Proper battery venting...

couchsachragacouchsachraga Solar Expert Posts: 78 ✭✭
First off, a big thank you to Northern Arizona Wind & Sun for hosting this forum, and for all that have shared their knowledge. What a great resource!

I'm sure this has been discussed before, but the search terms I've used just haven't brought up the answer / explanation.

My question is this: Must batteries (liquid (Trojan 1275's) ) be in a battery box and vented to the outside? I have 2 currently, and expect to increase to 4 next year potentially. Right now I only have 180 watts (maybe) of solar panels (6 Solarex SX100's - given their numbering scheme I thought these were 100 watt panels, but they are from the late 70's / early 80's and have been passed around a bit... one of the previous borrowers of said panels said they were 30 watts each when new...).

Right now (just set up) batteries are out in the open (2nd floor of a 30x40 space, cathedral ceiling if you will with 40' ridge line), mostly to keep them near the panels and warm (this is the only heated space.. and won't be heated when we aren't there). I can certainly poke a hole in the wall and run some PVC outside, but try to poke as few holes in the wall as I have to - I'm in the Adirondacks of upstate NY where we have more cold and snow than sun;) . In the one post I DID find it was mentioned with a small system hydrodgen buildup wasn't as much a problem as protecting the batteries from people and vice-versa. I can certainly pick up a few plastic battery boxes (for boats) that would help contain any acid spills... but these tend to have holes in them for venting as well.

Any thoughts would be greatly appreciated!

For the curious we're keeping a nice simple set up, the big power draws at this point are a few incandescent lights (that get turned on and off quickly, compact fluorescents for the rest), a 12v pump (I have gravity feed water to the floor, perhaps sink, the pump brings it up to household pressure which keeps the propane hot water heater happy (which makes my wife very happy:) ), and a freezer / fridge unit that is the size of a cooler and designed for offroad expeditions (a National Luna Weekender) that I've had for a few years. If we spend more time up there now the fridge may get upgraded. So far my best purchase has been a trimetric meter so I can see I'm actually using less power than I thought I was...and know when the batteries are fully charged. Oh, and the controller is a used 30 amp Sun Selector NDR 30.

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Proper battery venting...

    Welcome to the forum.

    Given your set-up I'd say the biggest problem will be keeping those batteries alive rather than controlling any off-gassing. Those are 150 Amp hour 12 Volt I believe, and if you have two in parallel on a 12 Volt system that's 300 Amp hours (fits with a 30 Amp controller). As such you'd want about 400 Watts of array on them (depending on the actual current of the panels).

    If I were you I'd see about measuring the short circuit current on each panel in full sun so you have some idea what sort of output to expect. Six 30 Watt panels would be woefully short. And don't add any more batteries unless you have the panel to support them or it will just get worse.

    Most places are airy enough that actual venting to outside is not necessary in my opinion. They really do not produce large amounts of gas. Just keep them away from flame or other ignition source because the hydrogen and oxygen is quite a flammable combination.
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Proper battery venting...
    In the one post I DID find it was mentioned with a small system hydrodgen buildup wasn't as much a problem as protecting the batteries from people and vice-versa.

    That is key! The batteries must be protected from conductive things falling on them. In your reading have you seen any of the stories about what happens when batteries are shorted out?

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • couchsachragacouchsachraga Solar Expert Posts: 78 ✭✭
    Re: Proper battery venting...

    From doing a bit of welding I'm well aware of what a short can do!

    I'm also well aware that the panels are rather weak. Soon I hope to have an idea of exactly what they are putting out on a good sunny day (first we need one of those...) and try and determine if they are indeed 30w panels. I'm guessing next spring I may be picking up 2-4 new panels, each with more output than the 6 I'm currently borrowing.... and likely a new charge controller to match.

    From what I'm reading (as well as the "post like yours" that helpfully popped up) it sounds like battery boxes would be fine and my big worry is shorts and people, not H and O
  • BB.BB. Super Moderators, Administrators Posts: 29,706 admin
    Re: Proper battery venting...

    If you put in a covered/sealed battery box--Then you want to vent so that hydrogen does not collect under the lid.

    A pair of 150 AH @ 12 volts in parallel gives you 300 AH at 12 volts.

