Can you safely use a motorbike 12V GEL battery in a PV system ?

HaglunHaglun Registered Users Posts: 1
I am trying to set up a PV system that is as cheap as possible.
Eventually, my goal is to build IoT functionalities on top of it, using micro controllers. This way I will be able to monitor the PV, battery and control loads from a web app. I can do a few things in IoT, but I am a complete beginner in PV systems.

For the moment, the cheapest parts I found are the following:
- 18v, 85 watts solar panel

I suspect that the system will be pretty inefficient. I also know that the battery is insufficient to store all the electricity i can get from the solar panel. It is ok, my goal is to get a first experience and and the focus is on implementing IoT.
But I have the following question:

Is it safe to use the GEL battery to charge home appliances (using a 12v-5v DC converter) ?
I read that the GEL batteries are safe because they do not reject Hydrogen. But the battery manual says that the battery may reject hydrogen, and advises not to use it for any other purpose than engine starting.

Please tell me about any potential risks of using such a battery to store the PV generated electricity and charge small appliances (I will connect it to a 12 to 5V DC converter). Also, I have a lot to learn about PV systems, so I'm interested in any other remark you have.

Comments

  • mcgivormcgivor Solar Expert Posts: 3,274 ✭✭✭✭✭
    Welcome to the forum 

    The Gel motorcycle battery is not well suited to the application as it is designed for starting primarily, to achieve the high current needed for the starter motor, the battery will have many thin plates to increase the total surface area within each cell, they also are immediately recharged by an alternator.  Deep cycle batteries on the other hand have fewer thicker  plates because higher current in short bursts are not a requirement, the thickness of the plates will have an effect on life expectancy as the plates are sacrificial loosing material as they age.

    The materials used in the plates themselves will differ, most sealed motorcycle batteries are lead calicum, which provide properties needed for the application such as low self discharge, deep cycle commonly use pure lead, or an alloy of lead anttomony, lead carbon and other materials needed to suit the demands of long slow discharge low water consumption in the case of wet batteries, and so forth.

    Would it be safe to use a motorcycle battery ? It probably is safe but the life expectancy will be dramatically reduced, perhaps lasting a few months, whereas the correct battery used within its limitations and properly charged may provide years of service.

    Without trying to overwhelm you with all the details I've kept the focus on battery types, there is a wealth of information to be found from sites like this https://batteryuniversity.com/learn/article/lead_based_batteries an excellent starting point.

    Always remember going cheap is a false economy, you'll go broke saving money. 
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • EstragonEstragon Registered Users Posts: 4,451 ✭✭✭✭✭
    Haglun said:
    ...

    But I have the following question:

    Is it safe to use the GEL battery to charge home appliances (using a 12v-5v DC converter) ?
    I read that the GEL batteries are safe because they do not reject Hydrogen. But the battery manual says that the battery may reject hydrogen, and advises not to use it for any other purpose than engine starting.

    Please tell me about any potential risks of using such a battery to store the PV generated electricity and charge small appliances (I will connect it to a 12 to 5V DC converter). Also, I have a lot to learn about PV systems, so I'm interested in any other remark you have.
    One thing to note is the DC voltage on the "12v" side can actually vary from <10v (battery essentially dead) to >15v (cool/cold battery in absorb charging cycle).  You'll want to make sure the converters will provide stable 5v out with the variable input (or use a 12v voltage stabilizer in series ahead of the converter).

    Also, I'm about to do something similar, and I'm a bit concerned about whether the switching DC converters will present any problems for SBCs (rPi zeros w in my case).  If so, may have to add a linear regulator or something into the mix.  Hopefully output caps on the SM converters alone will smooth enough for the SBCs.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • BB.BB. Super Moderators, Administrators Posts: 30,049 admin
    The issue with most GEL batteries (at least those found in the USA) is that they can only be charged at a very low current (C/20 or 5% rate of charge).

    If you charge a GEL battery at too high of rate (or too high of voltage, typically >14.2 volts @ 25C/75F), they start to gas and form permanent gas bubbles in the electrolyte GEL. Which permanently reduces the capacity of the battery.

    For systems with Utility Power (24x7), you can take 10+ hours to recharge a 50% discharged battery bank. For solar, when you have ~6 hours or so of "useful" sun in a day (something like 9am to 3pm of full/direct sun on the panels)--It can take several days just to recharge the GEL battery.

    If the system is only used (for example) on weekends or one day a week, you have the rest of the week to do 5% rate of charge--GEL could work OK.

    If the system is used daily, you will never get the batteries back to fully charged (>~90% state of charge) and they will sulfate and die an early death.

    GEL--Great for UPS functions (Float 24x7) and 20 minutes of high discharge. Just not great for day to day deep cycling and "short" charging cycles.

    There are many european GEL batteries that seem to accept >5% rate of charge--But I do not know what is different and if they have other limitations (i.e., high rates of charge below 80% state of charge and 5% at over 80% state of charge).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
Sign In or Register to comment.