The other day I was baffled to hear a report from a friend who had recently purchased something called a Ranger EV. (A Ranger EV is an electrically powered ATV, shown at right.) My friend described that she found she has no choice but to charge her Ranger EV outdoors, because if she charges it in her garage, it sets off her carbon monoxide detectors. She is thinking about purchasing one of those new Ford F-150 Lightning EVs and was worried whether this means she would have to charge it outdoors too.
As I say, I was baffled by this. Eventually I figured out what was probably going on.
As you probably know, lots and lots of owners of passenger car EVs do all or nearly all of their car charging indoors. You never hear about somebody who is charging their Nissan Leaf or Chevy Bolt or Tesla car setting off a carbon monoxide detector.
I clicked around a bit on the web page for the Ranger EV. I was able to gather some information that permitted me to arrive at some guesses as to what the mechanism of action might be for this odd business of the carbon monoxide detector being triggered.
Part of the answer turns out to be that most carbon monoxide detectors are stupid and will sound a false alarm in the event of the presence of a variety of gases that are not carbon monoxide. One of the gases that the CO detector will trigger with a false alarm is H2 (hydrogen gas). It is possible to get carbon monoxide detectors that are smart enough not to do a false alarm on other gases, but they cost a lot more than residential ordinary CO detectors, and they are bulky and require frequent maintenance and calibration and the sensor is a consumable and they are not certified as devices that would satisfy local building codes for residential CO detection.
The first clue for me in the direction of making sense of this baffling story was that the Ranger EV is said to use “traditional lead-acid” batteries. The first passenger EVs, back in about 1905, used traditional lead-acid batteries, for the simple reason that back then, that particular kind of electrical battery was “the only game in town”.
The first car I owned, a 1966 VW bug, had a traditional lead-acid battery that is probably almost exactly like the batteries in this Ranger EV. Of course that battery was not providing motive power. It was just for starting the car and powering a few accessories during times when the engine happened not to be running. The charging-up of that battery never happened indoors. It happened when the engine was running which was, by definition, always outdoors. I came to be the owner of that car in about 1972.
The battery in that 1966 bug had what were called “open cells”. Each cell of the battery had a little screw cap that a person could open up and you could peek inside to see if the level of the liquid electrolyte was low. If it was low, you were supposed to pour a bit of distilled water into the cell until the level was back up to normal. The liquid electrolyte was sulfuric acid. People had to be careful not to spill the sulfuric acid onto themselves or onto their clothing.
Around the time that I came to own that car, the companies that were making car batteries started making SLAs (sealed lead-acid batteries). The SLAs did not have screw caps. The battery chemistry was all the same, with liquid sulfuric acid in the cells, but it was pretty much sealed up. There was a safety port that would blow open if too much gas pressure were to build up inside, but the assumption was that in the life of the SLA, this would probably never happen.
I played around a lot with electricity in my early days, and at around age 11 I was making O2 gas and H2 gas by running DC current through water. Little bubbles could come off the electrodes and I would catch the bubbles in upside-down cups. The fun was to put a lit match near one cup or the other to find out experimentally which captured gas was O2 and which captured gas was H2. The O2 gas merely made the match flame light up a little brighter, but the H2 gas would make a nice popping sound as the gas exploded gently.
And of course that is what is going on in my friend’s garage when she is setting off the CO detectors. She is charging up the Ranger EV and when she does, the charging activity is electrolyzing the water that is in the sulfuric acid in her open-cell lead-acid batteries, and the resulting H2 gas is causing false alarms in her CO detectors. And she ends up with the liquid level being a bit low in one or more cells in her batteries, and the sulfuric acid is a slightly higher concentration than it was before.
There are quite a few things that can be said about this situation.
One is that in all the years that I owned that VW bug, I never actually had to top up the liquid in that car battery. Back before SLAs were common in passenger cars, everybody’s car batteries were open-cell but the vast majority of car owners never had to top up the liquid in their car batteries.
When the owner of an open-cell lead-acid battery discovers that there is a need to pour a little bit of distilled water into one of the cells of the battery, this means that some electrolysis has occurred. Some of the H2O in the cell has gotten electrolyzed into H2 and O2.
