Running EQ with shorter days (less time with PV)

Riley · August 2022

Hi Folks -

This thread is an offshoot of my other thread regarding high cell differences with a newish Rolls battery bank. I am planning to do my first corrective EQ cycle.

I am now getting near the end of August in the Pac northwest. As the days are already getting shorter, it's challenging to have enough PV time to fully charge the bank plus run EQ cycle from 4+ hours of quality PV. I thought I would ask for advice. I am off-grid and trying to reduce generator run time.

Here's my PV situation:

I will need about 10A to 20A to perform EQ process (2.5% to 5% of 428AH bank).
I should have enough PV to meet this requirement from around 10:30am to 4:00pm at this time of year (would have been much easier 1 month ago). At 10:00am I have PV output which is enough to do the lower power needs to end the absorb cycle.
The end of absorb doesn't take much power but can take a long time.

My proposed process to reduce generator run time:

Start generator at 7:00am and charge at 15% of the AH of bank capacity (about 60A).
Run the generator to complete Bulk charge and the high current levels of the absorb charge. Assume this will be about 3 hours.
So at 10am, the absorb current should be low enough that the PV solar can take over. Turn off generator.
Use PV solar to finish absorb and start and run the EQ process. This should give me from 11:00am (maybe sooner) to 4:00pm for EQ process (5 hours). If more EQ is needed (hope not), I can restart generator to finish off.

Any thoughts or recommended changes to the above process?
I assume other off-grid guys are dealing with the same issue and curious how you approach this.

Good thing is that this is a seasonal cabin so I don't need to do this in the winter time (which would be tough). Over the winter, I leave the batteries fully charged and then open circuit through the winter months. That topic is discussed in another thread from last winter.

Thanks and great site and advice here,

Riley

littleharbor2 · August 2022

If you can't complete the EQ over the course of one day you can start the process the next day and hopefully finish.. Being that your battery bank is, as you say, "newish" you should be able to finish in one day with your plan.
I have read that the biggest cause of battery failure is under charging. From what I have been seeing in my area I'm not surprised. Many people are reluctant to set their charging specs higher and quite a few don't EQ their banks. 3 -4 years max on their batteries.

Dave Angelini · August 2022

The most valuable screen on Insight is the battery summary screen. It shows you what you did and will show someone like you that is probably light on solar how your loads or clouds are pulling down charge voltage. Below are a couple screenshots.

Image: https://us.v-cdn.net/6024911/uploads/editor/wd/hi5ddod7a0c2.png

Above is a perfect charge and EQ. It assumes that you really are getting enough absorb time and have calibrated it to SG.

Below is either clouds or loads causing a bad charge. Your chargers may time out and tell you that you finished charge. Use the battery summary and you will be fine. It is one of the best things Schneider did when they went to a graphically based system after Xantrex and Trace.

Riley · August 2022

Agreed Dave. I have been using the earlier 'ComBox' for the previous 5 years and as of this spring, I upgraded to the Insight cloud system for monitoring. I have also recently started to look at the CSV file for detailed timing of current and voltage events. That's how I was able to arrive at the times above (understanding that the timing change as we enter the fall).

In your EQ example above, I looks to me that the bank went from Bulk -> Absorb ->
Float -> then EQ.

I am surprised to see that, I thought it would go from Absorb to EQ and skip float.

I do wonder how off-grid folks handle winter time with their generators. Our days are too short here to get a long absorb time with PV and nobody wants to run a generator for 4 to 6 hours of absorb. Maybe I should start a different thread on that topic.

In the shoulder season, I have been following the principles of the practice above when I start Bulk before the panels are in the sun and get a running start (as well as run heavy loads at that time). I then use PV to do the lightly loaded (low current) back half of Absorb phase. In winter I can't do that at all.... so it's either all genny OR don't come here in winter.

Dave Angelini · August 2022

It is about location. If you live in the southwest (other places also), and design for no genset or minimal genset you can live off the solar.

It does take much money and part time really is hard to make a case better than a genset. Full time is a different story. If you doubled, tripled, or more your solar, you could go longer into the fall, and use less genset.

There is nothing new about this BTW and the strategies have long been used. I have clients well north of you up in Alaska and Canada that have huge arrays for winter. They surprise me with the power they get on the long cloudy days.

It is also about managing loads and using most frugal loads.

Riley · August 2022

I just sat down the read the specs on my CC
(MPPT 60/150) to see if I can add more panels which would help things a lot. This is a summer home and I have tons of power from May until early August.

I do have pretty low power demands and just a few high loads that I can control then I use them (bulk water pump and dishwasher). Winter time is another story once I get snow on the panels and also low light in this valley.

Running EQ with shorter days (less time with PV)

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