More Surrette problems

Re: More Surrette problems

Sorry to keep you in suspense, team. The rest of my life is interfering with my solar-dominated life.

I had 4 hrs solar absorbing then 2 hrs solar equalizing then the clouds rolled in. At that point, four sample SGs were 1250, 1250, 1255, 1255 so there had been some improvement. I decided to follow the local installer's recommendation to now do 4 hrs of EQ by generator (an act approved by Surrette). After that, the four SGs were 1260, 1250, 1250, and 1250.

At this point, I suspect my refractometer is having inaccuracies due to operating at the edge of its automatic temperature compensation (ATC) range. The specs say it's good from 50 to 86 F and the battery room is at 86 F due to hot local weather combined with the heat generated by the inverter/charger and batteries during equalization. I did some surfing and found that the bimetal expansion used for the ATC is linear but the SG-temperature varience isn't linear, and thus the ATC has more error as you approach its limits.

The local installer is lending me his more expensive refractometer this afternoon, and I'll be able to see if that gives different readings. I've also opened the battery room to the rest of the house to bring the temp down some and will see if that changes my readings.

To support this direction of refractometer error, I took some SGs using my hydrometer too. They're 1250-1255, but the difference is that the hydrometer has a thermometer/compensation-scale on it that tells me at the current temp to add +8 to those readings, which brings me much closer to our goal of 1265.

I'll get back to you once I try the better refractometer and in a cooler room. If only my darned hydrometer bulb wouldn't keep sticking to the glass wall such that I can't trust it. I've taken it apart and cleaned it but no diff. I always pull several loads of battery fluid into it before reading but it still sticks. Sigh, I need a $500 digital refractometer, or maybe just a hot cuppa tea and a calmer attitude.

...Terry

Re: More Surrette problems

Sigh, after an EQ last week, the bad cell's gravity got worse (1100) and the other 47 cells are slightly lower (down to 1240-1250), with a couple of 1235s and a 1220! My conclusion is that the bad cell is pulling the others down. Surrette appears to agree with me, as they've agreed to ship me a replacement for the bad battery next week.

(Reminder: that's to replace one of the 16 S600s they replaced two months ago. Argh.)

Now I have to hope future cycling will bring all the others back up to 1265 range without permanent damage (e.g., reduced lifespan).

So at this point I need to address the bigger question: aside from that one bad battery, several of you in past messages on this thread have suggested I have a problem with the balance between my energy supply (12 REC 215 W panels, and a 10 kW Generac Guardian generator) and my batteries (16 S600s in two 48 V strings of 8 ). E.g., Coot says "215 * 12 = 2580 Watt array. At typical 77% efficiency: 1986 Watts / 57.6 Volts = 34 Amps peak potential current. Sixteen 450 Amp hour 6 Volt batteries is 900 Amp hours @ 48 Volts. That would want 90 Amps of charge current, so you've got no place near enough panel to charge that much battery."

So at this point I see three possible solutions:

1. Buy 3 more panels (I have four sets of 3 now). Cost including racks and labour is $4300 up here.
2. Disconnect one of the two 8-battery strings and sell them. Somebody local wants them next week so I could jump on this opportunity.
3. Disconnect one of the 8-battery strings and see if the gravities return to 1265 over the winter season before deciding to sell them.

Solution #1 doesn't address the trouble that the generator + inverter/charger may not be able to give the batteries a full charge without long hrs of Absorb charging. The generator has a 45 A circuit breaker and the Magnum MS4448PAE has a 60 ADC continuous charger output, thus 30 ADC per string. I don't recall the math but Surette's man thought this translated to ten hours in Absorb, a ton of propane in our cold winters up here.

Solution #2 is tempting but I'd only have half the Ah for cloudy days, thus requiring more generator charging in winter. My local installer (who recommends this solution, and is also the installer of the guy who would buy my 8 batteries) says that while that is true, it wouldn't take the generator as long to charge a single string and it wouldn't need to run as often since the solar charging would take less hours. But what would my fallback be if the winter season turned out to require tons of propane? Buying eight new batteries plus more panels would be a big $ hit and I thought you weren't supposed to mix old and new batteries.

Solution #3 means I could reattach the unused string at some point if going with a single string proved too fuel-heavy. But it would be more difficult to sell the batteries after a few months of storage, and would the unused batteries 'go bad' over the winter without use? Perhaps I could alternate between string A and string B through the winter, keeping all batteries healthy in case I wanted to restore the system to all 16 batteries? Or hey, is there a gadget that lets me keep all the connections and just alternate between charging string A or string B as each gets fully charged?

So what d'you guys think? Is my original premise flawed (that the panels/generator can't match the # of batteries)? If not, what solution would you recommend? Am I missing some things completely?

