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Old 22-01-2015, 12:57   #16
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Re: Batt To Inverter Cable Length Question

Quote:
Originally Posted by btrayfors View Post
smac999 had it exactly right. AWG 4/0 cable is larger than AWG 2/0, and is the proper size for a 2000-watt inverter installed about 10 feet from the batteries (one way).

Be advised also to install a proper fuse. Only three types are acceptable, in order of preference:

1. Class-T
2. ANL
3. MRBF (terminal fuse).

These should be installed as close to the batteries as possible. ABYC calls for "within 7 inches".

Bill
Only when you get into the /0s.

10 is larger than 12, isn't that a bitch. I probably only have 2/0 coming into my house. Battery cables probably run in the /0s. I doubt that is the problem.
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Old 22-01-2015, 13:10   #17
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Re: Batt To Inverter Cable Length Question

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Originally Posted by Cadence View Post
Only when you get into the /0s.

10 is larger than 12, isn't that a bitch. I probably only have 2/0 coming into my house. Battery cables probably run in the /0s. I doubt that is the problem.
I don't know what "problem" you're referring to, nor how wire size into your house (AC) has anything to do with the discussion here.

We're talking about the correct way to wire a 2000-watt 12-volt DC to 120-volt AC inverter on a boat.

Bill
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Old 22-01-2015, 14:21   #18
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Re: Batt To Inverter Cable Length Question

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Originally Posted by btrayfors View Post
I don't know what "problem" you're referring to, nor how wire size into your house (AC) has anything to do with the discussion here.

We're talking about the correct way to wire a 2000-watt 12-volt DC to 120-volt AC inverter on a boat.

Bill
I guess it was the assumption that up a size was referring to wire gauge not wire diameter. I guess he should just run bus bars,
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Old 22-01-2015, 15:50   #19
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Re: Batt To Inverter Cable Length Question

No matter how You size up the wires wich will cost U dearly.
The best place is still the old one

CLOSE TO THE BATTERIES
The closer the better

Don´t fix it if it´s functioning
specially if U don´t dominate OHMS LAW
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Old 23-01-2015, 03:45   #20
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Re: Batt To Inverter Cable Length Question

You calculate the cable area this way.

Distance between battery and inverter 2.7 m, cable length l = 5.4 m
Coppers resistivity ρ = 0.0174 µΩ m = 0.0174 Ωmm²/m
System voltage 12 V
Desired max voltage drop 3% gives U = 12 V * 3% = 0.36 V
Max load 2000 W
Or current I = 2000 W / 12 V ≈ 167 A
Max resistance in cable R = U / I = 0,36 V / 167 A = 2.16 m Ω
Cable area A = ρ * l / R = 0.0174 Ω mm²/m * 5.4 m / 2.16 m Ω≈ 43.5 mm²

If you desire to have max 1% voltage drop, the cable area will be 3 * 43.5 mm² ≈ 131 mm²

If you take half the distance then you can have half the area and the inverter will not feel any difference. It’s the same in the other direction. If you double the distance and double the area, the inverter will not feel any difference.

But if you have it closer, you can have smaller area and shorter cable and both things make it cheaper.
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Old 23-01-2015, 13:12   #21
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Re: Batt To Inverter Cable Length Question

Quote:
Originally Posted by warrior 90 View Post
No matter how You size up the wires wich will cost U dearly.
The best place is still the old one

CLOSE TO THE BATTERIES
The closer the better

Don´t fix it if it´s functioning
specially if U don´t dominate OHMS LAW
But not "on top of the batteries" (that's where the original apparently was installed).


BTW: You don't have to understand ohms law to do electrical work on your boat. Strangers on the Internet will give you conflicting instructions.
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Old 23-01-2015, 13:15   #22
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Re: Batt To Inverter Cable Length Question

Quote:
Originally Posted by Lars_L View Post
You calculate the cable area this way.

