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Old 02-13-2013, 01:20 AM   #1
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How much hydrogen do lead acid batteries realisticly produce?


I have 2 12v marine batteries in parallel right now for my backup system and planing to add more.

At what point do I need to actually worry about it accumulating H2 faster than it can dissipate through the house walls? My setup is standby, so the batteries arn't constantly being drained and charged at same time like a telco setup. Idealy I should use sealed batteries but what I like about non sealed is they are cheaper, and can be maintained, so they can last longer if I take good care of them. If the room itself is well ventilated so the H2 does not just keep hanging in the same spot, is it safe?

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Old 02-13-2013, 04:30 AM   #2
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How much hydrogen do lead acid batteries realisticly produce?


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Originally Posted by Red Squirrel View Post
I have 2 12v marine batteries in parallel right now for my backup system and planing to add more.

At what point do I need to actually worry about it accumulating H2 faster than it can dissipate through the house walls? My setup is standby, so the batteries arn't constantly being drained and charged at same time like a telco setup. Idealy I should use sealed batteries but what I like about non sealed is they are cheaper, and can be maintained, so they can last longer if I take good care of them. If the room itself is well ventilated so the H2 does not just keep hanging in the same spot, is it safe?
If the charging process is controlled and done properly,
then the amount of gass produced is small.
If the room has good ventilation
and the batteries are not over charged
then the risk is small.

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Old 02-13-2013, 06:32 AM   #3
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How much hydrogen do lead acid batteries realisticly produce?


I can't tell you how much gas is generated in the batteries but I had one in my car blow up in my face several years back. The car had been sitting for a few minutes but was still pretty warm, one spark is all it took.
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Old 02-13-2013, 07:30 AM   #4
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How much hydrogen do lead acid batteries realisticly produce?


A lead acid battery is quite likely to explode if (1) it is frozen and you either draw a lot of current or try to recharge it, or (2) you cause a short circuit (way more current draw than the car starter draws).
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Old 02-13-2013, 08:24 AM   #5
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How much hydrogen do lead acid batteries realisticly produce?


Unless the batteries are in some sort of a seal container I would not be concerned.
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Old 02-13-2013, 09:16 AM   #6
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How much hydrogen do lead acid batteries realisticly produce?


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Originally Posted by Red Squirrel View Post
I have 2 12v marine batteries in parallel right now for my backup system and planing to add more.

At what point do I need to actually worry about it accumulating H2 faster than it can dissipate through the house walls? My setup is standby, so the batteries arn't constantly being drained and charged at same time like a telco setup. Idealy I should use sealed batteries but what I like about non sealed is they are cheaper, and can be maintained, so they can last longer if I take good care of them. If the room itself is well ventilated so the H2 does not just keep hanging in the same spot, is it safe?
I don't see much cause for concern as others state. Only issue is if charge circuit goes bad and/or a battery cell goes dead, then battery can then get overcharged and that is when it out-gasses. This is because the charger will raise current to seek a certain voltage level and with a dead cell it can never get there, so the remaining cells all get overcharged and out-gas.

You mentioned that you like that it can be maintained but if you are maintaining, i.e. adding distilled water to cells, then something is wrong. You shouldn't need to add more than an ounce or so per year to a cell if it is being properly charged. If you are adding water frequently then you are probably overcharging and out-gassing. I have a DC power sump pump as a backup system. The charger that came with the system caused me to regularly top up the battery liquid and the batteries were done in 18 months. I switched to a marine grade charger (http://www.xantrex.com/power-product...ruecharge.aspx) and now seldom add liquid and the batteries seem to last 4-5 years.

b.t.w. Telco system batteires aren't charged and discharged at the same time. The batteries are just in the DC current path between the ac/dc stage and the dc/ac stage all the time. They should typically be in a net float charge bias all the time when AC is available.

Last edited by curiousB; 02-13-2013 at 03:14 PM.
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Old 02-13-2013, 09:28 AM   #7
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How much hydrogen do lead acid batteries realisticly produce?


Feel the batteries....if they are not warm then your likely not cooking off Hydrogen gas. The cook off is a result of putting more energy into the battery that it has room for....1st sign is heat...once they get hot, the hydrogen starts to cook off.

