how to wire battery bank? wire size? log types?

Equalization "typically" for AGM is just holding the charging voltage set point (~14.4 volts for AGM typically) for something like >8 hours to slowly help balance the cells.

Best to check with the battery vendor/documentation to see what they recommend. As I remember, the recommendations have changed over the years (from no EQ to Extended "absorb" EQ for AGMs in general).

The big thing is to keep AGM from gassing very much--This wears out the catalyst (there is a limit of XXX AH of life for the catalyst pellet during gassing, there is heat generated by the catalyst/gassing, and too much gassing/pressure causes the battery cell to vent and lose electrolyte/hydrogen/oxygen--not a good thing). As I understand.

-Bill "others know better than I" B.

For the DC fan... See if you can find a data sheet like this:

https://www.jameco.com/Jameco/Products/ProdDS/2306263.pdf

This above fan has a 10.2 to 13.8 volt rated voltage range. Pushing to 15+ volts is a bit much...

You could find an over-sized 24 volt fan and run it slower/lower voltage (12 volt range).

It is always a big issue between running stuff out of spec, vs adding additional hardware (buck/boost power supply) is another point of failure.

Fusing is to protect wiring and is generally mounted "close" to the source high current (like the battery + bus bar, or load center). A fuse at the destination does not protect a wire getting shorted to ground 1/2 to the load.

Running a little power converter (good cooling, protected from dust/dirt/moisture/high temperatures) should be OK.

There is always the risk of running your battery down when nobody is around (snow on array, failed wiring/panel/charge controller, etc.).

If, for example, you can live with the fan just running during the day, a small solar panel connected directly to the DC fan is another option. Let chances for failures to take out your $$$ battery bank (if unattended for months at a time).

I agree with you that alligator clamps make for very unreliable connections.

Anderson power pole connectors are very nice for DC power--Common for HAM radio. Probably overkill for a simple DC fan:

https://www.amazon.com/s?k=anderson+power+pole+connectors&crid=36AYBN49RQ6ET&sprefix=anderson+power+pole+connectors

You can also try any RV style plugs--Here is one:

https://www.amazon.com/Electop-Weatherproof-Universal-Flush-Mountable-Connector/dp/B07V6NJ37P

Some folks have used twist lock AC plugs and outlets, they are for 120/240/etc. VAC, but you can find good quality/cheaper ones for your DC wiring. I would not go with the "cigarette lighter" style plug and socket--I don't think they are reliable.

Again, the fuse inside the inverter does not protect your wire run from inverter to battery bus. Adding a fuse or breaker (breakers are nice--You can use them on on/off switches too). The idea is to protect your wiring from shorts (short wires are less likely to get shorted--Wiring from charger to battery bus should not be very long). Make sure no sharp edges where wire can get cut, etc...

And what you want is "equal length" wiring between multiple strings of batteries. If one string end to end bus connections are short, and the second string has 5 feet longer total length of wiring, the "extra resistance" of the longer wire run will reduce loading and charging currents for that longer string/wire run vs the "short run" string.

http://www.smartgauge.co.uk/batt_con.html

The DC +/- wires to the charge controller from the battery bank--The two wires do not have to be the "same length".

With any devices that can create Radio Frequency Interference (aka electrical noise) and/or if you have lightning in the area, you want your DC (and AC) wire runs to be close together (in same conduit, or bundle tied together, or twisted together, etc.). Doing that makes for a "poor antenna".

If you have "loops" (Hot/Neutral or +/- wires take "different routes"), makes for better antennas (more possible radio interference, more susceptible to lightning induced currents).

-Bill

For battery charging, I would use a 1/0.80 or 1.25x NEC derating for a 30 Amp output battery charger--Because batteries can take 30 amps for hours if they are well discharged... FLA batteries start to taper down from full charger current to less current (bulk vs absorb charging) when the bank is >~80% State of Charge:

• 30 amp continuous load * 1.25 derating = 37.5 Amps ~ 40 amp rated cables and breaker/fuses suggested

For NEC rated breakers/fuses, most will not blow below 80% of rated current and will pop/open/blow when >~100% rated current (could take minutes, or could take hours). Between 80% and 100% of rated current--may or may not trip.

I notice you are looking to automotive breakers... Go ahead and try them. If they fail, don't be surprised (I know nothing about these specific devices).

Here are some examples of 40 amp breakers from our host NAWS:

https://www.solar-electric.com/search/?q=40+amp+breaker

6 AWG is a good size to run "everywhere" for grounding. You do not worry about "single path" ground connections. That is not an issue because only fault current flow (lightning, short circuit).

