Condensation in battery box venting

terrynew

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

Cariboocoot

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

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

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

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

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.

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

terrynew

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

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.

BB.

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

Cariboocoot

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! 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.

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

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

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

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.