Of what I just wrote is silly. Of course almost no owner of an open-cell lead-acid battery “discovers” that there is a need to pour a little bit of distilled water into one of the cells of the battery. Most owners of such batteries never go to the trouble of once every week or two popping off the seat cushions or opening their car hoods and unscrewing the caps on their batteries to peek inside to see if the liquid level looks low. And anyway as I say back when ordinary passenger cars had open-cell lead-acid batteries, it was commonplace for months or years to pass without any need to even peek inside the cells.
One of the problems about all of this is that in general if the owner of a lead-acid battery finds that more than just a few times in the life of the battery there is a need to top off a cell with some distilled water, then this is not normal. It is the battery’s way of signaling that something bad is going on.
So what’s going on here?
What’s going on is charging a battery too fast, or overcharging the battery. (It is recalled that the word “battery” means “more than one cell”. This is why a AAA cell or AA cell or C cell or D cell is not, strictly speaking, a “battery” at all.) Quite often when the electrolysis is happening (when H2 and O2 gas are being given off) it means that bad things are happening in the charging process. The multiple cells of a battery are in series. What happens is that although the manufacturer tries as hard as possible to make each cell physically and chemically and stoichiometrically identical to its neighbors in the battery, common sense tells us that no matter how hard the manufacturer tries, they will never be absolutely identical. And even if they were identical when they departed from the battery factory, as time goes on, each cell will gradually come to be slightly different from its neighbors.
When the battery is being used to power some device, be it a flashlight or an EV, the electricity comes out of the battery the “right way” and powers a light bulb or a motor or whatever. When we charge up the battery, we are pumping electricity into the battery “backwards”. The idea is to try to force the chemical reactions to go backwards, so as to store lots of energy in the battery.
But the cells are not identical to each other. As we pump lots of electricity into the string of cells (that is, into the battery) what happens is that inevitably one of the cells gets charged up all the way before the rest of the cells get charged up all the way. Of course we keep forcing the electricity to go backwards through the battery because we want the rest of the cells to get charged up all the way too. But meanwhile what about that cell that was already charged up all the way? The chemical reaction that was being forced to go backwards in that cell (converting lead sulfate back into elemental lead and sulfuric acid, or something like that) already ran backwards as far as it could. All of the lead sulfate that had been present in the cell has already been forced to convert back into elemental lead. But meanwhile we are still forcing electricity backwards through that cell, just like we are forcing the same electricity backwards through all of the other cells. In the other cells, the electricity is doing what we want. It is forcing chemical reactions to go backwards. But in that one cell that was already by now fully charged, what does the electricity do? It does the only thing that is left to do in that cell, which is to attack the very water molecules that are sitting in that cell, being the only thing left for the electricity to “work on”. And the electricity breaks up the water into H2 and O2. And, because the cells in the battery are “open” (meaning the little screw caps have vent holes in them to permit gases to escape) then the H2 gas is emitted through the vent holes (along with the O2 gas but nobody notices the O2 gas) and then the H2 gas floats around the room and eventually triggers the CO detectors.
So we have just talked about overcharging. It’s like winding a watch or clock so that the mainspring is wound up all the way. If you keep winding it then, something bad might happen because the spring is already wound up all the way. (Many of today’s kids, they would never make any sense of such a metaphor, because they have never wound a watch or a clock.)
The other nuisance mode besides overcharging is charging too fast. If you “trickle charge” a lead-acid battery, you are forcing a trickle of electricity to go “backwards” through the battery and you are forcing the chemical reactions to go backwards but not too fast. And if it is only a trickle, then hopefully the chemical reactions can keep up. But if you fast-charge a lead-acid battery, then it is like drinking from a fire hose. You are forcing a rush of lots of electricity to go “backwards” through the battery and you are forcing the chemical reactions to go fast. But all of those little lead atoms and sulfur atoms can only migrate or diffuse so fast through and among the other atoms that are in the way. The consequence is friction. The battery gets hot. Water evaporates from the cells. And probably some electrolysis happens too, and some H2 and O2 gas are generated in a mix with the steam or water vapor from the overheated battery. And then later if you peek inside the cells maybe you see the need to add some distilled water. And yes maybe the CO detectors get tripped.
