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Author Topic: Back up power  (Read 713 times)
ND8M
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Posts: 40




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« Reply #15 on: May 24, 2016, 07:11:19 PM »

I use a car battery in a battery box under my desk.  It's kept on a trickle charger, and the power runs to a DPDT knife switch so I can switch between the power supply or the battery.  Could hydrogen off gassing cause an explosion?  It's certainly possible.  So could my propane lines in the basement, or my gas cans in the garage.  It's also highly unlikely.  I wouldn't consider putting a solar/wind power battery bank indoors without being in a vented enclosure, but I'll take my chances with the car battery under my desk.  Eventually I'll upgrade it to a deep cycle, but the car battery was free, and I've gotten several years of use out of it.  I get several hours of operating time including charging my laptop.  I don't worry about over discharging, either.  The goal is to operate my station, not preserve my battery.  When this one dies I can just go to the junkyard and get another for $20 if I don't feel like buying a new one.
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DRBEN
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Posts: 223




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« Reply #16 on: May 24, 2016, 08:04:17 PM »

This comment is for the benefit of all, especially our over-the-top nervous Nellies.

All lead-acid storage batteries release hydrogen when charging, at very low levels when trickle charging and at much higher levels when fast charging.

The lower level of hydrogen that can result in an explosive concentration is 4% by volume.

In a well ventilated room, with only one battery, the risk level approaches zero.

There are hydrogen detectors for poorly ventilated industrial battery rooms that usually have lots of batteries.

Here's one:

http://rkiinstruments.com/pages/application_briefs/Backup_Batteries_Emitting_Hydrogen.htm

When hydrogen reaches 1.2%, an alarm sounds. If that happens, the detector manufacturer says to take corrective action by ventilating the room.

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N3HFS
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Posts: 366




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« Reply #17 on: May 24, 2016, 08:30:28 PM »

This comment is for the benefit of all, especially our over-the-top nervous Nellies.

All lead-acid storage batteries release hydrogen when charging, at very low levels when trickle charging and at much higher levels when fast charging.

The lower level of hydrogen that can result in an explosive concentration is 4% by volume.

In a well ventilated room, with only one battery, the risk level approaches zero.

There are hydrogen detectors for poorly ventilated industrial battery rooms that usually have lots of batteries.

Here's one:

http://rkiinstruments.com/pages/application_briefs/Backup_Batteries_Emitting_Hydrogen.htm

When hydrogen reaches 1.2%, an alarm sounds. If that happens, the detector manufacturer says to take corrective action by ventilating the room.


This sort of monitoring equipment is great for safety, and the market for it obviously would not exist if there were no potential danger involved.  Even more importantly, the equipment is a backup in case of the failure of well-designed charging equipment designed to minimize the production of excess hydrogen.

This does not prove, however, that there is any intrinsic safety involved in the use of rechargeable batteries, especially unsealed lead acid batteries.  Poor charging regimens, where a battery is subjected to prolonged exposure to excess voltage, will easily create a hazardous environment under the right circumstances.  It remains important to understand this, and to know why and how these circumstances can come to reality. 

I am not saying that such batteries cannot be used safely; rather I am trying to make it clear that it is quite possible to use them unsafely.  Knowing and understanding the potential dangers is a wise course of action before committing to bringing them into the house and making good use of them.
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AG5BC
Member

Posts: 91




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« Reply #18 on: May 24, 2016, 08:34:43 PM »

This comment is for the benefit of all, especially our over-the-top nervous Nellies.

All lead-acid storage batteries release hydrogen when charging, at very low levels when trickle charging and at much higher levels when fast charging.

The lower level of hydrogen that can result in an explosive concentration is 4% by volume.

In a well ventilated room, with only one battery, the risk level approaches zero.


It is reckless to tell people that there is no danger using flooded Pb batteries indoors without ventilation and isolation from possible ignition sources.

It's not filling up the room with hydrogen folks should be concerned about. If you're engaged in a heavy charge cycle, flooded Pb batteries can heat up and generate just enough hydrogen to fill the headspace inside the battery with enough coming the vents to hit the ignition sweet spot.

One spark ignites the outside gas and fuses back to the hydrogen built up inside the battery and BAM! You just got a complimentary sulfuric acid and plastic shard shower, quite possibly in your face. As a chemist for over thirty years who's worked with more hot mineral acids than most folks (outside of plating facilities), I have a healthy respect for acid. I've seen what sulfuric acid does to skin and to your eyes. I guarantee that most people in that situation would not have a happy outcome if that happened to them.

Choosing an AGM Pb battery is the way to avoid this. The electrolyte is absorbed into the porous plates and the design resists H2 generation. It's not that much more expensive than flooded batteries. They're better-designed for the job.

Quote from: N3HFS

I am not saying that such batteries cannot be used safely; rather I am trying to make it clear that it is quite possible to use them unsafely.  Knowing and understanding the potential dangers is a wise course of action before committing to bringing them into the house and making good use of them.


What he said.

Brian
AG5BC
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