Distance between battery and inverter 2.7 m, cable length l = 5.4 m
Coppers resistivity ρ = 0.0174 µΩ m = 0.0174 Ωmm²/m
System voltage 12 V
Desired max voltage drop 3% gives U = 12 V * 3% = 0.36 V
Max load 2000 W
Or current I = 2000 W / 12 V ≈ 167 A
Max resistance in cable R = U / I = 0,36 V / 167 A = 2.16 m Ω
Cable area A = ρ * l / R = 0.0174 Ω mm²/m * 5.4 m / 2.16 m Ω≈ 43.5 mm²

If you desire to have max 1% voltage drop, the cable area will be 3 * 43.5 mm² ≈ 131 mm²

If you take half the distance then you can have half the area and the inverter will not feel any difference. It’s the same in the other direction. If you double the distance and double the area, the inverter will not feel any difference.

But if you have it closer, you can have smaller area and shorter cable and both things make it cheaper.
Or just get out your West Marine catalog and look it up.
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Old 23-01-2015, 15:03   #23
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Re: Batt To Inverter Cable Length Question

Unfortunately, it is not clear from their charts that it is a completely linear relationship.
I.e. do you have a location and a certain cable area, so if you increase the distance by 50% so you should increase the area by 50%.
Then you need the WM table to see what it will be for the AWG number.
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Old 23-01-2015, 15:59   #24
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Re: Batt To Inverter Cable Length Question

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Originally Posted by Lars_L View Post
Unfortunately, it is not clear from their charts that it is a completely linear relationship.
I.e. do you have a location and a certain cable area, so if you increase the distance by 50% so you should increase the area by 50%.
Then you need the WM table to see what it will be for the AWG number.
You don't need to worry about "area". The size and rating of the cable takes all that into account.
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Old 23-01-2015, 19:24   #25
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Re: Batt To Inverter Cable Length Question

I just had this same issue. Tried lots of different cables. Had to stick with keeping it close to battery bank. Kept having voltage drop on heavy loads. It would run tvs lights, ect. As soon as I cranked microwave or anything else. Low voltage shut off

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Old 23-01-2015, 19:35   #26
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Re: Batt To Inverter Cable Length Question

Just a thought.
If you decide to exceed the recommended distance from batts and therefore need an increased wire size, make sure that the lugs will actually handle it...
OK. Another thought.
Why two inverters? Why not just the one larger one?
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Old 24-01-2015, 08:28   #27
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Re: Batt To Inverter Cable Length Question

Thanks for all the replies. If I am sorting through it correctly,the answer to my question is to go buy 20 ft. of welding cable. Correct?
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Old 24-01-2015, 11:25   #28
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Re: Batt To Inverter Cable Length Question

2000 watt inverters (or inverter/chargers) are not small investments. Most would want to protect that investment so they can use it for as long as possible and still get the performance they need.

So - here are some thoughts:

Inverters hate to be too hot, but many are installed in engine spaces where it is very hot. And, many are installed under berths or salon cushions without adequate ventilation to help with the heat they generate. The harder they work the hotter they get. Sometimes you are limited in location but you can at least mitigate it by providing some ventilation under salon seats, etc. In engine rooms, it is hottest at the top but you may not be able to avoid that. You make your decision and you pay your price.

Battery fumes are even worse for inverters than heat. The connections corrode, the internal metals corrode, the boards corrode. The manufacturers ALWAYS state - "Do not locate them above or too close to batteries". Having said that I did do that over my AGM batteries. I would not have done that over wet cells. If you do, you will definitely have to replace the inverter quicker than you would if it were located elsewhere. Use longer, larger, cables to install it anywhere else than over the top of the wet batteries. You can cheap out short term but I guarantee you will not long term. Warranties don't cover corrosion and in any case will take longer than the warranty.

