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Battery University - Information you can use

Discussion in 'Ignition / Electronics / Batteries' started by BroadBand, Nov 23, 2015.

  1. BroadBand

    BroadBand Since late 60's

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    Welcome to Battery University!
    Battery University™ is a free educational website that offers hands-on battery information to engineers, educators, media, students and battery users alike. The tutorials evaluate the advantages and limitations of battery chemistries, advise on best battery choice and suggest ways to extend battery life.

    • Part One: Basics You Should Know
    Addresses the mechanics of the battery and deals with chemistries, charging and discharging techniques.

    Looks at battery personalities and discusses ways to get the most out of the packs. We talk about priming, storing and recycling.

    • Part Three: Batteries as Power Source
      Studies the battery in portable and stationary application as well as in the electric powertrains. We look at the kinetic power and cost of the battery in comparison to fossil fuel.

    LINK
     
  2. BroadBand

    BroadBand Since late 60's

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    Understanding Motorcycle Batteries
    By Stu Oltman - Technical Editor, Wing World Magazine

    How Batteries Are Made

    A 12-volt motorcycle battery is made up of a plastic case containing six cells. Each cell is made up of a set of positive and negative plates immersed in a dilute sulfuric acid solution known as electrolyte, and each cell has a voltage of around 2.1 volts when fully charged. The six cells are connected together to produce a fully charged battery of about 12.6 volts.

    That’s great, but how does sticking lead plates into sulfuric acid produce electricity? A battery uses an electrochemical reaction to convert chemical energy into electrical energy. Let’s have a look. Each cell contains plates resembling tiny square tennis racquets made either of lead antimony or lead calcium. A paste of what’s referred to as "active material" is then bonded to the plates; sponge lead for the negative plates, and lead dioxide for the positive. This active material is where the chemical reaction with the sulfuric acid takes place when an electrical load is placed across the battery terminals.

    How It Works

    Let me give you the big picture first for those who aren’t very detail oriented. Basically, when a battery is being discharged, the sulfuric acid in the electrolyte is being depleted so that the electrolyte more closely resembles water. At the same time, sulfate from the acid is coating the plates and reducing the surface area over which the chemical reaction can take place. Charging reverses the process, driving the sulfate back into the acid. That’s it in a nutshell, but read on for a better understanding. If you’ve already run from the room screaming and pulling your hair, don’t worry. Maybe next month’s topic will be more to your liking.

    The electrolyte (sulfuric acid and water) contains charged ions of sulfate and hydrogen. The sulfate ions are negatively charged, and the hydrogen ions have a positive charge. Here’s what happens when you turn on a load (headlight, starter, etc). The sulfate ions move to the negative plates and give up their negative charge. The remaining sulfate combines with the active material on the plates to form lead sulfate. This reduces the strength of the electrolyte, and the sulfate on the plates acts as an electrical insulator. The excess electrons flow out the negative side of the battery, through the electrical device, and back to the positive side of the battery. At the positive battery terminal, the electrons rush back in and are accepted by the positive plates. The oxygen in the active material (lead dioxide) reacts with the hydrogen ions to form water, and the lead reacts with the sulfuric acid to form lead sulfate.

    The ions moving around in the electrolyte are what create the current flow, but as the cell becomes discharged, the number of ions in the electrolyte decreases and the area of active material available to accept them also decreases because it’s becoming coated with sulfate. Remember, the chemical reaction takes place in the pores on the active material that’s bonded to the plates.

    Many of you may have noticed that a battery used to crank a bike that just won’t start will quickly reach the point that it won’t even turn the engine over. However, if that battery is left to rest for a while, it seems to come back to life. On the other hand, if you leave the switch in the "park" position overnight (only a couple of small lamps are lit), the battery will be totally useless in the morning, and no amount of rest will cause it to recover. Why is this? Since the current is produced by the chemical reaction at the surface of the plates, a heavy current flow will quickly reduce the electrolyte on the surface of the plates to water. The voltage and current will be reduced to a level insufficient to operate the starter. It takes time for more acid to diffuse through the electrolyte and get to the plates’ surface. A short rest period accomplishes this. The acid isn’t depleted as quickly when the current flow is small (like to power a tail light bulb), and the diffusion rate is sufficient to maintain the voltage and current. That’s good, but when the voltage does eventually drop off, there’s no more acid hiding in the outer reaches of the cell to migrate over to the plates. The electrolyte is mostly water, and the plates are covered with an insulating layer of lead sulfate. Charging is now required.

