Sorry Bunkie, it is not. It is a disease of the battery whether in your motor home, travel trailer, car or truck that occurs when you put the battery to bed hungry.
A battery whether it is an Abosorbed Glass Mat, sealed maintenance free or a flooded type, does not make electricity, it converts with a chemical reaction to cause the flow of electrons, electricity. All batteries are made of two dissimilar materials dunked in an acid of some sorts called an electrolyte. The conventional auto battery that we all know and tolerate, uses plates made of lead, PB, and lead peroxide, PBO2, that are dissimilar metals. They are separated from touching each other by separator plates that are insulators. Not heat insulators but electrical insulators to stop the flow of electricity from plate to plate. The insulators also known as separators are pourus so that the electrolyte will flow back and forth.
The acid in the common car battery is a sulfuric acid solution that has a specific gravity reading of 1.275 when the battery is fully charged. The chemical symbol is H2SO4 or two parts of hydrogen, one part of sulfur and 4 parts of oxygen. This is important as the compound will change as the state of the charge in the battery changes.
When this cell is attached to a load, like a light bulb, the chemical reaction starts and electron flows out lighting the bulb. As the reaction take place transferring sulfur to each plate and oxygen to the lead plate. So as the battery approaches the dead zone the plates become similar, PBSO2, or lead peroxide plates with a coating of sulfur. The electrolyte now has become more or less H2O, which has a specific gravity of 1.000.
The problem is that the sulfur released from the electrolyte that now coats the plates has a tendency to form a skim coat over the plates that will harden if left on the plates. When it hardens two things happen: First it forms a barrier over the plate that blocks the flow of the liquid electrolyte to act on the plates. Second, the sulfur will not flow back to the liquid to re activate the electrolyte. The film does not form evenly and there are holes that still leave some of the plate surface that can be acted on. This action means that the battery will still function but at a reduced level. It is the surface area of the plates that results in how much load the battery can create. Reduce the surface area and we have a battery that will produce less amp hours of useable energy.
Most of the time re charging the battery will drive the sulfur back into solution and there will be no residual effect of the discharge cycle. And if the film of sulfur is left for a period of time nothing will drive the sulfur back into solution short of a little guy with a hammer and chisel climbing down into the cell.
The accepted test for sulfation is a two part test. The first is to take the open cell voltmeter test. That is with the voltmeter connected across the battery terminals and read the voltage. If the voltage is near 12.7 then we load test the battery. That is to apply a heavy load to the battery, usually three times the amp hour capacity that is listed on the case or one half the Cold Cranking Amps listed on the case. Apply the load for 10 to 15 seconds watching the voltmeter. If the voltage falls below 9.6 volts the battery has failed this part of the test and the three minute charge test is required.
When testing an automotive battery use a fast charger set at about a 45 amp charge rate. Again the voltmeter is the tip off as to the condition of the battery. If the voltage rises quickly and reaches 15 volts before the three minutes is up the battery has failed the test, probably due to sulfation. It has charged too quickly indicating a reduction in plate surface. The battery is no longer serviceable.
Sulfation is not some mysterious thing and is straight forward and can be tested. In the old day, when I was teaching Automotive Electricity at Sun Electric, we used carbon pile rheostats to apply the heavy load, but today there are computer based testers that using a computer model can and do test on a battery using very little current draw (load) and use the voltage time and amperage reading to model a pattern and give readings.
The trick to preventing battery sulfation is to not let a battery remain uncharged for a period of time. We used to say that a dead battery used to start sulfation after about 72 hours if inactivity and a low state of charge.
This is a general primer on batteries and sulfation And the numbers and formulas are close for academic explanations but a little off for engineering standards. But, who among us is going to build his own battery, just understand a little better the principles so that when the guy in the shop says, “your battery is sulfated and you need a new one”, it won’t sound like all Greek (no offense to the Greeks intended). This is also from the lecture at the beginning of the study of batteries when I was activly teaching. The finer points were deverloped after the student mastered the basic concept, so please accept it as it was ment.
Cliff Thew
I recently read and article that stated that the converters built into most RV’s will not fully charge the batteries and that is the major cause of sulfation. They went on to state that inverters have a better charging circuit in them which will bring the battery bank up to better level to prevent sulfation. Any comments, Thanks
G.M.
Brad…
While on the subject of charging batteries and leaving them at a low level over time…
Their have been some serious concerns about using aux and engine batteries for power.. i.e to recharge them and put them in parallel.