You can always mitigate the voltage drop from wiring with larger wire. Some inverters are more sensitive to voltage drop than others but you should always follow the manufacturers recommendations and if in doubt go bigger. I used 2/0 for mine and it was very close to the batteries. It is a wiser investment to go larger wire to get the inverter to a cooler, better ventilated, and less corrosive place. This is not an area to go cheap on.

Lug sizes are a consideration, especially on the safety ground, for some inverters. But I can't remember seeing a recent 2kw inverter that would not take 2/0 wire. If there is an issue with putting a big crimp on a post I would take my dikes or other cutter and trim the lug done on the sides a bit. If it will not accept the wire into the screw down type insertion connection, you can carefully reduce some of the battery wire up to the insulation. This is not my preference but better that than using too small a wire. Or, you can take a smaller wire off of the inverter and take it to a cable post and put the smaller cable from the inverter to a much bigger wire from the post to the batteries. This is perfectly workable but you do have two or four more crimps to do right and you have to make sure the posts are kept tight.

Also, make sure you install the safety ground of the same size, or only one size down, from the main positive/negative cables. If the inverter has an internal failure the full current might have to flow through this wire. If it is too small it will overheat and possibly start a big electrical fire.

Most voltage drop problems I have seen have been from running down the batteries and not from the wiring (if the wiring was the right size in the first place). We would often run the inverter hard with a microwave, on boats with them, with a cup of water if we needed to test the charging function of the charger or the alternator. If the voltage of the batteries was too high, the charging regulators or the inverter regulation would not kick in full charge mode. So we could test the alternator or charger quicker than waiting for a smaller load to bring down the batteries. Granted this was only done for 1-2 minutes with just a cup of water in the MW. During regular use and you run the inverter for harder/longer, it will drop the voltage of small banks quickly and even larger deep cycle banks for really steady heavy use (like a hair dryer). The battery bank size is a big factor in how long you can run the inverter hard.

Last - welding cables are cheaper than marine grade cables of the same size but are NOT recommended on boats - in general - especially in the engine room, bilge spaces, or anywhere else they may get wet or oily or where they can get diesel on them. Some welding cable may be rated for oil and chemical resistance but the standard stuff is not. I have literally pulled out welding cable where the insulation would be soft and pull off the cable by the dissolution of the cover by oil/diesel. Insulation failure is usually on the side of the cable that is down, or under, where it is difficult to see. No insulation can lead to fire and equipment failure. My new(old) boat came with welding cable. I have inspected all of it and have a plan to replace it soon. It is a cost I don't really want since large marine grade cable is so expensive, but I will sleep better at night knowing my boat won't burn up either with me on it or not.

Also, if you do use welding cable you need to make sure its temperature rating is equivalent to the rating of the wire recommended by the manufacturer. If you take a look at battery wiring sizing tables there are multiple columns for different temperature ratings with the larger wire size (smaller gauge) required for lower rated cables. Welding cables are usually not rated as high as the good marine wire cables are so you need to go up in wire size.

This is not an area to go cheap.
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Old 24-01-2015, 11:50   #29
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Re: Batt To Inverter Cable Length Question

Quote:
Originally Posted by exMaggieDrum View Post
2000 watt inverters (or inverter/chargers) are not small investments. Most would want to protect that investment so they can use it for as long as possible and still get the performance they need.

So - here are some thoughts:

Inverters hate to be too hot, but many are installed in engine spaces where it is very hot. And, many are installed under berths or salon cushions without adequate ventilation to help with the heat they generate. The harder they work the hotter they get. Sometimes you are limited in location but you can at least mitigate it by providing some ventilation under salon seats, etc. In engine rooms, it is hottest at the top but you may not be able to avoid that. You make your decision and you pay your price.

Battery fumes are even worse for inverters than heat. The connections corrode, the internal metals corrode, the boards corrode. The manufacturers ALWAYS state - "Do not locate them above or too close to batteries". Having said that I did do that over my AGM batteries. I would not have done that over wet cells. If you do, you will definitely have to replace the inverter quicker than you would if it were located elsewhere. Use longer, larger, cables to install it anywhere else than over the top of the wet batteries. You can cheap out short term but I guarantee you will not long term. Warranties don't cover corrosion and in any case will take longer than the warranty.