    Self Discharge

    One not-so-nice feature of lead acid batteries is that they discharge all by themselves even if not used. A general rule of thumb is a one percent per day rate of self-discharge. This rate increases at high temperatures and decreases at cold temperatures. Don’t forget that your Gold Wing, with a clock, stereo, and CB radio, is never completely turned off. Each of those devices has a "keep alive memory" to preserve your radio pre-sets and time, and those memories draw about 20 milliamps, or .020 amps. This will suck about one half amp hour from your battery daily at 80 degrees Fahrenheit. This draw, combined with the self-discharge rate, will have your battery 50 percent discharged in two weeks if the bike is left unattended and unridden.

    When A Battery Is Being Charged

    Charging is a process that reverses the electrochemical reaction. It converts the electrical energy of the charger into chemical energy. Remember, a battery does not store electricity; it stores the chemical energy necessary to produce electricity.

    A battery charger reverses the current flow, providing that the charger has a greater voltage than the battery. The charger creates an excess of electrons at the negative plates, and the positive hydrogen ions are attracted to them. The hydrogen reacts with the lead sulfate to form sulfuric acid and lead, and when most of the sulfate is gone, hydrogen rises from the negative plates. The oxygen in the water reacts with the lead sulfate on the positive plates to turn them once again into lead dioxide, and oxygen bubbles rise from the positive plates when the reaction is almost complete.

    Many people think that a battery’s internal resistance is high when the battery is fully charged, and this is not the case. If you think about it, you’ll remember that the lead sulfate acts as an insulator. The more sulfate on the plates, the higher the battery’s internal resistance. The higher resistance of a discharged battery allows it to accept a higher rate of charge without gassing or overheating than when the battery is near full charge. Near full charge, there isn’t much sulfate left to sustain the reverse chemical reaction. The level of charge current that can be applied without overheating the battery or breaking down the electrolyte into hydrogen and oxygen is known as the battery’s "natural absorption rate." When charge current is in excess of this natural absorption rate, overcharging occurs. The battery may overheat, and the electrolyte will bubble. Actually, some of the charging current is wasted as heat even at correct charging levels, and this inefficiency creates the need to put more amp hours back into a battery than were taken out. More on that later.

    How Long Will My Battery Last?

    There are many things that can cause a battery to fail or drastically shorten its life. One of those things is allowing a battery to remain in a partially discharged state. We talked about sulfate forming on the surface of the battery’s plates during discharge, and the sulfate also forms as a result of self-discharge. Sulfate also forms quickly if the electrolyte level is allowed to drop to the point that the plates are exposed. If this sulfate is allowed to remain on the plates, the crystals will grow larger and harden till they become impossible to remove through charging. Therefore, the amount of available surface area for the chemical reaction will be permanently reduced. This condition is known as "sulfation," and it permanently reduces the battery’s capacity. A 20 amp hour battery may start performing like a 16 amp hour (or smaller) battery, losing voltage rapidly under load and failing to maintain sufficient voltage during cranking to operate the bike’s ignition system. This last condition is evident when the engine refuses to fire until you remove your finger from the start button. When you release the starter, the battery voltage instantly jumps back up to a sufficient level. Since the engine is still turning briefly, the now energized ignition will fire the spark plugs. In the next installment, we’ll see exactly why increased internal resistance due to sulfation causes less power to be delivered to the starter.

    Deep discharging is another battery killer. Each time the battery is deeply discharged, some of the active material drops off of the plates and falls to the bottom of the battery case. Naturally, this leaves less of the stuff to conduct the chemical reaction. If enough of this material accumulates in the bottom of the case, it’ll short the plates together and kill the battery.

