MidNite Battery Monitor Question

marsofold
marsofold Solar Expert Posts: 45 ✭✭
in Off Grid Solar & Battery Systems #1
I purchased a MidNite Solar Battery Capacity Meter from our forum sponsor.
The gadget works well, however it trips a caution light if a 14.7 volt charge
has not happened for a week. Since my only intended use of my off-grid
solar system is to cope with a catastrophic post-collapse situation, I am
currently only using it as an uninteruptible power supply for my dog's
invisible fencing. So except for tests, the batteries actually never get drawn
down significantly. Which causes my Xantrex XW-MPPT60 solar charge
controller (also purchased from our sponsor) to only feed a 13.6 volt float
voltage to the battery bank. Is a long-term floating voltage OK? The solar
charger works fine, if I briefly draw the batteries down a bit with an electric
space heater, then the XW-MPPT60 feeds them enough voltage to keep the
battery monitor caution light off for a week. However, I really don't want to
draw the battery bank down weekly to keep the monitor happy. Nor do I feel
comfortable with ignoring the warning light. So what I have done as a
compromise is to run my IOTA DLS-90 IQ4 charger overnight every two
weeks. But I'm feeling less comfortable with that since it cranks out almost
15 volts in doing so (getting close to equalization voltages). And I feel leery of
almost equalizing every two weeks. So what should I do: draw down the batteries
every two weeks, continue using the IOTA charger every two weeks, or just ignore the
warning?
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Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: MidNite Battery Monitor Question

    You've probably surmised that the warning light is designed to indicate a fault with an "in-use" system that is experiencing daily discharge of a significant amount. The fault light says: "you haven't gone through a Bulk/Absorb cycle this week". For a typical off-grid system this would be an indication of a problem; prolonged bad weather, or something defective in the charging circuit.

    Some from that point of view you can ignore it.

    From another, deep cycle batteries actually prefer being occasionally discharged and recharged. So you might be better off hooking up a timer to a load that will take the batteries down to a point that will trigger the full recharge cycle once a week.

    You should not substitute equalization charging for this. That is only for keeping specific gravity aligned across all cells. The extra high Voltage is otherwise not good for batteries.

    In my opinion it's a toss-up whether you cycle the batteries or ignore the light.
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  • boB
    boB Solar Expert Posts: 1,032 ✭✭✭✭
    #3
    Re: MidNite Battery Monitor Question

    You don't even have to discharge the batteries. If your charger has an adjustable equalize voltage, you can set it to
    14.8V or so and just do a 2 hour EQ which will do the same thing as a charger would do when it does an Absorb cycle.

    The Absorb cycle helps reduce sulphation of the battery plates from sitting. A long term float voltage will not accomplish
    the same thing, unfortunately. The voltage must be brought up to Absorb for a while once in a while. That was the
    main intention of the MNBCM.

    There is a jumper in the MNBCM that should adjust that warning voltage threshold if 14.7V is too high.
    Just check the electrolyte level in the batteries from time to time to make sure they don't boil away
    if they are flooded (not sealed) batteries.

    boB
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