More Surrette problems

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Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: More Surrette problems

    I believe he has a FM80--which I don't think has remote voltage sense leads...

    At this point, only these units have remote voltage sense connections:
    There may be others--I am not in the business so I certainly do not have extensive knowledge about other controllers/brands.

    Note, you should place a small fuse (or a resistor) in the + battery sense lead near the battery... You don't want a short (shorted/broken battery sense lead) to cause a fire either.

    My two cents, I would aim at a maximum of 0.05 to 0.10 volt drop between controller and battery bank for a 12 volt battery system.

    For a 48 volt system, somewhere around 0.2 to 0.4 volt maximum voltage drop for accurate battery voltage measurement.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jeffkruse
    jeffkruse Solar Expert Posts: 205 ✭✭✭
    Re: More Surrette problems
    mike90045 wrote: »
    Thicker Cable. DO NOT adjust the setpoints. As the batteries charge up, the voltage drop becomes less, and you would end up overcharging batteries.

    How much less than 5 amps do you think it can go?:confused:

    Your charging current will be much higher than 5 amps and you will have more of a voltage drop. IMO the batteries should see at least the recommended voltage. You have low SG that implies you aren't charging the batteries. Remember that once you complete the Absorb you will go to your float voltage where the current and voltage will be much less.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: More Surrette problems

    0.5 volt drop at 5.2 amps...:
    • V=I*R
    • R=V/I= 0.5 v / 5.2 a = 0.096 Ohms
    Sounds like a small resistance--but now try to pump ~35 amps through that wiring:
    • V=I*R= 35a * 0.096 Ohms = 3.36 volt drop
    That is a fairly large drop--I would suggest that you need ~1/10th the resistance to get the drop around 0.336 volt (somewhere around 0.4 to 0.2 volt drop maximum)... That would be (at least) around 10 AWG heavier wire than you have right now (or a mix of heavier wire and shorter wire run from controller to battery bank) to reduce the voltage drop to something more reasonable...

    If you plan on adding more solar panels later, you would even need heavier gauge wiring.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    Re: More Surrette problems

    Hi Terry, don't leave us in suspense ;) - what was the result of the EQ, did the SG rise to expected levels?
  • terrynew
    terrynew Solar Expert Posts: 48 ✭✭
    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
  • jeffkruse
    jeffkruse Solar Expert Posts: 205 ✭✭✭
    Re: More Surrette problems

    Whats your EQ voltage set for and what do you measure on the batteries when your EQing?

    If you have 35 amps going in you may be dropping over 3 volts turning your 62V into 58.8 volts which is a good Absorb voltage....
  • solarvic
    solarvic Solar Expert Posts: 1,071 ✭✭✭✭
    Re: More Surrette problems
    terrynew wrote: »
    I'm sorry, everyone. Jeff was right, I typed 47.1 V at the battery posts but it was actually 57.1 V, a difference of 0.6 V from what the CC said it was sending to the batteries. Mia culpa.

    Wow, I hadn't realized how dangerous putting the ammeter across the posts was. Scary stuff. Lesson learned (and hopefully for others out there reading this, should there be others as unknowledgable as me in electricity).

    The cable runs 1 foot from the CC to the e-panel and then three feet to the battery box. Does the 0.6 V drop mean I need thicker cables or that I should bump up the bulk, absorb, float and eq settings on my CC by 0.6?

    Clamp-on DC ammeters are $140 at Home Depot here in Ontario, not available at Sears Canada. I'll look to see if I can borrow one instead.

    Darned clouds are ruining my solar EQ. I'll likely have to switch to inverter/charger + generator.
    ...Terry
    Wonder if you can do mail order from Sears in USA? They one Bill is suggesting has been on sale for around $50.00 us. I also saw the sears models on ebay for sometimes less. I get a subscription from Canada for something and it is automatically charged to my credit card. :Dsolarvic:D
  • terrynew
    terrynew Solar Expert Posts: 48 ✭✭
    Re: More Surrette problems

    Solarvic, it does appear that I can order from Sears U.S. (sears.com). When I state my country is Canada, they tell me that the Crasftsman clamp on meter model 73756 is available for $98 Cdn, but with shipping and duties it comes to $128. I'm just unsure I'll get value from this tool.

    Jeff, my EQ voltage is 63.2, but I can't measure the battery voltage during EQ until my next EQ.