    We generally recommend around 5% to 13% rate of charge (based on 20 hour capacity of battery bank). And Trojan recommends 10% (as I recall)... So:
    • 300 AH * 14.5 volts charging * 1/0.77 solar panel+charger deratings * 0.05 rate of charge: 282 Watt array minimum
    • 300 AH * 14.5 volts charging * 1/0.77 solar panel+charger deratings * 0.10 rate of charge: 565 Watt nominal array
    • 300 AH * 14.5 volts charging * 1/0.77 solar panel+charger deratings * 0.13 rate of charge: 734 Watt array "cost effective maximum"...

    And if you double the battery bank size, then you would double the above numbers.

    I don't know how much power you use or how much sun you have--The above numbers are just based on battery bank capacity. The more power you use, the higher rate of charge you probably should have.

    Also, I am not a fan of paralleling lots of batteries and adding more batteries to an existing bank (for lots of reasons, if you can avoid it).

    Wiring the bank is fairly critical--So read this link about wiring.

    Your next bank, I would suggest going to a larger AH battery and/or going with a higher bank voltage--But again, this depends on your existing loads (and array size).

    Sorry, more questions than answers.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • couchsachragacouchsachraga Solar Expert Posts: 78 ✭✭
    Re: Proper battery venting...

    Bill (and all)
    Thank you for your replies.

    I am aware my current solar set up is not optimum to say the least - I was thinking I had 600w, not 180.... If anyone has any info on SolarEx SX100 panel's I'd love to see it... mostly to pass along with the panels at some point!

    It is in an old barn with a place to crash - we're not up there every weekend, and I hope to spend more time there sometimes. So far I seem to use 15% of my system per day, no recharging for said day. I had hoped to get two days out of that battery capacity at this point - looks like I might stretch it to 3.

    Thank you, too, for the wiring link. I'd seen it here before, and have tried to educate myself as much as possible so as to do things right. So far I've learned that everything the exits the battery needs fuse, and the bigger the wire the better (especially the battery to battery cables...).

    FWIW I figured in theory to use 75 AH per day (and am using much less than that - water pump is using less than I thought, as is the fridge which are by far the largest draws), hence the 300 AH battery setup (giving me 2 days to draw to 50%).

    I was thinking a top hole in the marine battery boxes and I'd be good to go - am I wrong in that thinking, and as such should I just be building a box to set them all in, and using 2" PVC to vent (I take it with caps on the end with 1/16" holes drilled in them, and "out" higher than "in" pipe)?

    Thanks again!
  • BB.BB. Super Moderators, Administrators Posts: 29,706 admin
    Re: Proper battery venting...
    I was thinking a top hole in the marine battery boxes and I'd be good to go - am I wrong in that thinking, and as such should I just be building a box to set them all in, and using 2" PVC to vent (I take it with caps on the end with 1/16" holes drilled in them, and "out" higher than "in" pipe)?

    Should be OK... It is actually pretty difficult to contain hydrogen gas (light, very tiny molecule that goes through many materials). But anything that increases ventilation a bit and, if there is a spark near by, keeps the concentrations down--Is a good thing.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Proper battery venting...

    one more detail: make sure that your opening for the conduit (for your battery cables) is lower than the tops of your batteries. That helps to prevent hydrogen from entering the conduit and corroding your equipment.
    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • Volvo FarmerVolvo Farmer Solar Expert Posts: 209 ✭✭✭✭✭
    Re: Proper battery venting...

    Hydrogen is not a corrosive gas.
  • BB.BB. Super Moderators, Administrators Posts: 29,706 admin
    Re: Proper battery venting...

    Hydrogen is not the corrosion problem--It is the sulfuric acid mist that is vented from the (typically flooded cell) batteries during equalization/heavy charging.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Proper battery venting...
    vtmaps wrote:
    That helps to prevent hydrogen from entering the conduit and corroding your equipment.
    BB. wrote: »
    Hydrogen is not the corrosion problem--It is the sulfuric acid mist that is vented

    Bill, VolvoFarmer,
    Thanks for the correction. I meant to write: "That helps to prevent hydrogen from entering the conduit and exploding your equipment." :p

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • BB.BB. Super Moderators, Administrators Posts: 29,706 admin
    Re: Proper battery venting...

    Both are bad news...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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