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Notes about lead acid battery usage
There were some initial concerns about hydrogen emission from the lead-acid batteries being used on the Segway robot. The first email detailing out concerns and options is listed first. At this point, we consulted Scott Sutcliffe (one of the CS Shop guys) who told us that there was no cause for concern.
On Thu, May 23, 2013 at 3:05 PM, Piyush <[email protected]> wrote:
Hi Liang and Peter,
A couple of weeks ago someone commented to Robert in the lab (I wasn't present) that we should not be charging lead acid batteries indoors due to release of Hydrogen. I have been looking into this issue for the past hour and a half and here is my status report. I don't have any expertise in the matter, and as such am not sure how trustworthy some of these sources are. I have also cced Ali and Sam, with whom I have had conversations about this yesterday and today.
Here is my current understanding of the problem
- Both charging (normal conditions) and overcharging (abnormal conditions) a flooded lead acid battery leads to the release of hydrogen and oxygen 1 (Pg 1 Sec 1). Hydrogen is not poisonous 2, but it is inflammable at a concentration of 4% to 94% (I believe this means 40k ppm to 940K PPM) 3 (Pg 8 Sec II)
- Under normal conditions, our battery chargers should not overcharge these batteries 4 (See Product Description)
- We currently have this battery: Energizer Deep Cycle Marine Battery 5. I am not sure whether this is a gel battery or a flooded battery.
At this point, I would like to hear a bit more as to what Liang thinks. My understanding is that unless one of the battery chargers is malfunctioning, we should not be producing hydrogen gas in combustible quantities. Additionally, the room has some ventilation. We have run 3 months with the chargers being almost always on already, albeit unknowingly.
Here are possible options if action is required:
- Procure a hydrogen gas detector 6. I've looked up the cost at a vendor, and it's approximately $1000. Figure out if we are above 2% hydrogen by volume and take action as necessary.
- Replace the batteriy:
- Here is the battery I have in mind. This still fits in our battery box, and is roughly the same weight 7.
- It is an AGM style battery. From this reference, even under adverse overcharging conditions it will produce far below the 4% hydrogen emission required for combustion [6]. This suggests that multiple battery chargers will have to fail simultaneously for this problem to arise.
- Cost is $300 for 1 battery, or $1500 for 5 robots (In contrast, our current batteries are < $100). This is comparable to the cost of replacing the segway batteries themselves ($400 per 1 battery), but provides power for much longer since the laptops cannot stay operational on their own batteries for more than 2-3 hours under computational load.
- We will lose some capacity
- Current batteries are 125Ah with a reserve capacity of 210 minutes
- Optima batteries are 75Ah with a reserve capacity of 155 mintues
- We have measured our power draw in the past to be about 100W. With a 75Ah battery, this gives us a theoretical maximum of 9 Hours. Assuming 2/3rd efficiency, this still gives us about 6 hours without digging into the reserve capacity.
- These batteries have additional benefits 8.
I would like to hear what you all of you think.
Thanks!
Piyush
On Fri, May 24, 2013 at 3:55 PM, Scott Andrew Sutcliffe <[email protected]> wrote:
I had a look and they are lead acid. The highest amperage they'll be charged at is 6 amps so there is no real hazard. Just to be safe, I gave them the ABC Extinguisher out of the shop.