    Overcharging is an insidious killer; its effects often aren’t apparent to the innocent purchaser of the ten-dollar trickle charger who leaves it hooked to the battery for extended periods. A trickle charger charges at a constant rate regardless of the battery state of charge. If that rate is more than the battery’s natural absorption rate at full charge, the electrolyte will begin to break down and boil away. Many a rider has stored a bike all winter on a trickle charger only to find the battery virtually empty in the spring. Also, since charging tends to oxidize the positive plates, continued overcharging can corrode the plates or connectors till they weaken and break.

    Undercharging is a condition that exists on many Gold Wings. Your voltage regulator is set to maintain your system voltage at around 14 to 14.4 volts. If you’re one of those folks who rides the interstate highways with your voltmeter showing only 13.5 volts because you’re burning more lights than Macy’s Christmas display, you should be aware that that voltage is sufficient to maintain a charged battery but insufficient to fully recharge a depleted one. Remember, we said that gassing occurs when all or most of the lead sulfate has been converted back to lead and lead dioxide. The voltage at which this normally occurs, known as the gassing voltage, is normally just above 14 volts. If your system voltage never gets that high, and if you don’t ever compensate by hooking up to a charger at home, the sulfate will begin to accumulate and harden just as plaque does in your mouth. Consider a thorough occasional charging to be like a good job of flossing and brushing your teeth. If you practice poor dental hygiene, you can go to the dentist, and have him blast and scrape at the yucky stuff. When your battery reaches that stage, it’s curtains!

    What Type Of Charger, And Why

    Your alternator and a standard automotive taper charger have a lot in common; they seek to maintain a constant voltage. Here’s the problem with trying to quickly charge a deeply discharged battery with either one. Remember, we discussed how a heavy current draw would make a battery appear dead. Then, as the acid diffused through the cells, the concentration at the plates’ surface would increase and cause the battery to spring back to life.

    In similar fashion, the voltage of a battery during charge increases due to the acid concentration that occurs at the plates’ surface. If the charge rate is significant, the voltage will rise rapidly. The taper charger or vehicle voltage regulator will taper the charge rate drastically as the voltage rises above 13.5, but is the battery state of charge commensurate with the voltage? No! Once again, it takes time for the acid to diffuse throughout the cells. Although the voltage may be high, the electrolyte in the outer reaches of the cells is still weak, and the battery may be at a much lower state of charge than the voltage would indicate. Only after charging for an extended period at the reduced current will the full capacity be reached. This is the reason you must not judge a battery’s state of charge by measuring voltage while charging. Test it only after allowing the battery to sit for at least an hour. The voltage will reduce and stabilize as the acid diffuses throughout the cells.

    Within the past several years, several companies have developed chargers that can charge a depleted battery quickly, and then hold the battery at a voltage that will neither cause it to gas nor allow it to self-discharge. These are sometimes referred to as "smart chargers" or multi-stage chargers. Here’s how they work.

    We said that a battery could accept a much higher rate of charge when it’s partially depleted than when it’s near full charge. These multi-stage chargers take advantage of that fact by beginning the charge in a constant current, or "bulk charge" mode. Typically, they provide a charge rate of between 650 milliamps and 1.5 amps, depending on make and model. This bulk charge is held constant (or should be) till the battery voltage reaches 13.5 volts, thus allowing the battery to absorb a larger amount of charge in a short time and without damage. The charger then switches to a constant voltage or "absorption" charge. The idea here is to allow the battery to absorb the final 15 percent of its charge at its natural absorption rate to prevent undue gassing or heating. Finally, these chargers switch to a "float" mode in which the battery voltage is held at a level sufficient to keep it from discharging but insufficient to cause overcharging. The various companies disagree generally on what this float voltage should be, but it’s usually between 13.2 and 13.4 volts. Actually, the float voltage should be temperature compensated between 13.1 volts at 90 degrees Fahrenheit to 13.9 volts at 50 degrees. Most of the very expensive high power multi-stage chargers for use on larger RV batteries are temperature compensated, but none of the motorcycle units are to my knowledge; they use a compromise float setting.