We want "single point" grounding so that, for example a genset (or inverter) has AC neutral tied to safety ground, and you have AC neutral in the main panel tied to safety ground in the panel--You now have two parallel current paths. You have the White ground bonded neutral, and you have the green ground bond neutral. Each carrying a part of the current.

This is not only not wanted (we do not want the green wire to be "part" of the normal current path), there is an issue with AC power. You have some current going with Hot and Neutral into knockout in the panel, and you have the balance of the current on the green wire going into a second knockout in the panel. With AC power, those separate conductors act like a transformer and can cause circulating current in the panel sheet metal--And with high current flow, can actually cause the panel sheet metal to overheat.

1. Probably not, and is actually the standard method of ground bonding the neutral. HOWEVER, this should only be done with PSW/TSW AC inverters. With MSW (modified sine/square wave) AC inverters, the bonding of an AC output wire can short out the inverter. Also, you need to confirm that your AC inverter has floating AC outputs (no Neutral to Chassis bonding) and your genset has no AC Neutral to Ground bonding (previous paragraph). From what little I have seen, in North America, it appears that inverters+gensets at 3,000 Watts or smaller, have floating AC Neutrals. And I would guess that gensets >~3,000 Watts or so tend to come with AC Neutral bonded to generator chassis/ground connection.

2. Wheelman's suggestion of burying plastic conduit is nice... If you every need to replace wiring (larger genset down the road, bringing AC inverter wiring out for an AC outlet/lighting/etc. remotely)--Having a pipe makes it easy without having to retrench (I am cheap, I used pretty large diameter ABS pipe for my DIY trenches--But Gray color rated conduit may not be expensive either).

2a. Tie the ground wire to the genset chassis ground, and to your normal AC ground connection (in the J-Box for transfer switch, or in the main AC panel would be my first choice). If you have lightning (which you do not?), a ground rod next to the genset and at the outside of the foundation, tie ground wire there first, and then continue bring ground into the J-Box. If lightning, then surge suppressors at the "wall" of the residence to shunt lightning surge to ground before it gets into the building is recommended.

3. Ventilation when hot and/or battery charging. Good idea. Heat kills batteries (for every 10C/18F over ~25C/75F, batteries "age" 2x faster or 1/2 the battery life--age faster when hot). Also, if you have a relatively air tight box, you want to vent hydrogen gas and electrolyte fumes when charging... FLA batteries normally vent when charging. AGM will vent if over charged and as they near failure). You could do things like a voltage controlled switch... I.e., turn on fan when battery voltage is >13.8 volts (example).

4. You can use a DMM to estimate the battery state of charge and monitor the charging/discharging. But it is not accurate:

http://www.scubaengineer.com/documents/lead_acid_battery_charging_graphs.pdf

And, as always, there is "hardware" for that...

For flooded cell lead acid batteries, a Hydrometer is the gold standard:

https://www.solar-electric.com/search/?q=hydrometer

And meter wise... You can get Voltage Only based meters:

https://www.solar-electric.com/midnite-solar-mnbcms.html
http://www.smartgauge.co.uk/products.html

And shunt based meters (more accurate, but can still "drift"):

https://www.solar-electric.com/residential/meters-monitoring/battery-monitoring.html?product_list_limit=all

Trimetric, Xatrex, Victron are well known... Trimetric may be a bit "tricky" to program (like the VCR Clock--Confusing button presses).

And there is a flood of Amazon/eBay "battery monitors"... You have to read closely to see if they are battery monitors (i.e., operate during charge and discharge) vs simply current/power meters (do not reflect battery state of charge):

https://www.amazon.com/s?k=battery+monitors&ref=nb_sb_noss_1

If you use a simple voltmeter--You can get a pretty good idea of how things are working (i.e., battery reaches 14.75 volts for several hours to fully recharge, resting voltage around 12.7 volts is full, around 12.4 volts is 1/2 charge resting, avoid taking bank below 11.5 volts under light to moderate loads (short surge current can drop to 10.5 volts).

If months/years down the road, you see the battery bank behaving "differently", then you need to investigate. The expensive hardware is nice, but not needed. If you have multiple people using the system (spouse, friends, etc., a true battery monitor may be more helpful).

-Bill

You can run multiple ground wires to one (or more) ground rods. I.e., from panel/mounting rack to ground rod, from main panel to ground rod, even from battery bank to ground rod. Multi point grounding is fine, and in cases of lighting, is actually a good thing. You want (for example) the ground(s) from your array frames (and wall mounted panel surge suppressors, if used) to go directly to the ground rod at the base of the wall (rod(s) outside the wall). You don't want to (for example) bring the grounds from the roof, into the building, then to a ground rod. You don't want to bring lightning into your residence (I know the lightning is not a concern for your location, as I recall).

