Inverter Cable Question

[Rabbit]

I've got a working solar power system in my cargo-trailer conversion, and am now using leftover panels to build a nearly identical one at my home base, so that these panels won't be wasted. In my trailer system, I've got the leads to my inverter connected to the physically-opposite diagonal ends of my battery bank, as according to what I've learned so far (here mostly-- thanks, folks!) that's a more efficient setup than connecting them to terminals at the same end. (Though there are even better, more balanced setups, they require more spending on cables than I'm prepared to shell out.) With my home setup, however, this won't be as easy. For one thing, I have a perfectly-good set of cables already in hand that're too short to allow hooking from both ends but would work perfectly if connected to the same end. For the other, there are physical limitations that require me to locate the inverter at one end of the bank regardless of how I wire it, so that if I do buy new cables and want to keep them equal length they'll have to be be at least 5-6 feet long instead of the 2-footers I already own. Since this is a 2000 watt inverter, we're talking a good bit of money for large-enough-gauge cables that long.

So... My question is this. How much real-world efficiency am I really losing if I simply hook up the cables I already own to the terminals on one end of my 6x6 volt (wired to 12 volt) FLA (golf-cart) battery bank? Yes, I know it's less efficient, but... $60 or (probably) more worth of less efficient?

Thanks!

 

[highdesertranger]

so you have six 6v batteries, 3 banks wired in a series and those 3 banks wired in parallel.

if you do it the way you described the bank that you connect the inverter to will get abused long before the other banks shortening its life. highdesertranger

 

[John61CT]

Yes don't do that.

Not a question of efficiency, but longevity of your bank.

 

[Rabbit]

so you have six 6v batteries, 3 banks wired in a series and those 3 banks wired in parallel.

if you do it the way you described the bank that you connect the inverter to will get abused long before the other banks shortening its life. highdesertranger

Thank you both. And yes, that's how they're wired.

 

[DannyB1954]

You can buy automotive jumper cables cheaper than you can buy just the wire. I bought 4 gauge 20' for $20 at walmart and home depot. So that actually is 40' of wire, (20 + 20 -).
Another thing that you can do is convert to a higher voltage system like 24, 48, or even higher. The higher the voltage, the thinner the wire can be. They make inverters that take all sorts of input voltage.

 

[Rabbit]

Thanks, Danny!

 

[bigskybob]

It will work fine.

 

[Weight]

Walmart jumper cables are not designed for long term high ampere use. Just very short bursts of starter current. Get decent cables, your battery will last longer, your devices will work better, and you will be safe. Genuine Dealz, google it, I can't post links.

 

[highdesertranger]

yeah the cheaper jumper cables are copper clad aluminum. highdesertranger

 

[DannyB1954]

Walmart jumper cables are not designed for long term high ampere use. Just very short bursts of starter current. Get decent cables, your battery will last longer, your devices will work better, and you will be safe. Genuine Dealz,   google it, I can't post links.

Jumper cables not made for high amperage use? What kind of current does a starter and dead battery take? What is 4 gauge wire made for then? Why not tell them they need silver or gold welding wires? They are powering a 2,000 watt inverter. The length of his run is 6'. What sort of voltage drop do you figure he will have instead of using 2 gauge wire?

As far as being made of aluminum, when cut mine are not silver on the end. How did the plating go all the way through? They also solder just fine.

 

[Canine]

Here is how to hook up your battery cables: http://www.smartgauge.co.uk/batt_con.html

12 volt systems are the way to go for small builds except for some very rare exceptions. I have posted about that (among some other info) here: https://vanlivingforum.com/showthread.php?tid=30424&pid=380179#pid380179

I wouldn't cheap out on wire. We need every drop of electrons we can get from our small systems.

Batteries are expensive. When you don't hook a bank up correctly one battery will live a short life and it will have to be replaced sooner than it should have. Then when you need to replace on one, or two in you case, batteries, you have to replace the whole bank! Because the other batteries are old and will drag on the new batteries, wearing them down faster. Is $60 worth it? YES!!!!!!!

I highly recommend 4/0 cable of high quality.

Rabbit, I will PM you in a minute...

 

[Rabbit]

Thanks so much to everyone, and especially Canine for his PM!

I've ordered a set of 4' 2/0 cables to connect to opposite ends of my battery bank, based on reading three separate website amperage guides. It should be noted that that, though I have a 2000 watt inverter on the way I only plan to run it at anything resembling full power very rarely and never for more than ten-twelve minutes at a time (to power an electric kettle or pressure cooker either during an extended power outage or when I have extra juice to burn, which I don't expect will be often). It'll be in steady use at only 500 watts, tops (and even that's probably high and only for relatively short periods.) I suspect these 2/0's will do the trick, so long as I don't push the inverter to its absolute limits on a regular basis or for hours at a time.

You guys here are the greatest! I could not be successfully getting this done without you, and I'm truly grateful for the support.

 

[John61CT]

Jumper cables only need to carry the high current for very short time.

When you use them for hundreds of anps for long, you'll feel them get hot right quick, and cheap ones will melt all over the place.

The good stuff is tinned boat cable, UL-1426 with a 100+°C rated jacket

 

[Canine]

Rabbit, I agree with your assessment. Since you aren't going to be running high current for long periods of time, you will be totally fine with the small voltage drop compared to 4/0 cables.

 

[Weight]

My 2000W inverter instructions specified 2/0 cable for up to 10 feet.

I don't care how much a starter draws, Walmart jumper cables should not be used for a 2000 watt inverter.

 

[jasper]

My old-fashioned technique for determining if a wire and connections can handle the load (ampacity) is to use a digital voltmeter with long test leads.

With the inverter at maximum load, place one voltmeter test lead at the battery positive and the other test lead at the inverter positive.  

In a perfect world, the voltage should read zero.   If not, there is a power loss. I run this test occasionally to try to identify a connection problem before it gets worse. Same for solar wire runs.

If there is a voltage measured from a battery to inverter single wire run, it is subtracted from battery voltage to determine the voltage the internal "voltmeter" inside the inverter sees.  If it drops too low, for whatever reason, the inverter should automatically shut down. I can usually sleep through those aggravating beeps, but my wife quickly wakes me up to tell me.

The negative lead must pass the same test.

 

[Rabbit]

Interesting. Thank you!

 

[Weight]

That is not 'old fashioned' That is a proper trouble shooting procedure. The same principal is used to check voltage drop across connections. It is important to use an accurate voltmeter capable of 3 decimal points below 1 volt. My free Harbor Freight multi-meter is not the one I grab for these tests. I go for the $300 one.