Battery Venting System

[RCpilot]

I finally got around to sealing up my battery and installing a forced air vent on it. I just have to figure out how to trigger the fan to only run when the battery is gassing. I'm thinking of a small circuit that measures the battery voltage and turns the fan on at a set voltage. I'm guessing somewhere around 13.0V to 13.4V or so but I guess I will have to experiment with the actual voltage trigger while watching the battery charge to see when it starts gassing good. I used a small 12V brushless fan and ground the square legs off of it leaving it just small enough to fit inside some oddball 2" pipe I had. Then, the oddball pipe's ID is just big enough to fit over standard SCH40 2" pipe. I made a small 6" piece that houses the fan and put the fan in the horizontal portion of the vent pipe. Outside, one more elbow aiming down with a small screen over it completes the run. I used plastic lawn edging to seal the edges of the battery and the holes in the sides with aluminum rails to help hold it in place. To open the battery I have to unhook the pipe from the battery but I didn't glue a couple of sections just for this. The battery has enough leakage to allow air to go into it from several places so it will be under negative pressure from the fan sucking on it. Anyone have any circuit Ideas, I'm all eyes! Here's some pics.

Kelly

[snowcrow]

Hi Kelly,  I think this is just the thing you are looking for.

http://www.fieldlines.com/story/2007/8/24/172521/889

Blessings, Snow Crow

[wooferhound]

You should pressurize your battery compartment. That way you won't be sucking Flammable Corrosive gases through your fan.

And Ghurds charge controller will do exactly what you need . . .

[TomW]

woof;

I disagree. If the box is under positive pressure the gasses can leak out anywhere. If it is under negative pressure it only has one way out. Plus I doubt the mostly sealed computer fans will be affected by the uglies. It is not sitting stagnant around parts and when the fan is blowing the concentration will be minimal.

Just a couple points.

Cheers.

TomW

[RCpilot]

Comments are always welcome, thank guys, especially for the link to the circuit. I am looking hard at Ghurd's controller and for the price, will probably order one to play with.  As for gasses affecting the computer fan, it may mess it up over time but I have a box of these things and if the fan fails, I will just put another in it's place. I can't really see that the gas should affect it that much but time will tell.

Kelly

[DanG]

As a C-average student of human nature myself its interesting to see the Jeff Foxworthy 'Hey, everybody, lookit here' famous last-words syndrome postings. No, RCpilot I aint picking on you, just how many of us end up posting expecting to get positive feedback after investing a bunch of time and energy and I end up squirming in my chair with alternative ideas that more often than not get deleted before hitting the post button...

I know its too late but two 45° elbows beat a 90° every time for flow - and using a ramped lid to a larger side mounted stack would induce a passive 'chimney effect' that would allow not having the electronic muffin detonator unit in the hydrogen flow circuit.

The industrial solution I am familiar with is a squirrel cage type fan in the plenum with a small sealed motor placed outside the vent stacks plenum - the key point isn't huge airflow but a constant draft drawn off the highest point of battery enclosure to keep any sulfuric acid mists or free hydrogen from ever pooling. A low RPM motor with charging aware switch-on and an explosion proof temperature sensor that will continue power venting for some time after charge switch off to allow batteries to finish their bubbling, then the passive smokestack flow to continue to allow them to cool off...

Anyhow - a handsome RE install RCP.... thanks for raising the bar yet again : )

[ghurd]

The circuit will work well for the fan.

I don't think my batteries bubble much until about 14V, but the maximum charging current is usually only 5% of the capacity.

G-

[RCpilot]

The reasons I post here are for BOTH types of comments. I know my ideas aren't always the best and look forward to negative comments so that I can improve what I am doing. Without this board, I wouldn't be as far as I am right now as it has contributed greatly to helping me learn about RE. I thought about just running the pipe vertically through the roof and allowing nature to take it's course but didn't want to cut holes in the roof. I agree that two 45deg elbows connected together would do better but didn't think of that when setting up, I may do that anyway as it's a cheap mod. My lid is part of the battery itself and doesn't allow it to be ramped without doing a bunch of mods. I also thought about making a Wooden Lift off type of lid that has the ramping built in. I know my setup should get the job done. I do like your suggestion of the motor being outside of the airflow and may consider rigging something like that up and think I could. As for picking on me, I know your not and like I said above, need both types of comments to ever improve. There are WAY too many OFFENDED people walking this planet these days that, as Glen Fry of the Eagles said in a song: Get Over it. Thanks for the comments. Keep watching my diary and you may see changes that are a direct result of them!

Kelly

[snowcrow]

What if he was to do something like this:

Blessings, Snow Crow

[RCpilot]

That looks like a pretty cool Idea, I may have to try it!