If you are going to install a ground bus bar in the main panel (vs current wire nutting), you do not need an insulated bus bar--A standard bolt to the sheet metal type will also take care of the bus bar "ground bonding" too.

That point at which you tie Neutral to Ground bus is the "single point" of grounding we are looking for.
With mixed DC and AC power system--Safety Grounding becomes a bit more "complicated".

More or less, you want to avoid a fault current that should go to your battery bus directly, to not go through an AC ground wire.

What the issue is that your 12 VDC bus input current is about 10x the AC output of your AC inverter. If you have 10 amps of AC rated inverter (around 1,500 Watts), and that would be about 100 Amps of 12 VDC. If, for example, you connected a 14 AWG green wire to your chassis ground of the AC inverter and to the AC ground bar... The current for an internal AC inverter ground fault will have to go through 14 AWG to the AC panel, then 14 (or whatever) to the ground rod (your common AC/DC ground point), and back to the battery bank. And you may have around a 120 Amp fuse/breaker on the 12 volt inverter connection. That means your 14 AWG cable must handle >120 amps of fault current to trip the DC inverter fuse/breaker.

Instead, you connect your inverter chassis ground (6 AWG minimum, or even up to your AWG of your +/- DC cables) back to the battery bank (or ground rod--either is fine). That way, if there is an inverter internal ground fault, the heavy DC current flows through the 6+ AWG wiring back to the battery negative bus, and trips the OPD (over current protective device).

For switches, you can always try and automotive or marine store. For 1 amp circuits and less (LED lighting, small fans, etc.)... Not usually anything to be very concerned about. 10 amps and above, there is significant energy that could overheat a switch (cause fire) if the failure is "bad enough".

For arcing DC switch issues... 12 VDC is really at the minimum of the capability of an electrical circuit to even sustain an arc. 24 VDC and higher system voltages are really the issue for switch arcing.

For shocks, 12 volts (at 8 amps, as I recall from UL years ago--I think) is considered "touch safe". 24 to 48 volts is questionable (trained personnel, behind locked doors/screwed shut panels). And >60 Volts is hazardous.

I have worked on aircraft where I have gotten a mild shock from 24 volts (if I am sweating). Felt like a was getting poked by a sliver of metal or similar--Was not even sure it was a shock at first.

The Graingers switch is fine. Carling makes very nice products in general. Note that there DC rating is 12 volts max... Probably to stay under the minimum arc voltage (and allow them the 20 amp rating).

As long as you are working with 12 VDC, an similarly rated 120 VAC system (i.e., XX Amps) is probably fine for your needs. Unless I had a Grainger near by--I probably would not bother driving very far out of may way for that switch.

And, the other battery bank warning. Lead Acid (AGM) and Li Ion batteries can output a whole bunch of current into a dead short (100's of Amperes, or even a LOT more for large banks). As always, remove jewlery and rings, and use electrical tape wrapped around tools/wrench handles, etc. when working on the batteries and their wiring. Avoid (for example) welding your wrench to the battery buses.

If you are really careful, wear a face shield when working on lead acid batteries. There is always the possibility of hydrogen gas build up around batteries and in the cells. And a small spark of setting it off. Battery tops/bus wiring needs to be protected (box, cover, locked room) from children/unauthorized access. You don't want your tools/parts on bench top falling into the battery wiring.

I am a little confused with the ATS (automatic transfer switch?) vs an "extra plug" inline. Generally you hardwire ATS switches. No extra plugs. However, also very safe, a short cord and plug to your AC main panel input, and two AC outlets. One to the inverter and one to the genset and you choose which source for your AC paenl--A "manual" transfer switch.

If the extra plug is, for example, at the cabin wall going to the genset--IT is not going to hurt anything. Yes, the extra plug is always an extra point of failure (blades overheat, get water in/on the metal and corroded, etc.).

If you are burying the wiring to the genset--You can always hardwire your buried cable to the ATS/AC J-Box.

If you had lightning as an issue--some folks will unplug the genset wiring from the wall and move it back 10 feet to avoid bringing a lightning strike inside... But if you have lightning issues, then surge suppressors on solar DC panel wiring, and genset wiring--Put SPDs at wall where they enter the living space. And install an SPD on the main panel.

https://www.solar-electric.com/residential/circuit-protection/surge-protection.html

Not cheap, but repairing/replacing an AC inverter or genset is not cheap either.

-Bill

Down the road, there are "companion" type eu2x00i gensets (and the 3k+ models) from Honda that have 30 amp twist lock 120 VAC plugs...

-Bill

Don't ask so many "its complicated/it depends" questions in one post.   

Always ask for clarifications when needed. Try not to get to deep unless it is needed.

-Bill