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Solar Problems

Discussion in 'Off Grid Living' started by Nadja, Nov 30, 2010.

  1. Nadja

    Nadja RIP 3-11-2013 Forum Leader

    I am having a current problem with my solar, and I imagine a lot of you on solar will have this very same problem. What happens is this: My batteries go into bulk charge at about 14.6 for a couple of hours and then drop down into a float charge of about 13.4 for the rest of the day. As soon as the sun goes all the way down, the points start dropping as well. After talking to a couple of the so called experts I am no disconnecting about 6 of my batteries at a time, allowing them to sit for about 4 hours to level off and then testing them as six volt batteries. If no noticeable change then it will almost have to be a bad dioade in one of my panels. Anyone out there know how to check out dioads ? This one has me stumped so far.
  2. ghrit

    ghrit Ambulatory anachronism Administrator Founding Member

    Fair to assume you are looking at the cells as well as the diodes as a failure mode?

    Diodes are sorta like check valves. OUT OF THE CIRCUIT you use your ohm-meter alternately in one direction, then the other. Due to inherent leakage there will be a high but not infinite resistance in one direction, and almost no resistance in the other, the difference is what tells the tale, higher is better. To give exact values, you have to go to the mfr for numbers, but this quick and dirty will separate failures from probably good ones. I'm assuming for now that your diodes are in the input from the panels, and not a rectifier bridge that you might have on the windmill. (Well, you DID say solar ---)

    It would be worth the effort to find an old submarine electrician that can tell you a lot more than I can about charging batteries. There are several charging schemes that were (and may still be) used with lead acid "cans." Your description looks like what is generally used for in-service charging and using. I don't remember that cells were taken out of the banks (electrically) for resting, but I do remember that there was an "equalization" charging process that supposedly eliminated or reduced the effects of a cell that was tired.

    Assuming you have lead acid cells, charge at 14.5 +/- should be good. Float at 13.5 +/- is probably OK, although a fairly new and freshly charged cell should hold 13.8 for a while if not in use. In use, you should see 12.8 or .5, slowly dropping to something that won't power the load. Often, a few minutes off service will allow a limited recovery, but don't count on it being able to carry a load for very long. (Use half these values for 6 volt cans.)

    If you don't have a pretty accurate gravity tester, you should get one, very useful to keep an eye on can health (unless the cans are "sealed.") Generally, gravity testers are not too precise, but are repeatable, and that counts if you log the readings to find trends.

    All this is out the window if your cells are other than lead acid. I've been told, but have not confirmed that subs are not using lead acid these days, so finding that boat electrician is more important.

    To mention what I'm sure is obvious to you, make sure that when you test at 6 volts, that the other half of the series is also out of the circuit if you have more than one bank of cells in series service. There will be an un-nice result of paralleling a bank of 6 volts with a bank of 12s. But you knew that ----

    IIRC, the modes/schemes were constant potential, modified constant potential, constant current, and maybe others. Different, but meaningful to those that grok batteries. I don't so grok, I was a machinist's mate and ran the steam plant (among other things.)
  3. BTPost

    BTPost Old Fart Snow Monkey Moderator

    Sounds completely normal for a typical Battery Bank made up of 6 Vdc Batteries, on a solar system. When Bulk charging, your charge controller holds the voltage at whatever the Bulk Rate Setpoint is, and the current is, the Charging Rate, plus load. Then in Float, the controller holds the batteries at the Float Setpoint, with the current being the load, plus what the batteries need to stay at the Float Setpoint Voltage. Once the sun no longer is illuminating the panels, there is no incoming current to maintain the Float Setpoint Voltage, so whatever load is on the bank, begins to draw down the voltage of the Battery Bank. A hydrometer is a very good thing to have around in these cases. How often have you done an Equalized Charge on this Battery Bank, and do you have a schedule for that?
  4. Nadja

    Nadja RIP 3-11-2013 Forum Leader

    Hey Bruce. I equalize about once a month. Ususally when the S.S. check goes into the bank. RidX in the septic tank, equalize the batteries, pay the bills. My Schedule. At least what there is of it.
  5. BTPost

