Condensation in battery box venting

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terrynew
terrynew Solar Expert Posts: 48 ✭✭
Hi, All. I'm getting condensation drops from my PV battery box's hydrogen vent, landing on my batteries. Any suggestions on avoiding this?

The box is indoors, with an ABS plastic 2" vent running vertically six feet to the ceiling then four feet through a well-insulated attic and then two feet above the roof, before ending in an upside-down 'U' to prevent rain/snow entry. It's an eastern Ontario location with cold winters.

Is this a common problem? I guess one step would be insulating the vent pipe within the attic? Anything better I can do?

Thanks,
...Terry

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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
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    Re: Condensation in battery box venting

    It's too long of a run for the box to vent naturally; it needs a fan to ensure air change.
    Any chance you could take it out through basement/crawlspace or such?

    For now I'd rig some sort of plastic shield so the condensation doesn't drip on to the batteries, but this is a problem that needs to be solved.

    Change to AGM batteries and there's no need for the vent. Expensive solution, but perhaps not as much so as altering the vent or putting a fan in.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
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    Re: Condensation in battery box venting

    got a cup or plate you can set below the end of the pipe? it would drip onto the plate or cup to be collected and tossed out later. that is a long run for that as marc pointed out. maybe a small muffin fan can be cycled on/off periodically.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
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    Re: Condensation in battery box venting

    A fan would be the preferred solution, but barring that I would insulate the length of pipe through any unconditioned space. If you keep the column of air rising through the vent warm until termination, it can't condense in the pipe.

    Tony
  • terrynew
    terrynew Solar Expert Posts: 48 ✭✭
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    Re: Condensation in battery box venting

    Thanks, guys. The cup approach is working fine as a low-tech solution, and I'll try to insulate the pipe in the attic but I have two feet of blown cellulose in there so who knows how I'll get to it. I'll go with the inline fan as a permanent solution because I also want that for when I'm equalizing. (It set off the CO detector on my first equalizing!)

    The drawback of an inline fan is the use of electrical power in a system making electrical power -- yuck, especially if it needs to be on all the time in the winter. Would that be the case? Anyone recommend a low-power DC inline fan?

    Thanks again,
    ...Terry
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
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    Re: Condensation in battery box venting

    What sort of charge controller do you have? Some of them (like Outback) have a programmable auxiliary output which can be used to turn on a vent fan when the batteries reach Absorb or Float. There are also Voltage-controlled switches which can be utilized for much the same function:
    http://www.solar-electric.com/moredr.html

    No need to run the vent fan all the time!

    12/24 Volt computer muffin fans are usually easily available and should be sufficient to move the air. Remember that ever bend in the pipe is like adding several feet of length.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,477 admin
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    Re: Condensation in battery box venting

    And, for example, you can connect a 24 volt computer fan directly to your Vmp=17.5 volt solar panels (or its own 10 watt panel)... Will run a bit slow (and quiet) only when the sun is up... Should be fine unless you do a lot of night time generator charging.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • terrynew
    terrynew Solar Expert Posts: 48 ✭✭
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    Re: Condensation in battery box venting

    Marc, I indeed have an Outback controller with an auxiliary to turn on the vent fan. But doesn't the condensation occur 24/7, not just during absorb/float charging, since there's always a stack effect draw up the vent?

    Bill, I like your idea of a 24 V computer fan tied to a dedicated 10 W panel (I've got an old one that might still be working, although I think it puts out 16 V so I don't know what that would do to the 24 V computer fan). The solution still only runs part of the day, but it's 0 impact on my batteries. More installation work than Marc's approach though.

    Guess I'll go with one or the other above approaches plus the 24/7 cup sitting in the battery box!

    Thanks again,
    ...Terry
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
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    Re: Condensation in battery box venting

    condensation: likely any time your batteries are warm enough to "steam". Do you have any idea how warm they are ?? Could moisture in the house be leaking thru and showing up in the battery box ??

    There really should not be condensation - not enough water should be coming off the batteries to measure.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • BB.
    BB. Super Moderators, Administrators Posts: 33,477 admin
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    Re: Condensation in battery box venting

    Try a 12 volt fan too... Possibly with a small resistor to limit voltage/current/speed if needed.

    Used computer fans are cheap--so a bit of experimentation (with failure) should not be a big deal.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
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    Re: Condensation in battery box venting
    terrynew wrote: »
    Marc, I indeed have an Outback controller with an auxiliary to turn on the vent fan. But doesn't the condensation occur 24/7, not just during absorb/float charging, since there's always a stack effect draw up the vent?
    ...Terry

    Nit-picking time! :p If there was always a stack effect drawing up the vent there wouldn't be any problem!

    But seriously; I know what you mean. The question is what Mike said; where's the moisture coming from? If this is off-gassing of the batteries, it only happens during charge. If it's moisture coming in from the house - that's another issue. As is if the source is cool, damp air migrating back down the vent. Tricky things, vents. Did you know properly installed bathroom vents should have a slope down away from the fan outlet so that any condensation flows out the pipe instead of into the fan? You'd be amazed at the number of contractors who don't! Or who think it's all right to just go up into the attic or do any one of a hundred other bad things that end up damaging the house. Seen it. Fixed it. Presented the bill. :p

    I mention this because you may have to run up, then horizontal and slightly down, and then either out the gable end or (not so good) through the eave. That way any condensation occurs in the horizontal run and flows to the outside.

    Or you might end up running a fan 24/7. Believe it or not, but around Vancouver that's standard practice; running a vent fan all the time to ensure positive air flow through the house to keep moisture levels down. Big problems with mould around there.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
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    Re: Condensation in battery box venting

    Try one of these:

    http://zephyrvent.com/

    Coupled to this:

    http://www.solar-electric.com/volconswit.html

    Turns on only when needed, draws ~15 watts, runs quiet, brings peace of mind, and should cure your condensation problem, especially if you insulate the vent stack.

    Tony
  • terrynew
    terrynew Solar Expert Posts: 48 ✭✭
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    Re: Condensation in battery box venting

    The condensation hasn't occurred the last few days, even during a 5-hr generator charging. We had a run of near-freezing humid weather last week, and this week has been much colder (closer to 0 F). So I think this means the condensation isn't due to battery charging but rather to humid external air coming down the vent pipe.

    This is coupled with moist air coming into the battery box from the house. I need that air source to get the draft up the pipe, and it's humid because this is a brand new house with lots of moisture still in its concrete, wood, and drywall.

    If this is what's going on, am I right that a vent fan triggered by being in absorb phase wouldn't be as useful as a vent fan on a manual switch, for when equalizing and in times of high outside humidity? I would also insulate the vent pipe in the attic. Is there any value in insulating it in the battery room too, which is about 60 F?

    Thanks, everyone, for your ideas and experience!
    ...Terry
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
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    Re: Condensation in battery box venting

    If the pipe is black ABS, it's already usually a "foamy" ABS with lots of pores, I don't know if more insulation will help, but it can't hurt.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,