how important is battery matching for parallel

Discussion in 'General Questions' started by little fridge, May 28, 2016.

  1. Hi new to solar, I did some 12 volt wind in the past with great success. So now I have a very small fridge in my little SUV the plan was to run it off a dedicated system with option to run off the SUV system while on the highway. I am having trouble getting my one optima AGM and one g35 lead acid battery to work together in parallel
    the fridge is I think 3.2ft. the fridge is working as advertised, when running it pulls between .75 and.9 amps 110vac. start amps is 6.0amps 110vac I have also confirmed with my nifty accumax meter and a good clamp meter a bunch of other specs, in rush current while on a 12v inverter is 79amps @12v. running amps on 12v inverter is about 6amps dc. this was a few days ago If I remember it was 63amp hours and or .53kw per 24 hours closed up in the SUV sitting in the sun.
    So I don't need that much power to run it.

    3 years ago I bought a super stupendous flexible solar panel that I thought was the do all end all , and it was new old stock then, so lets say over 5 year old technology. maybe somebody knows? it is a unisolar pvl-136 panel, USA made, but out of business, the nice thing is you really can roll it up and it fits in a 18" box.
    Then I also bought a few years ago a power bright 24 volt 400 watt inverter. the inverter is advertised as 800 watt start load, but will not run my little fridge, as I have now found out the start current is only rated for exactly 1 second, maybe a half a second too short to get the fridge started. fridge runs fine on a 10 year old 4oo watt 12v inverter. so I will be forced for now to solar charge at 24vdc, and then run the fridge at night with 12v parallel

    sorry for the long winded. intro. I have only tried 2 nights so far, but the AGM battery is hogging the load, and the group 35 is not doing much if anything. How important is it too have the 2 12v batteries be identical for good paralleling? how big do the link wires need to be between the 2 batts, remember the run load is only 6 amps I have the 2 batteries connected with 10 g wire, I think the 12 volt inverter has 8g wire going to the accumaxx meter


  2. tough crowd, well the little fridge is working, charging 24 volts from the p20l on a series bank, and tapping a 12 inverter in to one or the other of the 12v batts while during the day, at night the 12v that is running the inverter takes all the load I think. This was the first time the fridge has made it thru the night, with no low voltage alarms,
    this morning the inverter bat of the series had 12.3v, and the other series bat had 15v. so I switched the inverter to the 15v battery, and see how the charge goes into last nights battery.
    Just in case I have a pretty big 12v parallel bank that should charge off the main engine when running, and run the fridge at the same time I hope??
    so for the answer to the question about battery size, I think it does matter a bit, the smallest I have is a g24, it is also the oldest, but age, and connections are also important, I think bigger jumpers helps the batteries work together better.
    Do metal dendrites form in lead acid batteries?
  3. Tuicemen

    Tuicemen Solar Guru

    All batteries in a battery bank should be the same type, size, and age.
    1: The older the battery the less efficient
    2: Your bank is only as strong as your weakest battery( one bad battery in your bank can decrease its performance dramatically)
    3: Standard lead acid batteries need regular equalization to clean of the build up on the plates. Gel Cel and AGM batteries should never be equalized (they will explode)

    The larger the gage wire in DC runs the better (less power loss, less likely of overheating as well)
    Also the length of the cables from your bank to inverter should be as short as possible.

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