    Today I measured all 58 cells with my refractometer after 6 hours of solar charging. 43 of the 48 are between 1250 and 1260; the others are 1235, 1240, 1245, 1245, and a whopping 1170. ARGHHHH, I don't know what happened there! I get the same reading with both refractometers and my hydrometer. The voltage is 6.14 V compared to 6.18-6.20 for the rest, so it's a mystery why its gravity is so low with a voltage not much different from the rest. And this is after 6 hours of equalizing! Any ideas, anybody, on what I should do?

    Hope you're all enjoying the weekend,
    ...Terry
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: More Surrette problems

    Check the voltage on each battery in that string when charging.

    You are looking for things out of the ordinary (high/low voltage during charging).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • solarvic
    solarvic Solar Expert Posts: 1,071 ✭✭✭✭
    Re: More Surrette problems

    terry you have the wrong model no. model no. is 82369. I will check the model no you tryed to buy. Solarvic
  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    Re: More Surrette problems

    Given that these are supposed to be new batts, I'd contact Surrette.
  • RandomJoe
    RandomJoe Solar Expert Posts: 472 ✭✭✭
    Re: More Surrette problems

    Regarding the 0.6V difference between meter and FM80, have you checked what the FM80 says the battery voltage is when NOTHING is happening? (Not charging, not running the inverter.) If it still shows a 0.6V offset, then there is an adjustment in the FM80 for that. Your cables may be fine.

    On the other hand, if the voltage measurements match at idle but are off when charging, that confirms you have a voltage drop somewhere - either too-small cables or perhaps loose / bad connections.

    And I'm not an SG expert, but my impression from reading various forums over the years that the exact SG numbers aren't what's important as long as you're "in range" and the batteries are all equal. Different batches of batteries will tend to have some variation anyway. Is there really a problem if yours are all at 1250? If you're seeing the same numbers now as when they were new, my understanding was they are fine...?
  • jeffkruse
    jeffkruse Solar Expert Posts: 205 ✭✭✭
    Re: More Surrette problems

    Any updates on your batteries?
  • rplarry
    rplarry Solar Expert Posts: 203 ✭✭
    Re: More Surrette problems

    Terry
    It sounds like you have at least one bad battery. 1170 sg is way too low.

    "Today I measured all 58 cells with my refractometer after 6 hours of solar charging. 43 of the 48 are between 1250 and 1260; the others are 1235, 1240, 1245, 1245, and a whopping 1170. ARGHHHH, I don't know what happened there! I get the same reading with both refractometers and my hydrometer. The voltage is 6.14 V compared to 6.18-6.20 for the rest, so it's a mystery why its gravity is so low with a voltage not much different from the rest. And this is after 6 hours of equalizing! Any ideas, anybody, on what I should do?"

    Are the cells that measured 1235 to 1245 on the same battery as the 1170 reading? I would recheck that battery and if it is still low then I would contact Surrette again.
    Good luck with it,
    Larry
  • Ralph Day
    Ralph Day Solar Expert Posts: 1,019 ✭✭✭✭
    Re: More Surrette problems

    I had 2 cells go bad on my Surrette's too. Regardless of charge or eq they wouldn't come up when all the others were fully charged. At 6 years old I had to pay 60% of the cost of the cells, plus shipping. It did take a lot of emails to get through to them that the cells were defective and no amount of charging would save them. Be persistent.

    Changing cells out was not a big chore, but a chain hoist for lifting was helpful. Putting the new cells in was just a grunt lift.

    Ralph
  • terrynew
    terrynew Solar Expert Posts: 48 ✭✭
    Re: More Surrette problems

    FYI: That one cell is still 1150, while the other 47 are between 1250 and 1265. Surrette recommends I just let them cycle through the rest of the month and report back after an end-of-month EQ.

    Thanks, everyone, for your support.
    ...Terry
  • terrynew
    terrynew Solar Expert Posts: 48 ✭✭
    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
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: More Surrette problems

    my vote is more panels, and run the genset for an hour in the AM's to bulk the batteries, and let the PV do the absorb.

    But you also need to address your loads, what's pulling the batteries so low nightly ? You should get to float every couple of days.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • sub3marathonman
    sub3marathonman Solar Expert Posts: 300 ✭✭✭
    Re: More Surrette problems
    terrynew wrote: »

    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.

    ...Terry

    OK, I'm definitely not one of the experts here, but would it be possible to set it up as two 8-battery strings, get the one charged either on a sunny day or by the generator, then switch to the other string and predominately use that? And have a switch so that when needed, or something like every other week, you could switch to the other string? The string going into off-line would have to be fully charged when switched, but I would think that could be done. Then the capacity would be there when needed, and the panels could charge one string at a time.

