Are You Killing Your Batteries?

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  • Sunking
    Solar Fanatic
    • Feb 2010
    • 23301

    Are You Killing Your Batteries?

    Yes you are killing your batteries if you use Solar to Charge them and follow battery manufactures recommended 3-Stage Charging Voltage Set Point. Stop that stupid, you are killing your batteries. You are sheep being led to slaughter. Step out of that line. All it takes is one Step to the RIGHT.

    It is not that battery manufactures are wrong or misleading you, It is the application the manufactures assume are wrong. They think you are using a commercial AC Powered Smart Charger with unlimited time and power. Wake up you do not use commercial power or AC chargers expect once a month for maintenance on a generator right? You use Solar which is a very SOFT SOURCE of limited Power and Time. You got just 4 short hours in 24 hours to get the job done. Guess what?

    Greater than 90% of all of you are killing your batteries from deficit/severe under charging, and following the manufactures recommendations are only making it worse.

    With a commercial charger you start charging in Bulk until you hit about 80% SOC, then switch to Absorb which lowers the voltage a bit, current slows down and tapers to 2% of C. (about 6 clock hours) then you switch to Float and your battery continues to charge overnight and becomes saturated and fully charged by morning.

    Well guess what? It is impossible for you to fully charge a lead acid battery on Solar unless properly oversized by design which you likely failed to do to start with. Even a properly designed system is going to come up short in winter months. There is just not enough Sun Hours in a Day to fully Saturate your battery.

    Battery manufactures are getting slammed with warranty claims from Renewable Energy users. The claims are a result of chronic under charging and sulfated batteries. Many manufactures have revised their charging procedures for RE users. They have done away with Bulk Absorb, and Float voltage Algorithms. Today they aim at Maximum Smoke. Trojan calls it a Daily Charge of 2.47 vpc which use to be roughly Equalize voltage levels. What they are doing is forcing your Charge Controller to operate in Bulk mode or Max Smoke from Sunrise to Sunset. Still may not get your batteries fully charged. But still significantly more power stored than setting the voltage to a lower value.

    So what do you do? Well what you should have been doing from the start. Use your Temperature Compensating Hydrometer to find the right voltage if there is one. For roughly 90% of you there is No Voltage High Enough you can set your controller to get the batteries fully charged up, because you do not have enough panel wattage to begin with. For those of you who find yourself in that situation, all you can do is limit the damage by cranking the voltage to MAX, and then every couple of day run the genny to get your batteries back to 100%. Don’t like that idea? Tough Titty said the Kitty, you made your bed, now sleep in it.

    For the rest of you where you do have enough power panel wattage to get fully recharged most of the time, you are not going to use the manufactures recommendations, you are going to find the exact setting using your Hydrometer.

    So that leaves you with only 2 voltages to concern yourself with Daily Charge on your Charge Controller, and EQ on your AC charger used on your generator. OK at this point you may be asking yourself how I do that when my Charge Controller is a 3-Stage Controller? The answer depends on what Controller you have:

    • Set Bulk = Absorb = Float if your controller allows. Initially set it to 2.47 vpc
    • If your Controller will not allow you to set all three modes to the same value start by setting Float to the desired voltage like 29.6 on a 24 volt battery system. Then set Absorb as high as the software will allow that is less than Float like 29.5 and 0 minutes or hours. Set Bulk like Adsorb except try the same as Float first, or lower like 29.4

    What this is doing is forcing your controller to behave like a simple Constant Voltage – Current Limit algorithm. (Max Smoke) Basically your Controller will stay in Constant Current charging until the battery reaches the Float Set Point. When that is reached the current will taper off, and if you’re lucky enough to have enough Sun Hours and panel wattage you should see that current taper down to about 1 to 2% of C indicating full charge. C is the battery AH specification at the 20 hour discharge rate. So if you have a 100 AH battery would be 1 to 2 amps. The point of doing this is to get as much energy as possible into your batteries with the very limited amount of time you have with Solar. If you have the system designed properly and lucky you will get back to 100% SOC, but do not count on it.

    So how do you know if it is right or not? Pull out the Hydrometer, that is what you bought it for. When the Sun starts to set low in the sky, check your Specific Gravity. If it is too low, you need to raise the voltage, if voltage is maxed out and you still are not fully charged up, GUESS WHAT? You do not have enough panel wattage.

    If you have enough panel wattage, you will find the right voltage. But do not relax, your job is not over. Conditions change by day, week, month, season. What worked last week may not work this week.

    So let’s get started on a proven method that works. First order of business you have to have a Temperature Compensated Battery Hydrometer, and you must learn to use it and use it often. You cannot use a volt meter to tell the State of Charge in a battery. Voltage is only an indicator. It can only tell you if something is way out of acceptable limits like Equalization or equal voltage between cells, or if your batteries are really low. But a volt meter will not tell you the SOC. There is only one way to measure SOC and that is with a Temperature Compensated Hydrometer. Don’t worry they are not expensive, less than $10. Deka makes a really good one and you can order it online. So get to it. To learn how to use a Hydrometer read this.

    OK regardless of how new or old the batteries are we need to get them fully charged and Equalized. This is best done with a generator, and if you are off grid, you had better have a generator and a commercial AC charger. A generator is required to perform Preventative Maintenance like equalizing your batteries as needed (about every 4 weeks or as needed). And carry you through cloudy days. If you do not have a generator you have no choice but to use your controller, but it could take several days using your controller. EQ can even take 12 to 24 hours with a generator.

    To Equalize is a controlled over charge. Check your battery manufactures specifications for the correct EQ voltage but it should roughly be 2.5 to 2.6 volts per cell. So if your battery voltage is:

    • 12 Volts = 15.6 volts
    • 24 Volts = 31.2 volts
    • 48 volts = 62.4 volts

    To learn how to equalize read this. You are going to need the Hydrometer. Did I mention you must have a Hydrometer?

    OK now that you have EQ time to set your controller voltages. Take note this is a starting point, not a definitive. Initially set your voltages to 2.46 volts per cell:

    • 14.8 Volts @ 12 volt system
    • 29.6 Volts @ 24 volt system
    • 59.2 Volts @ 48 volt system

    When you notice your controller indicates the batteries are fully charge or current has tapered down, take a hydrometer reading and see what the SOC is. If it is low, you need to raise your voltage. If it is high you should notice gassing and need to lower the voltage. Repeat as often as necessary until you find the sweet spot. Do not be surprised if you cannot reach 100% SOC. That would mean you panel wattage is too low and you will need to be using your generator more frequently. Don’t EQ the batteries to frequently. If you are not able to get to 100% bring them up with a generator about every 2 or 3 weeks. Just don’t let the batteries get below 50%.

    Once you have found the sweet spot don’t completely relax, because it will not last. Seasonal and even monthly changes will be required because the Sun Hours change from week to week. What worked last week may not work next week. Basically in warmer months you will be running lower voltages than cold months. In cold months you will be running higher voltages than warm months. Don’t fear because you should be performing weekly Preventive Maintenance which checking Specific Gravity with your new Hydrometer. Did I mention you need a Temperature Correct Hydrometer?

    That is it for now. If you have questions start a thread.

    Hope this helps.

    Last edited by inetdog; 05-29-2015, 04:50 AM. Reason: typos
    MSEE, PE
  • inetdog
    Super Moderator
    • May 2012
    • 9909

    Originally posted by Sunking
    Thank you!
    The thread has now been closed since it really does not need confusing member input.
    Let us know if you ever want to edit.
    SunnyBoy 3000 US, 18 BP Solar 175B panels.