All thoughts are GREATLY appreciated. My offgrid experience has been a complete nightmare, and exhaustingly time consuming, but you guys are the shining light that gives me hope (if I could only understand you!).
...Terry

Re: More Surrette problems

Okay, let's sum up the responses to the question in post # 48. The question was how to handle an apparent inability to charge a large number of batteries with the current solar and generator current limits. Three proposed solutions were:

1. Buy 3 more panels (I have four sets of 3 now). Cost including racks and labour is $4300 up here.
2. Disconnect one of the two 8-battery strings and sell them. Somebody local wants them next week so I could jump on this opportunity.
3. Disconnect one of the 8-battery strings and see if the gravities return to 1265 over the winter season before deciding to sell them.

Of the 7 responses to date:
- one has been for #1 or more conservation (thanks, Stephen);
- one has been for #1 + daily a.m. running of genset for bulking (thanks, Mike);
- one has been for #3 unless I can get a good sale price on all 16 batteries to buy 8 better-sized batteries (thanks, sub3marathonman);
- four were discussions on the 10% current idea, with one (Coot) making a general recommendation for #1 (thanks, Stephen and Coot and Vic)

So if it were a democracy, #1 would win and I'd buy more panels and see how that goes over the winter. It also makes sense to reduce loads to keep a higher SOC (and lower genset usage). Does anyone wlse agree with Mike's tip for daily a.m. bulk charging by genset? (I assume that's just for the high-demand winter season, Mike?)

What I haven't heard from any of you is what you think of my local installer's concept that removing one of the two 8-battery strings will solve my problem by charging those 8 more fully (both by solar and genset). Coot is right that adding more panels can always improve the situation, but could I get the same results by reducing batteries instead of adding panels (without doubling my hours on the genset)?

Sub3marathonman, can you clarify your suggestion of replacing the 16 batteries with 8 correctly-sized ones? My installer thought the 16 S600s were correct based on their 900 Ah giving me 2-3 cloudy days of power with my load estimation. He said nothing about current issues. What should I do the determine the 'correct-sized' ones, please? Or is this asking for a Tolstoy novel...

Thanks again, everyone. I thought I was a tech-savvy guy until I went off-grid.
...Terry

Re: More Surrette problems

Thanks for those responses, guys, particularly Coot's summary in posting #57. So will the reduced number of batteries meet my needs? I asked a third local installer (not the one who supplied my system, and not the other one who is suggesting I go to half my batteries and he'll buy the other half) and got these numbers:

First look at my needs: This first year off-grid, my BMK says I averaged about 62 Ah/d in summer and 65 Ah/d in winter. Now let's look at my power:

My panels give me 44 A (12 x 215 W / 48 V). Here in eastern Ontario we assume 5 hrs of sun/day (summer) and 2.5 hrs/day (winter), so that gives 220 Ah/d (summer) and 110 Ah/d (winter). Assume 70% efficiency and that becomes 154 Ah/d (summer) and 77 Ah/d (winter). Compare those to my 62 and 65 Ah/d loads, and my third local installer concludes I have all the power I need, so no need to get more panels. Of course I'll need more generator use mid-Nov to Mid-Jan, when it's more like 2 hrs/day of sun.

As for generator charging, he noted my MS4448 inverter/charger is set for 90% Max Charge Rate and has a 60 ADC charger output, thus sending a max of 54 A, so say it averages 50 ADC. If I were to go to a 50% DOD on my full 900 Ah battery bank (2 strings of 8 S600s), it would ideally take 9 hours at 50 ADC to recharge 450 Ah. That's more likely 12-14 hours with all the inefficiencies, and that's an unhealthy long time to run a generator. Thus he recommends I either stick to a 25% DOD or half the batteries (and double the frequency of charging).

His final point is that we can't assess if the panels or generator are incapable of fully charging my battery bank until we see some results from a fully-working battery bank. My winter gravities were affected by a faulty battery, causing all 16 to be replaced, and my summer gravities were affected by one of those replacements being bad too. So he recommends the following:

Once the bad summer battery is replaced next week, disconnect one of the 8-battery strings so I can bring the remaining 8 up to full charge (gravities close to 1265) more quickly. Try this for a while to see if the gravities remain stable. Then switch to the other 8 batteries and get them up to a full charge too. If I can't get either string up to a full charge, it's likely a panel and/or generator vs battery imbalance, so try Mike's idea of generator bulk charging on mornings to do absorbs by solar (still on a single string of 8 batteries). If I can get them up to 1265-ish but I don't like the reduced storage capacity, hook all 16 batteries back up and see if their gravities gradually drop -- another sign of a power vs batteries imbalance. If they do drop, either return to a single string or try Mike's morning gen charging. Then make a panel-buying decision next summer based on all of this.

Do you guys see reason (or flaws) in the above logic and approach?

Thanks a ton,
...Terry
P.S. Mike, how frequently in winter do you suggest the a.m. gen bulk charging -- every day seems like a lot, but one local installer suggests that for 2 hrs daily for the worst months of mid-Nov to mid-Jan.