But again circling around to the 1960s or 1970s when car owners had open-cell lead-acid batteries. Why is it that in the life of the car they rarely if ever had to top off the liquid in the cells? The answer is in those days it was quite rare to actually run the battery way down and then charge it all up again. They call this “deep cycling” and for most car owners in those days, the car owner would almost never deep-cycle the battery.
But if the reason for the existence of the battery in the vehicle is not merely for starting an internal combustion engine, but instead if the reason for the battery in the vehicle is that it is the only thing that powers the vehicle at all, then it would not be such a surprise if “deep cycling” might happen dozens or even hundreds of times in the life of the battery. Meaning that dozens of times, or hundreds of times, the owner might find the need to pour a bit of distilled water into one or more cells of the battery.
Deep cycling shortens the service life of lead-acid batteries.
Charging the lead-acid batteries slowly instead of fast reduces the life-shortening effects of the deep cycling. But of course the natural reaction of most people is that they don’t want to sit around for sixteen hours waiting for a battery to get charged up if there is the prospect of charging it up in a mere eight hours.
It turns out that this is “a thing”. In retirement communities in Florida where the residents use golf carts instead of regular cars, the fire department first responders apparently are by now familiar with this problem. They get called out because the CO detector is connected to a central system and it calls the fire department, and they come out and use their own CO sniffer and sure enough, their own CO sniffer agrees that there must be excess CO floating around. And eventually they figure out it is that golf cart generating H2 gas.
As most readers probably know, H2 gas is non-toxic. Harmless to humans. Well, in high concentrations it could displace all of the oxygen in the room, just like what could happen if you play around a lot with making ice cream with liquid nitrogen, which is also non-toxic. Or just like what could happen if you play around a lot with liquid carbon dioxide in large storage cylinders as some people do to make carbonated water. (When I am transporting liquid nitrogen in my twenty-liter Dewar, I keep a car window open just in case.) And I guess the other thing is that in a high enough concentration maybe the H2 gas from charging of batteries could support flame or conceivably could even explode. But you never ever read news stories about people in retirement communities in Florida having their garages explode because of H2 gas from golf carts getting charged a bit too fast. The concentrations just never get that high.
The companies that make Nissan Leafs (Leaves?) and Chevy Bolts and Teslas (Teslae?) give lots of thought to this problem of what happens if one cell in the battery reaches full charge sooner than its neighbors. One of my favorite clients, Sendyne (web site) has lots of patents on things to do to be smart about controlling the problem of one cell in a battery getting full before its neighbors get full. (I wrote the patent applications.) The cars have lots of electronics intermingled with the individual cells of the battery to deal with risks of one cell getting overcharged just because it got fully charged at a time when the neighboring cells still need to charge some more. And none of those cars use lead-acid chemistry. They use other chemistries that are variants of lithium-ion chemistry.
What this means for my friend, circling back around to her original question, is, no, she does not need to worry at all about charging a Ford F-150 in her garage. It will not set off her CO detectors.
Why are you lugging around liquid N2?
Liquid nitrogen is fun to play with. Science demonstrations for nieces and nephews and neighbor kids, that kind of thing.
Fascinating. Nice bit of detective work there, Carl!
This reminds me of my college days working summers on the swing shift in a warehouse. Before we clocked out and shut down the warehouse, part of our job was to top off the cells in a bank of 6-8 lead-acid batteries in the electric pallet jacks and fork lifts (we called them “walkies” and “stand-ups”) and plug them in to charge overnight. This was a deep-cycle charge since we ran down the charge throughout the day using the walkies and stand-ups. We added water to at least a few cells every night, indicating the imbalances in the overnight trickle charging process. Because this was during the mid-80s before CO monitors were common, we never had the false alarm problem. I suspect they may have come across that problem in later years after I was long departed.