    Also, the price offered in option 2 would need to be considered. Somewhat, if it was possible to start over and sell both strings that might be acceptable. Instead of 16 smaller 6-volt batteries you could buy 8 correctly sized 6-volt batteries.
  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    Re: More Surrette problems

    For what it's worth, I think the emphasis given to the ratio of charging current to battery bank size is vastly overstated. The problem seems more to be a case of not having enough charging capacity relative to the amount you're discharging. The size of the bank is not that important.
    IMO you'd be in a much worse situation if you attempted options 2 or 3, since you would then be discharging to twice as deeply and so shorten the battery life. My vote is for option 1 or option 4: Reduce your consumption.
  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    Re: More Surrette problems

    terrynew,

    Regarding the lagging cell dragging down the others;

    In my experience, lagging cells cause some level of overcharge on the remaining cells in one string -- the laggard has a lower terminal voltage during charge, causing the other cells with higher SG ro have higher terminal voltages. When the charge target voltage is reached, the laggard needs more/much more charge, and the remaining cells have been overcharged, because they have had a higher charge voltage.

    This is just my personal observation in banks of SINGLE STRINGs.

    Having batteries composed of single cells can allow remedial charging or EQ at the single cell level, altho this usually involves using a Home Brewed charger. The larger Surrettes, with removable covers, also allow access to individual cells.

    Good Luck, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    Re: More Surrette problems

    And, stephendv,

    I am in complete agreement with you on the "standard" 10 % minimum charge current of 20-hour capacity (was 5-13%).

    To me, it is important to have about the 10% value available for occasional charging, or if the bank needs to be cycled below 80-ish SOC. BUT, to me, this high charge current value is NOT required for daily charging from the solar array, if there is typically good sun available, and the bank is not taken below 85 or 90% SOC.

    Good electrolyte mixing occurs during the Asorb stage, and if the bank almost always reaches Float each day, the high charge rates need only occur every month or two.

    I do realize that if one does not watch the bank carefully, it can be easy to get farther and farther behind on the SOC of the bank. This may well be where this "standard" has come from.

    I will say that on an FLA bank that was was in Float service, using about 1.5% of capacity max charge current, that it took about 3 to 4 hours to reach Float each day, and the long grind of getting to Float, caused the bank to use a bit more water than expected. Think that 3 or so percent charge current might have been better for that bank.

    Not to argue with anyone, just MHO, based on info from the provider of most of my batteries. YMMV and so on,
    Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: More Surrette problems

    I think people get confused about the 10% peak charge current idea. It's an arbitrary target to make sure your batteries charge well over-all, taking into account loads reducing the net charge rate and the fact that the sun doesn't shine brightly every day. If you calculate an array sized based on that simplistic formula I keep tossing out you will have enough power to recharge most days. If you use too much power one day you'll fall short. If you use less than average one day you'll have surplus. Quite a number of things affect panel output, not the least of which are insolation (angle of the sun varies throughout the year), temperature (hot day down, cold day up), and elevation (higher systems inevitably outperform those closer to sea level).

    So even though you may do the numbers like this:
    22.5 Amps @ 14.8 Volts = 333 Watts less 77% efficiency derating = 432 Watt array
    That does not mean you will see 22.5 Amps @ 14.8 Volts from sun up to sun rise. You may never see peak current and maximum Voltage. In fact if you do you're probably running the system too close to its limits.

    It's a lot of numbers that take a lot of understanding, including which way to "err" to make sure you don't fall short. And that's the bottom line; no one ever complains about having more PV power available than they need, but we sure do hear from those who don't have enough! It usually sounds like this: "My batteries are dead after just one year. I don't understand it. Shouldn't 85 Watts of panel be able to recharge 1200 Amp hours of battery in five days?"

    I run my system on the ragged edge of the catastrophe curve - so you don't have to. :D

    P.S.: If anybody can think of a short way of explaining this to people so they understand it without each and every post becoming a Tolstoy novel I'd like to hear it. ;)
  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    Re: More Surrette problems
    P.S.: If anybody can think of a short way of explaining this to people so they understand it without each and every post becoming a Tolstoy novel I'd like to hear it. ;)

    Hehe, I'll be of no help in that department ;)

    As you point out, the 10% rule of thumb hides some important details and the fact that it is a system recommendation and not an absolute requirement of the batteries is getting lost somewhere along the way. People seem to be taking the home the message that if the battery is not receiving at least a 10% of capacity rate of charge, then they are not charging properly - which isn't right.

