Setting up a solar system at camp

[Skead]

Start off by saying thank you to the experts you contribute to this forum, I have read several threads now and there is a vast amount of knowledge on this site.

This summer I purchased a lot with plans down the road to build a camp (if lumber ever goes back to normal). In the meantime, the wife and I purchased a newer park model trailer which we will leave there for the next few years while we make up our minds. The steady humm of a generator is not overly appealing to me so we will go solar with a gas generator for the higher consumption items.

I was given a 4000W inverter, a 150W panel and 2 - 100W panels. My vision, was to have the panels, a bank of 6V batteries (I have not yet done he math to see how many I need) the inverter, a 40 amp MPPT controller, a good battery charger and a 5000W gas generator and call it a day. My plan was to have the inverter remote start in the trailer and the generator on a automatic starter when the batteries dip down.

It does get hot for a few weeks of summer and that tin can will heat up, so A/C would be nice for a couple hours before bed. Otherwise, I really only have a 12v radio onboard, 12v lights, 12v water pump. 12v 45w fridge, occasional use of a microwave, occasional use of tv, cell chargers, etc. 40W Cpap machine, nothing too crazy.

Question 1: Does it make more sense to run items like the A/C direct off the generator, or have it through the inverter and the generator can keep the batteries topped up? I looked up the specs on the A/C unit and it draws a little under 2000W (not sure what it pulls on start up). I did read SunKing's post a the top of the forum where he does not recommend an inverter over 1000W making me think this is a bad idea, but I wanted to ask because it would really simplify things. Affordable generators are hard on electronics and inverter style generators large enough to run the A/C are costly, which is why I wanted to go the route of the big inverter.

Question 2: Can you mix match types/brands of batteries? I have built battery boxes to securely and safely house the batteries and have air flow to vent the gases, I have all the batteries going into a bus bar on either side of the box. In my head, I would have 2 6V batteries (or more), wired to make 12 going into the bus bar. There is a lot of cost to the batteries and I do a few 12V batteries that I have load tested and are OK which could get me through the summer so I can save more sheckles to buy more 6V batteries next year. Can I mix them ?

Question 3: The whole trailer runs on a 30 amp plug so it shouldn't ever really exceed 30 amp's in theory. The plug in at the back supplies the 110V system which I assume has an onboard battery charger somewhere that recharges the batteries at the front which in turn runs the 12V system, lights, radio, etc. Does it make sense to utilize only the 110V system and let the trailer sort it out, or have my battery bank wired to the 12V system, the inverter to the 110V system and disconnect the onboard charger? Let's assume my dream of running the A/C off the inverter has been crushed and I have isolated it to the generator.

I am sure there's more questions to come as my Visa balance starts to climb. This will give me some decent starting point.

[Mike90250]

I'm not sure I can believe a 12v 45w fridge will be viable Educate us - is it a vari-speed-compressor, Thermoelectric, or Danfoss compressor ?

As to batteries & inverter size vs loads. The caution on 12v 1000w inverters, is due to the large amount of DC current they can consume, which requires thick, expensive wires. Going beyone 12V @ 1000w gets into dangerous areas, where a partially bad cable crimp can start a fire in 10 minutes.
24V @ 2000w is fine, as the voltage goes up ( 12v - 24v - 48v ) the DC amps requirement goes down, and the fire risk stabilizes.

If you want to have the capability to run the AC off the inverter for half an hour, I would suggest at least a 24V battery system. Yes, it's a bummer because it's not 12V to match the rest of the gear, but it's easier and safer. Can be done with four 6v batteries wired in series. ( another disadvantage of many parallel batteries is the best one covers up the failures of the others, till they all finally (and suddenly) die and the connection schemes to share the loads becomes clumsy after 2 parallel strings ).

[bouree]

Question 2: Can you mix match types/brands of batteries? I have built battery boxes to securely and safely house the batteries and have air flow to vent the gases, I have all the batteries going into a bus bar on either side of the box. In my head, I would have 2 6V batteries (or more), wired to make 12 going into the bus bar. There is a lot of cost to the batteries and I do a few 12V batteries that I have load tested and are OK which could get me through the summer so I can save more sheckles to buy more 6V batteries next year. Can I mix them ?

I have no experience with multiple batteries, but I have researched the same question as some day I will want to expand my storage capacity. Most experts say that within the same battery chemistry, you should be fine to add batteries in parallel as long as the specs are the same. But preference is to have the same brand if possible. Connecting in series seems to be something where more caution is required. Some batteries are even marked as not ok for series connection and even those that are, I see reviewers warn against series connection - especially low quality ones. It appears to me that mix and match within a series needs to be treated with a lot of caution. FYI - I used youtube videos by Will Prowse and a few others for most of my research.

Also a 24V battery system seems to be the recommended way to go for higher loads like A/C as Mike90250 mentions.

[Mike90250]

There are now 2 major types of batteries.
Lead Acid & Lithium based

The bare batteries themselves can be wired in series to nearly any sane voltage.
The problem is many Lithium "drop in" batteries have an internal (or external) BMS that is unable to manage batteries in series. So it's the BMS that determines if a Li battery can be wired in series or not.

Batteries in parallel need to be watched also. but for different reasons, Differences in age and capacity will cause some batteries to degrade faster than others. The better ( newer) battery will do most of the work and degrade quickly to the level of the other batteries ( Lead acid does this more than Li)
and there are the interconnect issues with parallel batteries - and making sure they have the chance to share the loads and charging equally. Yes, even the copper wire and crimps make a difference and can ruin one string of a battery bank quickly.

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