    So, I can just set it and forget it, right? Well, not exactly. For one thing, you need to monitor the battery occasionally for correct fluid level (unless you own a sealed battery). Another problem is that of exercising the battery. Even if held at 13 volts, the unwavering voltage will allow the battery to eventually begin to sulfate. With most of these units, I recommend that you unplug the charger at least once every 60 days during seasonal storage. Allow the battery to rest for a couple of days, and then plug the charger in again. One charger that I’m aware of, the 1.5 amp Yuasa unit, has a feature found mainly on the aforementioned high priced RV chargers. It drops off the float charge and sends the battery through a complete new charge cycle every 28 days, thus eliminating the need to do that manually. There may be other motorcycle units that do that, but I’m not aware of any.

    Still Here?

    If you’re still reading this, you’re a real trooper. I realize that the subject can be confusing or even boring, but take heart; I went easy on you. There’s far more left untold than what appears here. This was "Battery’s Greatest Hits." I hope that it was enough to get you interested without sending you into information overload, and, maybe, now that you know how many ways there are to shorten a battery’s life, you know why no one can predict how long a battery will last. A lot of riders who believe they take excellent care of their batteries are actually killing them with kindness.
     
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  3. BroadBand

    BroadBand Since late 60's

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    Electricity Hopefully Made Understandable
    By Stu Oltman - Technical Editor, Wing World Magazine

    How Long To Charge A Battery


    In describing what happens as a battery charges, we found that charging is a process of reversing the chemical reaction that produced the electricity we used. Charging takes the sulfate out of the battery plates and returns it to the electrolyte, and we said that as the charging process is almost complete, hydrogen and oxygen bubbles would be seen rising from the plates. The electrical energy of the charger is converted to chemical energy stored in the battery, but the process isn’t 100 percent efficient. Some of the charger’s energy is wasted as heat and some is spent breaking down the electrolyte into its gaseous components. Therefore, if we drain 10 amp hours from a battery, we must replace those 10 amp hours plus an additional amount (usually around 10 percent). So, in this example, 11 amp hours would be required to replenish a battery that had 10 amp hours of its capacity drained.

    How do you know exactly how much your battery is depleted? You don’t. Therefore, you need some other way to determine when it’s fully charged. If you’re using one of the available automatic battery maintainers, you simply plug it in, and let it do its thing. When the battery has reached 14.5 volts, the charger considers the battery fully charged, and it drops to the float mode (discussed last month). If using a trickle charger or taper charger, you have two test methods available to you: voltage or specific gravity.

    Remember we said that a battery’s state of charge couldn’t be accurately determined by measuring voltage while the battery is charging. The reasons were examined last month. However, we can examine the change in voltage while charging. If the voltage fails to increase in any half-hour period during charging, the battery can be considered to be as charged as it’s going to get. Disconnect the charger, let the battery rest for at least one hour, then measure the voltage. A fully charged lead/acid battery of the flooded variety (free acid) should read 12.6 volts or slightly higher. A sealed battery (absorbed acid) should read at least 12.8 volts. Another method, and a more accurate indicator of state of charge, is measurement of the specific gravity of the electrolyte. Wait – don’t turn to that article written by the talking trunk mascot! I’ll explain!

    Quick – which is heavier, oil or water? Wrong! Water is heavier than oil. That’s why oil floats on water. Liquids have different weights, and this fact makes it convenient to use weight as a measure of how much acid is in solution in the battery electrolyte. By convention, we assign the number 1.000 to the specific gravity of distilled water. As we dissolve “stuff” in the water, the solution becomes heavier. Battery electrolyte is a solution of water and sulfuric acid with a specific gravity of 1.265 for flooded batteries and around 1.310 for sealed (absorbed glass mat) batteries. This means, in the case of flooded batteries, that the electrolyte is 1.265 times heavier than distilled water. The specific gravity can be easily measured with the use of a battery hydrometer, a glass tube with a calibrated float inside. The higher the specific gravity of the solution in the tube, the higher the float will ride in the solution. This is the same principle that causes you to be more buoyant in salt water than in fresh.