Kelly

[scottsAI]

Hello Rcpilot,

With the battery box in the living space, do not use positive pressure, Negative pressure is the way to go, idea is to get the gas out of the box and house.

The fan, a brush less motor is not a detonator. Additionally if the fan is doing it's job the H2 will be below 4%, H2 is not capable of ignition below 4% air mixture. If the air's acid content is high over time it might leak into the fan requiring it to be replaced. For the trouble to prevent this not worth the effort, expect it would take years.

Do not worry over much about the bends, if the air flow is OK, then leave it alone.

Theory is nice, but you can get carried away with it. The 1.5" plastic has long turn elbows, beats out two 45's. If the air is taken from the side at the top, then you would not have to dissemble the vent system to open the box. I know I might start out this way then not assemble it thinking I would before I charge it again... forgetting later to assemble it.

To save power use a carbon dioxide detector ($15) to detect H2 then turn on the fan. Generally most CO2 detectors detect any combustion gases not just CO. When the alarm triggers on the battery operated sensor, turn on the fan. One 9v battery a year for power to CO2 detector, I expect the fan will rarely run, unless you do a lot of over charging.

Have fun,

Scott.

[RCpilot]

Thanks for the comments Scott. I have read a lot of your electronic posts, you know your stuff! I really thought about a detector but a search for H2 detectors just turned up a lot of expensive stuff. I didn't know a standard CO2 detector would detect H2. As for my current setup, I have the fan sucking on the battery box which allows air to enter around cracks in the lid keeping the gas inside the box. Also as far as the fan being in the airflow I wasn't worried about it being a detonator as it is brushless fan with no way to spark or ignite the mixture unless it actually shorts out and flames or something. I have a box of these fans and had no concern of the gas killing it and figured it would take a long time to kill it. I did make sure I used a ball bearing fan as the sleeve ones don't last that long. I get excellent output from the pipe outside and during battery charging can smell the gas being removed. Just for my curiosity, I collected some of the gas in a jar and attempted to light it with a lighter and it wouldn't even ignite, I am guessing there is so much airflow that it dilutes it too much to really be that explosive. I do have to take it apart every time I check the battery and am working on an idea just like you said to attach it to the side of the box so I can open the lid without anything in the way. My setup is outside in a standard 12X20 metal barn style metal shed. I insulated the shed and a small baseboard heater actually makes it warm enough in the winter to work out in it. Summer, I have a small AC in it. My biggest concern for the gas was keeping it out of the inverter which is directly above the battery. I have ordered one of Ghurd's circuits for now to trigger the fan at a preset voltage and turn it off at another. The fan is rated at 170MA so I'm not worried about it running off of the battery directly.

Kelly

[scottsAI]

Hello Kelly,

I took care of a 1MwHr battery in the Navy, the H2 meter rarely registered any H2, even under equalizing charge. The Fan was not big for the battery size, most of what I see is grossly over sized. But in this situation I would rather be grossly over sized then under!

Limiting the running of the fan based on battery voltage sounds like a good simple idea.

Gassing occurs when charging above 80% capacity. Problem the voltage changes based on temperature.

Have fun,

Scott.

[DamonHD]

Hmm, how much did that MWh beast weigh?  A substantial fraction of my house I'll bet!

BTW, my SOC chart says a (12V SLA) battery on charge already at about 80% full will have a terminal voltage of around 13.45V.  Scale as appropriate for other nominal voltages.  Does that sound right to you?

Rgds

Damon

[spinningmagnets]

I am certain Snow Crow's suggestion will work very well. I have seen water pumps and air pumps shaped like this. I think they are called an "eduction jet". Seems to work like a venturi?

[scottsAI]

Hello Damon,

I'm not sure, something like a Ton each cell, they were big, stood about 5 ft, 18 x 12, never saw the sides, access was a crawl space above, 24 inches worth. (25 years ago.)

Several things effect the terminal voltage and SOC determination.

If the battery is under charge and the current of the charge.

If the battery is discharging and the current of the discharge.

If the battery has set for a while.

The battery temperature.

Battery chemistry, materials etc.

Take a look at: (Document is about flooded cells.)

http://www.azsolarcenter.com/technology/batteries/pdfs/ch3.pdf

Might be more than you want 1Mb, good read.

Mid way through shows battery voltage temperature compensated.

Everything else is assuming room temp, great if it's 25'c, outside few times a year!

Sealed have different Voltage numbers from the various manufactures

Mine state charge to 14v, if frequently discharged charge to 14.2v.

No mention about temperature or SOC.

Have fun,

Scott.