but due to the constraint of available space (I have a 16-foot trailer, space is very limited), the inverter has to be mounted far from the batteries. about 10 feet of cable run.

I have read many posts on similar topics. In most posts, "bigger is better" suggestion was often offered, which I understand - can't hurt if the size of the wire isn't going to get in the way. But I want to really understand the problem that a setup could run into will smaller gauge wires (say 2awg). So here is the setup I am considering -

- Renogy 2000w pure sine wave inverter (11v - 16v working voltage range)
- 210ah LiFePo4 batteries (2 105ah in parallel with 2 120a JBD smart BMS)
- 9-10 feet 2awg from batteries to inverter, roundtrip 20 feet
- Load - most of time < 200w AC, 2-3 minutes 800w microwave, 2-3 minutes 1200w coffee machine, 1500w hair dryer for 2-3 minutes(very rarely), 15A AC breaker ensures the load would never go above 1800W.

BTW, my original factory installed 1000W inverter also has a very long 4awg cable run between battery and inverter (9 feet or so). I tested it with a space heater @ 800w for about 5 minutes and it seems to be fine, without any cable overheating.

AWG 2 pure copper wire is rated for 200A, so I don't think I need to worry about safety here, especially when I will never go above 150A, anything above 100A would only be used for ~ 3 minutes. But for safety's sake let's say I will run 150A for 2 hours, I expect the wire will get warm, but shouldn't be a fire hazard anywhere.

The next one is voltage drop. according to Blue Sea Wire Wizard, 12v, 150A, 20 feet (roundtrip) would have up to 4%(0.48v) voltage drop, my LiFePo4 batteries should stay above 12v most of it's discharge cycle, so 12v - 0.48 = 11.52v, still well within inverter's operational range. not too mention this is the extreme case @ 150A.

So are there any other problem this setup would likely run into? Again I am full aware a 4/0 wire would be better than 2awg, but I just want to understand the issue with smaller gauged wire.

Anyway, I think the folks that came up with amp ratings for different wire sizes already built safety margin into them. So I am wondering if layers of oversizing are really necessary.

Thanks in advance!

Heat will kill any inverter and the more the voltage loss before it reaches the inverter, the more heat it will create as more amps are needed.

I always use the calculators and upsize to the next gauge. But I'm a fanatic about voltage drop.......

 

[sunrise]

Heat will kill any inverter and the more the voltage loss before it reaches the inverter, the more heat it will create as more amps are needed.

I always use the calculators and upsize to the next gauge. But I'm a fanatic about voltage drop.......

why would ~5% voltage drop makes inverter generate excessive heat in a vicious loop? This makes no sense. Inverters have their operational voltage range, outside of that, they shutdown. inside of that range, it makes not difference if the 12v was from battery(zero drop) or was from 12.5v dropped to 12v.

 

[sunrise]

I always use the calculators and upsize to the next gauge. But I'm a fanatic about voltage drop.......

This is exactly the practice I was trying to avoid - layers of oversizing on top of layers of oversizing...

 

[eXodus]

- Renogy 2000w pure sine wave inverter (11v - 16v working voltage range)
- 210ah LiFePo4 batteries (2 105ah in parallel with 2 120a JBD smart BMS)

can you put the inverter where the second battery sits?

Battery 1 - long cable - battery 2- short cable - inverter.

The drops the amps on the long run of the cable by half.

 

[sunrise]

OK, so far I have not seen any new concerns besides heat & voltage drop.

I am fairly sure 2awg will not generate excessive heat to start a fire, this is based on what 2awg copper wire is rated for, and my 1st hand experience of running 800w continuous on 4awg wire (+2c after 5minutes).

On voltage drop, I think 4-5% drop is not ideal but the math says it should work, folks here might have different opinion on margin needed. For that I will get the 2awg wires and test it. Plan to do this in a few months when my trailer isn't in active use and I can take the batteries out. I will post result back here either way.

Thanks all for your input!

 

[eXodus]

- Load - most of time < 200w AC, 2-3 minutes 800w microwave, 2-3 minutes 1200w coffee machine, 1500w hair dryer for 2-3 minutes(very rarely), 15A AC breaker ensures the load would never go above 1800W.

If you can ensure that you don't use the power more then a few minutes a at a time - I wouldn't worry to much when using a gauge 2/0.

I personal try to stay away from anything above 100A. It's just not very practical.

When you need 2000w for extended time - go 24V or 48V

 

[sunrise]

can you put the inverter where the second battery sits?

Battery 1 - long cable - battery 2- short cable - inverter.

The drops the amps on the long run of the cable by half.