You can always mitigate the voltage drop from wiring with larger wire. Some inverters are more sensitive to voltage drop than others but you should always follow the manufacturers recommendations and if in doubt go bigger. I used 2/0 for mine and it was very close to the batteries. It is a wiser investment to go larger wire to get the inverter to a cooler, better ventilated, and less corrosive place. This is not an area to go cheap on.

Lug sizes are a consideration, especially on the safety ground, for some inverters. But I can't remember seeing a recent 2kw inverter that would not take 2/0 wire. If there is an issue with putting a big crimp on a post I would take my dikes or other cutter and trim the lug done on the sides a bit. If it will not accept the wire into the screw down type insertion connection, you can carefully reduce some of the battery wire up to the insulation. This is not my preference but better that than using too small a wire. Or, you can take a smaller wire off of the inverter and take it to a cable post and put the smaller cable from the inverter to a much bigger wire from the post to the batteries. This is perfectly workable but you do have two or four more crimps to do right and you have to make sure the posts are kept tight.

Also, make sure you install the safety ground of the same size, or only one size down, from the main positive/negative cables. If the inverter has an internal failure the full current might have to flow through this wire. If it is too small it will overheat and possibly start a big electrical fire.

Most voltage drop problems I have seen have been from running down the batteries and not from the wiring (if the wiring was the right size in the first place). We would often run the inverter hard with a microwave, on boats with them, with a cup of water if we needed to test the charging function of the charger or the alternator. If the voltage of the batteries was too high, the charging regulators or the inverter regulation would not kick in full charge mode. So we could test the alternator or charger quicker than waiting for a smaller load to bring down the batteries. Granted this was only done for 1-2 minutes with just a cup of water in the MW. During regular use and you run the inverter for harder/longer, it will drop the voltage of small banks quickly and even larger deep cycle banks for really steady heavy use (like a hair dryer). The battery bank size is a big factor in how long you can run the inverter hard.

Last - welding cables are cheaper than marine grade cables of the same size but are NOT recommended on boats - in general - especially in the engine room, bilge spaces, or anywhere else they may get wet or oily or where they can get diesel on them. Some welding cable may be rated for oil and chemical resistance but the standard stuff is not. I have literally pulled out welding cable where the insulation would be soft and pull off the cable by the dissolution of the cover by oil/diesel. Insulation failure is usually on the side of the cable that is down, or under, where it is difficult to see. No insulation can lead to fire and equipment failure. My new(old) boat came with welding cable. I have inspected all of it and have a plan to replace it soon. It is a cost I don't really want since large marine grade cable is so expensive, but I will sleep better at night knowing my boat won't burn up either with me on it or not.

Also, if you do use welding cable you need to make sure its temperature rating is equivalent to the rating of the wire recommended by the manufacturer. If you take a look at battery wiring sizing tables there are multiple columns for different temperature ratings with the larger wire size (smaller gauge) required for lower rated cables. Welding cables are usually not rated as high as the good marine wire cables are so you need to go up in wire size.

This is not an area to go cheap.
Grats! You are the first person to indicate mounting an expensive inverter directly above the batteries may not be a great idea from the standpoint of fumes. They may be sealed batteries? If not kiss the inverter off more quickly than normal.
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Old 24-01-2015, 13:39   #30
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Re: Batt To Inverter Cable Length Question

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Originally Posted by Canibul View Post
Thanks for all the replies. If I am sorting through it correctly,the answer to my question is to go buy 20 ft. of welding cable. Correct?
No. It's a boat, not a welder so go buy 20 ft of boat cable. Ten feet of red and ten feet of black or yellow, whichever color is used for negative on your boat.

genuinedealz.com is a good source and they will install the connectors if you wish.
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