    Since we know that the electrolyte started life with a specific gravity of 1.265, our goal in charging is to return the electrolyte to that condition. Remember that during battery discharge, some of the sulfate from the electrolyte bonded to the battery plates. This means that it’s no longer in solution, so the specific gravity of the electrolyte must be less, and it is. If we can return that specific gravity to 1.265, we can be assured that we’ve removed all, or almost all, sulfate from the plates. As with the voltage test, and for the same reason, we can’t use specific gravity readings taken during charge to indicate the battery’s state of charge. However, as with voltage, the rate of change is useful. If the specific gravity fails to increase at all in any one-hour period, the battery is as charged as it’s going to get.

    Sometimes you’ll encounter a battery with low specific gravity, 1.240 for example, and no amount of charging will cause it to rise much. This is a case, as I described last month, where the sulfate crystals have hardened to the point that charging won’t remove them. This battery is now useful for many things, but starting an engine isn’t one of them. Can’t I just pour out the old acid and pour in fresh? That would restore the specific gravity, wouldn’t it? Certainly, it would restore the specific gravity, but what of the sulfate that now clogs the plates? Since there’s little plate surface area left to conduct the chemical reaction, the specific gravity of the electrolyte now becomes immaterial. Don’t ever try this stunt, and don’t bother with “magic pills” that supposedly restore dead batteries. With your new knowledge, gained from reading these articles, your next battery will probably provide better service than your old one.

    Enough About Batteries Already!

    Well…just one more thing. Why is it that if you measure your battery voltage and find it to be 12.6 volts, it drops to something like 12.4 (or less) when you turn the ignition switch on? I asked this question of several people and got answers like “because the key is on,” or “because you’re draining it,” or “because the lights are using some volts.” Nice try; no cigar. Yes, the lights are using some volts. In fact, they should be using all of the volts in their circuit, but they can only use what they can get. Right now, they’re only getting 12.4 volts. Where did the other .2 volts go? Let’s answer this question as an introduction to voltage drop testing.

    Take a look at the circular diagrams. To find any one thing in either diagram, simply cover that thing with your thumb, and do the indicated math on the other two things. For instance: if we want to find volts, we see that we should multiply amps by ohms (resistance) or divide watts by amps. To find amps, we divide volts by ohms or watts by volts. By substitution, we can come up with several more ways to arrive at our answers, but we don’t need to get that involved right now. Go get a calculator, take a break, and come back ready to learn something that’ll make you a big hit at cocktail parties!

    [​IMG][​IMG]

    The Missing Volts




    [​IMG]

    You must understand a couple of things before proceeding:

    1. No current flows in the circuit unless the switch is closed (dashed arrow).
    2. When current flows, the exact same amount of current flows through ALL points in the circuit.
    3. All of the voltage rise (battery voltage) will be consumed by the voltage drop or drops in the circuit.
    4. No voltage drop will occur across any load unless current is flowing in the circuit.
    5. Internal resistance of a fully charged battery in good condition is about .010 ohms.
    6. NEVER, EVER, attempt to measure the resistance across the battery terminals. You’ll fry your meter, and there could be more serious consequences.
    With these things in mind, assume that the battery voltage is 12.6 volts with the switch open. The load will draw 18 amps (normal for a GL1500) when the switch is closed (ignition switched on). The voltage drop due to the battery’s internal resistance is found by multiplying amps by ohms as the circular diagram indicates. Doing this, we find that 18 x .010 = .18 volts. Therefore, the voltage at the load will be 12.6 minus .18 = 12.42 volts. The instant the switch is turned on, the voltage would indeed be 12.42, but as the battery begins to discharge, the internal resistance increases as we discussed last month, and the voltage drop increases as a result. If the load is great, such as an electric starter, the acid depletion at the plates (check Part IV of this series) accelerates the reduction in voltage, but ignore these factors for the purposes of these examples. Consider only the drop due to resistance.

    Now let’s see what happens when we use the electric starter. The starter draws about 100 amps after it gets up to speed, but the amps required to start it turning against a stationary engine will peak at around 200 for a split second. Using our little circles again, we see that .010 (battery resistance) multiplied by 100 (amps flowing) yields a voltage drop across the battery of 1 volt. This means that only 11.6 volts are available to the starter after it stabilizes at speed. To get the starter spinning, the drop would be twice as much (200 x .010), and the voltage at the starter would be only 10.6 volts. This is with a fully charged battery.