    BTPost Old Fart Snow Monkey Moderator

    My Trace SW4024 (for the Main Cabin) has 3 strings of L16's, in parallel for 1200 AmpHours, and I usually equalize them once every other month. I usually get about 10 years out of a set, working on Set #3. My schedule is to charge them twice a day, for around 5 hours, for each charge. (7Am to Noon and 5Pm to 10Pm) I have to run the Genset for other purposes, so the recharge just happens while the Genset is running. My Trace U2624 (for the Winter Shop and MicroISP) charges off the Same Genset power and has a 700 AmpHour Absolyte II AGB Battery. Sounds like you in the ballpark on your readings, alright... assuming that you have a load connected to them. If not then get an Amp Meter and start looking for which panel is drawing current when it goes dark. Shouldn't take to long to isolate the phantom load.
  6. RightHand

    RightHand Pioneer in a New World Moderator Founding Member

  7. Nadja

    Nadja RIP 3-11-2013 Forum Leader

    Right hand, I looked it up on the internet, and is that stuff expensive. I use bakers yeast for the most part, and it only cost me a few dollars a pound. Has worked for me for about 15 years now, in my homemade septic tank. I have never had to have it pumped or have it overfill. But thanks
  8. Nadja

    Nadja RIP 3-11-2013 Forum Leader

    I just finished equalizing my batteries today. Ran them up to about 15.4 for a couple of hours and will see how they act tonight. This is an ongoing problem with solar as the batteries tend to build up sulphates all the time from the constant chargeing and discharging.
  9. RightHand

    RightHand Pioneer in a New World Moderator Founding Member

    I've also used yeast in my hand made 72 year old cesspool. The yeast works well but I've found the bio-clean is better in the drains. You don't have to use as much as they recommend either. I have the advantage of getting it wholesale.
  10. fireplaceguy

    fireplaceguy Monkey+

    Intended or not, that's a hell of a pun. My compliments!
  11. Nadja

    Nadja RIP 3-11-2013 Forum Leader

    Fireplace guy, to be perfectly honest, it was not intended, but is kinda neat isn't it ? LOL Nadja
  12. Kingfish

    Kingfish Self Reliant

    Hi Nadja, Just got here and have to make 5 posts. Here is one. Kingfish
  13. Nadja

    Nadja RIP 3-11-2013 Forum Leader

    Welcome to your new home Kingfish. Nadja
  14. stilagrrl

    stilagrrl Monkey+

    This is my first post here. so I'll describe my system at the end of my post. However, regarding your issue, while you didn't specifically say it, I take if your inverter is turned off/disconnected and you're still seeing the voltage drop? The reason I asked is because even with nothing plugged into the AC side of my inverter, it still draws a few amps. As for a bad diode in a panel, doesn't your charge controller prevent backflow?

    As for my system, it's made up for six 180w 24v Mitsubishi panels, an Outback Flexware combiner box, a Xantrex MPPT charge controller, 12 170 amp/hr 12v batteries, a MidNite Solar 250a Disconnect box, a Xantrex ProSine 3000w inverter and a Square D AC breaker box.
  15. Maxflax

    Maxflax Lightning in a bottle

    Is there any advantage in 24 volt panels for a 12 VDC battery bank system or is it a wash, vs 12V PV panels?
  16. BTPost

    BTPost Old Fart Snow Monkey Moderator

    The only advantage is that you only have to buy panels in one'ies for a 24 Vdc system, and in two'ies for 48 Vdc. Where if you deal with 12 Vdc Panels, then expand your system you have to do it with double that number each time to expand. Your Charge Controller, IF it is MPPT, will be able to deal with the difference for you, as far as the Battery Bank Voltage goes. For systems of less than 1Kw, it is a wash, but if your planning to expand as you go, and money is an object, then these issues must be taken into account, in the original design of the System.
  17. Maxflax

    Maxflax Lightning in a bottle

    So are there 48 volt PV panels, or normally only 12 V and 24 V?
  18. Nadja

    Nadja RIP 3-11-2013 Forum Leader

    I have never seen 48 v panels, ususally around here if you want them to be 48, you simply wire 4-12v or 2- 24v panels to make the 48 volts. The one advantage that I know of is that you are pumping less amps through your wire, which will reduce the size of the wire needed to make the run.
  19. Maxflax

    Maxflax Lightning in a bottle

    Thanks. My panels will be on the battlement roof directly above my battery/controller room in the 3rd floor of a tower, so the lines will be short
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