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Old 01-27-2007, 06:26 AM   #11
Join Date: Nov 2005
Posts: 213
Originally Posted by Les Lampman
A standard automotive alternator will not fully charge deep cycle batteries. The best it can do is about 85% to 90% and that's if the batteries are good, all the connections are good, and the alternator acts as it should. There are three stages to charging deep cycle batteries consisting of a bulk charge, an absorption charge, and a float charge. If your charging source can not accomodate all 3-stages (be it an alternator or a charger) then it can not fully charge deep cycle batteries.

The regulators in standard alternators are very simple switches and simply sense voltage; when the battery voltage is at some low point they turn "on" and send current to the batteries, when current is at some high point they turn "off" and stop the flow of current. Think of it as a light switch, it's either on or off. On the other hand multi-stage chargers are like a dimmer switch, not only does it have the on/off function but it can determine "how much" current to send; a stock alternator does NOT do this and always send all the current the alternator can produce to the batteries. Automotive alternators are voltage regulated and not current regulated (other than by maximum alternator output) which means they can not following the charging curve set by the battery manufacturer to fully charge deep cycle batteries. A good multi-stage charger (or 3-stage regulator on the alternator) will current regulate the charging and will bring the batteries back up to 100%. It does this by sensing the voltage of the battery and regulating current flow to the battery based on set points programmed in.

Automotive alternators are designed to charge starting batteries which have many thin plates with a lot of surface area that will quickly absorb the charging current and bring the battery voltage back up quickly. In this scenario the on/off switch operation of the regulator works fine. They are not designed to charge deep cycle batteries which have much thicker plates with a much reduced surface area that takes a comparitively long time to charge. When the simple on/off regulator senses that the voltage of a deep cycle battery is "ok" the battery still has another 15% or so to go before it's 100% charged (beacuse the interior of the thick plates hasn't reconverted) but the regulator doesn't know how to deal with that.

An OEM automotive alternator is not "hot rated"; it can not and should not put out it's rated amps for any length of time or it will die a quick death. You can not expect an alternator that's labeled 120-amps to put out more than perhaps 100-amps or so if you want it to last. If you add enough batteries to your bank to drive the required charging current higher than that you'll damage the alternator.

Charging deep cycle "house" batteries from an automotive alternator that has not been fitted with a 3-stage regulator is a "make do" situation. That is, you're only doing it to get the batteries at least partially charged between times when you can plug in a multi-stage charger. You can get your bus alternator to do the job correctly but it takes a rather expensive 3-stage regulator added to it to make that happen and you need to make sure the alternator is sized appropriately to the battery bank being charged. You can add enough batteries to limit current to any individual battery but you'll exceed the capacity of your alternator's continuous duty rating very quickly. Either way you'll end up replacing something.

I replace deep cycle batteries all the time that an automotive alternator has killed. The problem is that in what should be the the last two stages of charging (when you're trying to reconvert the interior of the plates) the alternator which only has one stage is sending way too much current to those thick plates and they're being damaged. That's specifically why a multi-stage charger is a multi-stage charger, for the life of the batteries the current must be reduced in the absorption and float stages and a standard alternator regulator can not do that. Limit the time you have your house batteries connected to the engine alternator.
Nice read and thanks, over the years I have read a bunch of info on deep cycle batteries and here is what I gather from all that reading, dont buy a deep cycle battery because their is no proper way to charge them without spending 400 bux on a charger, then you cant run that charger off a generator because it wont work right so you can only "charge properly" off shore power but if shore power is available you dont need batteries.

Maybe its just me but I have yet to read a article on charging deep cycle batteries that I can come close to conforming to.

I bought a new charger that is automatic and has a setting for "deep cycle" now people are telling me the charger is too small LMAO its max is 12 amps.
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Old 01-27-2007, 07:18 AM   #12
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Here is my new charger

I also have an older one of these that I used last season to charge my batterys it was charging my batterys when ever I had my generator running

I usually turn the generator on when I make coffee in the am it runs for about an hour, then when I use the microwave to heat lunch and supper, my 2000 watt inverter runs the micro just fine but my refrigerator runs off the inverter so I like to give it some charge, at night we usually use the computer (old desktop) as a multimedia center to watch recorded TV shows and DVD's and forget to turn it off so it runs most the night but only draws 124 watts for everything, monitor, PC, powered speakers, external hard drive...
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Old 01-27-2007, 12:35 PM   #13
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Well im biting the bullet tomorow. Going to order a 55 amp Iota charger with built in IQ4 3 stage charging. Also going to get the Iota 50 amp transfer switch right away so all i have to do is start the genn and the load will transfer automatically to gen and kill the inverter. at that time when the transfer switch goes to genn side it will also power up the iota charger to replenish the house batteries
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Old 01-27-2007, 01:21 PM   #14
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Originally Posted by hoser
Nice read and thanks, over the years I have read a bunch of info on deep cycle batteries and here is what I gather from all that reading, dont buy a deep cycle battery because their is no proper way to charge them without spending 400 bux on a charger, then you cant run that charger off a generator because it wont work right so you can only "charge properly" off shore power but if shore power is available you dont need batteries.
I don't think it needs to be that bad. Lead acid is about the most forgiving battery chemistry out there. All it asks of you is that you charge it back up soon after discharging it. The difference in importance between a perfect charging and doing the best you can with what you have really depends on how the bus is being used, your battery bank, etc.

For Les who will most likely end up with a $1000 bank of 8D AGM deep cycles and has mentioned fulltiming in it, proper charging makes a lot more sense finacially and out of convenience. It's also a lot easier to justify the expense of "proper" charging equipment when you're going to be using it so often. For those of us who are seasonal weekenders wit ha bank of two or four GC2's it becomes a little less important. As long as you have battery power when you need it, it doesn't much matter. The service life between a golf cart battery that has had perfect care and one that has had the best a person can manage isn't going to be all that different. I just don't think it is that hard to swallow replacing a battery bank after 3 years as opposed to 4 when it was cheap to begin with. Neglected batteries will not live to see their third birthday though so it's important to atleast TRY and take care of them.

As for not having a big enough charger...there are maximums in place of how fast you acn charge a battery, but not minimums so much. In most battery chemistries, the slower you charge a battery, the better it is. Same goes for discharging. The reason people like to run bigger charging circuits on their house batteries is because it will charge faster. Other than the rare case where we have to "wake up" a starting battery that someone brings in which has been sitting for a while, we prefer to use a 10 amp charger at work. I, for one, don't like cleaning up bubbed out electrolyte. The same even carries over for me at home. I tend to use my 1.25 amp Deltran Battery Tender to charge batteries instead of my big charger. That mostly has to do with the fact that I don't have to pay attention to it, but the only real penalty is that it takes longer.

Long story short...I wouldn't be scared away from buying a deep cycle just because of all the maintenance you hear about. I kind of equate it to the dentist telling you to brush after every meal, floss daily, use flouride mouthwash, etc. While that is a perfect solution, if you brush twice a day and make an honest effort at flossing daily, the service life of your teeth should be 80 years or more.
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