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Pete(Palisades area, WA)says...
Van - followed your blog since I too am a part-time desert dweller in a trailer and entirely off-grid. I saw your newly added thread with Backwoods and MK.

I'm an electrical engineer but much enjoy working with my hands and installed a multi-panel system with a 2KW Magnum Energy inverter (the last of several systems working up to this). I also worked in commercial telecommunications including Mt. Top sites.

I noticed immediately some things you might consider. You do not have a system monitor such as Bogart Engineering (available from Backwoods) or as an optional accessory for an inverter charger system such as from Magnum Energy. Without one you cannot accurately track your actual battery state of charge.

The Outback MX 60 and Mate work for the charge controller only. It seems both Backwoods and MK failed to advise that with four strings of batteries, the maximum available current from your charge controller divides by four. Thus, if you have, say, 24 amps at MPPT from the MX 60 each string is charging at only 6 amps.

Parallel strings of batteries inadvisable. Better to have bigger batteries, because bulk charging requires a large enough constant current to 'stir up' the electrolyte (this is true of AGM and Gel batteries as well) and without this current the battery may sulfate.

With 4 strings and the relatively small array on your roof you may never fully charge 4 strings. Fewer strings would actually be better.

Equalizing is a partial solution - but equalizing has limited effectiveness with AGM since there is no actual liquid electrolyte to 'boil' as in a flooded lead-acid.

Also, consider the 'charge efficiency' of the battery system which is partly a function of the battery chemistry (AGM is less efficient than flooded) AND the battery temperature.

The charge controller's temperature sensor is reducing the charging voltage if it's hot, to a lower programmed set point.

In the middle of the Central Washington desert (it can get to 110F) max charge voltage is 1.2V - 1.6V (24V system - double for yours) lower than 'normal', and lower panel efficiency reduces the available power as well.

In winter shorter days reduce charging time even with full power from the array.

Remember all the usual ratings for batteries are under STC (standard test conditions (usually spec'd between 68 -75 degrees F). Charge efficiency and max charging voltage decline from STC upward.

My system is 750 W solar with a midnight classic MPPT, Magnum 2KW sine wave inverter with battery monitor.

Powers deep well pump, electric fridge, power tools, lights, TV, coffee maker, washer, computer, satellite internet and web cams.

2 Strings X 4 ea L-16RE. I max is 28 - 31 Amps which is about 14 Amp per string. Typical daily discharge is 15 - 25%. Latitude 48 north.
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Van Blakeman(East Sandwich)says...
Pete, This is fantastic. Thank you.

What do you mean by "I max is 28 - 31 Amps ..."? The max?

Dan Pritchet has suggested almost exactly what you have said, except that you have given it more meat; something for me to chew on.

In my reply to his evaluation, I said "I do want to ... read and tweak the settings on my computer". With the Bogart Engineering PentaMetric monitor and software that you suggested, i should be able to do that, though I still need to study their web site more thoroughly to confirm that it will work with my configuration, or if I will first need to upgrade my controller and/or inverter.

You are right that I did not know that going from 3 strings to 4 would reduce the amperage going to the batteries. And it makes sense. In all fairness somebody along the line very well could have told me that. Due to the way my head works, if it was said to me over the phone, I probably would not have retained it. In writing I can read and reread until I do get it, even if it is a year or two down the line of multiple assimilations feeding into each other until it suddenly makes sense - and as new information such as yours clarifies.

Thanks, Van
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Pete(WA)says...
Hi Van

Yes, Imax is the maximum solar array current available from the output of my MPPT controller. "I" is the symbol for current or amperage in electronics.

The controller is spec'd at 60 Amps capacity but I'm about out of room to add additional panels without extending the roof of the powerhouse.

At some point you may want to consider replaceing your Exceltech inverter with an Outback inverter/charger (since you already have the MX 60 and Mate. Every few days you could run your generator for 3-4 hours and 'top up' the batteries while you are there.

From the 'resolve' link it looked like you're getting some knowledgeable help. I wish I had your carpentry skills.

best, Pete
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Van Blakeman(East Sandwich)says...
Pete, Have added your contribution to the web page.

Are you the guy on FB that just got married and who is also known as The Saflund Institute?

Impressive. Van
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Pete(WA)says...
Hi Van

Yes, and no. I'm the person behind the Saflund Institute. My good wife of 37 years made a mispost on Facebook and has been trying to live it down ever since.

It seems the posting date was somehow interpreted as the marriage date or perhaps it was a senior moment. In any case - it's one of the many reasons why I don't do a lot on FB.

It's there for the business I'm slowly retiring from and to see all the things going on with the 2nd and 3rd generation behind us - kids - nephew career Navy in nuclear sub, etc and their beautiful family.

I'll take a look at the website after a bit - off to a meeting now. Pete