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My Battery Always Dies - Part 6 Sizing your Alternator Considerations
Previous : My Battery Always Dies - Part 5 Checking the Sizes of Wires, Why and How
Next: My Battery Always Dies - Part 7 Adding Land Based Chargers, Generators, and More!
What size Alternator should I use and what will be my charging times?
Again, the million dollar question. The answer is very dependant upon the type of battery you have.
- If you are using flooded deep cycle batteries, the charger should be rated for the size of the batteries in question. In addition, if flooded deep cycle batteries are routinely discharged beyond 50%, it is reccomended that you equalize these battery banks routinely. This is a forced overcharge to reset the batteries' internal chemistry, and mix the contents if you will. This forced charge is closer to a 1.5 multiplier, and the voltage jumps to 15.5 volts per 12 volt battery.
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If you are using AGM deep cycle batteries and discharge beyond 50%, the amperage taken by the batteries is 100% system capacity to provide it. In other words, AGM batteries will suck down the power as fast as you provide it to them. This brings voltage drops in wires to their fullest, stresses fuses, blows up cheap alternators, and exposes other electrical system weakpoints. If it is done right, there are no problems.
DO AGM BATTERIES BLOW THINGS UP???
Well no, but they do make the things around them do what they are supposed to do. For instance the alternator. When an alternator is rated for 100amps, the battery (battery bank) is not fully charged, and you have AGM batteries; the AGM Batteries takes the power, and ask for more.
This runs the alternator at 100% capacity for X period of time. The larger the battery bank, and the further you deplete it, the longer the period of time an alternator is required to run. The quality of the alternator shows up quickly let's just say. Cheap alternators run at full blast do not last as long as high quality, "racing", and "High Output" models. We will leave it at that.
The largest alternator you should ever install is one with an amperage output equal to the depth of discharge on your deep cycle battery bank expressed in amp hour load. This results in a charging run time of approximately 1.25 hours per day. This charging time is assuming that the charging voltage of the alternator is no less than 14.4 volts and the battery capacity more than 2 times the size of the load removed*. HUH?
Okay, again in plain English, we will discuss the size of the battery bank below.
Alternator sizing example 1
Let's say you run 100 ah from a 200 ah bank of batteries in your vehicle routinely, you wouldn't want more than a 100 amp alternator, so it runs for about an hour.
Let's say you have installed a larger 100amp alternator to replace the 65 amp stock variety
Battery bank is 12 volts, and the alternator outputs 14.4 volts.
100ah needed = 100amp alternator * hours * 1.25(inefficiencies)
(100/100)=(100/100) * hrs * 1.25 = 1 * x * 1.25
solved for time = 1.25 hours
Resulting run time to charge your 200 ah bank would then be 1 hour 15 minutes
Alternator Sizing Example 2
80ah system, 65amp alternator, and you just ran 40 ah from the battery with the stereo or winch system.
You ran 40 ah from a 80 ah bank of batteries in your vehicle.
Let's say you have the 65 amp stock variety alternator
Battery bank is 12 volts, and the alternator outputs 14.4 volts.
40ah needed = 65amp alternator x hours x 1.25 (inefficiencies)
(40/65)=(65/65) * hrs * 1.25 = 1 * x * 1.25
.615/1.25 = 1 * hrs * 1.25/1.25
solved for time = .49 hours = 30 minutes roughly
Resulting run time to charge your 80 ah bank would then be 30 minutes
* Deeply discharged batteries require more charge to recover their complete capacity than the 1.25 multiplier for inefficiency, especially over time.
Alternator Horsepower Drag, Alternator Motor Problems, etc.
The last thing we consider as electrical folks, the first thing the engine and part manufacturers think about, is the size of the engine driving the alternator. The alternator robs the drive train of Horsepower, and when running at 100% capacity adds significant drag to the engine. The manufacturer usually has multiple models of alternators sized for their engines if you just ask. Please check with the manufacturer of your motor and drive train for appropriate models.
If you put to much of a strain on the engine, you create other drive train, and gearing issues. Basically the alternator can't use more than a certain percentage of the horsepower provided by the engine or it leads to rough idling, backfires, timing issues, and other problems. The engine manufacturers think of an alternator as trying to race with the emergency brake engaged. You can't blame them, the main purpose of a vehicle from their perspective is to move from point a to point b, either fast, or efficiently. Electrical accoutrements don't aid in either pursuit.
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BD Batteries
Previous : My Battery Always Dies - Part 5 Checking the Sizes of Wires, Why and How
Next: My Battery Always Dies - Part 7 Adding Land Based Chargers, Generators, and More!
Legally: REMEMBER, ELECTRICITY HURTS, IT CAN KILL YOU. BD BATTERIES TAKES NO RESPONSIBILITY FOR YOUR ACTIONS WITH THIS INFORMATION. IF YOU AREN'T TRAINED TO WORK WITH ELECTRICITY, CALL SOMEONE WHO IS. IF YOU CHOOSE TO MEDDLE, YOU AGREE TO TAKE RESPONSIBILITY FOR YOURSELF! THIS GUIDE IS IN NO WAY A COMPLETE ELECTRICAL GUIDE, AND SHALL NOT BE PRESENTED AS SUCH IN ANY FORMAT OR FORUM. PERFORMANCE BATTERIES ARE CAPABLE OF ARC WELDING STEEL AND OTHER VERY INTERESTING THINGS INCLUDING YOUR HEART. BE CAREFUL, DON'T HURT YOURSELVES.
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