I guess should start at the beginning… first off we saw in one article how one could use an isolator contactor to recharge the two bats together. i.e. Once the engine starts off the “engine battery” the relay contactor then gets energized from the key run circuit. Placing the now run down aux battery across the good engine bat and tied to the alternator. Seems pretty simple but….
Problem is … the good battery should dump a lot of current into the lower battery… not good is what others say… because it strips the plates?
The second article shows one is using a solid state isolator. However as the article states… this then doesn’t seem to allow the two batteries’s to come up with a full charge due to the diodes 0.7v drop from what I read. Nor will it allow the aux battery to be used to help start the engine if the engine battery is low. Seems like it only works one way… to charge only… and the alternator has to work harder to come up with a higher voltage to overcome the diodes… while the batteries see less. Once the good battery charges the alternator starts shutting down while the low battery is not sensed (aux) and thus is always at a low state of recharge… sulfating
If we are going to need both batteries for say… getting unstuck and use the winch … how does one do that using a solid state isolator?
Some say to use the large boat switch arrangement… which then either allows both batteries to be on line charging and providing current or each to their own. We read that the problem here is the fact that you have to mechanically do something. Forgetting can get costly. Especally after starting and switching the alternator to the open position.
So what the question is.. Using the contactor will make both batteries appear as one.. but will the isolator contactor type cause damage to the lower battery as some seem to suggest…due to the high current inflow… or will it not hurt it because of?
Placing a contactor across the solid state battery isolator.. It was suggested, will it again damage things it if we want to get current out of both batteries in a winching operation?
Problems we have heard about using the boat switches… wiring nightmares due to the size of the I/R of the cable…which then doesn’t allow the batteries to fully charge due to the wire resistance and problems with the switch getting hot and almost catching fire in heavy current demands because its plastic .
So which one is the right one for the off roading motor home?
We surely don’t want to have one battery charged and the other only slightly thus causing sulfation.
Yet we also don’t want to destroy the low battery when the contactor drops the good almost fully charged battery across it when the contactor closes.
One seems to find that the contactor vs the diode isolators is a on going battle. Some say contactors is better .. others say diode isolators are the way to go….
Which will hurt the battery.. which will leave it discharged?
Thanks for your help.. if you could respond back to the email address also
Roger
One of the BEST explanations of how car batteries work I have ever heard. Short, concise and easy to understand. I rate it 6 star!
phil
Hey Brad, Great article & accurate description of sulfation. ( I have seen many off base descriptions of this problem). I would like to add a tip for battery capacity recovery related to sulfation. All sulfated batteries are not scrap. Working for many years with motive power batteries, we have a process to recover capacity in a large percentage of sulfated batteries.1. Top off water levels if below the plates. 2. Give battery a full charge, recording gravity readings (wet cell) hourly until gravity stops rising.You will need to monitor electrolyte temps. & compensate for temps. above 77 deg. F. Basically for every 3 deg. above 77 you add 1 point to your hydrometer reading. After gravity has stopped rising, allow battery to cool to ambient temp. Give a full discharge cycle. Repeat the above process for 3 cycles. If the battery is recoverable, you should see an increase in discharge time for each of the 3 cycles. While some batteries are sulfated beyond recovery this process will help a large percentage. Also, sulfation is caused by a continued lack of full recharge, so periodically check your gravities at the end of full charge to verify you are getting them back to 1.275-1.285 SG.Adjust charger or charge times if not.
Fred
Brad, that was a darn good article. You can be my professor anytime.
You state, “The trick to preventing battery sulfation is to not let a battery remain uncharged for a period of time. We used to say that a dead battery used to start sulfation after about 72 hours if inactivity and a low state of charge.”
For my situation this statement is a bit arbitrary, and may not aplly to some of today’s types and brands of battery.
I would be interested in some kind of measurement – in volts or in lapsed time remaining before re-charge of a discharged battery. Your estimate of 72 hours to the start of sulfation for a discharged battery may be a rule of thumb, but may not be valid for all batteries.
I refer to the brand Optima. It is a sealed AGM battery. I don’t think they are allowed to be discharged to 9.6 volts. I monitor the voltage and AH remaining during my use in the RV of my Optima batteries.
The only voltage measurement I strickly use right now is to watch for a low of 10.7 volts. That measurement came not from the Optima battery company, but the manufacturer of my inverter. It has the low set-point of 10.7 volts, at which time the inverter shuts off and sings an alarm.
Can ypou be of some help? Thanks, Fred