    A big unspoken assumption with using any % of battery capacity rule is that the discharge of the battery is unknown. You'd need a very different sized array to charge a 200Ah battery that is discharged 10% every day vs. one that is discharged 50% every day. Basing the charge current just on the absolute battery capacity hides this information.

    Absolutely agree that it's better to err on the side of more array, but then it should be clear that the recommendation is based on this, else it could mean people putting in more array than is needed.... and by now we're already in Tolstoy territory :D
  • terrynew
    terrynew Solar Expert Posts: 48 ✭✭
    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
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: More Surrette problems

    The issue of adding panels vs. reducing the number of batteries comes down to: Will the reduced number of batteries be able to meet your power needs? If "yes", then do that. If "no" then go with Mike's suggestion of Bulk charging with the generator and letting the panels handle the "finish" charging (you may have to run the gen for part of the Absorb cycle if the current demand of charge and loads is still too much for the panels) until you can afford to add more panels.

    It isn't that one answer is right and the rest are wrong, it's that there is more than one viable solution to the problem and you have to pick the one that works best for you.

    Off-grid systems are always a matter of having enough battery capacity to meet the load demands and then having some method of recharging those batteries fully and properly so they don't need to be replaced too soon.

    In planning for that figure your loads against a 25% DOD for daily use. If the sun doesn't shine for two days you've got 25% in reserve (and ever day will have enough light to produce some charging, even if not very much). On day three you start the generator.
  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    Re: More Surrette problems

    Yes, definitely agree with Mike. Running the gen or adding more panels has the same effect: more energy into the batteries.
  • sub3marathonman
    sub3marathonman Solar Expert Posts: 300 ✭✭✭
    Re: More Surrette problems
    terrynew wrote: »
    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

    I was responding more to this portion of your experiences, rather than an absolute knowledge of your battery requirements. I always would try to avoid doing any parallel batteries, it is much better to get the larger capacity single battery. But since you currently have two sets in parallel, I simply suggested a single set of higher capacity. I don't really know if you need the capacity or not, and from the installer's suggestion, it may be that you really don't need it. It just seemed that since you have them now, and since things aren't working correctly, and since the installer suggested using just one string, if you could somehow set up two strings with a switch between strings it would mitigate the situation you have. I don't really know if such a switch that could withstand the current even exists.

    There are also now additional factors due to possibly selling one or both strings. Why does the installer now think you can get by with one, when he sold you two??? Why does the installer now have a buyer who's willing to jump on the used batteries, but maybe at a very low price? The installer may be a great guy trying to help, but people must examine the possibilities.

    It really is a problem for a non-expert, of which I am one too, when there are so many conflicting opinions. Many people are telling what works for them, but it might not work for you. It is great to have 3 days of battery backup, but if you never use it in 10 years that money could have been used better. Hindsight of course. As Yogi Berra would say, "It's tough to make predictions, especially about the future."

    But, from reading the experts here, I have found the following:

    It is ALWAYS better to have a larger capacity battery string than two strings of half the capacity connected in parallel.

    The batteries are the most essential, and most difficult part, of a battery-backup/off-grid system.

    If your batteries are too small for the situation, there are major problems.

    Flooded lead-acid batteries take more abuse than AGM batteries, and cost less, but there is a sacrifice of a small bit of efficiency with the charge-recharge cycles.

    That's just for the batteries. Then there's the grounding, where there is another huge debate. There is the NEC codes, and then there is the local authority having jurisdiction, and the fact that even that is just the minimum allowed, when it is probably better to go beyond the requirements. I finally had to just move forward as best as I could figure at the time, and if there was a problem, do as you're doing and try to see the options. And yes, the people here are a huge help.
  • terrynew
    terrynew Solar Expert Posts: 48 ✭✭
    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.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: More Surrette problems

    Let's see if we can distill this down a bit.

    You use a maximum of 65 Amp hours per day @ system Voltage according to your measured usage.
    For 25% DOD that's a battery bank capacity of 260 Amp hours (gives one day reserve before 50% DOD is reached).

    Why on Earth would you have 900 Amp hours of battery? Sounds like you got sold a lot of battery you do not need with a typical insufficient amount of panel to recharge them. And yes you can assess in advance if the panels or generator are capable of fully charging the battery bank. I suspect your installer doesn't know what he's doing. Or he's a crook.

    We don't do the old "the panels will recharge the batteries over time" bit anymore because you end up with dead batteries too quickly. When batteries were cheap and panels were expensive the financial trade-off made sense. Now batteries are expensive and panels are much cheaper so we try for quick (daily) recharge which will keep those batteries around a long time.