Inverter Battery Cable Length

Ericbsc · October 28, 2009, 06:56:22 AM

I am installing a Freedom 3k inverter in an 05 Eagle. I had planned to put the batteries in the old ac bay in the back passenger corner. The inverter will be in the back bay. This would make the battery cables app. 20-22 ft. long. I am going tio use 4/0 welding cable. The manual says not over 10' run for battery cables. I called and the tech guy said I would loose power? I know of others who run that far with no problems. Suggestions comments?

grantgoold · October 28, 2009, 07:04:46 AM

I kept my length to less than 4 feet with a shield between the batteries and the inverter. I too spoke with a tech and he said they could use the length as a reason not to service the warranty. As I read the installation materials, it seemed like the longer the wire the less efficent the system and the more pull from the bank would occur. I used large battery cable for the entire system and it works awesome. I got the expensive cable on ebay.

Good luck!

bevans6 · October 28, 2009, 08:13:43 AM

I found this to be an interesting question. I know there are others who do this sort of calculation professionally, but I did a voltage drop calculation based on 3,000 watts at 12 volts, and found that you will have a 5% nominal voltage loss, or 0.6 volts. That means, to me, that when your batteries are fully charged the inverter will act as though they were at 12 volts, or pretty much discharged. What that means, I don't know, but I would like to hear!

Brian

Len Silva · October 28, 2009, 08:23:12 AM

Using this calculator: http://www.nooutage.com/vdrop.htm

260 amps (3000 watts / 12 volts + some loss) through 22 feet of 4/0 = 5.8% drop or almost 0.7 volts, far too high. You want to try for less than 0.2 volts or less than 2%.

You would need three 4/0 cables in parallel in both directions (6 runs) to accomplish that.

Using that same calculator, about 7-1/2 feet for 4/0 cable.

It is only an issue if you use all the 3000 watts the inverter is capable of. A single run of 4/0 will handle about 90 amps or about 1000 watts.

Voltage drop in the 120 volt wiring is not an issue for all practical purposes. Try to locate the inverter as close to the batteries as possible.

bevans6 · October 28, 2009, 08:43:24 AM

I just had a thought, probably a bad idea but - could you ground the battery bank and the inverter 12 volt negative side to the chassis and use the bus chassis for the return? As I said, I suspect there are reasons not to do this.

Brian

belfert · October 28, 2009, 10:03:05 AM

Voltage drop is supposed to be hard on inverters. A guy who services inverters also told me that really long DC cables will somehow form small amounts of AC that will hurt the inverter.

Sean has said it is not a good idea to put a 4/0 cable's worth of ground through the chassis. I don't recall why not.

tomhamrick · October 28, 2009, 01:15:25 PM

I am running the same length run that Eric is talking about and have been for several years. I am running a 3000W Heart and I have never had any problems with the invertor half as it runs my house fridge. Only problem is I cannot keep the batts clean. It seems to charge a good bit but the voltage does not get too high. If the invertor is not seeing full voltage then it would make sense that it would try to keep charging even when full. Now that I have removed the generator from the back bay I may try to move my batts a little closer to the invertor.
Tom Hamrick
1984 Eagle 10S