Marine solar install

[gbynum]

What I don't have is the resistance per foot of various wire sized committed to memory.

I remember (memorized long ago) 2 things ... 10AWG is 1 ohm/1000 ft, a change of 3 gauges doubles or halves the resistance. That'll get you to #1 (is there a 0?) but not to the large "ought" sizes. So 16AWG is 4 ohms/1000'; 4AWG is 0.25 ohm/1000"

This helps more in household stuff than battery circuits, I'll grant.

A use full example ... 16AWG 50 ft extension cord (100' of current carrying wire), 0.4 ohms, 4 volt drop at 10A. Reasonable (3.3%) at 120V, not so (33%) at 12V.

[Mike90250]

> I got a larger inverter than I need as the chinese over state the numbers. I never run more than 2000 w at a time..

Then I'd suggest that any inverter over 2500w is wasted power keeping the internal electronics warm. But if you have it already....

[upston]

Hi Mike,

I got a larger inverter than I need as the chinese over state the numbers. I never run more than 2000 w at a time..

Upston

[Mike90250]

Often, I see the inverter mounted low on a bulkhead near the batteries. then 120Vac is run to the main power center.
the example I dummied into the spreadsheet, was to minimize all resistance, except for the inverter cables

How large of an inverter do you need ? Are you running a 1500w microwave or hair dryers ? Refrigerator ? The size of your inverter is dictated by the size of loads reasonably expected to be run together.

[JSchnee21]

I agree. Why not keep the inverter with (or very near) the batteries and just extend the AC side of things? Large diameter copper wire is very expensive per foot.

The current coming from the panels to the MPPT/Charge Controller (Xantrex SC), and from the Charge Controller to the batteries will be very small. But the current coming from the batteries to the Inverter can be quite large and the inverter can shutdown if the voltage sags too much under load.

[PNW_Steve]

I think that I would be taking a long and hard look at what may be done, practically, as far a moving the inverter closer to the batteries.

Just me though..... I tend to try and keep inverter and batteries as close as I am able.

[upston]

Hi Mike
Wow that is a great spread sheet, thanks a bunch. I have 90Volts apx coming from the array to the controller not 48 but that would half the amps right? The panels are flat, it's a boat, so I never get the full 2000w even in summer.

The base question I have is is it ok to hook the controller output to the inverter or should it be run all the way to the batteries? Also can you advise a good 48v inverter .
Thanks Upston

[Mike90250]

Well, I am so conditioned to seeing 12v and giant inverters, I shot this down too early. It still does not feel right, with 30' between batteries and inverter, but 125A & 2/O cable, it would work in theory, if the cable impedance is not too bad.

125A_60FT_dROP.jpg

[bcroe]

I do not memorize charts, I just look them up when I need them. Then a couple grade
school level calculations will give results. I certainly would not trust some unknown
software until I had throughly tested it out for sanity, if needed for frequent use.
Bruce Roe

[PNW_Steve]

Doesn't anyone understand Ohms Law anymore? Bruce Roe

Are you referring to OP or me?

I have a good understanding of Ohm's Law. What I don't have is the resistance per foot of various wire sized committed to memory. I may be a bit lazy as I use a calculator instead.

Works well for me but I have never installed a 6kw interter with a 60' connection to the batteries. I tend to lean a little more conservative and limit the inverter capacity to match actual needs and keep the inverter much closer to the batteries.

Just me though....

[JSchnee21]

Memorizing at best, "exposure" at worse, and actually understanding and internalizing a concept are two completely different things (-: I learned and applied Ohm's law in HS. But, to be honest, most of the applications involved calculating the current give a certain voltage DC battery and different sized resistors in various series and parallel configurations.

Understanding that V=IR, and that V can also equal VD (Voltage Drop) is what they might call "extension" these days (-: Though I believe I do recall a few examples. Most folks get hung up fingering out the typical resistance of the conductor depending on its cross sectional area and material.

This is a nice calculator that does AC 1-phase, 3-phase, and DC. No "knowledge" required (-:

https://www.calculator.net/voltage-drop-calculator.html

[bcroe]

What size wire do you have running from the battery bank to the inverter?

I tried plugging the numbers into a couple of online wire size calculators and they all choked on:

48v/125a and a 60' run to the batteries.

Doesn't anyone understand Ohms Law anymore? Bruce Roe

[upston]

Hi Steve

The cable is 0 ort and the run is 30 so do you double it pos and neg ?. My max load is 15 amps at 110 ac so 35 amps or so. How does that look to you ?

[PNW_Steve]

What size wire do you have running from the battery bank to the inverter?

I tried plugging the numbers into a couple of online wire size calculators and they all choked on:

48v/125a and a 60' run to the batteries.

[upston]

Hi Mike,
Thanks for the reply SC is Solar controller. Roger on the inverter so what would you advise on a new one. Batteries have to go in the bilge as 1000 lbs of of lead needs to be low. Not wise to have electronics in bilge so not sure how to make them closer.