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Old May 29, 2014, 01:15 AM
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Why does the CO alarm in my garage go off when I charge my vented NiCd batteries?

I use a pair of 28V 46 AH Nicd batteries for field charging. I usually fast charge them at home at .5C the night before I head out to the field. My CO detector is placed right above where I charge my batteries. Just before my charger detects a battery is fully charged (3mv delta V peak detection) my CO detector will go off and show somewhere around 300 PPM.

I don't think CO can possibly be generated by charging a Nicd, but I know charging a nicd does produce hydrogen and oxygen. I'm guessing the the hydrogen is what's causing the alarm to go off. If this is the case, can a NiCd produce enough hydrogen to cause a fire?
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Old May 29, 2014, 08:55 AM
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Perhaps it's electronic interference from the charger that is triggering the CO monitor. I believe chargers use square wave forms that can generate a lot of spurious signals that may adversely affect other electronic devices. Try moving your charger a few feet away from the monitor and see if it is still triggered.
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Old May 29, 2014, 09:06 AM
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Originally Posted by RS2K View Post
I don't think CO can possibly be generated by charging a Nicd, but I know charging a nicd does produce hydrogen and oxygen. I'm guessing the the hydrogen is what's causing the alarm to go off. If this is the case, can a NiCd produce enough hydrogen to cause a fire?
I don't believe NiCd produce any gas at all. Think about it: if hydrogen was released at every recharge and nothing was added into the battery, it would run out of chemicals quite quickly.

Wet lead-acid batteries do produce H2 and O2 through electrolysis and need to be periodically topped up with distilled water.
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Old May 29, 2014, 10:19 AM
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I'll try moving the CO monitor and see what happens.

I do have to top off the electrolyte at least every 6 months with distilled water. I checked the electrolyte level just a few days ago, The battery looks like this:


The center cap on each cell comes off and the electrolyte, a mixture of potassium hydroxide (AKA lye / potash / caustic soda) and water, needs to be 22 mm from the top.
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Old May 29, 2014, 10:56 AM
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If it's gassing it is likely giving off hydrogen. A quick search of Google turns up several reports that hydrogen gas can interfere with carbon monoxide sensors. Most people report it when charging lead acid but in this case you're dealing with the same gas.
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Old May 29, 2014, 10:58 AM
WJH
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United States, FL, Spring Hill
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Quote:
Originally Posted by RS2K View Post
I use a pair of 28V 46 AH Nicd batteries for field charging. I usually fast charge them at home at .5C the night before I head out to the field. My CO detector is placed right above where I charge my batteries. Just before my charger detects a battery is fully charged (3mv delta V peak detection) my CO detector will go off and show somewhere around 300 PPM.

I don't think CO can possibly be generated by charging a Nicd, but I know charging a nicd does produce hydrogen and oxygen. I'm guessing the the hydrogen is what's causing the alarm to go off. If this is the case, can a NiCd produce enough hydrogen to cause a fire?
Are you sure your field batteries are nicad?
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Old May 29, 2014, 11:11 AM
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Are you sure your field batteries are nicad?
That's what he has. I didn't realize such a thing as vented nicd existed but it does:
http://en.wikipedia.org/wiki/Nickel%...cell_batteries
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Old May 29, 2014, 12:06 PM
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I was finding information about hydrogen suflide being able to set off a CO alarm, but nothing about pure hydrogen. I found that it takes 40,000 PPM for hydrogen to be flammable. I don't think it's possible for these batteries to produce hydrogen at a high enough rate to pose a problem.

These are condemned private aircraft batteries. Per manufacturer specs they need to hold at least 100% of the rated capacity at 1C for 1 hour to be flyable. They were condemned because they could only hold a 95% charge. They work great for field charging. I can get just over 80 AH out of both of them at over 24 volts.
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Old May 29, 2014, 01:21 PM
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Well it's supposed to take 400 ppm to set off a CO detector. This page indicates that (for their CO measurement tool) hydrogen will generate a false positive at a rate of 10-15%. So assuming your CO detector is similar anywhere between 2666 ppm and 4000 ppm of hydrogen will set off a carbon monoxide detector. Which as you found is far from the flammable point.
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Old May 29, 2014, 01:38 PM
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Originally Posted by grimbeaver View Post
Well it's supposed to take 400 ppm to set off a CO detector. This page indicates that (for their CO measurement tool) hydrogen will generate a false positive at a rate of 10-15%. So assuming your CO detector is similar anywhere between 2666 ppm and 4000 ppm of hydrogen will set off a carbon monoxide detector. Which as you found is far from the flammable point.
Thanks! That's great information. My CO meter has a readout. It goes off when the level is 100 ppm for XX amount of minutes. The higher the PPM level the less time it takes for the meter to send an alarm. My CO alarm goes off just before the charger switches to trickle charge.
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Old May 29, 2014, 05:29 PM
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We used a lot of those wet cell NiCad's on aircraft instrumentation back in the late '50's. Very good for high current use but rather bulky and could get messy at times but far superior to the other choice which was a Pb cell.
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