Twelve volt wet battery, rated at 675 CCA, mounted on a small tractor. Battery charger with 3 settings: 2 amps, 10 amps, and 50 amps. (Also an older charger with settings: 2, 5, and Start). Would it be safe to leave the battery charging, unattended, set at 2 amps, for a couple of days? How about 5 or 10 (amps, not days)? @Frank Sanoica ? Anyone?
I tend to think the setting of "2 amps" really means that. Given the fact of that, picture two batteries, one fully =charged, and the other nearly dead. if you connect those two batteries together, + to+, - to -, the stronger battery will discharge into the weaker, bringing it up in charge, until an equilibrium situation exists; each battery then exhibits the same output voltage, and activity ceases. FWIW, this is EXACTLY what happens in your car. Except one battery is the ALTERNATOR, driven by the engine. No matter what setting you choose, as the charger restores energy to the depleted battery, the current (amps) it feeds into the battery diminishes, until equilibrium exists. So, yes, a 2 amp setting left ON for several days is likely to result in no problems, but higher settings would not either: it's a question of how soon one wants the battery fully re-charged. From a standpoint of battery life, the quicker energy removed from the battery is restored, in general, the shorter may be the overall expected battery life. Example: Starting your engine: Battery is called upon to provide energy to crank the engine over, provide spark for ignition, provide energy to power the electronics (fuel injectors, air bag supplements, ABS, etc.) then the engine starts (hopefully). At that point, ALL energy supplied subsequently comes from the ALTERNATOR: the battery, drained a bit of power to achieve all this, is re-filled energy-wise while the alternator supplies ALL the need demanded by the vehicle. Headlights, A/C, turn signals, power this and that, ALL come from alternator. IOW, the battery sits there waiting, doing almost nothing (keeping computer alive), then suddenly a HUGE demand is placed upon it: crank the engine: the biggest draw of all, fire up ignition, power fuel pump and injectors, provide power for any other user-desired frivolities, radio, telephone, etc., and the engine starts, spinning the alternator, which then takes over as the energy-needed provider as long as the engine runs, after which time it has REPLACED the energy removed from the battery during starting, and the cycle awaits repeat. So, starting an engine: how long to replace the energy needed to start it back into the battery? Varies, but with today's systems, not much more than (normally) a few minutes. The alternator is the workhorse, the battery the stored-up ability to get going from a standstill. Is this understandable? I'll help more anyway I can, gladly! Happy you asked. Frank
Thank you for replying, Frank. The first part of your answer seems to imply that the tractor battery will never charge fully at the 2 amps setting (2 < 675). I'm interpreting that wrong, correct? Because the last part implies it will. So I'm going with the last part, and assuming the 2 amp setting is best for the life of the battery? What I would like to do is put the charger on the lowest setting that will likely bring the tractor battery back to full charge, or as close as possible, in at most 3 days, without checking on it. From a safety standpoint, is there any chance a fire, or an explosion could happen?
The settings on the battery charger indicate the amps PER HOUR of output. At a 10 amp setting the battery will recharge 240 amps in 24 hours. As you can see a 2 amp setting will be much slower but in my opinion the lower setting is better for the battery. The larger settings, 50 amp and start should not be left on except to try and start the engine.
So then the "equilibrium" comments meant that when the battery is fully charged, the charger will know to stop trying. (?) I've never seen that happen yet, but could be I've just never got that far. Since I only have to do this about once or twice about year, I think I'll take a chance at the 2 amp setting. I'm tired of fooling around with it a couple of hours at a time, when I remember. (It's a long story) Thanks
@Nancy Hart There is misunderstanding about amps and time. Amps is an amount of flow in electricity, so your (2 < 675) has no meaning. Is 675 supposedly some maximum rating stated on the battery? IOW, amperage is the intensity of a current flowing through a circuit. Generally, battery chargers charge rather quickly at first and gradually the rate of charging drops as the battery voltage increases and "bucks" the flow from the charger. Not all have discreet settings, which yours seems to have, if the dial is marked "2 amps". Yes, 2 amps will in time recharge a battery completely, probably in 3 days or less. A lot of other variables are in play, however, one being the general condition of the battery itself: if a battery will not accept a charge any longer, it must be replaced. Danger? Yes! Charging a lead-acid battery generates hydrogen gas, which escapes into the surrounding air, and is violently explosive if concentrated. Charging a battery in a living quarters is strongly discouraged. The most reliable means of checking the condition (state of charge) of a battery is through use of a simple tool called a Hydrometer. You can buy one for under $10. Looks like a turkey baster with a float inside which indicates the state of charge of each cell in a battery. Thus if one cell is bad, it can readily be seen without wasting time and energy trying to recharge a battery which is no longer capable of accepting charge adequately. Electrolyte is drawn up into the tube from each cell of the battery in a vertical position, keeping the spout submerged while observing how submerged the float remains. A full charge is indicated by the top pf the liquid surface remaining in the green portion, yellow is half-charge, red is dead. This simple device beats sophisticated test equipment, meters, etc., in that it will show a bad cell (12 volt batteries have 6 cells) where no other instrument will. Another word of caution. Battery acid is Sulfuric Acid, nasty stuff. After use, best to rinse the hydrometer out with clean water. Charging too quickly often results in frothing of the battery contents, bubbling it out over the top and sides. BAD NEWS! Clean up with water and baking soda solution. Soda neutralizes the acid, rendering it harmless. Take care not to get acid on your skin or clothing, above all, protect the eyes. Frank
Thanks Frank. You have scared me enough to abandon the plan {sigh}. I will get one of those hydrometers. It's something I don't have. I like to have at least one of everything. I'll move the setting up to 10 amps and hang around, and not worry about the life of the battery. The only problem is it's unbelievably .difficult to replace. It dies due to lack of use, I think.
@Nancy Hart You need not be scared, just cautious. Not sure if instructions come with hydrometers or not, so if you try one and have difficulty, please ask! Thing about batteries is they are just like old-time Christmas tree lights: a 12 Volt battery has 6 cells each delivering 2 volts. The cells are connected in series, like those old lights: one goes out, and they all go out. Then, which bulb was it out of maybe a dozen? Few mechanics even realize that a bad battery cell can cause partial function, and cause lots of head scratching! Frank
@Frank Sanoica, I got a hydrometer. They didn't have one that looked like yours. This one cost $6. I'll try it out as soon as it stops raining and the sun comes out. Thanks.
My battery charger has readings that indicate voltage and percent of charge right on the charger. It automatically switches to a "float" setting when the battery is charged. It is the best small charger I have ever seen. I have seen the results of battery explosions on two occasions, and it wasn't good, but I think both of those occasions were due to jumping, not charging with a charger. I also knew a guy who would "recycle" batteries using a DC welder. He blew up a lot of batteries, but he was prepared and well away from the action.