Unlike NiCad's...lead acid batteries are not self limiting on voltage..but they are on current. As long as you don't apply more voltage than it can handle, as soon as the battery is charged, it will stop drawing current...but if you have a bad cell...then you end up applying more voltage to the remaining cells....which causes problems.
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Old 02-13-2013, 04:20 PM   #8
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How much hydrogen do lead acid batteries realisticly produce?


This is great to hear. I had some people on a tech forum freaking out over this saying I'll blow up my house and need at least 10CFM of air exchange etc...

The batteries always feel cool to the touch, and I do monitor the voltage so if something was to go wrong and they are overcharging I'd get an alarm.

As for adding water I have not yet needed to add some, but I just like the idea that I can since I can prolong the life by making sure they're always topped up. I need to read up more on proper maintenance such as knowing WHEN to add water. From what I read as long as the plates are completely under water I'm ok. Also want to blow air over them before doing anything so any standing hydrogen is cleared off.

Another thing I could probably do is monitor their temperature as well.

Using this as a charger right now:

http://www.tripplite.com/EN/products...xtModelID=2938

Essentially a UPS with extended run time.
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Old 02-13-2013, 09:33 PM   #9
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How much hydrogen do lead acid batteries realisticly produce?


I've seen batteries "explode" only once. I was working in a shop where the mechanic was charging a couple of batteries on the workbench. I was working about 6" from there, when he decided to use the grinder on the same bench. From the sound of "gunfire" I'd think that the hydrogen gas must form bubbles in the atmosphere directly above the battery....pop pop pop pop and a cracked battery top was the result. Nobody hurt fortunately, and the old mechanic laughed and said it happens all the itme. Scared the crap out of me. But in your case, I would think that you are safe.
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Old 02-13-2013, 10:11 PM   #10
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How much hydrogen do lead acid batteries realisticly produce?


Yeah I would imagine sparks immediately over it would do that. That's why one thing I always am careful with is when removing or adding connectors. I usually blow air over the battery before that.

I'm actually trying to produce hydrogen as a test in a big enough quantity so I can get a pop, so I can put my sensor, get a reading, and get an idea how much it takes. The sensor reading is basically a number from 0 to 1024. There are advanced ways to translate it to PPM but it's not trivial as the numbers can also be altered with the little sensitivity knob on it.

Once this server room is built I'll have that sensor on the sealing near the battery rack. It definitely works though, I have it on top of the pipe where hydrogen is coming out of my system and as soon as I turn the power on the values go up. I imagine copper is probably not the best for the anode/cathode rods either. It's making the water turn green and probably reducing the effectiveness. It looks cool though. :P

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Old 02-14-2013, 06:27 PM   #11
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How much hydrogen do lead acid batteries realisticly produce?


Quote:
Originally Posted by Red Squirrel
This is great to hear. I had some people on a tech forum freaking out over this saying I'll blow up my house and need at least 10CFM of air exchange etc...

The batteries always feel cool to the touch, and I do monitor the voltage so if something was to go wrong and they are overcharging I'd get an alarm.

As for adding water I have not yet needed to add some, but I just like the idea that I can since I can prolong the life by making sure they're always topped up. I need to read up more on proper maintenance such as knowing WHEN to add water. From what I read as long as the plates are completely under water I'm ok. Also want to blow air over them before doing anything so any standing hydrogen is cleared off.

Another thing I could probably do is monitor their temperature as well.
As previously mentioned, the full charge state is optimal for reduced gases, IEEE has a formula for calculating percentage H from number of cells being charged, max allowable 2%. Generally, do a complete 100% air exchange in the room every couple days and all will be well.
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Old 02-14-2013, 07:41 PM   #12
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How much hydrogen do lead acid batteries realisticly produce?


My original plan was actually to seal the room and use a water based cooling system, but I changed my mind and will make it an air exchange system. One intake for the "cold isle" and an exhaust for the "hot isle". I can maybe pass the exhaust through a Venmar/HRV unit, as well. I wont worry about a HRV for now but if I add more batteries think I'll consider it, for piece of mind.

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