I have always been told a alternator is better keeping a battery maintained at full charge then charging a low battery where a generator is supposed charge a low battery better,I think that is true since on a couple alternator equipped vehicles I needed to charge the battery after it got low after I thought I ran it long enough to charge. So what I would like to know is what is the differences in the systems to make one better at maintaining then charging and one better at charging a ow battery.
15 Amps is 15 Amps and the electrons don't know if they are being excited from an alternator or generator. It really doesn't matter, at a constant rate of charge, they both would take the same amount of time to properly charge the battery...Now, I'm speaking in general terms and I don't suppose the generator will only put out 5 amps max and the alternator is 105 amps....but then that could be the other way around...so the assumption here is that they both have the same ampacity The best way to charge a low battery is with a battery charger An alternator has output at lower engine RPM than a generator....do you do lots of idling, a generator needs a higher engine RPM to charge at the same rate as an alternator at idle in general terms. A generator, once field voltage is established, will continue to make power so you can disconnect the battery jumper cables and the engine will continue to run maybe not the case with an alternator if the battery very discharged.
Well said winduptoy. A buddy of mine had a new 63 Impala and an old ski boat. The battery for the boat died so we used to back the boat in the water, remove the car battery with the engine running, and go park the car and trailer. The battery went in the boat for a day of skiing. We would reverse the procedure at the end of the day. It probably wasn't smart as the voltage may have been sky high, but we did it.
There might be a few variables you haven't considered...like the condition of the battery, for one. And the method for determining if the battery is fully charged.
Generators don't charge very well at low RPMs, that's why they have a mechanical cutout. It's also why generator equipped cars and trucks had very big heavy batteries, for the best possible reserve capacity because at times it would have to support the entire electrical system. Alternators have a diode pack for kind of the same reason but there just isn't any charging to speak of going on, down low with a generator. I would expect it isn't much of a factor for most of us these days who still run generators, but "back in the day" people commuted back and forth to work on short trips, or sometimes drove at night a lot. Think about stop and go driving, at night, in the rain, wipers on, radio on, heater running.... That's going to nuke a battery quickly. Sure, it might still start the engine but it will be chronically undercharged. Higher charging setpoints cause excessive outgassing. Back when generators were the only game in town Autolite advertised a battery that "only" needed watering 3 times a year. That tells me ordinarily they needed it probably once a month or so. And a top of the line battery was only warranted for 18 months.
Generally speaking, batteries 'prefer' to be charged 'low and slow', i.e. at a lower rate for a longer time. High charge rates heat them up, too much and damage can result. Generators by design can't deliver the high charge rates that most modern alternators can so that's what makes them 'better' at charging a really discharged battery. But as a practical matter, it doesn't matter much anymore as modern batteries are designed to tolerate this.
I ran into the same issues with my lawn tractors,the ones with the starter/generator seem to charge the battery better then the ones with the alternator under the flywheel. I have found when the ones with the alternator have a low battery I just charge it before using and then it will stay up.
That has more to do with how rudimentary the 'flywheel' alternator is than the fact it is an alternator. In most cases these use the same flywheel-mounted magnet as the ignition so you only have one 'pole' to work with which limits output.
The ones I have are from the late 60s to early 70s and the alternator has nothing to do with the ignition,cast iron Tecumsehs with the solid state ignition and the charging systems put out 14 volts like a car. It takes me a hour to cut the grass and they will not charge up a low battery in that time.
Electrically there's no connection between the ignition and charging system. But the magnet is what generates both your spark voltage and the charging output. One coil for spark, another for charge. Unless there's something more elaborate under the flywheel or it's a gear or belt-driven unit...
Well heck, if we are talkin lawn mower strangeness, my kubota with a dynamo thing, charge light always on, meter shows it puts out 2 volts. it takes 4 hours to mow, and i never have to charge the battery all summer. why?/
I'm thinking what you heard was that" A generator will charge a stone dead battery or charge with a dead battery in the car. This is true. Back in the day it was fairly common to push start a car with a stone dead battery and the generator would charge enough that the coil would fire and the engine would run. An alternator has to have a reasonable amount of power in the battery to excite the alternator. If you have points a battery that has a little poop left in it will usually give the engine enough spark to fire the the engine but if the battery is stone dead you are SOL on a push start. Not that many guys these days are going to get their buddy to push start them but back in he day it wasn't uncommon at all to have your buddy push start your beater if you had a dead battery rather than jumping it.
FWIW. An generator is more resilient, it's not the optimum charger. An alternator can easily be burned up if the charge circuit is open or the battery is heavily discharged, but is a far superior battery maintainer. With a low charge battery it is not a good idea to use an alternator as this can damage the alternator itself. With a low charge battery, an generator will not be damaged, it will take its sweet time fully charging the battery but it will do it eventually. So what someone may have been inferring is that an generator will be able to recharge a severely discharged battery, but is fairly weak at maintaining system voltage under full load. Where as an alternator can maintain a fully charged battery/system under heavy load, but can be damaged by excessive low voltage battery charging. Usually with a charge light. There will also be a resistor(so incase the bulb burns out the alternator will still self excite) and a diode. Purpose of the charge light is to show if there is a problem in the charging system. Resistor is run in parallel to aide in self excitation of the alternator. With Engine Off/Ignition On the charge light will illuminate as current from the battery is flowing across the filament and it illuminates. Once Engine On/Engine Running and the alternator has begun charging there will be a reversal of current flowing from the battery(draining), to current flowing to(charging) the battery. With this reversal the charge lamp will no longer see a current flow across the filament due to the diode(one way check valve). If the diode fails it can allow current to flow from the alternator to the battery via the charge light circuit. Since current is flowing across the filament, the lamp will illuminate. Granted, other conditions can occur that will cause the lamp to illuminate under normal running/charging conditions, but it usually related to a faulty charge light circuit and not a charging issue.
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