rv off grid solar charging system questions.

animatt wrote: »

I have peel and stick panels. They are much bigger for the amount of power they provide. Also it heats rv up much more as effectively not it has a dark roof. Panels mounted off the roof with an air space would stay much cooler. For me there were other considerations, like stealth pv and to draw less attention.

I also had to move vents and do a bit of work to get panels to fit. Currently have 464watts of flexible panels on the roof and i have some more traditional panels lane out. I to have same amount of battery but wired as 24v 460ah.

Matthew

Cariboocoot wrote: »

You know what's a great thing to use for batteries? Blue Sea's terminal post fuses/holders. It keeps the protection very close to the source reducing the amount of unprotected circuit (against the dropped tool short you mention).

Sizing any over-current protection follows the same rules: wire has to be large enough to take the continuous current, fuse/breaker has to be large enough too. Your inverter should actually have specifications for this in the manual; you can't do better than what they recommend. A 12 Volt 2500 Watt inverter will probably have a 250 Amp fuse recommendation.

Best case scenario: each parallel battery string is fused against the full amount, and a single fuse of the same rating on the main lead to the inverter. That way if the total inverter current draw goes over the limit the main fuse will blow. If something goes wrong in the wiring nearer the battery the affected string fuse will blow. Possibly all will go in a 'cascade failure', but if only one gives out then the others can still provide power up to the limit.

Minimum scenario: the one fuse for the inverter, mounted as close to the battery bank as possible. Not recommended for more than two parallel battery strings.

BB. wrote: »

Worst case "code" calculations for an inverter usually look something like:

2,500 Watt AC power * 1/0.85 Inverter Eff * 1/10.5 volt batt cutoff * 1.25 NEC derate for Wire+Breaker+Fuse = 350 Amp minimum Branch Circuit

Nominal current may look more like:

2,500 Watts * 1/0.85 * 1/11.5 volt batt = 256 Amps "nominal" @ 2,500 watts

If you plan on using less wattage, you can back down on your fusing/wiring requirements.

-Bill

zoneblue wrote: »

This is a bit more than a toy system, those batterys have the potential to burn, and explode if mishandled.
Hencegood quality components and attention to assembly is well justified. If you have room for a 10kWh bank you have room a proper MNDC disconnnect, and proper carling inverter breaker(s).

So you have 2 pairs of 4awg (40mm2 total) from bank to inverter? Ok at a squeak, but you have a big inverter (for 12v). It draws a lot of amps, and under surge youll need every tenth of a volt you can get out of the bank. Hence to my mind you need a minimum of 50mm2 (1/0 AWG), hard core guys would even go 70mm2. Even 1/0 at 6feet is going to drop a third of a volt. http://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=0.3224&voltage=12&phase=dc&noofconductor=1&distance=6&distanceunit=feet&eres=250&x=57&y=16

With four strings youll then need a busbar, with exactly equal length subcables to the cells. While you might think those could be smaller, under fault conditions one string might take the entire load. So i wouldnt go much smaller. Check the ampacitys and temp ratings on the cables.

On the bank front, one solution to your 4 string predicament is getting a couple of those 500A battery switches, and charge and discharge them one at a time. Youd need to check if the bank can still keep up with the inverter. Getting a decent bit of amps into the cells helps keep stratification at bay.

If you are going to rewire it, that wire is relatively cheap in short lengths. Get a local auto sparky to do the crimps if you dont have a crimper.

Youve probably got a fair dose of reading ahead of you. Its a great hobby, enjoy. Stick around here for a few months and youll be an expert!

Cariboocoot wrote: »

With the bus bar method negative and positive are wired to common points through equal-length wires. The 'bus bars' don't actually have to be bars; the poor man's method is to use a single bolt in wood to pile all the wire lugs on.

4/0 will definitely handle 300 Amps. You can usually get the cables made to your sizes locally, rather than trying to buy pre-made lengths.

The wiring from the common points to the inverter can either be carried on single 4/0 as with the batteries or using the parallel 2 AWG (each with its own fuse).