    Now assume that you’ve had the bike stored in the garage for one week without being on a charger. As discussed previously, the self-discharge of the battery would have removed about 7 percent of the battery’s capacity. The draw from the keep-alive memories would remove another 18 percent. Therefore, the battery would be around 25 percent discharged with an open-circuit voltage of around 12.5 volts. The battery’s internal resistance will also have increased, perhaps to around .020 ohms. Turn on the key, and you no longer see 12.42 volts. We now have a voltage drop across the battery of 18 amps multiplied by .020 ohms = .36 volts. This leaves 12.14 for the lights rather than 12.42 as before. Operate the starter, and things really go downhill! We see that with 200 amps needed momentarily, the voltage drop at the battery would be 200 x .020 = 4 volts. This leaves 8.5 volts at the starter. If it can manage to grunt and groan and get the engine spinning, the amps flow may be reduced to 100 amps. In this case, the battery voltage would rise back up to around 10.5 volts. While this may indeed spin the motor, it may not be sufficient voltage to operate the ignition. However, I believe you can now see that removing your finger from the start button will reduce the amount of current flowing through the battery to around 18 amps again. As a result, the voltage will immediately jump back up to a level more to the ignition’s liking. If the engine is still spinning, it’ll likely fire up.

    Troubleshooting A Slow Starter

    [​IMG]

    As a last exercise in this installment, let’s take a look at what happens when we have a loose or dirty connection at either end of the wire running from the starter solenoid to the starter, and why voltage drop testing rather than resistance testing is necessary to find the problem.

    A weak battery as previously demonstrated could cause a slow starter, or one that won’t turn the engine at all. The problem could also be the result of mechanical difficulties inside the starter or the engine itself. Quite often, however, it will be seen that the starter is not getting the voltage or current it needs to do its job even though the battery, starter, and engine are all in good condition.

    We said that a fully charged battery has an internal resistance of around .010 ohms. A starter has a resistance of around .05 ohms. So, the total resistance in the starting circuit would be about .06 ohms ignoring any other factors. To find the current that will flow in the starting circuit, we divide the battery voltage by the total circuit resistance (as shown by our circular diagrams). This gives us 12.6 volts divided by .06 ohms (.010 plus .05) = 210 amps. The battery voltage drop would be 210 amps multiplied by .010 ohms = 2.1 volts, leaving us with a battery voltage of 10.5 volts. But what happens if a loose or dirty connection at either end of the starter cable causes a small resistance ahead of the starter? Consider Load 1 in the diagram to the immediate left to represent the dirty connection and Load 2 to represent the electric starter. Let’s assign a value of .05 ohms to the resistance caused by the bad connection.

    You’d need an extremely accurate ohmmeter to find a resistance as small as .05 ohms. It’s likely that your equipment isn’t nearly sensitive enough. Nevertheless, let’s see what this seemingly harmless resistance does in our starter circuit. Again, referring to the circular diagrams, we figure the amps that will flow when the starter button is pressed by dividing the total voltage by the total resistance. Doing this, we see that 12.6 volts divided by .11 ohms (.05+. 010 +. 05) = 114 amps. The voltage that will be dropped by the electric starter will be 114 amps multiplied by .05 ohms (resistance of the starter) = 5.7 volts! What you’ll likely hear is “click” and nothing else! Where is the rest of the voltage getting used up? The battery is dropping 114 amps times .010 ohms = 1.14 volts, and the bad connection is dropping 114 amps times .05 ohms = 5.7 volts. The total of these numbers only equals 12.54 due to rounding off the previous answers, but you surely get the idea, and notice that the battery voltage drop is only 1.14 volts. This means that the battery will be reading almost 11.5 volts during this failed starting attempt leaving the uninitiated scratching their heads. So if you can’t measure the small resistance of this bad connection, how do you find the problem? You connect one lead of your voltmeter to the solenoid terminal at which the starter cable is attached, and connect the other lead to the terminal on the starter. Remembering that a voltage drop will occur across any resistance in a circuit when current flows, press the starter button while watching your voltmeter. You should see a reading no more than a few tenths of a volt. Any more than that, and you need to do some cleanup work on those cables to eliminate as much resistance as possible.
     
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