I am having trouble finding space just for the inverter, let alone a battery but it's side

 

[chrisski]

I am having trouble finding space just for the inverter, let alone a battery but it's side

I am making a lithium battery from Eve 280 cells. When I'm done, I will have over twice the storage capacity in less space than the 4 Golf cart batteries it is replacing.

I saw a picture of an all in one inverter / charger, and this saved a bit of space also.

AWG 2 pure copper wire is rated for 200A,

The chart I use does not have 200 A ampacity until 4/0. If the insulation is 90° C, them it is limited to 130 amps. If that wire were rated for 60° C insulation, then the insulation may melt, and that could mean a short. I think you could probably use Bare copper wire for a 200 amp rating, but not insulated. There's lots of caveats to that and maybe the wire you mention has a special insulation. A decent manufacturer will publish trusted specs on their wire. There's others that will publish numbers.


Whatever you decide, I'd like to see pics when you're done.

 

[Hedges]

The chart I use does not have 200 A ampacity until 4/0. If the insulation is 90° C, them it is limited to 130 amps.

NEC chart for cable of up to 3 conductors (the chart you have) shows 2/0 has ampacity 195A. Round up to 200A breaker.
The chart for single conductors in free air shows 2 awg has ampacity 190A

With batteries next to inverter, I loop them through the air and call the well cooled.
For OP, it is going to depend on whether they are stuffed neatly inside a wall, or draped in the breeze under the trailer.

Fuse protection should be for the ampacity of the wire, given its insulation temperature rating and routing situation (bundle or free air.)
With a suitably slow-blow fuse it would let a microwave run 3 minutes but still protect wire from continuous overload.

 

[eXodus]

Just found this chart:

https://www.amazon.com/Gauge-Flexible-Welding-Battery-Copper/dp/B07KBBRYRK/

which has EPDM insulation, that stuff has pretty high ratings for the diameter. Service rating for this over 250 F - 120C.

For an intermittent application where you don't have anything flammable on the cable you could potential downsize.

 

[A.Justice]

This is exactly the practice I was trying to avoid - layers of oversizing on top of layers of oversizing...

Oversizing electrical is standard, and safe, practice. I also always use one size up on wiring, charge controllers, and lugs / busses. It allows for upgrades later, and more importantly leaves a margin of safety. Remember, a trailer will get hot outside, so the insulation should be de-rated for the ambient temperature.

I have a 2200 watt inverter ran from a 12 volt system. I use 2/0 for an eight foot run.

I tried 3 different online wire-size calculators, and all 3 of them are saying that for a 20 foot run at 170 amps, you need anywhere from 1/0 to 750MCM to avoid serious heat and voltage drop.

@Hedges has, IMHO, the best and most cost effective idea. Put the inverter as close to the batteries as you can, and run AC. You could run 12 or 10 awg rather than a massive DC wire.

 

[sunrise]

Just found this chart:
View attachment 54025

https://www.amazon.com/Gauge-Flexible-Welding-Battery-Copper/dp/B07KBBRYRK/

which has EPDM insulation, that stuff has pretty high ratings for the diameter. Service rating for this over 250 F - 120C.

For an intermittent application where you don't have anything flammable on the cable you could potential downsize.

Thanks, @eXodus, in real world there are many factors affecting the result, like the quality of wires (pure copper?) I will definitely run a stress test before I put anything that does 150a-200a in my trailer. I'd run a 1500w load for 10 minutes, if it gets uncomfortably warm, I will upsize.

Again I am doing this because I have done this with the 1000w inverter (800w load) on 4awg (factory install) for at least 5 minutes and the wire barely get *any* warmer I had to use a temp gun to see it went up a little.

The cable isn't going to be in the wall, it will pass through a couple of cabinet at the floor level. not very tight, but not in open air like under belly of a trailer.

It's camping season, so I will hold off this for a few months, but I will definitely post the result back, either way we will all learn something.

 

[sunrise]

I am making a lithium battery from Eve 280 cells. When I'm done, I will have over twice the storage capacity in less space than the 4 Golf cart batteries it is replacing.

I saw a picture of an all in one inverter / charger, and this saved a bit of space also.

The chart I use does not have 200 A ampacity until 4/0. If the insulation is 90° C, them it is limited to 130 amps. If that wire were rated for 60° C insulation, then the insulation may melt, and that could mean a short. I think you could probably use Bare copper wire for a 200 amp rating, but not insulated. There's lots of caveats to that and maybe the wire you mention has a special insulation. A decent manufacturer will publish trusted specs on their wire. There's others that will publish numbers.

View attachment 54018
Whatever you decide, I'd like to see pics when you're done.

I made my battery from cells as well, about a year ago, when 280ah cells and > 120a BMS aren't available, or as popular as it's today. I did that just so I can fit >200ah next to my fresh water tank. It has worked beautifully so far.